Scooter motor 72V 3000W for propulsion

I have an idea of using a 72V 3000W scooter motor as an underwater motor.
These motors are all over aliexpress, there seems to be several brands of the same motor. Examples are Yalu BM1109 and Kunray MY1020. However they all look the same.

The highest power version is rated for 3000W at 72V. This is a continuous rating (I think), so the peak power can be much higher. This is discussed on endless-sphere, the user coleasterling claims he’s running the motor in a toy car at 150 phase amps. That is a lot, three times the rated current (45A rated). Another user claimed 300A(!) peak in a go-kart.

To use the motor in water it needs a protective case of some sort, as it’s not waterproof. If it’s used under water however, it may be possible to double (or even triple) the continuous power rating.

The motor has a kv of around 70, which is good for direct drive. It has a quite large diameter at 107 mm and is also heavy at 5 kg, so it’s maybe not suitable for efoil. However I have plans on building an electric outboard motor with direct drive, and this motor is compelling. The construction seems solid and it’s sensored, which would allow for an advanced controller, e.g. a kellycontroller.

What do you think? Innovative or stupid, or maybe both? :slight_smile:


  • attractive price 66usd for a 48V/2000W motor

(Many) cons:

  • 107mm diameter, efoil standards are 63-65 (in and out runners) to 80mm (outrunners)
  • 72V can be deadly in water, efoilers don’t go over 58v (14s max) to stay on the safe side,
  • not waterproof since a bike motor
  • power at 48V is half of the efoil standards : 2000W vs 4000W so you wouldn’t necessarily have the grunt to take off from water
  • tbc…

If used in water the rated power would be much higher, maybe around 4000W with 12S. And that is the continuous power (I think), the maximum power can go much higher as said in the forum thread I mentioned (endless sphere).

Kind of relevant rant: I don’t like that maytech/flipsky/etc almost never mention continuous current/power. They always specify max power, which is kind of useless. How long can you use the max power? 1 second, 10 seconds? It’s very important to know, but anyways…

The fact it’s not waterproof is probably the biggest problem, it will require some large 3D-prints and well sealed construction.

Heavy heavy heavy, used for high torque at low relatively low rpm, trike, gokart etc. Did I mentioned heavy? Yes, how about also not waterproof? will be a pain in the a$$ to be mounted on a foil mast.
If you told me you wanna use it as a boat outboard style motor, I would say absolutely go for it, not for efoil.