Today I had chance to put the ROV back in the tank and begin work on turning the PID controllers. PID controllers are a software device which are used to manage a closed feedback loop (see Wikipedia for an overview). In this case I'm using them to manage the thrusters, and the first ones I'm working on are the pitch and roll stabilizers. The goal is to keep the craft stable in the water regardless of changes to the ROV's environment.

All was going well for a while, then suddenly all the electronic failed! :-(

I initially suspected that water must have entered one of the enclosures, but once I'd removed it from the tank, I couldn't find any evidence of this. Dragging the ROV back to the workbench and attaching it to the bench power supply, I could see that it was no longer drawing any power. Thinking the power regulator must have failed, I remove the main pcb and was met by the familiar smell of a component that has blown up. It was easy to spot ...

The component is the main current resistor used to measure the power from the batteries. For whatever reason, I'd obviously put too much power through it and blown it up.

The resistor the failed was rated at 3W which I've worried is insufficient for running the motors.

I've patched the board and jury rigged a new resistor in place of the old. This one is rated at 5W and is substantially meatier (compare it to another current resistor above and right)

We'll see if this works tomorrow.