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Flying High With Aerial Robots part 2: Design and Compromise

July 7th, 2014 by

Competing for Compromise:Air Frame Design Considerations

In this lesson students will learn about the different parts of the quadcopter air frame: their functions, and things to consider when designing these parts to achieve sufficient lift to get airborne. Students will make use of an online calculation tool that helps guide their choices based on parameters selected by the instructor. Here they learn first hand the art and science of compromise based on the goals of an engineering project. First, an introduction to the air frame components.

Most multirotor airframes have several common components, some of which may be separate or combined as modules. They include:

Center Stack

The center stack links and supports the arms. It also provides a mounting point for the flight controller, battery, receiver and other electronics. The weight of these components adds up and these parts must be quite resistant to bending and breakage. The stack may be built with as little as two levels. Its design needs to take into account access holes for wire routing, holes for mounting electronics and the attachment of the four arms of the quadcopter.

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Different materials mean different choices. Here are center stack components in garolite, aluminum, and hdpe plastic.

Arms

The arms of the copter are often its most most distinguishing feature. They can be made from simple materials such as square tube towel rods from the hardware store, carbon tubes, or custom cnc machined aluminum like the one we build in this tutorial. The length of the arms must allow for propeller clearance, room for landing gear, reasonable weight, and sufficient strength. Arm design should consider the location of motors, controllers and wire routing. Each arm should mount to the center stack with a minimum of three bolts, four if possible.

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Students may be tempted with ultralight materials, but some such as acrylic on the right are not appropriate for an arm in this configuration. Aluminum is a good compromise.

 

Motor Mounts

The motors will be mounted to the ends of the arms in some fashion. With simple square tube, it is possible to drill holds and mount the motors directly to the arms. With round tube and/or fragile materials, a separate motor mount must be fabbed or purchased. The machined aluminum arms in the TSN quad incorporate motor mounts into the design. Proper hole alignment and sizing is crucial which ever technique is used. The spacing of the holes on the motor should be determined in advance of the final design of the mount. This information is often available on the manufacturer’s web site, or if you have the motors in hand that makes a precise measurement a simple matter.

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This machined motor mount interfaces between the motor itself and the arm of the quadcopter.

Landing Gear

Landing gear will set the airframe itself above the ground for several reasons. The battery is typically mounted on the bottom of the craft and needs to avoid ground contact due to its fragile structure. Landing gear also isolates the spinning props from the ground making it less likely to break one in a minor tipping incident. Finally, landing gear permits the addition of undercarriage accessories such as a camera that can be placed under the field of view of the propellers. The design and overall height of the landing gear must will depend on the design goals of the craft. These must be established before manufacturing and construction take place.  Will the robot  be used for acrobatics, aerial photography, or as a learn to fly platform?

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Tall and wide landing gear provides plenty of room for hanging cameras underneath the quadcopter.

 

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Shorter landing gear still protects the battery and props, while allowing for better maneuverability under flight.

 

The Great Compromise: Strength vs Weight

This is an ideal subject for students to be exposed to the process of engineering compromise. Here students are engaged in engineering practices with an activity that has no predetermined outcome. Often in class when students work problems with the forces of motion, certain facts are ignored for the sake of simplicity and convenience. Wind resistance is often assumed to be absent when learning how to calculate the speed of a falling object. Friction is ignored when calculating acceleration of a moving vehicle. With aerial robots, these forces and many others can not be ignored or there will be expensive consequences.

It will become obvious to any student that the design of the motor mounts, arms and chassis do need to be as light as possible. But along with weight considerations the job of these components must be considered. Their task is to not only carry the weight of their respective component parts, but also to withstand the forces involved when countering gravity, wind, and various twisting forces that accompany the complex movements of a multirotor. Additional strength is required to handle the occasional rough landing, or yes, even crashes. Strength therefore is important, and mass can add strength-but the machine must be able to rise of the ground and maneuver in three dimensions.

So where do we start off? This is the most difficult question, because committing to one aspect of the multirotor design narrows down the options for the rest of the design and components.

A good rule of thumb is to choose a combination of parts that allow thrust be at least double the weight of the ‘copter-just to get off the ground. In other words, after all the parts of the airframe, battery, motors, escs, props, etc are tallied (referred to as AUW or all up weight), the upward thrust of the motors together should at minimum double the downward force of gravity acting upon them. Achieving this goal used to be more difficult than it is now thanks to some remarkable online calculation tools. Therefore my students always begin this process with some simulation time in front of the computer. Here there is a tool that can add virtual components from their online catalog, and run calculations with various component combinations. The calculator will will automatically tally up machine weight, as well as theoretical thrust, estimate flight time among many other things. The tool we like to use is called Ecalc. A limited(but very useful) version is free, but its only a few dollars for the full version.

Visiting the ecalc site and Hobby King or another vendor with commonly available components will give students a pretty good representation of what their components can do before their machine is even designed. Let’s run through a scenario. For teachers, setting some parameters for students in addition to budget is easier from a management perspective, and you can still allow for advanced designers to customize airframe components during the process. Let’s say your budget is $150.00 for components. In a classroom, it is easier to have as many common parts as possible. In our example we will choose:

2100 mah battery

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1100 kv 28/36 motors

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20 amp speed controllers

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I also tell students they should strive for at least 6 minutes of hover time.

 

Student Exercise: All Up Weight

One of the parameters to enter first is the weight of the model with or without components. Look at the motors we have chosen. You can see they can, according to the manufacturer achieve a maximum thrust of 1000 grams. Multiply that by four and we have a maximum of 4000 grams of thrust with the right props. Using our rule of doubles, that means theoretically we can have a 2000 gram aircraft.

Using ecalc to add up the masses of the components shows that they add up to 613 grams. These do not include flight controller, power distribution board, wires etc. Add ten percent for those. This gives 674.3 grams, leaving us with 253 grams for our chassis, including materials and fasteners.

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In the TSN Quadcopter design, the arms with motor mounts weigh 28 grams each if made from aluminum. The 3 centers weigh 12 grams each if made from plastic and 8 grams from garolite. That puts us at 112 + 24= 136 grams. Adding fasteners will still put us well under acceptable weight.

Once the calculations are run, the results give a great deal of insight into what to expect. Here we see that our flight time estimate shows our goal of 6 minutes can be achieved with this configuration.

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There are loads of variables to explore in the data stack generated by ecalc. One estimates how much extra payload can be carried by the aircraft. If you want to add a camera, extra battery or retractable landing gear, this figure comes in really handy. In our example, you can see that we have some room for some goodies with an additional payload of 420g.

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You can also see that there is room for improvement as well. Students should be encouraged to try different combinations of propellers, including those recommended by the motor manufacturer and those that might not be. Remember you can’t break or burn components that are not real! If students choose a particular prop size, remind them that there must be space between the arms sufficient to clear the props from hitting each other should they embark on their own designs.

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Whether they work alone or you pair up students on the computers, a great deal of classroom energy starts to generate. This amazing transformation takes place as students realize they are in an impromptu engineering competition as they crunch number, look up specs and compare notes. You’ll quickly hear kids turn in their chair saying “I got 6 minutes!” and another says “I got 6.5 minutes!” as others frantically check their figures and try to find the perfect combination of parts that will yield the longest flight time. This really gets them excited to start the design a build process! Have students document several different combinations in their engineering journal so they don’t forget what works in the simulation. If you have a projector, share out a couple of combinations that work and some that didn’t for discussion.

