Quadcopters are very much in fashion nowadays and their functionalities are immense. They can be used for recreation, experiments, learning, surveillance and much more. There are mainly two configurations of a quadcopters, + and x. For this guide, we will be using the X configuration.
How do Quadcopters work?
First thing’s first, we have to know how these lovely machines actually work. Basically, a quadcopter (as its name suggests) has 4 propellers, each powered by a DC brushless motor. Every motor turns the opposite way to its neighbour motor. For example, in the figure above, propeller 1 and 4 turns clockwise, whereas propeller 2 and 3 turns anti-clockwise. All propellers push the air downwards, so why do we make them turn in different directions? This is because rotating motors and propellers create angular momentum in the opposite direction to their rotation according to Newton’s third law of motion, these momentums have to be balanced so that the quadcopters does not spin about its axis indefinitely.
Intentionally changing these momentums by increasing/decreasing the motor speeds of say motors 1&4 or motors 2&3 makes the quadcopters turn about its axis either clockwise or anti-clockwise owing to the overall effect of the dominant momentums. This is equivalent to the Yaw effect seen in airplanes. Similarly, to change the pitch of the quadcopters, both the motors at front or back have to rotate at higher or lower speeds, thus, creating a differential in thrust and pitching the quadcopters’ front upwards or downwards. To induce a roll effect, adjacent motors on one side have to be intentionally spun at different speeds compared to the opposing motors on the other side, once again creating a differential in thrust that raises one side of the quadcopters for a roll manoeuvre e.g. higher speed of motors 1&2 will tilt the aircraft’s right side up.
The brown arrows indicate the torque produced by each motor and its direction. You can see how all the torques nicely balance out each other and that is why quadcopters are such stable designs. All this is explained nicely in the diagram above.
Basic Elements of a Quadcopter
Now that we know the basic Physics behind how a quadcopter flies. We need to understand the essential components of just about any quadcopters out there. They are:
- Flight Controller
- Electronic Speed Controllers (ESCs)
- Radio Controlled Transmitter/Receiver
- Battery and Power Distribution
Frame (3D printed Frame)
You have to 3D print one platform and four arms as part of a frame. The frame needs to have holes in it that can be used to fasten various electronics or batteries etc, these holes also reduce weight and help in allowing airflow during rapid ascent/descent. Connecting them up is pretty straightforward; you will need to screw the arms to the platform using appropriate nuts and bolts. The size of a quadcopter frame is determined diagonally (motor to motor) and this is very important for selecting propeller sizes later.
Generally, lightweight, strong and small frames are preferred so that the quadcopter can give maximum performance. It is also recommended to use a landing gear under the frame. There are two general types of 3D filaments: the PLA and ABS but it is recommended to use ABS for this project since they are flexible and strong. If you can, try to give extra support at places where the arms/booms and the main platform connect, as there is a danger of snapping due to extreme loads at these points, a simple solution is to use metal strings running under the arm and tied to the main platform. You may use strong double-sided tapes, mounting, spacers, nuts and bolts or strong glue to stick all your components onto the frame and arms.
This is one of the most crucial parts of any quadcopter; they are the engines that power flight. So, you have to choose a suitable motor to be mounted at the end of each arm. In general, DC Brushless motors are the preferred choice. Why? Because they are compact and give excellent controllable rotation speeds with almost no maintenance needs. They have excellent Power to Weight Rations and that is the most important factor when it comes to aerial vehicles. Another aspect of these motors is that they are outrunners, which means that the rotor that spins is the outside body of the motor, this is very good for generating high torques that are required to balance the quadcopter or turning it about its axis.
As a general rule of thumb, if your fully loaded quadcopter weighs 1 kg, you will need an overall thrust of about 2 kg (i.e. twice as much as its weight). This thrust can be divided onto the four motors; hence, each motor will need to give 500g of thrust (as we have 4 motors).
For this project, we will be using the MultiStar 2212 920kV DC Brushless motors as part of a Combo Set that comes with two motors and matched propellers. Now you might be thinking what do these numbers mean? 22 means the diameter of the motor stator in mm (stator is the part where all the windings are located and it does not turn but produces electromagnetic fields to influence permanent magnets placed on a rotor to make it turn), 12 means the height of the motor stator in mm, 920 kV means it will rotate at 920 revolutions per minute (RPM) if 1 volt is applied at no load conditions. Taller stators give you more power, whereas wider ones give more torque.
