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Abhi Verma
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Electronics Engineer
 · DelhiIndia
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TUTORIAL

Tutorial: Quad Copter parts and working explained

For someone new to the multirotor hobby, putting together your first quadcopter parts list can be extremely daunting. Trying to figure out what to buy and what parts will work together is tough, especially for people who don’t come from a background in radio controlled planes or helicopters. Forums are packed with people who want to build a quadcopter but don’t know where to start. It can be frustrating trying to sort through the thousands of posts on forums and blogs and figure out what to do. this post is designed to spell out exactly what you need for your first quadcopter build. While we will recommend a complete list of specific parts that we have used and tested for a complete quadcopter build, the main purpose of this post is to provide a general overview of the parts needed to build a quadcopter. Here’s what you’ll need:

  1. Frame
  2. Motor x4
  3. Electronic Speed Control (ESC) x4
  4. Flight Control Board
  5. Radio transmitter and receiver
  6. Propeller x4 (2 clockwise and 2 counter-clockwise)
  7. Battery & Charger
    You will also need some miscellaneous things like zip ties, double sided tape and/or velcro, a small amount of heavy gauge wire, battery strap, and some female to female servo leads or jumper wires. As far as tools go, you will want to have access to a soldering iron, small screwdrivers, hex wrenches, needle-nose pliers, and a hot glue gun. Now we’ll go over each part in detail and provide a specific recommendation.

FRAME:-

Every quadcopter or other multirotor aircraft needs a frame to house all the other components. Things to consider here are weight, size, and materials. Your Frame will also have power distribution board (PDB). PDB is used to provide power for all the ESCs, Motors, flight controller boards etc.
Your frame should be light weight yet strong enough to handle all the components and thrust generated by Motors.
Quadcopter frame have four booms (arms). Motors are mounted on the ends of these arms.
One thing to keep in mind is that when you are placing the components on your frame, try to keep gravity point as near as possible to centre of frame to balance the quadcopter.

MOTORS:-

The motors have an obvious purpose: to spin the propellers. The motors being used in quadcopters are brushless dc motors (BLDC). These motors have great speed and power to weight ratios. Brushed dc motors are not usable to high speed operations as they are heavy and generate spark at high speed due to brushes and commuters. And their efficiency is around 70-80% while bldc motors have 80-85% of efficiency. Also bldc motors are good for speed control applications.
BLDC motors are very light weight and comes with two types-

  1. Out-runner
  2. In-runner
    Both types have their pros and cons. In-runner motors are not good for fast operations is because the inner armature tends to expand due to heat at high speeds and this causes problems. While out-runner doesn’t have this issue.
    There are tons of motors on the market suitable for quadcopters, and usually you don’t want to get the absolute cheapest motors available, but you also don’t want to break the bank when some reasonably priced motors will suffice. Motors are rated by kilovolts, and the higher the kV rating, the faster the motor spins at a constant voltage. When purchasing motors, most websites will indicate how many amps the ESC you pair it with should be and the size of propeller you should use. We have found that a 1000kV motor is a good size to start with.
    This kv rating also indicates that RPM per volt. So 1000Kv will spin 1000 RPM at 1 volts and 8000 RPM at 8 volts.

Electronic Speed Controls (ESC):-

The electronic speed control, or ESC, is what tells the motors how fast to spin at any given time. You need four ESCs for a quadcopter, one connected to each motor. The ESCs are then connected directly to the battery through either a wiring harness or power distribution board. Many ESCs come with a built in battery eliminator circuit (BEC), which allows you to power things like your flight control board and radio receiver without connecting them directly to the battery. Because the motors on a quadcopter must all spin at precise speeds to achieve accurate flight, the ESC is very important. These days if you are building a quadcopter or other multirotor, it is pretty much standard to use ESCs that have the SimonK firmware on them. This firmware changes the refresh rate of the ESC so the motors get many more instructions per second from the ESC, thus have greater control over the quadcopter’s behavior. Many companies sell ESCs that have the SimonK firmware already installed.
ESC takes input form of pulse. It counts the microseconds of pulse high time and then control the speed of motor according to that. In most of the remotes maximum position of joystick produces 2000us pulse and minimum is 1000us. Our ESC calibrated to this input range will rotate the motor at lowest speed when input pulse is 1000us long and max speed when input pulse is 2000us long.
Flight controller gives many instructions per seconds to ESC to stabilize the quadcopter. it is around 400Hz for SimonK firmware ESC.

Flight Controller:-

Flight controller board is the brain of quad copter. It is the most important part of any quadcopter. It has integrated sensors like gyroscope to detect angular velocity of quad, accelerometer to detect which side high or low and leveling itself. It also receives remote control signals via Radio receiver and control the flight of quad copter.
Flight controller board controls the speed of all the motors via ESC by giving them appropriate pulse signal. There are many flight controller boards available in market e.g. Hobby king KK 2.0, Ardupilot APM 2.8 etc.
For starting at low cost kk2.0 is good, while for apm2.8 is good for better options and control costing higher then kk2.0.
Some boards also have additional ports to connect extra hardware and sensors e.g. barometers, GPS, magnetometer, Gyroscope and accelerometer etc.
It depends on your application and budget to choose one.

Radio Transmitter and Receiver:-

The radio transmitter and receiver allow you to control the quadcopter. There are many suitable models available, but you will need at least four channels for a basic quadcopter with the KK2.0 control board. We recommend using a radio with 8 channels, so there is more flexibility for later projects that may require more channels. The Turnigy 9x is a great choice for a first radio. It’s inexpensive yet still has some advanced functionality. There is also a large community of 9x users out there, so troubleshooting is easier. Chances are any problem you have has been experienced and solved before, or someone on a forum like rcgroups will be able to help you out.