Depending on your students’ design skills, they can use software to do some analysis of different arm designs. They can apply different forces to the arms and see how much they bend and twist. They will be able to adjust and redistribute mass, material types, and length of the arms themselves before ever machining a single part. The ‘ready to manufacture’ design of the TSN Quad is a starting point for teachers and students to get off the ground. After that, the sky’s the limit.

 

Next: CNC Machining the Air Frame

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Students Fly High With CNC Machined Quadcopters

May 3rd, 2014 by

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The study of robotics has proven over the years to be the perfect storm for STEM education.  Robots are highly visible in the media and recognized as complex, captivating machines that represent the future of innovators in today’s classroom.  Students who build robots are provided with a unique opportunity to think for themselves as they troubleshoot problems and stay engaged with high level science and engineering practices.  Skills in programming, advanced manufacturing and design become second nature to students who have been through a comprehensive robotics-based STEM program.

Aerial robots can fill a similar role in your STEM  program, with the added dimension of flight control. Often referred to as multi-rotor copters or just multicopters, these devices are fascinating to watch, fun to fly, and are in the media spotlight enough to make even the layperson aware that students working on them must be doing something important.  Multicopters in the field are used for surveillance, photography, mapping farmland, scientific research, and search and rescue.  For educators who use robotics to engage students in genuine science and engineering practices, multicopters provide another way to develop and refine news layers of technical and problem solving skills that make sense for the demands of today’s workplace.

While there are many parallel skills developed with terrestrial robotics, multicopters require specialized skill to operate and are a bit more demanding in terms of manufacturing tolerances, programming and balance than most classroom project robots. Teachers who are accustomed to seeing junkbots (robots made from recycled materials) wobbling around the room will need to help hone students abilities to make accurate and repeatable parts. CNC machines are made specifically for accuracy and repeatability, so taking advantage of this capability is a key focus of this series.

Building multicopters from scratch is not a simple undertaking. The machines and their operation is complicated, and they can be dangerous if proper precautions are not taken. The cost of components is far lower than at any time in the past, but they are not an inexpensive item. However, the immense payoff for students is worth the initial trepidation and time required to make multicopters work for you and your class room. TeachSTEMNow has dedicated this series to removing obstacles by providing specific, classroom-proven instructions, low cost component and supplier recommendations, addressing safety issues, and project management guidelines that will make multicopters a new step in your STEM revolution.

Multicopters are named based on the number of rotors present.  Octocopters have eight rotors, hexacopters have six, and so on. A four-rotor quadcopter is a good compromise between cost and functionality, making it the most popular choice for general use. In this STEM tutorial series teachers lead students to manufacture, test and tune their own quadcopter made using CNC.

Key Concepts and Take Home Skills:

Aeronautics/Physics of Flight

CAD/CAM/Advanced Manufacturing

Energy/Sustainability

Electronics/Soldering/Wiring

Critical Thinking and Problem Solving

What You Need To Get Started: 

As teachers, research is something we are accustomed to doing when learning how to improve our content knowledge, instructional strategies, and classroom management skills. If you are reading this article, you are doing research now. The recommendations we provide here  for components are for just one variation of the many choices available. If you purchase these components, they are known to work in the configuration shown. However, you are just as likely on your own to find performance and value equal to or better than these with some additional research.  But for those who just want a list of what to buy and get their students flying, these bits are proven.

One of the most interesting parts of building a quadcopter from scratch is the process of choosing component parts. We will discuss in detail the functions of these quadcopter parts and components later in the tutorials. It is essential to know how these parts interact in addition to their functions, because there is a domino effect in place. When you choose one component, it affects the other parts in terms of compatibility and capability. Again, this process will be clarified later for your students to be able to do original designs. For now, this list  is a proven set of parts that will work well with the designs here for download.

Electronic Components

1. Transmitter and Receiver

These components allow wireless control of the quadcopter. The transmitter is held in the hands and sends signals to the receiver on the aircraft. You will want a 2.4 ghz receiver/transmitter combination designed for simplicity and at least five channels. You will use four of the channels for each of the motors, and one for activating the self leveling function of the flight controller. If you don’t know what that means, don’t worry about it. Just get five channels. A good buy at ServoCity is the HiTec Optic 5 transmitter and minima 6e receiver available for under $90.00. Another option is the FlySky FS-T6 at HobbyPartz. This combination is an exceptional buy at the moment with a price as of this writing of under $55.00.

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2. Flight Controller

Multicopters rely on sophisticated electronic sensors such as gyroscopes and accelerometers to achieve balance during flight. The job of the flight controller is to coordinate the desires of the pilot with the data from the sensors while properly regulating the speeds of each motor/propeller. The simplest flight controller to use is the Hobbyking KK2.1. Unlike other flight controllers, this board does not need to be interfaced with a computer for programming. It has the convenience of an on board LCD panel and easy to use menu which allows the user to configure the ‘copter in the field. As with all HobbyKing products mentioned in this article, try to find the item from the US warehouse if possible. If it is out of stock there, then you will need to get it from the international warehouse which usually means a delivery time of 3 weeks or so.

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Motor Controllers (Electronic Speed Controllers)

Motor controllers or ESCs are small bundles of printed circuits which connect to the motors via the flight controller board. You will need one for each motor, so order four of them. Very generally speaking, they are divided into categories based on amount of current they can supply to the motor, and whether or not they need a separate battery to operate. For the sake of simplicity in a classroom, the recommended ESCs have a comfortable margin for current supply and have a battery eliminator circuit (BEC) which means you don’t need to worry about another dedicated battery. Hobbyking sells the Turnigy plush 25Amp ESC for about $13.00 apiece. Another option is the Multistar 30Amp for a bit more headroom and about the same price.

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Brushless Motors

The  motors for your quadcopter have a set of specifications that are very important but will prove to be quite confusing without some background information. With that information, you can make some informed choices that may prove to be better than our recommendation if your students build ‘copters with a different design than the one provided in this series. A detailed discussion of brushless motor specifications and how to choose the right motor will be forthcoming in another segment of the TeachStemNow quadcopter series. To get you started, the Turnigy D2830-11 1000KV motor(again don’t worry about the specs) will be fine at a price of under $10.00 each. These also come with both propeller mount and motor mount. Get a spare just in case.

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Propellers

Propellers are another component that must be chosen carefully. The most important thing to know at this juncture is that you will need four propellers on the quadcopter at a time, two designed to rotate clockwise and two that rotate counterclockwise. It is highly advisable to have a spare set of props since they will break. I repeat, they will break. Try these and these from Hobbyking. Both sets will run a total of under $10.00 and include a spare of each. Another advantage of these props is one set is black, the other green. Having a set of each color on the aircraft makes tuning and flight orientation much easier later on.

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Software and Programming Cable

There are a couple of (free) software applications that will be needed. One will be used  to update the flight controller board to the latest firmware, the other will be used as to simulate the effects on design and component changes on student copters. First and foremost, a special pair of programming cable adapters connect the KK2.1 flight controller to your computer USB port for a few dollars. Be sure that you get both ends of the cable. One is the programmer and the other converts the 10 pin wire to the 6 pins on the KK2.1 board.

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Power Distribution Board

This component is very inexpensive(around $3.00) and makes connections from the battery to the ESCs a simple matter for beginners. There is a limit however in terms of its power handling capabilities so it your student quad use much more than 20Amps of current they will have to build their own. Fortunately, if you are following the suggestions thus far, this board will work fine. In a later segment on more advanced machines there will be a tutorial on how to create wire harness for higher current situations.