Keep in mind that higher kV is not always needed as low kV can turn larger propellers due to their higher torques, whereas high kVs are needed for smaller but faster propellers, for acrobatic quadcopters and the like. Higher kV also consumes a lot of power and will drain the battery faster, these motors may not have a long lifetime as well.
These motors have to be mounted at the end of each arm with appropriate mountings. They do require complicated electronics to change their speeds but that is where the Electronic Speed Controller (ESC) comes in.
Propellers come in various lengths and pitches. The length is essentially the circle’s diameter that the propeller will create while spinning and the pitch can be considered as the blade angle or distance traveled at after a single rotation. They are affixed to the motor, they can turn clockwise or anti-clockwise but they send air downwards to generate thrust and achieve lift. This is why you will see two different pairs of propellers for every quadcopter, one that spins clockwise, another that spins anti-clockwise, however, both push air downwards.
The larger the propeller or larger its pitch, the more power it will require and more thrust it will generate. However, the drawback is that there will be a significant decrease in efficiency (due to more wind drag) and agility of the aircraft (due to larger inertia). Make sure that your propeller sizes are not too large or else they might clash with each other when turning.
For this project, we will be using 9×4.3 propellers (9” length and 4.3” pitch). Now you can choose two bladed ones or three. Three blade propeller will give more thrust and grip in the air but they will be less efficient, whereas, two bladed propellers are highly efficient. We will be using the MultiStar Combo Set that comes with self-tightening propellers. Propellers can be CW (Counter Clockwise) or CCW (Counter Clockwise), make sure you buy a pair of both types as they self-tighten when the motors spin. The propellers should be rigid enough not to bend during high RPM and they must be lightweight. It’s always advisable to get some extra pairs just in case!
A flight controller is the brain of a quadcopter. It controls the motors and their speeds through the Electronic Speed Controllers. It interprets the Radio signal received and gives the required outputs. It also has PID (Proportional Integral Derivative) Controllers for error correction and making sure that the quadcopter is responsive and stable in flight using various complicated algorithms. Some Flight Controllers come with GPS, Video Transmission and other Telemetry facilities.
For this project, we will use the Naze32 Rev6 Flight Controller board. This is a very popular and successful board among quadcopter hobbyists and it supports Cleanflight Configurator app that is available as a Google Chrome app online. The board is very compact and lightweight. It has an onboard Accelerometer and Magnetometer/Gyro and supports a lot of additional functions such as GPS, Barometer, LED Strips, On Screen Display (OSD) modules etc.
These boards are usually shipped with pin-headers and wires, so you just have to connect them up with the motors and radio receiver device. It is also highly recommended to use a vibration-damping platform for the FC as the onboard sensors are very sensitive and any vibrations can become problematic at times. A universal Flight Controller damping board will be used in this project. Also, don’t forget to connect a battery voltage buzzer to the Flight Controller.
Electronic Speed Controllers (ESCs)
ESCs are used to control the speed of your Brushless DC motor. Basically a Brushless DC motor or BLDC motor needs a 3 phase varying AC signal in order to turn its rotor for a given speed. However, your Flight Controller will be providing a DC signal and the ESC converts that DC signal into a signal that the motor understands.
The most important factor in choosing an ESC is its current ratings, in our case, our motor can draw a maximum current of 20 Amps, this means your ESC should at least be 25 Amps or more so that it can adequately provide enough current to the motor. You will need four ESCs and they can be attached at the middle of each arm of the quadcopter.
ESCs are connected to the Flight Controller as well as the Battery and the motors. Usually, you will find inline ESCs that have 5 wires on one side and 3 on the other. The 3 wires go to a BLDC motor (i.e. the 3 phase signal from ESC) and the five wires have two power wires for connecting with the battery, two for powering the Flight Controller and one signal wire (usually orange). Such ESCs are said to have a BEC i.e. Battery Eliminator Circuit and this makes it convenient to supply power to the motors as well as Flight Controller and Radio Receiver etc, all from one battery.
Radio Controlled Transmitter/Receiver
Any good radio transmitter and a paired receiver can be used to send commands to the Flight Controller. Make sure that the Transmitter and Receiver are both able to talk to each other. A process called binding is used to connect the transmitter with the receiver module. There are mainly two dominant systems nowadays: PWM (the old school system) and PPM/CPPM (relatively newer technology and uses one signal wire).
