56V motor in low-speed mode - which ODrive to use (24/48V)?

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Hi guys, I intend to use an e-scooter hub motor/wheel combo, which has the following general specifications:

  • max speed about 1200 RPM
  • many pole pairs, 15 or more
  • nominal voltage 56V
  • maximum RMS current 50-60A, I assume peak rating. The continuous is half of that
  • integrated hall sensors

We’ll use it a rover-type platform, which would be moving very slowly - so the actual motor RPM we’ll need would be about 80-100 RPM.
Thus even a battery voltage of 12V would suffice, but we’ll use 24V.
We’ve made a similar prototype last year, where the motor was different - 36V nominal, but again driven at low speeds, and we’ve successfully used the 24V ODrive back then, with a 24V battery, and it was working fine.
However, the motors there were too small, and we want to use a larger-diameter model, which is the aforementioned 56V one.
The question is - which ODrive model to use here?
I’m inclined to think that the 24V is more suitable, as the AC driving voltage is in any case less than 10 volts, we’d have enough headroom, we’ll never need more than 120 RPM for occupational safety reasons, and the 24V FETs would be lower resistance, meaning higher efficiency.
Our driving currents would not be trivial, we might actually need the 50A occasionally.

However I’m not well-versed in how such controllers work in general and how important is the matching of the ESC nominal voltage to the motor nominal voltage. We’re free to change the specs of the system.

Indeed, at least three battery/ODrive combinations are possible:

  • 56V motor / 24V battery / 24V ODrive - “best config” as per my intuition
  • 56V motor / 24V battery / 48V ODrive
  • 56V motor / 48V battery / 48V ODrive - closest match to the motor

What would you suggest as the best one?

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Any ideas, anyone?

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Just got in contact by ODrive, and they recommended the 56V motor / 48V battery / 48V ODrive combo for the following reasons:

  • the losses in the battery and the wiring to the ODrive will be lower and would offset the slightly higher losses in the MOSFETs
  • if the motor is particularly high inductance, a higher bus voltage will allow for faster current slew and thus slightly tighter torque control. Admittedly though, the difference is so small as to barely warrant mentioning.

In the end, I’ll be buying 48V ODrives.

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