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Battery

The battery is an extremely important component with many options and ramifications for each option. Lithium polymer batteries have a high energy density and are light weight, making the best solution for our needs. The price of the batteries is based on their quality and current storage. To keep things simple while gathering components, there are two main things to keep in mind when building the TSN Quadcopter. Use a ‘3s’ battery with minimum 30C rating, and get between 2200 and 5000 mah storage capacity. Different 0ptions and lots more on battery theory and safety will be discussed later. For now, choose one (or more depending on your budget) of these: 22oo mah Zippy battery or the 5000 mah version. They range from $20.00 to $50.00.

 

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Wire and Connectors

A few dozen jumper wires can be obtained inexpensively here. These wires will be used to connect the receiver to the flight controller.

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Another piece of the wiring puzzle are special gold connectors used on ESCs and motors. You can get a set of male/female pairs for a couple of dollars in the 3.5mm size here. Buy at least 2 sets per copter. These are not crimped connectors, and tips for soldering them will be coming in a later segment of the series.

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You will need heat  shrink tube to ensure strong and isolated connections. Get at least two different colors to easily identify wires.

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Add zip ties to the list as well.

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Charger

Lithium polymer batteries need a special computerized charger. This one gets the job done at $25.00 and has been proven reliable for us at a reasonable cost. You will also need an old laptop power adapter to connect it to your wall outlet, or just buy one here.

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Tools

You’ll need a soldering iron, solder and an iron stand. A “third hand” is useful as well. Have a 3/32 hex key for the socket head screws you will use as well as a small philips screwdriver.

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Fasteners and Connectors

Holding the parts of the quadcopter together is accomplished with a variety of nuts, bolts and standoffs. Most hardware stores do not carry what you will need, particularly the standoffs. There are some good buys on a certain popular auction site, as well as Hobbyking if you are buying metric. To make the build process pain free, order more than you think you will need. We generally use nylon standoffs to hold the flight controller board and bind the center sections together. You can use metric in 3mm thread size or 4-40 Imperial(our choice). Get a few sizes, such as 1/4 , 1/2 and 1 inch in length. Using female/male and female ended styles of each one gives you flexibility in configuring parts the way you want. In addition, you will need nuts and bolts. We recommend socket head bolts, both metal and nylon. Again 3mm or 4-40 is a good choice for size if you are building the TSN quadcopter. Lengths should be 1/4, 1/2, and 3/4 inch. An equal amount of nuts should be purchased for the bolts.

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Air Frame Components

The ‘arms and legs’ of the TSN quadcopter will be manufactured by students using CNC. Part 3 of our series will be dedicated to design and manufacture of these components. We will also go over some neat ways to customize parts using powder coating for some added pop. If you want to just get off the ground and practice before having your students tackle this project, one option as an instructor is to buy a kit of frame parts. This one will work with the parts on our list.

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Students will build their own quadcopter components using CNC machining in part 3.

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In part 2 of the TSN Quadcopter build, students will learn to use CNC using our design files to build their copter. We will also discuss choosing your own quadcopter components, flight design parameters and and how to use a fascinating piece of free software. Stay tuned.

 

 

 

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TSN BasicBot Part 5: The Eyes Have It

December 1st, 2013 by

Students who are given the opportunity to work on long term, multidisciplinary STEM projects are the best hope for the US to fill the ranks of qualified job seekers in high demand STEM fields. The development of critical thinking skills that push students to integrate cross cutting concepts are an fundamental tenet of robotics in the classroom, making the concept of robotics an appealing one for teachers. Kids who work in teams toward a common, well-defined goal where everyone can contribute feel good about being a part of your STEM classroom.  The TSN BasicBot project makes it easy, taking students from start to finish with Computer Aided Manufacturing, electrical component wiring and testing, to assembly and now programming for autonomous navigation with sonar. This is the fifth part of the TSN BasicBot series and links to prior segments will be found within the text. There are several design and programming files available for download as well to give your students a starting point before moving off on their own.

This version of the BasicBot requires a few changes from the prior iteration, which could be programmed to navigate a set course but had no way of independently responding to its environment. We divide this fifth part of the lesson into the following segments:

Chassis Updates

Machining The Sonar Mount

Wiring

Programming

Parts that are required in addition to the original version of the BasicBot  include:

9G micro servo motor

HC-SR04 ultrasonic sensor

12 jumper wires

Revised Upper Chassis

Sonar Mount

 

 

Let’s Begin.

The sonar sensor in the BasicBot has been designed to scan back and forth to give its better picture of the surrounding environment. The scanning is done by a small servo motor attached to the sonar mount. In order to accommodate the sonar and its servo motor, the upper section of the chassis has been revised to permit a clean low profile attachment of the servo to the robot. Thanks to the versatility of the BasicBot design, students can mix and match chassis components or add more levels to fit their own engineering requirements. The two chassis pieces are compared below, with the revised piece shown on the right.

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Original BasicBot and Sonar Enhanced Top Levels

The new upper segment has proper hole spacing for an Arduino Uno R3 microcontroller as does the original. It will probably also work for similar controllers and clones as well due to the large number of holes and slots on the chassis. The chassis can be machined from aluminum or plastic, even cut on a laser engraver. Students can mix and match to learn different manufacturing techniques as shown below.  A machining tutorial for the chassis is found in part one.

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Acrylic, Aluminum or Plastic, Take Your Pick

Machining the Sonar Mount

There are many inexpensive sonar sensors on the market today available at a low price. The HC-SRO4 sensor fits the bill with a low price(well under ten dollars shipped), accurate tracking and available arduino library files for testing. The sonar mount needs to be made from a non-conductive material or coated with one to avoid short circuits on the open pcb. We have had students make the mounts from aluminum after applying powder coating with success as well. The part is also easily made with a 3D printer. The video below shows how to use SprutCAM Computer Aided Machining software to prepare for machining the mount on a CNC mill. SprutCAM America offers teachers a very sophisticated, easy to use program at a very affordable price with free evaluations.

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Machining from plastic. Coolant clears the chips and keeps the finish smooth.

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3D printed from ABS

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Insert sonar directly and fasten with double sided tape or #2 screws

Now that the parts are all machined and gathered together, we can begin wiring up the robot. Let’s start with our wiring diagram. Students need to study and discuss the function of each wire. If they have already created a basicbot, they should be prepared to point out differences between what they have and what will need to be changed. Can they explain the purpose of the 5 volt regulator? Why don’t we pull 5V directly from the arduino to power the servos and sonar? And so on.

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The complete wiring diagram. We have added a servo and sonar sensor compared to the standard basicbot.

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Details showing pinouts. Note the sharing of a common ground rail among the 5V accessories.

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Take care to note the orientation of the breadboard in the schematic is flipped 180 degrees from the one on the robot photos. Use the 5V and 12V labels in the diagram.

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Use size 2-56 bolts and nuts to attach the servo upside down to the upper chassis section.

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Make note of the pin locations before attaching the sonar to the mount.

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The ‘horn’ that came with the 9G servo is used to connect the motor to the sonar mount with a small screw that is driven through the plastic.

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There are four wires on the sonar: VCC and GND will go the the 5V rail, while TRIG and ECHO are fed through to the arduino pins.

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The sonar should turn freely without binding any of the wires.

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Use tie wraps to keep things tidy and prevent wires from coming loose.

It always helps to have photos of a project from as many angles as possible, so here are a few to help with any wire routing questions.