PWM is basically Pulse Width Modulation, the position of a stick or any button determines the width of that channels’ PWM signal. In PWM systems, each channel has its own dedicated wire so a 4-channel quadcopter will have 4 signal wires coming from the receiver into the Flight Controller (one channel for every function). The signal can be between 1000 and 2000 value on Cleanflight.
PPM/CPPM means Pulse Position Modulation. This is also an analog system like the PWM, however, in this system, all the channel signals are stack against each other and sent on a single main channel, thus, you only need to connect one signal wire from the Radio Receiver into the Flight Controller as all the channels are combined together and the Flight Controller separates them. Usually, there will be three wires connected between the radio receiver and Flight Controller, two wires will supply power from the Flight Controller to the Radio Receiver and one signal wire will give a signal input into the Flight Controller. The benefit of this system is that you get more pins available on the Flight Controller for other tasks such as GPS, Light Indicators etc.
There is another system known as PCM i.e. Pulse Code Modulation, this is a digital system in which the position of transmitter stick is converted into a digital value and once again, all channels are combined into one main channel. This is good for low-interference and error-free signal transmission and reception.
Battery and Power Distribution
LiPo (Lithium Polymer) batteries are pretty much the standard nowadays as they are lightweight and have sufficient energy storage capacities. They come in various sizes but the most important factors in a battery are:
Voltage: Determined by the number of cells e.g. a 3S battery has 3 cells of 3.7V each, thus, making it an 11.1V battery (3 x 3.7V).
Capacity: This is the amount of energy or charge a battery can store. Usually, batteries come in mAh which means milli-Amp-hours e.g. a 2000 mAh battery can provide 2000 mA or 2 Amperes of current for 1 hour. The larger the capacity, the longer will be the flight time.
Discharge Rate: This is usually denoted by a number before a C e.g. 25C or 40C. The higher the C number, the higher current your battery can discharge and power the motors and other equipment onboard. You want to have a high discharge rate so that adequate power is available when needed, however, battery weight increases with higher C ratings. Let’s say we have a 2200 mAh 40C LiPo battery, so the maximum current that can be drawn will be = 2.2Amps x 40 = 88 Amps!
For Power Distribution, you have two options, either use a Power Distribution Board or simply use a Power Distribution Wire Harness. The job of a PDB or PDWH is to direct power from the battery into the ESCs using high current capacity cables. The ESCs will use this power to drive the motors as well as supply power to the Flight Controller via its built-in BEC. For this project, we will be using a Power Distribution Wire Harness. Be careful to match the connectors of the battery and ESCs with your PDB or PDH. Usually, LiPo batteries come with an XT60 connector (usually yellow) for discharging and a JST-XH connector (usually white) for charging via a battery charger. In case you get into trouble with connectors, you can always cut the ends and solder the wires directly to the board or any suitable connector of your choice.
List of Parts
- 1 x 3D Printed frame
- 1 x Universal Nylon Landing Skid Set (4 Legs). It can be bought here: https://hobbyking.com/en_us/universal-nylon-landing-skid-set-for-multi-rotor-frames-extended-100mm.html
- 2 x MultiStar Combo Sets (Each set has two 2212 920kV Motors and a pair of 9×4.3 self-tightening propellers – one is clockwise and the other is anti-clockwise). They can be brought here: https://hobbyking.com/en_us/multistar-350-to-450-frame-size-2212-combo-set-with-self-tightening-propellers-cw-ccw-set-of-2.html
- 1 x Naze32 Rev6 Flight Controller Board. You may buy it with pins already soldered or an unsoldered board that comes with various sets of pins and wires. It can be bought here: https://hobbyking.com/en_us/naze32r6-set-pcb-wire-pins.html
- 1x Naze32 Rev6 Flight Controller Mounting Base. It can be bought here: https://hobbyking.com/en_us/mini-flight-controller-mounting-base-30-5mm-naze32-kk-mini-cc3d-mini-apm-30-5mm-36mm.html. You may also use the Universal Damping Mount: https://hobbyking.com/en_us/hobbyking-universal-vibration-damping-mount-45x45mm.html
- 4 x MultiStar 30A Electronic Speed Controllers (ESC). They come with BEC (Battery Eliminator Circuit). They can be bought here: https://hobbyking.com/en_us/turnigy-multistar-30-amp-multi-rotor-brushless-esc-2-4s.html
