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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
You will need heat shrink tube to ensure strong and isolated connections. Get at least two different colors to easily identify wires.
Add zip ties to the list as well.
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.
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.
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.
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.