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Programming For Success

After you have checked wiring carefully, power up the robot and raise the wheels onto a platform. Open the arduino IDE and connect the robot to your computer via usb cable. If you have not already calibrated the servos, do so now. The sketch below will allow the BasicBot to navigate autonomously around obstacles within 1 meter or more. It can and should be altered by students to make the robot behave the way they wish. The comments written in the code itself are designed to be read by students as part of this lesson. Teachers should spend time going over these comments and the code with students to discuss alterations that can be made, and how they can  be expected to affect robot behavior. This technique can allow students to ‘reverse engineer’ how the code works by testing various parameters even if they have little programming experience. Take a look at the sample window below from the sketch. Student programmers should get in the habit of writing their own comments on all code they write.

 

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Downloading the code from the link below will provide more comments to look over. Loading it on to the robot should result in behavior similar to that in the video:

This concludes the TeachSTEMNow BasicBot series. Students have had the opportunity for high-level STEM skill development, and this simple project should serve as a springboard for others to come. Be sure and visit prior and future STEM lessons on TeachSTEMNow for more hands-on, manufacturing-focused STEM projects for your classroom.

 

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TSN BasicBot Part Four: Assembly and Tuning

November 14th, 2013 by

In the fourth part of the TSN BasicBot series, we will complete the assembly of  the CNC machined chassis, adding in the arduino microcontroller, breadboard, battery, and wire everything up. Next we will locate the center (zero) position of the modified servos using a simple arduino program.  Instructions for this STEM lesson are in order of assembly priority.

Getting Wired 

Now we will discuss the details of wiring up the various components so that your BasicBot functions as it should. As with any set of instructions, read through the entire procedure before proceeding. The BasicBot requires no special  knowledge in terms of wiring. An overall wiring diagram is shown below. Let’s find out how to make it work.

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Battery

WARNING: Despite what you see in the illustration above, DO NOT use a 9 volt  rectangular battery for this project. It is incapable of providing enough current to run the robot. You can use a AA battery pack (6-12v) or lipoly battery of at least 1800 mah. For example, the pack pictured below has 8 AA batteries for a total of 12Volts.

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Switch Harness

A switch is essential to power cycle the robot.It connects the battery to the robot. Here is how you build the switch wiring harness. You will need the following materials for this procedure:

12 inches each of 22 awg stranded wire

20 jumper wires

A reliable connector (we use Deans-style connectors)

A SPDT switch with two terminals

Heat Shrink Tube

Soldering Iron and Solder

Solder Fan (follow the link to learn how to make one)

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Start by soldering a positive and negative (preferably red and black) wire to the MALE half of the plug. The FEMALE half goes on the battery. This should be remembered as a general rule for students to keep in mind whenever wiring connectors.

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Cover the terminals completely with heat shrink tube to eliminate any chance of a short circuit.

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Solder two (+) red wires to the switch terminals and  cover with heat shrink tube. You will be left with two open ends. One will be joined to the red wire from the plug connector, the other will be pushed into the terminal of the breadboard to power up the ‘Bot. The dangling black wire from the connector will also go to the breadboard. Here is how it should look when finished.

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The switch will be clipped securely between the middle and upper levels of the chassis as shown.

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Secure the battery on the middle level of the chassis. Exact placement is not critical but use double sided tape, velcro or zip ties to ensure its stability during maneuvers. Pull the servo cables through and plug jumper wires into the plugs as shown.

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Next attach the Arduino Uno to the upper level using nylon nuts and bolts. If you are bolting the arduino to a metal chassis piece use an extra nut directly underneath the board to keep it electrically isolated. Once the arduino is mounted, attach it along with the chassis to the standoffs to complete the third level.

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Standoffs are used to elevate and secure the different platforms to one another. There are two types that we use in classroom projects. The first, and most versatile is simply a  bolt with a couple of extra nuts as shown below. This type of standoff can be fashioned easily and adjusted to any size at low cost. It is a bit more labor intensive to set up initially but works quite well overall.

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The second type of standoff is purchased in specific lengths and hole sizes. Having an assortment of sizes handy will avoid unnecessary trips to the hardware store.  They are available with and without studs and in nearly any hole size. We use hex-shaped 4-40 standoffs on the BasicBot.

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Both type of standoffs are shown side by side below for comparison.

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Breadboard and VR

Behind the arduino the solderless breadboard will be attached. This is particularly easy because breadboards generally come with an adhesive back. Just peel it off and you are done. A 8.2cm x 5.5cm x .85cm board fits the BasicBot perfectly. Along with the breadboard a 5 volt regulator is needed. This is required because it is best practice NOT to power accessories from the pinouts on the arduino. We want to avoid glitches caused by excess power draw that can cause intermittent resets on the arduino, possibly damaging it. The regulator will permit us to pull a steady 5 volts from the breadboard for the servos (and sensors we will add later), while providing the arduino with reliable power. WARNING: The regular will get warm, possibly very hot during use as it changes excess voltage to heat. Do not touch it.

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In these days of inexpensive electronic components, you may elect to add an LED voltmeter to the BasicBot. Available for less than ten dollars shipped, these provide an instantaneous readout of the current (no pun intended) state of your battery. They add some ‘bling’ as well. A standard digital multimeter is still essential for any robotics project. The two are devices are shown below.

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Pull the jumper wires from the servos and run the signal wires (yellow or white) to pins 9 and 11. Twist the red and black(orange/brown) together and run them to the ground and 5V power rail on the breadboard.

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The battery wires go the opposite rail as shown in the wiring diagram. This forms two separate power rails, a 12V for arduino power and 5V for accessories. If you are using one, the LED voltmeter is connected to the 5V rail as shown below. Remember to  refer to the diagram at the top of the article for reference on the complete BasicBot wiring details.

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Here is another look at the complete schematic (LED voltmeter not shown) for your convenience.

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Double check that there are no loose or dangling wires, and switch on the power. If all is well, it should look like this:

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On to programming!

Zeroing Out Your Servos

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Modifying hobby servos generally means that the potentiometer is no longer able to provide positional feedback, so we must relocate the center point in its travel. This way we can consistently program servo direction and stop on a dime.

Open arduino IDE on your computer and create a blank sketch. Elevate the rear of the robot on a block and turn on the power. Plug the usb programming cable into the robot, then your computer. Download the ‘ServoCenterCalibrate‘ code below into the blank sketch and name it ‘servocenter’.

Run this program on one servo at a time.  The critical value is the angle of the servo, generally around 90 degrees. You will change the servo_left.write() value, starting at 90. You should start there and run the program, observing which direction the servo turns each time. The idea is to find the point where the servo reverses direction. Gradually you will get closer to the zero value, most likely going past it as you see the wheel reverse direction. Once this has occurred, you are very close. Slowly ratchet the number higher or lower, and then the servo will stop. This is the zero value for that servo. Take a piece of tape and write this number down, placing the tape near the servo. Proceed in the same way with the other motor. Remember to change the servo.attach() value for the other arduino pin.

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The entire procedure is summarized in the video below.

 

The Box Test

Now we can put the servo calibration to good use with the Box Test. This is simply a program consisting of a series of straight lines and turns resulting in a box pattern. It indicates that the servos are running at the same speed and verifies that they can be stopped consistently. The code is found below with the rest of the downloads. Obviously you will need to incorporate values that work for your servos, but the numbers in the program should be close. Comments are contained in the program to describe the functions of each line of code for students to easily learn their way around programming arduino. See the video below for an example of a successful box test.

