Shiv Seetharaman

2018 · WET Design · Harvey Mudd capstone

Floating light-show robots

A junior capstone sponsored by WET Design. We built eight wireless floating robots that hold formation and run a synchronized light show.

Fleet 8 autonomous floating robots
Wireless nRF52 BLE, multilink UART
Lighting 4× 3W RGBW LEDs, constant-current
Control PID heading control (magnetometer)
Role Electronics & controls

The problem

For a light show on water, each robot has to stay in position and each light has to match the others in brightness. So each robot needed to hold its own heading, and the LEDs needed to stay at a constant brightness as the batteries drained.

What I did

Constant-current LED driver

I designed, built, and tested a PCB that drives four 3W RGBW LEDs at a constant current, independent of battery voltage. It uses an op-amp and a p-channel MOSFET as a current source, with thermal and overcurrent protection.

Heading control

I wrote a PID controller in Python that keeps each robot on a set heading using its magnetometer.

I helped design a Bluetooth PCB around the nRF52 for a multilink UART system, so the robots could be controlled wirelessly.

Outcome

All eight robots held their heading, and the LED brightness stayed constant as the batteries ran down.