Building a Quadcopter (Part 2)

In my last blog on quadcopter ( Part # 1), we learnt about how to assemble a Q450  quadcopter  .In  Part #2 , we will answer the common questions..

  1. What does channel mean for a Radio control and what is the minimum number of channels required ?
  2. What is RollPitch , Yaw and Throttle in Quadcopter?
  3. How does Radio receiver command the  Flight Control Board , how does the control signals look like?
  4. How to identify a clock wise and counter clock wise propellers?
  5. How to mount the (CW) and (CCW) propellers  ?
  6. What does kv stand for on brush less motor ?

1.What does Channel mean ?  

A typical Transmitter Digaram

 When you decide to buy a RC Transmitter+ Receiver pair ,the first question you’ll be faced is , ” how many channels should it support and what exactly does this mean? “ . The number of channel means the number of variables you can control  using your RC Pair  . Each channel allows you to control one parameter on the quadcopter. All the channels transmit at the same center frequency of 2.4Ghz and there are no separate transmit frequencies used for individual channels ( 2.33GHz -Ch#1 , 2.35 GHz Ch#2 , 2.36 GHz – Ch#3 and 2.8GHz -Ch#4) . So lets say i want to transmit rudder , throttle , Alerion and Elevator information , then all the four parameters can be sent in the same frame at 2.4GHz . The receiver will extract these parameters from the frame and control individual parameter accordingly.

  • One channel for THROTTLE , this allows you to gain or loose altitude. Depending on how the quadcopter is programmed you may control the vertical acceleration or the vertical speed (aka auto level mode).
  • Second channel for RUDDER controls the rotation around the vertical axis. This allows you to face North, East, South, and West.
  • Third and fourth channels  AILERON and ELEVATOR (2 channels) control the roll and pitch. This allows you to get the quadcopter at an angle compared to the horizontal plane, and move forward, backward, left, or right. Depending on how the quadcopter is programmed you may control the angular rate (aka manual mode) or the angle (aka attitude mode).
  • In addition you may have any number of spare channels to control the flight mode, trigger a camera, retract the landing gear, etc.

I found some pictures here  to explain Roll, Pitch and Yaw along with the motor control impact on movement of Quadcopter.In the second picture GREEN means low-speed and RED means high-speed.

Pictorial representation of Roll, Pitch and Yaw
Impact of Motor Control on movement of Quadcopter
5 Signals from the receiver

2.Signals from the Radio Receiver to Flight Controller?

Finally the above picture shows the control signals sent by RF Receiver to the flight controller board. Each signal varies from 1.1 msec to 1.8 msec in width and the periodicity is about 17.66 msec . In the above picture , signal 3  (Orange) is at a minimum of 1.1 msec and rest of them are around 1.45 msec ..Note that each signals starts (rising edge) at the end of the previous signal ( Falling edge) .The flight controller in turn controls the ESC ( Electronic Speed Controllers) and finally the brush-less DC motors are controlled.

3.What are modes (Mode 2, Mode 1, etc.)?

When people talk about transmitter modes they are really just talking about the default configuration of the sticks on the transmitter.  Almost everyone uses what is called “Mode 2” which means that the left stick controls throttle and rudder and the right stick controls elevator and ailerons.  Since the vast majority of people use only Mode 2 that’s what most transmitters support and you don’t need a transmitter that supports more than that.

4.What are CW and CCW propellers?

Important : The  propellers when rotate (CW or  CCW )should push the air downwards , developing a lift for the entire quadcopter. In a fully assembled  quadcopter , it would look like figure #6b in my  Part #1  of my blog. Imagine the top right propeller(shown below) to rotate in clock wise direction , the air gets directed/pushed downwards . Similarly the Counter clock wise propeller pushes the air downwards when it rotates anti clock wise.


5.How to mount the propellers ?

There are two types of propellers , clock wise and counter clock wise .  The same type of propellers are mounted diagonally opposite on the Quadcopter.  In  + ( Plus ) configuration and  x ( cross) configuration  ,

CW : Clock Wise and CCW : Counter Clock Wise

6.What does kv stand for on brush less motor ?

kv means RPM/volt. If you have a 850kv  motor then it means it can rotate 850 Revolutions/minute per volt.  At 10 V , it can rotate at 8500 RPM.  Depending upon the propeller size , you can choose a desired kv .

  1. Higher kv ( smaller propellers) means Higher speed but Lower torque .
  2. Lower kv means  Lower speed but Higher torque, more suitable for bigger propellers.

I would also recommend beginners to subscribe to  Robotics Stack Exchange  .

My First Quadcopter Assembling (Part 3)