 

In creating the TSN BasicBot, your students have demonstrated many of the proficiencies in the Common Core and Next Generation Science standards. They have used advanced manufacturing to build robot components, learned arduino microcontroller programming, experimented with and refined their robot with genuine engineering practices. Next we will raise the bar by making the robot able to respond independently to its environment with sensors. Keep STEM alive in your school with TeachSTEM Now!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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TSN BasicBot Part 3: Let’s Get Rolling

October 28th, 2013 by

The TSN BasicBot being manufactured in this tutorial is a STEM teaching platform designed to be versatile enough for expansion into other, more sophisticated roles with minimal changes. This is the third installment of the series, so be sure that students have checked out parts one and two as well. Now that the TSN BasicBot Chassis has been CNC’d (see part one) it’s time to get the machine moving. Two wheel servo drive is the force behind the rear wheels, and a unique 3-D printed caster is mounted at the front. The system enables the relatively low-powered motors to move the robot easily on any smooth surface, with highly responsive turning in a minimal radius. In this STEM lesson, students will manufacture the wheels and attach the servos and caster to the front of the chassis. All CAD files are available for download so your students can quickly CNC their way to their own TSN BasicBot.

Round ‘Em Up-Manufacturing the Wheels with CNC

The wheels can be made of metal or plastic. Plastic such as ABS or Delrin can be successfully milled and is shown in this example. The CAM process is the same which ever material is chosen. The feeds and speeds when milling may be different however, so consult the recommended settings for your particular circumstance. SprutCAM is our CAM software of choice thanks to its ease of use and education-friendly pricing from the folks at SprutCAM America.

As always we begin by importing the .igs file into the desktop.

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Next the faces are sewn together and the Z-axis is positioned at the top of the part.

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Our first machining operation is to cut the three interior pockets of the wheel. Select the edges of the pockets by holding down the ctrl key. Then choose add pocket under the job assignment tab.

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The default pockets are too deep but we adjust them to the proper value in the parameters tab. In addition to the -Z value for final cut depth, we can select the tool, adjust feeds and speeds and cut strategy here as well.

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The next operation will be to drill the mounting holes in the center of the wheel. Simply select a face on each hole and choose the center option on the job assignment tab.

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Double check and adjust the drill depth as necessary in the parameters setting. Here you will also set the feeds and speeds of the drilling operation.

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The final machining operation of the wheel is a 2D contour cutting it free from the stock material. Select the edges of the wheel after creating the operation.

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Choose add curves in the job assignment tab. The toolpath appears. Under parameters, adjust the depth of cut, feeds and speeds, and strategy.

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Remember to click run and look for the happy green checks for each operation.

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Next simulate the entire machining process.

Finally, clamp the stock material to your mill and enjoy the power of CNC manufacturing as the wheel is cut out.

Be sure and make two wheels for each robot.

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The wheels will be mounted to servo motors modified for continuous rotation. A detailed STEM lesson on servo modification can be found here. Servos are generally packaged with several servo ‘horns’ which are mounted to the splined gear protruding from the case. We use the round servo horns in this case, drilled out and bolted to the wheels as shown. Nylon 4-40 nuts and bolts were used in this instance. Metal works fine as well of course, but in class we often use nylon bolts. They are surprisingly durable and are easily cut to length.

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 A Question of Balance

The front end of the TSN BasicBot is supported by a caster. The caster is a 3D printed piece with a single bolt in the center and a decorative yet functional marble as the rolling surface. A metal 5/8 inch ball bearing can be substituted as well. The marble simply snaps into position and is firmly held in place by small overhangs on the walls of the caster. It can then be placed in a variety of locations on the BasicBot chassis.

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Assembly 

Attach the servo mounts (STEM lesson found here) to the upper and lower level of the chassis using 4-40 bolts. Bolt the servos to the mounts, making sure to route the wires forward toward the front of the chassis.

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One standoff at the front of the robot is sufficient for chassis rigidity thanks to the inherent strength of the rear servo mounting system. Pull the servo wires up through the curved ‘smiley face’ for access to power and signal from the microcontroller. The photo shows two additional standoffs at the front of the robot in preparation for mounting the third and final level.

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In the next TSN BasicBot STEM lesson, students will add a third chassis section,  power supply, microcontroller and breadboard, as well write a simple program to get the robot moving under its own power. Stay tuned.

 

 

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CNC BasicBot Part 2: Motor Mounts

October 1st, 2013 by

The TSN BasicBot platform is designed with hobby servo use in mind for simple, reliable and inexpensive motion. Multiple holes the in motor mount region provide for variations in servo size and wheel placement. The servo mounts themselves form a major structural element of the BasicBot, together with the servo motors themselves to resist twisting forces. In this STEM lesson, we will guide students to successful CAM programming the servo mounts for machining on the CNC mill. The activity teaches students how to create pockets, contours, and creating new machine coordinate systems for part rotation. The written summary below highlights the CAM process. A more in-depth video is available at the bottom of the page. For students that do not have the benefit of a CNC mill, the part can be manufactured from plastic on a 3D printer as well.

Step One: Import the part

Import the .igs file into SprutCAM and drag select the entire part. Sew the faces together and select the transform button. Locate the Z axis to the top of the part.

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Step Two: Pocketing

Click on the machining tab and create a pocketing operation.

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Make sure that the edge tool on the upper part of the screen is active. Then hold the ctrl key and select the edges of the pocket. Double check that no segments were missed.

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Go to the job assignment tab on the bottom left of the screen and choose add curves. The pocket will be created.

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Click the run button and the toolpath will be generated. Look for the green check to appear.

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The depth of the pocket will need to be adjusted in the parameters. Double click on the pocketing operation. Here you will select the endmill from your tool library, adjust feeds and speeds, as well as the pocket depth.

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Before selecting the endmill, verify that the tool number corresponds to that in the tool library. Manually adjust if needed.

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After adjusting the -Z value, the correct pocketing depth is achieved.

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Exit parameters, click run again and look for the green check. Go to the simulation tab and run the simulation.

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Step Three: Contouring

Create a 2D contour operation by going back to the machining tab. Go to finishing operations and find 2D contour. Holding the ctrl key, select the outer edges of the motor mount. Then within the job assignment tab, add curves as with the previous operation.

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A path is generated around the servo mount. Choose the parameters for your endmill, feeds and speeds, depth of cut, and final cut depth. We are using .25 material in this case and run the endmill slightly over. You can elect to run slightly under the actual depth to stabilize the part and then knock it  out, but this usually requires a bit of deburring.

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Once the operation parameters are completed, click the run button to get the green check. Verify all is well with a simulation.

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Step Four: Flip and Drill

This is a more advanced technique that will greatly benefit students, giving them the freedom to put all machining processes in one CAM program. Begin by rotating the part so the face to be drilled is oriented at the top. Create a hole machining operation. Click on the face and move up to the dropdown menu near the global CS tab. Choose the sense look vector option.

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SprutCAM will automatically create a new Coordinate System, moving the axes so the Z is on the new ‘top’ of the part.

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Next, go to the setup tab at the bottom left of the screen. Here we need to enable the machine setup parameters to recognize the new coordinate system.

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Change the local cs settings to the new coordinate system name (probably local CS1 in this case) for Local CS, Workpiece CS, and Workpiece Setup.

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Now to back to the job assignment tab. Select one of the faces in each hole that needs to be drilled while holding down the ctrl key. Click center and the holes will be recognized.

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Click the run button and the green check will appear as the toothpath is generated.

