Closed Loop Challange
Part 1: PID Control due before class Thursday 11/10
Part 2: Improvement on PID due in class on Thursday 11/17
Build a basic dual shaft setup:
Gear ratio 3:1 (small gear on motor shaft)
Inertia wheel of standard size on second shaft.
Symmetric Wheel. 3 10-32 bolts of length 2" loaded with 14 nuts mounted adjacently on one side of wheel and 3 similar bolts on opposite side.
Asymmetric wheel. 1 bolts as above mounted on just one side of the wheel.
Pot in line with inertia wheel.
Implement both Challenge 1 and Challange 2 using just regular PID control (not even with anti-windup).
Turn in plots on tuned system and Arduino code.
Describe tuning process and final gains used.
Grade is based on reaching specific target position without penalty for a long settling time, along with write up.
Implement both Challenge 1 and Challange 2 with the goal of improving the settling time relative to Part 1. Methods used could include adding anti-windup to PID, feedforward, bang-bang, velocity trajectory control.
Grade is based solely on how fast one settles at the target position.
Challenge 1: Symmetric Inertia Wheel
Implement a PID controller for a 180 degree rotation. Performance will be based on time to reach and settle in target position. Reaching target will be defined as:
position error < position threshold of +/- 1 degrees
velocity < velocity threshold +/- 1 degrees per second
Challenge 2: Asymmetric Inertia Wheel
Remove all bolts except 3 adjacent ones.
Start with bolts on inertia wheel at lowest position. Then implement a controller for a 90 degree rotation. Performance will be the same criteria as in challenge 1.
The performance will be based on potentiometer reading for the TA Arduino. The feedback sensor could be either the encoder, potentiometer, or a hybrid approach. Some Pros and Cons are:
Potentiometer feedback is more accurate since you are directly measuring the position of the object you care about. However, if there is a big lag between the motor and the pot due to backlash or twist in the flexible shaft coupling this cold lead to oscillation or even instability.
Encoder feedback will be more stable and possibly easier to tune, but backlash or twist in the flexible shaft coupling could lead to a steady state error that is not eliminated.
A hybrid approach would use the encoder to start with and then switch to the pot when one is close to the target, but there could be a time delay.
To quickly change gain values without recompiling, one can input gains through the serial port. An examples is provided in SampleP_Code. This example implements proportional control but not Derivative or Integral Control.
Make sure that your potentiometer is not going through the dead zone.
Note; not all pots are identical and thus may have a different calibration constant between counts and degrees. To easily address this, just play with the step size via the serial port input to achieve a desired 90 or 180 degree step. See void setup in SampleP_Code.
See Control Guidelines for PID tuning tips and other control approaches.