What is quadcopter?

A quad copter also called quad rotor or quad rotor helicopter is an example of multi rotor.In quad copter, generally there are two pairs of identical fixed pitched propeller.

Two clockwise and two counterclockwise propeller.By varying each rotor speed, thrust produced and as a result,the quad copter gets lifted up

How Does it Work?

        Before you start choosing your components, it's learn about how they work with your quadcopter. Let's begin with the frame of your quadcopter. The frame provides the structure and rigidity and it's where all the component will be mounted on it. The flight controller manipulates the RPM of the individual motor in responses to user input. If you tell it go backward, the flight controller adjust the RPM of motor so it go backward. The ESC are take signal from the flight controller and the adjust the speed of motor. The motor and propeller provide the thrust and lift for your quadcopter. The battery provide power to all component. The radio are control the movement of quadcopter Following materials required

• Frame
• Motor
• Propellers
• ESC
• Battery
• Transmitter
• Receiver
• Battery charger
• Flight controller
• Miscellaneous materials 
• Tools

Choosing the best Components

1.Frame Styles
            One of the most important part of multi rotor is it's frame because it supports motor and other component and prevents them from vibration. Two types of frame styles are common ACRO and FPV(First Person View). ACRO frame are perfect X shape. FPV frame are diffrent in shape and come in multiple styles X and H. Structure of the frame contain Arm,Central Plate and Landing Skid.
               You can make frame from any material like Carbon fiber,PVCpipes,Aluminium or Plywood but make sure it enough strength to withstand impact and rough landings. Frame wight should be 150-250 grams. Size of multi rotor frame, there is no thumb rule for medium size quadcopter(four rotor) 450-550 mm motor to motor frame is enough. If your frame is to big compare the your power setup(motor-prop,esc,battery) it will flight with each other.We want to build quadcopter so make sure the angle between two arms is 90 degree and also check arm are twisted.
              Making frame is truly depends your imagination,skill and availabel  of material. Also you can simply buy readymade Frame from the market

. Quadcopter frame and lipo battery and motor and propeller size matching table

Frame Size	Prop Size	Motor Size	Motor KV	Lipo battery
120mm or smaller	3 inch	1104 – 1105	4000KV+	80-800mAh 1s/2s
150mm – 160mm	3-4 inch	1306 – 1407	3000KV+	600-900mAh 2s/3s
180mm	4 inch	1806 – 2204	2600KV+	1000-1300mAh 3s/4s
210mm	5 inch	2204 – 2206	2300KV-2700KV	1000-1300mAh 3s/4s
250mm	6 inch	2204 – 2208	2000KV-2300KV	1300-1800mAh 3s/4s
330mm – 350mm	7, 8 inch	2208 – 2212	1500KV-1600KV	2200-3200mah 3s/4s
450mm – 500mm	9,10,11 inch	2212 – 2216	800KV-1000KV	3300mAh 4s or +  *source from rc dron

                                   

  2.Motor

                   One of the important part of multi rotor is its motor. It's a part of power system. Infact whole power system depends on selection of motor so you should be very careful while selecting motor. We use Brushless motors(BLDC) for multi rotor.              The motors have an obvious purpose to spin the propellers. There are tons of motors on the market suitable for quadcopters. Motors are rated by kilovolts(KV), 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. 

   Thrust Requirement

        First, of all, estimate the total weight of your quadcopter. Don’t worry if you can’t get the total weight precisely the first time, it can just be your best guess. It should include everything you plan to take on-board: frame, FC, PDB, motors, propellers, ESC’s, LiPo battery, payload . Once you’ve worked out quadcopter weight and frame size, you can now calculate roughly how much thrust the motors need to deliver in order to lift the aircraft, by using propellers of certain sizes.

Thrust to Weight Ratio

                     A rule of thumb is that the multi rotor should be able to at least provide two times the amount of thrust than the total weight. Remember that this is the minimum magnitude of thrust required by a drone so that it becomes easier to placing certain location. With a thrust that is not comparable to the weight of the drone, your device might not even possess enough power to take off.

                  Let’s consider this example. If we have a quadcopter with an over all weight of about 1 Kg, the total thrust that the motors should be able to produce at maximum throttle should be 2 Kg at the minimum or say 500 g per motor in case of a quadcopter.

             For faster flying like drone racing, you should expect the ratio to go much higher than this. It’s not uncommon to see someone build a mini quad that can achieve 8:1, even 10:1 thrust to weight ratio.Using For aerial videography and photography, we recommend you to go for a thrust to weight ratio of 3:1 or 4:1.

KV

         Motors are identified by a 4-digit number – AABB. “AA” corresponds to the stator width while the “BB” represents the stator height. KV is another factor(velocity constant) .It are refered to as KV, Kv, and kv but not in kV(kilo volt). It is the theoretical increment in rotor’s revolutions per minute (RPM) when the voltage would increase by 1 Volt without any load.The rotating speed of motor equal to the multiply of KV and Voltage.  For example 1000KV motor powered with 11.6V power supply. Rotating speed is 1000 x 11.60 = 11600 revolution per minute. KV are related to power out from a motor or more usefully the torque level of motor. Low kv motor, it will carry more volt at less amps and produce a higher torque and swing bigger and low pitched prop.  The higher KV value will cause lower torque. Therefore the KV value is highly affect choose of propeller, since larger propeller needs higher torque (lower KV) to rotate.