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Step Five: One More Time

There is one more hole to be drilled which means flipping the part again. Follow the same procedure as above, generating a new CS after selecting the new top face. Enable the coordinates on the machine setup tab, and select the hole. Click run to generate the toolpath.

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At this point the simulation tab should indicate all green checks and the toolpaths will all be visible. Run the complete simulation to double check before machining. Students always get a kick out of the final simulations.

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This completes the CAM process for the servo mounts on the BasicBot. These parts can be machined from Aluminum, plastic such as delrin or 3D printed. Using advanced manufacturing skills for genuine projects with long term educational value make STEM education an authentic experience with rewards that payoff all year long. For the complete CAM process in real time, check the video below.

 

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CNC BasicBot Adapts To All Your Classroom Needs

September 29th, 2013 by

The TSN BasicBot is a platform for STEM students to develop an array of future-ready skills that demonstrate mastery of key science and engineering concepts in the classroom. BasicBot is a scalable, multilevel chassis that is easy to manufacture,  build and modify. It has the capability to transform from a simple teaching platform to a combat ready sumobot in short order. With the BasicBot project, students will become proficient at a large number of STEM skills from writing code to advanced manufacturing. BasicBot is designed primarily for use with standard hobby servos and an arduino microcontroller, but thanks to its versatile design it can accomodate a variety of other options.   The chassis can be manufactured from a variety of materials, including wood, plastic, acrylic and metal. Teaching students advanced manufacturing is a key STEM skill, and the BasicBot provides an opportunity for teachers to get students comfortable using Computer Aided Manufacturing software due to its simplicity. In this STEM lesson, we will use SprutCAM software to prepare the BasicBot design for manufacture with a CNC vertical milling machine. The instructions are based on the .igs file supplied in this tutorial. The entire CAM process can be viewed on the video at the end.

Step One: Load the Model and Import

Import the .igs model into SprutCAM (SC) and save the project.

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Step Two: Transform Axes

Sew the faces together, and click the transform tab. Locate the Z axis to maximum. The default settings for X and Y will be fine.

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Step Three: Drilling Holes

Create a drilling operation by going to the machining tab. Choose hole drilling. Next, click job assignment on the bottom left of the screen. Drag select the holes that need to be drilled in groups. Be careful not to accidentally select one of the slots or outer edges. Add these to the job assignment by selecting center.

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Manually select the faces of each hole on the outer perimeter of the chassis. You can add each one to the job assignment individually or hold down the ctrl key and multiple select them.

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Double click on the hole machining operation to edit the parameters. You will need to set the appropriate tool from your tool library, the Z retract height, and the (-Z) drilling depth.

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Hit the run button to generate the toolpath, then simulate the operation.

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Step Four: Slotting

The slots in the model allow for wire passage and more versatile component placement on the BasicBot. To create the slots we will create a 2D contour operation. In the finishing tab click on 2D contouring.

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Make sure that the edge tool is highlighted on the upper right of the SC screen. Select the job assignment tab on the bottom left of the screen as before. Choose the edges of each slot while clicking the ctrl key.

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Click add curves after each complete set of slots. Make sure there are no gaps or SC will not generate a toolpath. Set the parameters for the job by double clicking on it. This includes selecting the endmill you will be using, feeds and speeds, depth of cut, and so on. More details are provided in the accompanying video. Run the operation to generate the toolpath, then simulate the operation. If it checks out, move on to the final step.

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Step Five: Final Cut

Create another 2D contour operation as shown above. This time select the outer edges of the chassis for final cut out. Add to the job assignment as before and generate the toolpath.

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Consider using a smaller endmill for making nice sharp inside corners if available. Parameters will need to be adjusted before hitting the run button and doing the final simulation with all operations.

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Summary

Using CAM to prepare for CNC manufacture of the BasicBot chassis is an excellent introduction to advanced manufacturing for students. Take advantage of SprutCAM America‘s offer of a substantial classroom discount for this powerful and easy to use tool. This series of BasicBot STEM tutorials will continue with further CNC component manufacturing, as well as programming and other lessons to maximize use of the BasicBot to make your students future ready for STEM Now.

Video:

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STEAM Education Takes Center Stage With Soldermites

September 16th, 2013 by

 

STEAM education has been getting a lot of press lately, and rightly so. Adding the ‘A’ to STEM means that STEM skills should not be the exclusive domain of science and engineering course work in schools. There is much in the way of cross disciplinary critical thinking that goes into the practices espoused by STEM educators, and many are of the opinion that STEAM will be the more common terminology going forward.

Soldering is an essential skill for any student who is serious about electronics of course, but this skill can and should be a part of less traditional areas as well. Artists routinely use metalworking skills in sculpture and jewlery, for example. The study of art also bring a different perspective than mere functionality to design that is the standard in engineering. The challenge as educators is to incorporate STEAM concepts into less traditional environments which may not have equipment or facilities that lend themselves to these objectives.  Learning to solder, and even identifying the basic function of electronic components in any classroom can be made fun through a project we call soldermites.  They are known as soldermites in class because they require soldering and often resemble insects (termites).  One student suggested ‘mite’ is the Aussie pronunciation for ‘mate’ or friend, so to him he was creating little soldered friends.  However students interpret the name, it is something they look forward to each year. Making soldermites a part of your curriculum is an excellent way to introduce STEM students of any level. The creativity and techniques are perfect for integration into an art activity. We have also used soldermites for Common Core ELA projects. Soldermites are a an excellent way to break into electronics and can be taken as far as you wish, from pure artistry to fully functional. These projects can come out amazingly expressive once kids get used to manipulating, bending, and soldering them together with confidence.

Tools Required

Pencil Soldering iron

Rosin Core Solder

Wire Cutters

Miscellaneous Salvaged Electronic Components

Helping Hands (To Hold Parts While Soldering)

Craft Foam (Optional)

Safety Goggles

Preface the lab with a soldering tutorial. This activity will be their first (for many) hands on soldering practice. If you have access to a solder fume fan, use it. In any case, a properly ventilated area is necessary to reduce fumes.

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1. Distribute:

Each student gets a handful of surplus parts.

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2. Functions:

With a general guide provided, students can look up the functions of these components in a circuit. Advanced students can get more detailed, such as explaining a NPN vs PNP transistor, or determining resistor values using color codes.

3. Sorting:

Students will sort the parts by functionality:resistors, capacitors, transistors, wire, ‘unknown’ etc.

4. Design:

This is the most difficult part of the activity for many students. Getting started requires some imagination and willingness to try things that may turn out unexpectedly. People, vehicles, robots, pets, seem to come naturally once they get going. Student who wish to draw or sketch should be encouraged to do this to help  them visualize ideas.

5. Solder/Assemble

Students should practice bonding the parts together as cleanly as possible, avoid ‘cold’ solder joints. They should make use of the trimmer to keep things clean.

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Sometimes it is not possible to solder parts together due to the nature of their materials. In this case you can have students use hot glue or in the example here, poke a hole and twist it into place.

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Have students build at least 2 figures each. To help them stand up, you can get some craft foam and poke them in with some wire or paperclips for balance. We have even used packaging peanuts for this. For a more permanent display you can use perf board.  Although this can be a  bit expensive, this is another skill that can expand this activity.

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6. For bonus points/extended activity, encourage students to create soldermites that are functional. This is generally limited to LEDs that light up, or possibly pager motors that vibrate-but it adds life to these creations. Caution: If you plan to allow students to have batteries (button cells are best) beware of capacitors that can be dangerously overcharged (explode). To avoid this don’t let students have more than one battery each.

