This thing is really working!
[ added July2023: more detailed write-up here! ]
I tried making my own waterproof motors a few years ago and tested them on the lake but switched to a new strategy in the past few months. As I struggled to make rapid progress earlier, I made a Dyno for the drive system where I could test at home to debug components rather than hauling the project out to a lake for each incremental test.
In the latest sessions, I’m cruising at ~9-14mph with 9+mi of range (batteries providing about 32aH)
Before building anything and knowing what components can even achieve this, We need to Estimate our Target:
A hydrofoil works the same as an airplane, but underwater. Thus I can use the Lift/Drag ratio of this Foil, knowing the required lift (me and the board) and the approximate cruise speed, to determine the drag required overcome. It’s also important to include the air drag of things above the water (primarily myself).
Motor Dyno:
It ain’t pretty… Scrappy is the word. Just a modest 80gal bin of water. The motor is providing static thrust upward into a loadcell with instrumentation on the ESC to monitor Power, Ah used, Mosfet temperature etc… This helped me to debug the entire drive system and learn more about which propellers would be optimal.
At present, the batteries are the limiting factor as they limit output current to 65Amps which produces >30kg Static thrust. Riding on Foil requires just 30-40amps. The ESC and Motor are rated for twice as much current, 150amps. I’m content as it is for now, but may like to access more power in the future!
The data out of this has helped to quickly inform incremental design: such as monitoring the heat rise (yellow line) helped me try out different heatsink and active cooling strategies.