- 1 x HobbyKing HK6S 6 channel Radio Transmitter (Mode 2) and Receiver Module Set. It can be bought here: https://hobbyking.com/en_us/hobbyking-hk6s-2-4ghz-fhss-6ch-tx-rx-mode-2.html
- 1 x 2200 mAh MultiStar 3S 40C LiPo (Lithium Polymer) Battery. It can be bought here: https://hobbyking.com/en_us/multistar-racer-2200mah-3s-40c.html
- 1 x Power Distribution Harness or you may buy a Power Distribution Board. These can be bought here: https://hobbyking.com/en_us/multistar-xt60-to-4-x-3-5mm-with-jst-plug-quadcopter-distribution-harness.html or https://hobbyking.com/en_us/hobby-king-quadcopter-power-distribution-board.html
- 1 x Strong Double Sided Tape. It can be bought here: https://hobbyking.com/en_us/double-sided-tape-for-outdoor-use.html
- 1 x Bag of Zip Ties. They can be bought here: https://hobbyking.com/en_us/cable-ties-200mm-x-4mm-green-100pcs.html
- 1 x Battery Plate. It can be bought here: https://hobbyking.com/en_us/turnigy-h-a-l-battery-mount-plate.html
- 1 x Battery Strap. It can be bought here: https://hobbyking.com/en_us/multistar-battery-strap-330mm.html
- 4 x Motor Mounts (16x19mm motor holes and 35mm mounting hole spacing). They can be bought here: https://hobbyking.com/en_us/hobbykingtm-carbon-fiber-motor-mount-for-sk450-42mm-pack-of-4.html
- 1 x Piezo Buzzer for Low Voltage Alarm. It can be bought here: https://hobbyking.com/en_us/piezo-buzzer-for-kk2-kk2-1-naze32-flight-control-boards-1pc.html
- 1 x LiPoly Battery Charger. It can be bought here: https://hobbyking.com/en_us/turnigy-p403-lipoly-life-ac-dc-battery-charger.html
- Required Nuts and Bolts and Wires.
- Soldering setup.
Step-by-Step Instructions for Building and Configuring
Have a look at the electrical connections diagram above. As you can see, the battery power goes to the Power Distribution Board, from where, it is re-directed to the ESCs that in turn power the motors. The ESCs also power the Flight Controller board (be careful in wiring). The Radio Receiver gets its power from the Flight Controller board and also provides the signals to it.
3D print your platform and arms/booms. Connect them using nuts and bolts. 14mm length or more would be good. Screw the Motor Mounts onto the Motor bases with screws (that come with Motors or use small size screws so that motor is not damaged) and then screw it to the end of the arm. The motors will be mounted in the middle of the mount and then the mount will be screwed onto the arms. Two screws on the opposite sides are enough, or else you might have to drill some holes for better grip.
Connect all four motors to their respective ESCs with 3.5mm connectors and attach the ESCs at around the middle of all the arms with zip ties. Three motor wires should be connected to three ESC wires, the order is not important.
Attach the Nylon Landing Gear legs to four corners of your platform, you may have to drill some holes in them and tighten with screws or use super glue.
Affix the battery plate under the main platform. You have two options, you may fix the plate well below the platform with some spacers/bolts and then place the battery on top of it or you can directly attach the plate to the platform and then let the battery hang below it via straps (in this case insert the straps before attaching the plate with the quadcopter platform).
Connect all ESCs to the Power Distribution Harness (one red and one black wire per ESC, make sure they are power wires for large currents). Leave the thin ESC wires unconnected for now. They will be connected to the Flight Controller.
Download the Cleanflight Configurator for Google Chrome and then launch it. Here is the link: https://chrome.google.com/webstore/detail/cleanflight-configurator/enacoimjcgeinfnnnpajinjgmkahmfgb?hl=en
Connect the Naze32 board to the computer via a USB cable to check it works. When the board connects, you will see a COM Port number in the Cleanflight app.
Click on the Firmware Flasher Tab at the left of the dashboard and select your board as NAZE, then select the latest stable firmware version in the drop down list. After that, select enable No Reboot Sequence, Flash on Connect and Full chip erase. This is how it should look like:
Then click on Load Firmware (Online) and after it has been loaded, click on Flash Firmware, this will install it on your board. Wait for Programming Successful!
Click on the Connect button in Cleanflight at the upper right-hand corner. You will immediately see a Quadcopter on the screen, move the board around now, the model Quadcopter on the screen will also move accordingly.
Now, place the Flight Controller completely leveled horizontally and click on Calibrate Accelerometer until it is finished. After this, click on Calibrate Magnetometer and turn the Flight Controller 360 degrees in all directions in under 30 seconds.