Propellers:-

A quadcopter has four propellers, two “normal” propellers that spin counter-clockwise, and two “pusher” propellers that spin clockwise. The pusher propellers will usually be labeled with an ‘R’ after the size. Propellers are made of light and strong plastic kind of material.
There are different types of propellers;-

  1. 2 blade propellers
  2. 3 blade propellers
  3. 4 blade propellers
    Choose any but 2 blade propellers are used most followed by 3 blade propellers. The size of propellers matters. Tiny propellers will spin fast easily but don’t have much thrust to lift the quadcopter. While large propellers will drain battery very soon, as they are hard to rotate fast due to inertia. Too choose the right propellers go to the datasheet of your motors. There will be a table which tells the amount of the thrust generated by motor using different size of propellers. With correct propellers your quad should be able to lift in the air at half of the throttle. So total amount of thrust generated by all your motors should be 2 times of your quadcopter weight with all the components.
    1000KV motors generate nearly 900 gram of thrust with 10x4.5 propellers. Total thrust will be 3.6 Kg. so these propellers are good for quadcopters having weight 1.5-2 Kg.

Batteries:-

Quad copters needs high amount of current from batteries. So ordinary batteries can not be used here. We need a battery with very fast discharge rate to provide the required power.
Quadcopters typically use LiPo batteries which come in a variety of sizes and configurations. We typically use 3S1P batteries, which indicates 3 cells in series. Each cell is 3.7 volts, so this battery is rated at 11.1 volts. Each cell can be charged upto 4.2 volts max, so battery max charge voltage will be 12.6 volts. Your battery should not cross that limit in charging. And minimum voltage is 9 volts, showing battery empty. Try not to discharge your battery below 30% to maintain the life cycle of the battery i.e. 10 volts. LiPo batteries also have a C rating and a power rating in mAh (which stands for milliamps per hour). The C rating describes the rate at which power can be drawn from the battery, and the power rating describes how much power the battery can supply. Larger batteries weigh more so there is always a tradeoff between flight duration and total weight. A general rule of thumb is that doubling the battery power will get you 50% more flight time, assuming your quadcopter can lift the additional weight. For starting 2500 mah to 3000 mah batteries are good to provide decent flight time with less weight.

Battery Charger:-

Charging LiPos is a complex process, because there are usually multiple cells within the battery that must be charged and discharged at the same rate. Therefore you must have a balance charger. There are many chargers on the market that will do the job, but be careful of cheap or off-brand chargers as many of them have faulty components and can cause explosions or fires. In general you should absolutely never leave LiPo batteries charging unattended. Many people charge batteries outside on a cement area or in a fireproof LiPo bag (although the effectiveness of these is up for debate).

Working:-
Flight controller maintains the level of the quad copter by varying speed of motors. But to know the correct speed for every motors it needs to handle multiple things. In starting when we arm the motors , our flight controller calibrate the gyro to get the adjustment readings. So it can find out absolute zero value even with noisy signal. After calibration of gyro it gives 1000us pulse to motors (min throttle pulse, depends on Remote calibration) . when throttle increases, it speed up the motors and continuously taking reading from gyro, accelerometer, magnetometer and other sensors to determine it’s position and tilting. If quad is tilted in any direction, it takes input from accelerometer and gyro and calculate the compensating values with the help of PID control loop. When user gives any input from remote like pitch or roll signals, flight controller again calculate the difference between desired position (Remote input ) and current position (sensor input) as error. And compensate this by again calculating signal with the help of PID loop.
Gyro tells the flight controller how fast it is moving over a axis, while accelerometer tells how much it is tilted on any of side in form gravitational force (g). magnetometer tells about the direction of quad copter to control yaw.
Flight controller process all this information and calculate the compensate signal with PID and give it to motors.
This whole stuff is done multiple times in a second, Few hundred times/second (250Hz to 400 Hz for standard ESC and Flight controllers). Thus controlling the flight of quad copter.

Motors regulation and stabilization of drone:-
Auto leveling or stabilization is the most important part of flight control in multi rotors.
Motor speed is controlled by ESC. ESC takes PWM signals from flight controller board and control the speed of motor.
To stabilize the drone flight controller needs to constantly adjust the output of motors and monitoring the position of drone. To determine the drone state flight controller have many sensors like gyro, accelerometer etc. it takes input from user and then read the current position of the drone, and generate the error.
Let’s assume that roll, pitch and yaw are at centre position or zero (or Stabilization mode).
It tells flight controller to keep all the sensor values near to zero, showing drone in horizontal leveling. So flight controller sets the desired position as zero for all the sensors stating no movement. It takes continuous readings from sensors and calculate the error between desired position and current position. This error is then multiplied by gain and a compensate value is generated by the PID control loop and this value is added to throttle value and then combined signal is fed to ESCs to control the motors. This process is done at very fast rate to control the motors efficiently and stabilize the drone.
PID control loop is the key here to stabilize or control the drone with efficiency. PID control is a complete topic to understand. But here is a video by joop brooking, which makes it easy to understand. Give it a try-

Drones
Quadcopter
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Edmund Leo Rico
 · Cavite CityPhilippines
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Great work as well as the article! A must read for noob builders like me.

Permission to share in a local drone group in PH.

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Ranjan Dailata
25 Contributor
Application Architect/Lead Developer
 · ChicagoU.S.
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Great work here. Really nice to see a fully furnished article 😃

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Jenson Palathara
Aeronautical engineer
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awsome

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Lucky Enamejewa
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great idea and good works

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Pruthvi Av
1 Apprentice
 · VisakhapatnamIndia
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Great work Abhi

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Abhi Verma
18 Contributor
Electronics Engineer
 · DelhiIndia
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Thanx everyone

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