In this article by Vasilis Tzivaras, the author of Building a Quadcopter with Arduino, we will go through almost every crucial component needed for the building of a quadcopter. All the parts will be explained and information about the usage of each one will be given. Furthermore, you will be able to find some simple instructions and a list of specifications that you should be aware of when buying a component. Thus, you will know how to choose your component based on your requirements. Hopefully, by the end of this article, you will be able to estimate the cost of your build and have a total overview. This is extremely important when building a craft because you always need to be aware of the final purpose. You always need to know and have an abstract picture of the parts you need and how they shall be connected.
In this article, we will cover the following topics:
- The motors and propellers
- The electronic speed controller (ESC)
- The flight controller
- The battery and charger
- The power distribution system
(For more resources related to this topic, see here.)
Radio transmitter and receiver (TX/RX)
It is important to have an overview of the connections between the battery, motors, and the ESCs. The following figure will make this clear:
Motors and propellers
A propeller is mounted on the shaft of the corresponding motors. The total number of motors that is needed depends on the build. For example, quadcopters use four motors, hexacopters use six, octacopters use eight, and so on.
Nowadays, brushless out runner motors are the most common type of motors used; they have minimal friction. A cylindrical shell of magnets rotates on precision bearings around a core of tightly and neatly coiled wire. The propeller is mounted at the top and is rotating at the same angular velocity as the motor. As a result, thrust is produced and the quadcopter lifts from the ground. Every motor requires a reasonable maintenance; dirt should be kept outside so that the motor can spin easily.
Common motor specifications
For every motor, there is a specification manual either provided from the manufacturer or the seller. The following is a list of specifications that almost every motor has:
- KV (rpm/v)
- Weight (g)
- Max current (A)
- Max voltage (V)
- Length (mm)
- Shaft (mm)
- Diameter (mm)
An example of the specifications can be found when choosing a motor, which is shown in the following table. These specifications were on the same webpage where the motor was bought from. Furthermore, motors typically specify a recommended battery cell count, for example 3S, 4S or even 5S. It is important to buy recommended parts in case you are not an expert:
It is important to be aware of each of the following specifications:
- The KV value indicates how many RPMs (revolutions per minute) the motor will make when provided with V number of volts. Notice that increasing the KV does not mean that your quadcopter will fly better or it will be more stable. There are many important factors that we should be aware of. For example, the more KV means more thrust. As a result, the motors will consume more battery and the flight time will decrease.
- The weight value indicates the weight of the motor. Note that we have four motors in our build, so we have to sum up for four times the weight of each motor.
- The only time when you should worry about the length, shaft, or diameter is when you build your own frame and you have to drill some holes.
- Lastly, the current and voltage will have an effect on the electronic speed controller (ESC), which will be mentioned later. For now, just keep in mind that we have to choose the appropriate ESC according to the current and voltage.
Choosing a motor
The first thing that we should ask ourselves is about the total weight that we are expecting to lift with our quadcopter. At first, it is difficult to calculate the weight as we have no idea how much it is; so usually, we choose all the parts apart from the motor and estimate a possible total weight.
Since the weight factor must be eliminated by the total thrust the quadcopter produces, it is important to choose a motor that has the desired thrust. Generally, motors should provide a thrust that is two times the weight. It ensures that the quadcopter has the best balance over those factors. Note that it is important to keep the balance. In other words, if the weight is too little or too much, compared to the thrust, the quadcopter will either have extreme sensitivity to all its maneuvers or it will not lift at all, respectively.
Motors that fit your needs can be found in the market. However, it is mandatory to keep in mind that more weight, even if your motor can eliminate it, means reduced flight time. After all, it’s all about the stability and flight time.
Choosing an appropriate propeller
A quadcopter uses two clockwise and two counterclockwise propellers. They are usually classified by their length and pitch. For example, 10×4.5 propellers are 10 inch long and have a pitch of 4.5. There are two factors that characterize a propeller, dimension and material.
