A quadrocopter has four rotors, with two spinning clockwise and two counterclockwise to cancel out torque. A motion control unit uses sensors like gyroscopes and accelerometers along with a complimentary filter and PID control to stabilize the copter without human control. The copter is powered by lithium polymer batteries supplying energy to brushless motors controlled by an Arduino microcontroller running the motion control software.

1. Quadrocopter
Kyle Bartholomew

2. What is a quadrocopter?
• Like a helicopter with 4 blades.
• 2 blades spin clockwise, 2 spin
counterclockwise = zero net torque
• Motion Control Unit
– Keeps the copter stable without human
control.
• Power system
– Based on lithium polymer battery

3. Power System
Motors
+
-
Motor Controllers
LiPo Battery
5V
Regulator
Arduino

4. Outrunner Brushless Motors
AC Power

5. Motion Control Unit
• Miniature computer (Arduino microcontroller)
– Runs at 16Mhz (Your computer runs about 200 times
faster)
– Takes electrical signals in, does math, spits out more
electrical signals.
• IMU – Inertial Measurement Unit – 3-axis gyroscope and
accelerometers.
Motor Controllers
Arduino
RF Receiver
IMU

6. Accelerometers or Gyros?
• What do you use to measure the angle of
the copter relative to the ground?

7. 3.3V
Accelerometers
• 3-axis, measures acceleration
– When incidental acceleration is
small enough, it measures just the
acceleration of gravity.
– Absolute angle relative to earth.
• Highly susceptible to noise:
∆0.11V = ∆30°
10 bit ADC = 1024 steps of
measurement
3.3V/1024 = .00322V/step
1g
1.95V
1g
0g
30deg
0g
1.65V
1.65V
(30°/0.11V)*(.00322V/step) =
0.88°/step
0V

8. Gyroscopes
•
•
•
•
3-axis, measures angular velocity (w)
Integrate w over time to get angle
Good at instant angle measurements
Bad at absolute angle measurements
because it drifts.
• Small error in w leads to big error over
time.

9. Combining measurements
• You want best of both with
– High speed low noise measurements
– Accuracy over long periods of time

10. Complimentary Filter
• Combines accelerometer and gyro to
produce a better angle measurement.
• High pass filter on gyro and low pass filter
on accelerometer.
• Aka only long term for accelerometer and
only short term for gyro.

12. PID Control
• Need to go from angle to motor output.
• Based on idea of error from setpoint.
• The ideal method is PID control –
Proportional Integral Derivative.
• Proportional – Controls the now
• Integral – Controls by looking at the past
• Derivative – Controls by looking forward to
the future.
Error = θdesired-θcurrent

13. Complimentary Filter
Accelerometer
Low Pass Filter
Angle
Gyroscope
PID
P Coefficient
Integration
High Pass Filter
Integration
Derivative
I Coefficient
D Coefficient
Motor Output (200hz)

14. How does it move?
CW
Hint: r X F
CCW
CCW
CW

18. I•ɑ

19. Going further
• Many people add other fancy things to
their quadrocopters:
– GPS
– Altitude Sensor (Barometer)
– Camera
– FPV (First Person View)
– Tracking Systems to do crazy stuff like flips
and multiple copter coordinated dances.