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7. Extension

The Common Core ELA connection brings soldermites to life in a short story. Have students write about the figures they make. Below is an example a student assembled from the three objects shown in the photos that accompany this lesson. He told a story about a war veteran who came back severely injured, and sat with his young son and their pet robodog for this first time since his return from the front.

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The figures in this activity were created by students and incorporate multiple learning domains. The skills they learn via STEAM allow them to combine a broad range of thinking skills into a fun, hands on activity that enhances their technical confidence and reaches into the common core. Consider doing soldermites in your class room for a chance to diversify your curriculum and challenge students to find the unexpected within themselves.

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Start The STEM Year Right With This Easy Solder Fume Fan

September 4th, 2013 by

Soldering is an essential STEM skill that empowers students to make things involving anything electrical. In the past decade or two, high school voc-ed courses typically included an electronics curriculum, complete with oscilloscopes, transistor radio kits and television repair. Modern throw-away electronics with built-in obsolescence have reduced the need for repair technicians and the desire to fix things ourselves has been a faded relic for many years.  While the realm of electronics as a venue for educating students in science and engineering has sadly been disregarded over the past decade,  thanks to the DIY and Maker movement more teachers bringing are looking to bring back soldering to their students as a valued skill set. Kids who become proficient at soldering have a whole world of possibilities not open to them previously.

When students disassemble salvaged electronics to repurpose the parts into their own projects, create circuits to run an animatronic display, repair a robot during the heat of competition, or anything in between, they apply the laws of electricity in ways that solving Ohm’s law problems on paper can not replicate. Instead, ideas can come to life that enable students to create moving, talking, roving projects that demonstrate proficiency in real science and engineering practices. Knowing how to solder means that the need to look for kits that exclaim ‘No Soldering Required’ is well, no longer required. In fact, the expense of kits of any kit is reduced to purchasing individual parts or expanding the use of the class ‘inventor’s inventory’.

The process of soldering does create some smoke and fumes and should always be done with adequate ventilation. Even with ventilation, directing smoke away from students is always desirable. In order to do this,  small portable fan can be used with a carbon filter can be made as a class project that doubles as a learning experience and practical tool to reduce smoke inhalation as students solder during the year.

Tools and Materials

Raw Material for Panel-.125 inch Acrylic, Aluminum or Wood Sheet

12V Computer Cooling Fan

Single Pole Switch

18 Gauge Wire

Wire Strippers/Crimpers

Carbon Filter Sheet

Double Sided Tape

Battery Pack

Batteries

Digital Calipers

6/32 bolts and nuts(4 each)

Test Wires With Alligator Clips

 

Learning Outcomes

-Students will use caliper to measure features for panel design

-Students will design a control panel/mount using CAD

-Students will manufacture a mount using CNC equipment

-Students will solder, crimp and strip wire

-Students will apply Ohm’s Law to creating a circuit with a switch and load

Step One

Discussion

What is soldering? Many people think it is the same as welding on a small scale, so it is important to distinguish between these similar looking processes. Spend time on soldering safety, including the requirement to wear safety goggles and keep the room ventilated. If you are using leaded solder, explain to students that the soldering iron does not heat lead to its vaporization point so they are not breathing in lead fumes.  A typical pencil type soldering iron is heated to about 500 degrees Fahrenheit, while lead doesn’t even think about vaporizing until at least 1000 degrees. However, they must wash their hands after soldering to avoid accidental ingestion of lead. Since soldering does produce some localized smoke, explain that this project will reduce the smoke and fatigue that can be caused by it, making things that much safer and more productive.

Step Two

Create a plan

Students should write a summary of the project purpose and describe their plan to achieve it. This plan should include a research component and simple outline of the proposed project workflow for the group.

Step Three

Gather Materials and Measure

One caveat for students is to use materials that can be accommodated by the panel they will make. If you provide them with a 4-inch high piece of aluminum, they should not choose a 5 inch high fan for this project. They will need to account for the space taken up by the other components as well, including the switch and battery pack.

Nearly any 12 volt fan will do. These are easily scavenged from computers, power supplies, copy machines, even old overhead projectors (remember those?) Some fans will have more than two wires. In this case one is probably used for speed control, another may be a sensor wire, etc. Test the wires in pairs using a battery pack to determine which two are needed to power it up. It is recommended to use a fan with plastic rather than metal blades. Either way, watch out for fingers when fans start up!

The switch can be salvaged from nearly any electronic device. High quality switches can be purchased very inexpensively in bulk at a variety of electronic supply houses as well, some for as little as a nickel apiece.

The carbon filter material can be purchased in sheets or rolls at your local hardware center. These are generally meant for air purifiers or home ventilation systems and can be cut to fit with scissors.

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Step Four

Test The Circuit

Before soldering or crimping, it is best to test the components working together in the circuit. Use the alligator clips, being cautious to avoid metal to metal contact and a short circuit. The switch simply needs to cut power (open the circuit) from the path of electrons, so place it in between the terminal of the battery and the load (fan). The switch should be cycled a few times to make sure all is well. Label the front of the fan where air is pulled in for proper orientation later during assembly.

Step Five

Measure and Design

Download the .dxf file provided for the panel that fit the components used in this article. If the students part’s fit perfectly, great. Either way, they will need to use the calipers to determine hole spacing, the size of the switch, and leave room for the battery pack behind the panel. The panel can be designed in any number of CAD programs that can export to your CNC machine. Note that there is a second, smaller panel that functions as a spacer to keep the filter from being caught in the fan blades.

 

Step Six

Manufacture Panels

The flat panel can be made on a laser cutter out of wood or plastic, or cut on a CNC mill. The example shown was cut on a laser out of acrylic. For quality control purposes, have students run the laser at low power over a piece of scrap cardboard, then double check the spacing of holes and components before making the final version from acrylic. Panels made from aluminum on the mill can be powder coated and laser engraved for advanced students. A tutorial on this process is forthcoming.

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Step Seven

Wiring and Assembly

The fan can be a bit fiddly so students should start with that. Verify that the fan is turned in the right to direction to draw air in toward it, which should be easy if students followed directions from step 4 above. They will need to position the filter between the main panel and the spacer to avoid having the fan stopped or slowed by the filter impacting the blades. Trim the fan wires to a reasonably neat length, leaving a bit extra for mistakes. Solder or crimp with a butt connector the negative lead of the fan to negative lead of the battery wire. Snap the switch into the panel. If necessary, use a file or small blade to trim the switch housing, not the panel if possible.

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The positive (+) wire from the battery will be wired to one of the terminals on the switch. Use soldered or crimped spade connectors for the switch end of the wire. Avoid soldering the wires directly to the switch unless it is unavoidable and you are absolutely sure that they will not need to be removed. The (+) end of the fan wire will be crimped to the other terminal on the switch, completing the circuit.

The penultimate step is to use the double sided tape to fix the battery holder  to the panel. Orient it in such a way that the batteries can be replaced without ripping the holder off the panel, causing a mess with the remaining tape.

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The final step is to reflect on the process of building their solder fumigator, describing the experience and how they would revise it if they had to do it again, knowing what they know now. Sharing this experience and documenting this process online allows students to demonstrate common core proficiencies in ELA areas.

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Conclusion

In the STEM activity, students have created their own version of a solder fume extractor while developing skills in design, manufacturing, soldering and building an electrical circuit. Students demonstrate their proficiencies in project planning, They will  use this device while continuing to improve their soldering abilities, empowering them to apply their creativity to real science and engineering projects in the classroom involving electronics to prepare them for the STEM careers that lie ahead.

