All posts tagged robot

Drones (quad copters specifically) are pretty cool – and it turns out they are insanely easy to build and fairly easy to fly. Just do a quick look on youtube and you will find countless examples. Custom builds, like just about any hobby level electric remote control vehicle, require the following:

  • Radio Transmitter (your controller)
  • Radio Receiver (usually included with your controller)
  • Battery
  • Battery Charger
  • Motor (4x for quad copters)
  • Speed Controller (4x for quad copters)
  • Propellers (4x for quad copters)
  • Fuselage (frame/body)

Quad copters require one additional item that airplanes and gliders don’t specifically require

  • Autopilot : This is an intelligent device chalked full of sensors (typically an internal compass, tilt sensors, barometer, voltage sensors, and some have built in GPS or input dedicated for an external GPS)  The main purpose of the autopilot is to keep the quad copter level and mix the motor speeds based on the input from the controller.

The logic diagram for your typical quad copter looks like this:

Logic Diagram for quad copter


The quad copter could be flown with a 4 channel radio, but most autopilots have flight modes, and those modes require additional channels.  We choose to use a six channel transmitter/receiver.  The logic lines coming from the radio to the autopilot are:

  1. Throttle (speed of motors / climb rate)
  2. yaw (spin left/right)
  3. pitch (tilt nose up/down)
  4. roll (tilt left/right)
  5. Switch 1 (used for flight mode selection)
  6. Switch 2 (used for flight mode selection)

On our system the GPS is external, so we modeled it here as a logic input.  What’s important to really grasp is that the receiver is not controlling the motors and really neither is the autopilot.  The human pilot tells the transmitter, the transmitter tells the receiver, the receiver tells autopilot, the autopilot tells the speed controllers, and the speed controllers tell the motors.  To spell it out even more:

  • The human pilot wants the drone to fly forward, so he pushes the pitch and throttle sticks forward on the transmitter
  • The receiver relays that channel 1 and 3 have new settings to the autopilot
  • The autopilot knows that channel 3 is the pitch, and it has increased and consequently tells the front two speed controllers to spin the motors at a lower % than the rear motors until the angle of attack matches the desired pitch based on the pilots input
  • The autopilot know that channel 1 is the throttle, and it has increased and consequently tells all 4 motors to increase in speed – but will do so while monitoring and maintaining pitch – so even if the throttle is maxed out, because the pitch control is forward, the autopilot will not allow the front two motors to spin at full speed – at least not until the proper angle of attack is reached.