Anti-Sway — Malachi Espinola

The problem

Adaptable House wanted a ceiling gantry to carry people. Drive the trolley fast and the load underneath swings.

Anti-sway and tracking mode, demoed at the capstone expo.

Hardware

Potentiometer amplifier PCB — Pot amplifier — printed PCB, low-pass filtered.

Motor and belt drive — Maxon DC motors, 2000-count encoders.

CAD of the potentiometer gimbal mount — Gimbal mount, as designed.

Two-axis gimbal carries the pots that read cable angle.

XY control wiring diagram — XY control wiring.

Model and control

An inverted pendulum on a driven trolley, linearized with a small-angle approximation. PI velocity loop, proportional sway feedback, K = 2√(l/g) for critical damping.

Free body diagram of trolley and suspended mass — Free body diagram.

Simulation

Tuning

Gradient descent on the PID gains against a squared-error loss.

Velocity step responses across training epochs — 33 epochs. Epoch 33 shipped.

Debugging

Encoders died after a few minutes of running. Noise on the lines was corrupting state transitions.

Oscilloscope trace of encoder noise — Observed encoder noise.

Quadrature encoder channel states — Valid quadrature transitions — noise faked invalid ones.

Results

0%overshoot (req. <5%)
1.45 ssettling (req. <2 s)
4.3 mmsteady-state error (req. <2 cm)

Measured versus simulated trolley velocity — Velocity — theory against actual.

Measured versus simulated cable angle — Angle — theory against actual.

Outcome

Best design award in the UW mechanical engineering department, out of 120+ students.

← All work