             For racing and acrobatics more suitable low kv motor that are rated over 1200kv. For a heavy paylod motor that are rated under 850kv or 1000kv. weight more than 1kg use a motor below 1000kv, between 500 to 1000 grams  use motor between 900 to 1300kv and craft below 500 grams motor around 1300 to 2200kv

Voltage and Current Draw

                 It’s important to understand that voltage has a large impact on your motor and propeller choice too. Your motor will try to spin much harder when a higher voltage is applied, and thus drawing a higher current. Always check thrust data first.Now you select ESC of the required current rating.

How to Read Motor Specification           

             When selecting motors, there is usually specification of motor are provided by the seller or manufacturer. You should be able to find information about the power, thrust,weight...ect. For example 

•  kv                              :1000kv
• Weihgt                         :47g
• Operating current        :4A~10A
• Peak current                :12A
• Dimension                    :27.5 30 mm
• Shaft size                     :3.17mm
• Suggested prop           :10.11 4.7
• Battery unit                   :2-3S Lipo                       

ESC(Electronics Speed Controller)

                       ESC are controlling speed of motor. ESC is ability to switch maximum current required to all motor and ability to withstand the voltage from the battery. Normally ESC is rated in Amerage rating. Standard rage of ESC is 12A-40A for multi rotor.

How to Select ESC                     

                         Selected ESC must be higher than max amp rating of motor.

• ESC max current rating is 1.5x max amp rating of motor
• ESC mini current rating is 1.2x  max amp rating of motor

For example, selected motor draw maximum 12 Amp so ESC rating should be in between 10A to 18A. It's not a thumb rule and also check ESC are programing facility.

Types

1. 4 in One

                  4 in one ESC which four ESC are join to get to form a single board. This are small wight and it improve wight distrubution.

   2.BEC

     Technically BEC stand for battery eliminating circuit.simple means that ESC with a BEC are able to output constant voltage and power the equipment (reciver,flight controller...ect)

    3.OPTO ESC

          ESC without BEC are often referred to as optoisolater.

It means ESC that receiver the signal from flight controller or R/C receiver is isolated from the higher voltage circuit that powering to motor 

              

Battery 

      In order to get a best flight time and performance it important choosing best Lipo battery. Lipo(Lithium polymer battery)have high energy density, high discharge rate and light weight. Lipo battery are specified in Discharging Rate(C rating),current Draw in mili-amp hours(mAh),and cell count(S)

  Max continous  Amps draw =Battery capacity(Ah)x10^-3xDischarging rate(C)

                  Choosing battery,first calculate total Amp rating of each motor in multi rotor.Quadcopter are four motor for example current draw of motor is 12Amp then 4x12=48A we have 2200mAh 3Cell Lipo battery 25C rating

therefor total continuous output=55A

            To get longest flight time you should use largest battery.Higher cell count more powerfull battery 

Propeller

           Basically propeller is type of fan that convert rotational motion into thrust and transmit the generated power.Propeller is specified by 4 digit number first two number is diameter and last two number is pitch Both are in inches. eg: 10x4.5 Diameter of prop is the diameter of a virtual circle make when it is spinning and Pitch can define as the travel distance of one single prop rotation.Larger prop. the more energy it take to spin it and more thrust produced.

          How to choose a propeller? Select motor first and decide ESC,Lipo battery and propeller . It is not a thrum rule.Calculate approximate weight of you multi rotor and take twise total weight.Then give thrust of each motor.Choose motor, and select Lipo battery from manual of motor thrust tabel also give propeller size

         Higher diameter or pitch prop required to low KV motor and Low pitch or diameter prop need to higher KV motor.On every multi rotor there are pair of CW(clockwise) and CCW(counterclockwise) prop.Normally two blad prop are using for racing and free style flying. Triblades are more grip in air but more current draw

Flight Controller

        A flight controller (FC) is the brain of the aircraft, which is basically a circuit board that has built-in sensors that detects orientation changes. It also receives user commands, and controls the motors in order to keep the multi rotor in the air.Nearly all flight controllers have basic sensors such as Gyro (Gyroscopes) and Acc (Accelerometer). Some FC might include more advanced sensors such as Barometer (barometric pressure sensors) and magnetometer (compass).Flight controller is also a hub for many other peripherals, such as GPS, LED, Sonar sensor etc.There are many Flight controller out now in the market. Some of them are KK, MultiWii, Ardupilot, Naza, Naze, Rabbit, WKM and many other. 

     A flight controller is required to keep the multi copter stable.In addition to stabilization, modern flight controllers include.

• Return to Launch
• Stay in one place at a fixed altitude
• Fly automatically through various GPS path, before coming back to land.
• Transmit important data like flight speed, direction, altitude, battery life, etc.

RC Transmitter and Receiver

       A RC transmitter (TX) is a device that allows the pilots to control the aircraft wirelessly. The signal/commands are then received by a radio receiver (RX) which is connected to a flight controller.A radio controller usually comes with a receiver (RX). It’s important to know that a TX normally only works with radio receiver (RX) from the same brand.