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Step Up to Stepper Motors II: Unipolar Motor Control

August 15th, 2013 by

Conquering The Mysteries of 5-and 6-Wire Stepper Motors

 

In the previous installment of this STEM lesson series, we learned about the basics of stepper motors: what sets them apart from other commonly available motors, how they function, and a few quick steps students can use to get them working. While stepper motors can’t be made to run simply by connecting them to a battery, they are easy to use with an inexpensive arduino and motor shield. To illustrate these concepts we used 4-wire bipolar stepper motors, commonly found in scanners, copy machines, and even some CNC machines. A basic program was used from the arduino library, along with a commercially available motor driver shield from Adafruit.

When disassembling broken printers and scanners it is common to find 4-wire bipolar as well as 5- and 6-wire unipolar steppers within. In this stem lesson, students will learn to use a technique that helps them identify wires in these motors to conveniently permit their use in projects. They will look at more precisely controlling the movement of the stepper motor by programming it to use half steps and microsteps, and the engineering compromises inherent within each choice.

The learning outcomes include:

Using a digital multimeter and record resistance values in a matrix

Interpreting resistance values to determine wiring sequence of a stepper motor

Programming stepper motors to move precisely in any direction or position

Applying  ohm’s law to ensure a safe match of components

 

 Five-Wire Steppers

After picking up their motor, students should identify the wire colors and create a matrix as shown, filling N/A into redundant matches.

Next, using a digital multimeter (DMM) set the resistance scale to 200 ohms, and begin probing each terminal. If you want to toss in some math, have students determine the number combinations possible so they can see why recording data in a table like this is essential scientific practice.

When examining the motor, a bit of luck and a google search may turn up a datasheet. While these can be intimidating, they can provide some clues as to resistance, voltage and step degree specification. Once done this information should be recorded as well as shared with others.

Here are some resistance values from a five-wire stepper pulled out of a copy machine:

black green yellow orange red
black N/a 119.6 119.4 119.3 60.4
green 119.4 N/a 119.1 119.5 60.4
yellow 129 118.8 N/a 119.4 60.1
orange 119.5 119.3 118.8 N/a 60.4
red 60.6 60.3 60.4 60.1 N/a

 

This particular motor had a readable sticker on that indicates a resistance of 61 ohms. This is confirmed by the numbers on the above chart in all red wire combinations. The specifications also revealed that this motor is 7.5 degrees per step, so a complete revolution will take 360/7.5 or 48 steps. Before connecting this motor to our shield, we need to be sure not to exceed the limits of the hardware. We will be supplying our motor with a 12v external power cell. Applying Ohm’s law we get I=V/R value of about .2 A of current draw, well within the specification of the motor driver we are using.

Students need to verify on their own that their motor falls within spec using this method, and record this information for later use.

Interpretation

Once the numbers have been generated, it becomes obvious that any pair with the red wire has a different value from the rest. It will be our center, common ground  wire inserted into the middle terminal on the Adafruit shield.

A bit of trial and error is called for next, where the remaining pairs are connected to the shield and the program is run. Students can load the Stepper Test program to use for this process, with a few changes as shown in the comments in the program image below. Note that this sketch is set up for a 7.5 degree motor with 48 steps. Adjustments may be needed for different spec motors, changing the ’48’ value to ‘200’ for example if you have a 1.8 degree motor.

wiringsketch

 

A quick swap or two will verify the right pair order when the stepper motor by observing a complete rotation. Student should attach a piece of tape to the motor shaft if needed to make the rotation easier to see. Again, recording the results of each swap and taking a quick snapshot of the final, correct sequence will prove to be extremely helpful for later.

5wireconnection

 

The Six-Wire Solution

 

6-wire steppers are also frequently used in electronics that are salvaged, and using the above technique will take the mystery out these motors. Students can again create their own matrix and use the DMM to record the resistance values for each pair of wires. Those with some resistance are connected, those with no connection show infinite resistance (a value of 1 in this case).Take a look at the chart for a 6 wire stepper.

 

Orange Blue Yellow Red White Lt Blue
Orange N/a 4.8 1 1 2.8 1
Blue 4.8 N/a 1 1 2.9 1
Yellow 1 1 N/a 4.8 1 3.2
Red 1 1 4.8 N/a 1 2.9
White 3.2 2.9 1 1 N/a 1
Lt Blue 1 1 2.8 2.9 1 N/a

 

Looking at the results, we find that two pairs of wires have the most resistance, red/yellow and orange/blue. We will connect them to our free motor ports. This leaves us with the two common wires, white and light blue. It is possible that there will not be enough motor terminals to go around if you need 6 on your breakout board/shield . In the case of the Adafruit stepper shield we are using, it provides five ports. The solution is simple. The two commons are combined together in the remaining center port where the single common wire was placed in the five-wire stepper.

6wireconnection

 

Precise Control

One of the advantages of using stepper motors is how accurately their movement can be positioned. Regulating the exact point to which our motor turns is simple within the program structure used above. We have already determined that one complete revolution is 48 steps, so we indicate 96 steps for two rotations. If we want to turn ¾ turns, we specify 36 steps. Students should run a few tests to verify this for their motors.

What about the microstepping option mentioned earlier? Where does it fit in this scheme? This topic is worthy of discussion, demonstration and experimentation. With a simple programming change, microsteps and other variants are possible. The most immediate effect of microstepping is a smoother motion during rotation, and is particularly noticeable if your motor has somewhat coarse movement to begin with, such as 7.5 degrees/step.

Here is a clip of a 7.5 degree motor turning single steps. Note the rather jerky motion as it rotates.

 

Cutting this down to ½, ¼ or smaller steps in the program does make it run smoother as demonstrated here:

However the tradeoff can be decreased precision, particularly at high speeds. The stepper running at ¼ steps may not always catch the same coil when asked to stop and start repeatedly, so you may lose steps over time. This is sometimes exhibited on 3D printers when they are asked to print too fast. On the other hand, if you start out with a 1.8 degree stepper motor, it is already smoother to begin with. It divides each rotation into 200 steps compared with 48, so each step is more refined, taking about ¼ the distance of the 7.5 motor. Because you can program it to run smoothly in single steps, a 1.8 degree motor is likely to be more repeatably able to start and stop at the same position for a desired amount of resolution. Shown below is a 1.8 degree motor running in single steps.

 

 

Students will wonder why products even use a motor with large steps then? Smooth motion must be balanced with another engineering trade off, available torque. The motors that run smoothly may not be able to carry the load needed for a particular application.  For example, moving a heavy spindle motor across a gantry is going to require some muscle, so a compromise between torque and smoothness will be needed, and half steps or smaller may be just the right option.

 

There are an unlimited number of ways to configure stepper motors both mechanically and in terms of programming. Engineers factor in the above considerations and many more before determining which stepper motors to use for a suitable for a particular application. As students engage in genuine science and engineering practices in your STEM class room, they are made continually aware of the need for compromises and tradeoffs in the real world.

In this STEM lesson students have used engineering tools and practices to determine how to make a salvaged stepper motor work for future applications. When taking advantage of harvested parts, they are repurposing electronic equipment that was destined for a landfill and adapting them for their own STEM projects. Taking advantage of what is available serves as a more genuine learning experience than using a kit from a box, as students must create and put to practice sustainable solutions to problems beyond the classroom.

 

 

 

 

 

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