I don`t understand all the technicalities of ebike controllers. 2 contacts from the batteries disappear into the controller. Cable from controller to the motor contains 3 wires. 3wires from the PAS sensor also disappear into the controller. Inside the controller all components appear embeded in sealing wax. I repeat it is a simple system that suited my requirements.
it might be simple, but that doesn't mean simple to replace. With only three wires, it's running without sensors. Only ebike controllers have connectors for pedal sensors, but I'm not sure that your average sensorless controller would be able to commutate fast enough for that motor. You could try any of the cheap ones from Ebay or Aliexpress, otherwise an RC motor controller (ESC) might work better.
Before anything, you need to figure out how many cells are in the battery. Look at the charger voltage written on it, then divide by 4.2v. It'll probably be 6S (25.2v) or 7S (29.4v). 24v ebike controllers are normally 7S, while as RC ESC are typically for 6S, but some can be programmed for 7S or anything else.
As ESCs are pretty cheap, I think I might try one of those first. This one seems to be programmable:
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