Click on Disconnect button in Cleanflight and take out the USB from the Flight Controller board. Time to solder/connect it up with wires.
If you have an unsoldered board, then it is recommended to solder header pins (straight and 90 degree bends as you like) for the motors and receiver.
Take the thin ESC wire of motor 1 (for signal and power) and connect it via the servo-type connector to the three pins inline in column 1 (shown above). The pin near to the edge of the board is Ground coming from the ESC, the middle pin is +5V coming from the ESC and the pin farthest from the board’s edge is the output signal pin that will control the motor speed via the ESC. Do this for the other three motors as well. You may use pin columns 1, 2, 3, 4 for four motors ESCs.
Connect the Radio Receiver Module to the Flight Controller via Female-Female Servo Cables. On the FC, GND, 5V, PWM1 wires can go to the first set of pins on the Radio Receiver and then only one wire needs to be connected to the respective PWM Pin on Receiver as well as the FC. You will connect four PWM wires. The GND and 5V will power up the Receiver from the Flight Controller.
Make sure that your Transmitter and Receiver are bound to each other, if they are not, then you need to follow a process to bind them. Basically, you have to turn off your Transmitter, connect the bind plug into the Bind pins of your Receiver as well as a battery, you will see a red flashing light. Then hold down the bind button on the Transmitter and turn it on, the flashing light on the Receiver will become stable and this means that your Transmitter and Receiver are now bound to each other. Remove the bind plug and it is good to go.
Connect the thin wires (JST connector) coming from your Power Distribution Harness (Battery) to the Flight Controller’s Battery Voltage Monitor pins (top is +ive and bottom is -ive), shown below:
Connect the buzzer +ive pin to the buzzer pin on the Flight Controller shown above (top is +ive and bottom is –ive). You may use pin headers or solder them.
Using strong double-sided tape, stick the Flight Controller firmly onto the platform. Do this for the receiver and buzzer as well.
Now that you have connected all four ESCs and the Receiver to the Flight Controller. Connect the Flight Controller to the Computer via USB and click on Connect Button in Cleanflight. Make sure your propellers are not mounted. It can be very dangerous. Connect the battery to your Power Distribution Harness (XT60 Connectors). You may hear some beeping music.
In Cleanflight, go to Configurations and change Maximum Throttle to 2000 and Minimum Throttle to 1000. Also, enable the VBAT (Battery Voltage) feature and set its minimum cell voltage to 3.4, maximum cell voltage to 4.2 and warning cell voltage to 3.6. If the measured voltage shown is incorrect (or the buzzer acts strangely), check the battery voltage with a multimeter and adjust the voltage scale feature such that readings on meter match with Cleanflight. Save it.
Go to Receiver Tab on the left inside Cleanflight and change your channel mapping accordingly. It can be edited to AETR1234 or TAER1234, depending on your receiver. A = Aileron (Roll), E= Elevator (Pitch), T = Throttle (Speed) and R = Rudder (Yaw). Check that your Transmitter is increasing/decreasing the bar graphs as needed. If channels are not correctly changing then you need to edit the text inside the Channel Map textbox. For example, Cleanflight shows TAER1234 and your throttle stick changes the Elevator instead of Throttle, then you write EATR1234, this will flip the Throttle and Elevator for you. Make sure that when your Transmitter sticks are in the middle, Cleanflight should show 1500 value for the horizontal bars, if not, then do some trimming on the Transmitters.
Disconnect the battery and turn off Transmitter. Go to Motors Tab in Cleanflight. Remember! DO NOT HAVE PROPELLERS ATTACHED. Turn on the checkbox that says I understand the risks, propellers are removed – Enable Motor Control. Take the Master slider all the way to the top, all motors will show full speed now.
Connect the battery and bring your Master slider completely down to 0. You will hear some beeps that tell us the ESCs are calibrated. Slowly move the Master slider upwards and all four motors should spin.
Make sure your motors are spinning in the right direction. Increase/Decrease each Motor’s slider bar and see if it is spinning clockwise or anticlockwise. In case a motor is spinning in the wrong direction, then simply flip any two wires between the motor and its ESC. You may refer to the Quadcopter diagram at the beginning of this guide.
To arm the motors, you have to push the Yaw stick all the way to the right (or left in some models). This will arm the motors and any change in Throttle Stick will change motor speeds. To disarm, do the opposite (take the Yaw stick all the way to the left). Disconnect the USB and your Quadcopter is ready to fly!