Choosing the right dimension
When choosing a propeller dimension, you need to find a good balance between the length and pitch. For quadcopters that do acrobatics or fly in races, we need acceleration and this means that we need torque. So, you will need propellers with small pitch and high KV motors; so that you have more RPMs and a higher torque. As a result, your quadcopter will have more acceleration and eventually will be faster.
On the other hand, for larger quadcopters that carry payloads such as a camera, large propellers and low KV motors tend to be the best choice. These have rotational momentum and easily maintain your aircraft’s stability.
Choosing the right material
There are different types of propellers, such as plastic, carbon fiber, and more. The plastic propellers are cheaper and more flexible. This means that there will be more blade flapping, which will make your quadcopter more unsteady; this is something that we don’t want. However, in the worst case scenario, if you have an accident with that propeller, you will not have a big injury. Also, when plastic hits an object it may not get damaged. On the other hand, carbon fiber propellers have lesser blade flapping because they are harder. If a spinning carbon fiber propeller touches your skin, it will be a big injury, so you may have to protect your propellers somehow.
It’s important to mention that blade flapping reduces flight time and craft stability. So, for your overall craft build, it’s better to buy carbon fiber propellers and keep a safe distance from any person that may be near it.
Gathering more information
It is a good practice to ask questions in Facebook groups or forums. There are many people who have different builds of quadcopters and the information about the motor and propeller used may be valuable. Furthermore, when buying from eBay or other sites, there are offers along with the motor that recommend you the propellers. Usually, there will be a diagram that explains how much thrust the motor will have as an output when a specific propeller is mounted.
The electronic speed controller or ESC uses a PWM signal coming from the flight controller to create an average voltage/current to control the speed of the motor. There are three sets of wires; one set goes to the batteries, one set goes to the flight controller, and one set goes to the motors. It consists of three wires, which we usually define as servo wires, two of which of are marked as Vin (small red) and Ground (small black). The third one is the PWM signal (white) from the flight controller. The stronger the signal, more is the current through the ESC. It is also connected to the battery via a T connector using a positive and a negative wire. Furthermore, ESCs’ output is through the three wires that are all connected to the motor (blue), as shown in the following image. Lastly, there is another input coming in from the battery. Each ESC has to be connected through a power distribution system to the battery. As shown in the following image, the two left wires (red and black) must be connected to the battery to power up the ESC and the motor. To sum up, ESCs have an input of 12V (depending on the battery used) and they have wires that go to the motor giving an input to the motors from 1V to 12V.
As mentioned earlier, we need to have two clockwise and two counterclockwise motors. Therefore, by swapping any two of the three wires that connect the motor and the ESC, we can invert the rotation. For now, connecting the wires in any combination will be fine.
Choosing the appropriate ESC
Many motors have a recommended ESC. The specification that changes in different ESCs is Ampere. When we covered motors in the Common motor specifications section of this article, there was a table that had a recommended ESC of 18A. So according to that motor, the ESC that we buy should be max 18A.
Battery and charger
Batteries usually last for 10 to 20 minutes. By the end of a flight, you will have to recharge your battery to prepare your quadcopter for another flight. There are various batteries and chargers out there and almost all of them will work. However, when building a quadcopter for aerial photography, we will not just hover over the ground so we need something light and, as much as possible, lightweight.
Choosing a battery
A battery can be described by the following factors:
- Milliampere hours (mAh)
- Number of cells
The following image shows a suitable battery:
Most of the DIY quadcopters have a 12.1V battery with a 500 to 5000mAh. The total flight time depends on the mAh that your battery has but keep in mind that the higher the mAh the more weight on your quadcopter. So it’s crucial to have a good balance and not buy a 10,000 mAh battery that will weigh 800 gms. There are batteries with 2, 3, or 4 cells. You will notice that in specifications the battery will have 3S or 4S. The S rating is the number of cells the battery has. A general rule says, the more the better but it also depends on your charger and on your ESCs.
