Journal CW25 - bjornburton/champbot GitHub Wiki
Yes, the little bipolar H-briges that I got quickly went into thermal shut-down. Fine for little motors but not for these. A better part is on the way. It's a 20A MOSFET drive. That also means I can use a 12 volt power system rather that 24 volts. That will offset the monetary loss a bit, in several ways.
For the props, two 3/8" bolts have been cross-drilled to accept the pins supplied with the props. Washers and Nylock nuts secure each prop against the pin. The hex-heads of the bolts have been cut-off so that they will enter the drill-chucks used on the motors. That hardware was coated with CRC Heavy Duty Corrosion Inhibitor rather than use costly stainless or brass parts. Issue: even with the keyless chucks very tight, there is slippage; not at all uncommon for keyless. I like keyless but not for conventional bits at this torque. They make keyless chucks bulky and slow to partly offset this weakness. Flats have been filed onto the propeller shafts so that they will not slip in the keyless chucks.
The drive unit housings are partially assembled: 2" schedule 40 tubes bonded into unthreaded couplings. Onto those tubes go caps that were reamed for a slip-fit and drilled for the 12mm shafts. The other forward side of the coupling will get the same treatment, except the caps will handle wire entry. I'm using epoxy since it's more forgiving to work with. It's one of our favourite glues.
3mm thick shaft-seals will be bonded to the nose of the gearbox.
Next, the motors will be mounted through the end-cap. It may get be tricky to seal. I want the torque to be carried through the cap and back into the tube so screws will secure the cap. I have some old closed-cell EPDM (exercise mat) that should make a fair gasket except there is a risk of it popping out. Maybe I'll keep an eye out for something better.