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1. 1. Quadrocopter Kyle Bartholomew
2. 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. 3. Power System Motors + - Motor Controllers LiPo Battery 5V Regulator Arduino
4. 4. Outrunner Brushless Motors AC Power
5. 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. 6. Accelerometers or Gyros? • What do you use to measure the angle of the copter relative to the ground?
7. 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. 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. 9. Combining measurements • You want best of both with – High speed low noise measurements – Accuracy over long periods of time
10. 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.
11. 11. 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
12. 12. Complimentary Filter Accelerometer Low Pass Filter Angle Gyroscope PID P Coefficient Integration High Pass Filter Integration Derivative I Coefficient D Coefficient Motor Output (200hz)
13. 13. How does it move? CW Hint: r X F CCW CCW CW
14. 14. I•ɑ
15. 15. 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.