So to conclude with, a good choice should be a battery over 2500mAh but lower than 3500mAh with 12.1V and 3S.
Choosing a compatible charger
The batteries last for 10 to 20 minutes. After that you will need to charge your battery and prepare your craft for another flight. It’s crucial to reach over 15% of your total mAh before charging. Many chargers will notify you with a message of low voltage. There are chargers that charge only LiPo batteries and chargers that charge 2 or 3 different battery types; it really depends on your budget. However, many people say that a good charger will make your battery last longer and keep your craft from voltage spikes, which may cause a crash.
An IMAX-B6 charger can charge LiPo and other type of batteries. Usually, multicopters use LiPo batteries but there are cases when you might need something else. It’s always a good choice to have something compatible with the NiHM batteries too. More information will be given in.
Power distribution boards
Usually, quadcopters have one battery. But how can we connect one battery to four ESCs? A power distribution board is the answer. It is a simple board that has two pins as input to the board and four or more outputs. Therefore, we can connect our battery and have up to 8 outputs and each one of them is connected to the battery. The following image is of a simple power distribution board that can be found in the market:
As you can see, there are four blocks of two outputs. Each output consists of two pins: one positive and one negative. There are two more pins, one positive and one negative for your battery connection.
Make sure that this board does not touch any other conductive material. To conclude we can say, through this board we can power up all our ESCs with the voltage of our battery.
Radio transmitter and receiver
Remotely piloted quadcopters are controlled from a ground station using some kind of transmitter and receiver mounted on the craft. This communication system is simple, reliable, and easy to install. Note that the ground station is actually a pilot with a transmitter in his hands. We can define a ground station with many more systems but a simplified model of communication is preferred. Transmitters usually look similar to the following screenshot:
They have two sticks and a screen for all the configuration setups. A joystick can also be used as a transmitter but a proper transmitter is recommended for new pilots. Let’s have a close look at what a transmitter consists of:
Four channels are used namely throttle, rudder, aileron, and elevator; yaw, pitch, and roll are fully controlled through these channels. Furthermore, a transmitter is equipped with two or more channels for extra functions; for example, a pilot may need to light up some LEDs, activate a system while flying, or capture an aerial photograph. All these are extra functions that a pilot can activate through any extra channel.
Usually, these systems have some kind of memory that stores its data even if the battery is disconnected. Memory is required for saving all the configuration a model has. For example, let’s say that we have two airplanes, one helicopter and one multicopter and we need to save all the configuration of our models without any conflict. The transmitters have this option and we can try to fly our craft, change the settings, fly again, modify configurations, and then lock our configurations and save them for future flights.
Apart from the four sticks that any pilot uses to control its craft, there should be four trim sticks with which we can change the trim of the craft according to the drag it has. Assuming that the minimum throttle is 1000 and the maximum is 2000, trimming the throttle channel has an effect on the min-max range. In other words, if we trim the throttle, minimum may be 1050, 1100 or even 1200. Practically, at the exact moment that we pull our stick a bit, the minimum throttle will be sent to the flight controller.
For each transmitter, there is a receiver of the same GHz. The receiver simply receives a signal from the specific transmitter and through the right pins passes the signals to the flight controller, as shown in the following image:
Quadcopters can be programmed and controlled in many different ways. Usually, there are two modes: acrobatic and stable mode. The difference is the way the controller board interprets the orientations feedback, together with your RC transmitter joysticks.
As shown in the following image, this is the transmitter that Parrot uses in some of their quadcopters. Even if it is quite strange, it actually consists of two sticks and a tablet where you can see what your quadcopter sees:
By now, almost all of the parts needed for your build should be clear and you should have a basic understanding of each part’s usage in the overall build. Before mounting everything on our frame, we need to solder and prepare all these and some more electronic parts and of course create a frame.
Resources for Article:
Further resources on this subject:
- Building a “Click-to-Go” Robot [article]
- Arduino Development [article]
- Prototyping Arduino Projects using Python [article]