Ah, well when I say “custom motor” I am actually referring to a hubmotor assembly. The best drive solution I have found so far is our modified Bafang wheelbarrow hubmotors pictured in detail here:
This hubmotor is a wheel hub, axle, motor, and gear reduction. The actual electric motor itself would absolutely be COTS. If we used a different COTS motor we would still need a wheel/hub, axle, and potentially some gear power transfer. A front bicycle wheel is not designed to accept power input and a rear wheel is only designed to accept power input in one direction. So we need something “custom” to make that work. At minimum would be a gear which bolts to the disc brake details interfacing with a gearmotor bolted to a custom square tube fork. And I suppose that’s not a bad idea so I will think about that. We plan to make a custom square tube fork already as our mounting needs vary from bicycles significantly.
So a “custom hubmotor” could be basically a custom axle and hub that would accept input from a COTS gearmotor. That would be no more complex than our current solution but would still require custom wheels which has been a pain. So I will think more about mounting a gearmotor on the fork. We previously used COTS forks and mounting anything to them is a pain, but that will change.