Building an electric mountain board. Questions...

[patrickza]

I've tried mailing sales@gm but had no response so hopefully you guys can help out a little. I'm building a three wheeled electric mountain board.

Firstly I need to know if it's direct drive or geared. I'll be using regen for the braking, and obviously I can't do that with a geared motor.

Secondly I'm curious about the power it can handle. My e-bike has an x5 on it and it happily runs 4kw (http://evalbum.com/2835). For this motor I'd like to be able to pull 750w at 48v. I know the issue with direct drive is heat, so hopefully if I only accelerate briefly at 750 and then get down to 250 I should be ok. Any opinions?

If someone knows what motor the wheel is based on that would help a lot.

Thanks

[Bikemad]

I assume you mean this 12" wheel:

For this motor I'd like to be able to pull 750w at 48v. I know the issue with direct drive is heat, so hopefully if I only accelerate briefly at 750 and then get down to 250 I should be ok. Any opinions?

The maximum power output for this motor is around 340Watts @ 48V and actually decreases if you use more than 500Watts of power!
(see power curve for further details)

I would expect the maximum speed on the level to be less than 15mph (24km/h) on 48Volts.

I don't know if this motor is geared or not, but it should produce around 20Nm of torque (approx 29lbs/13kgs of forward force) from a standing start, which will reduce as your speed increases.

Hope this helps.

Alan
 

[patrickza]

Yes, that's the motor. Those performance curves don't make too much sense to me. Why does the RPM decrease as power increases? It seems as if they're loading the motor to increase power, if the motor speed was allowed to increase while increasing power then surely effeciency would improve?

[Bikemad]

I've just taken a look at the figures on the second page (instead of the graph) and it appears that they were obtained with a 36V supply (Not 48V).
So the maximum speed should be approx. 33% faster on 48V. (Nearly 20mph instead of 15mph).

Those performance curves don't make too much sense to me. Why does the RPM decrease as power increases? It seems as if they're loading the motor to increase power, if the motor speed was allowed to increase while increasing power then surely effeciency would improve?

Electric motors only produce usable power when under load, applying a load to a freely spinning motor causes a reduction in speed when the load is greater than the power of the motor.

The performance graph is plotted using figures obtained from a dynamometer, a device which tests the motor (usually running at full throttle) by gradually applying a progressively increasing test load upon the wheel, whilst measuring the wheel speed, torque, the power consumed and the power produced at the wheel.

This is why the wheel speed is very high to start with and then decreases while the power and torque provided by the wheel increases.

In the Performance graph:
P1 is the measured power consumed by the motor in Watts. (Input)
P2 is the measured power produced by the motor in Watts. (Output)
I is the actual current being drawn by the motor in Amps.
n is the measured speed of the wheel in revolutions per minute.
M is the torque developed by the motor in Newton metres.
EFF is the efficiency and is calculated by dividing the power produced by the power used and then multiplying by 100 to give a percentage.
     e.g. If a motor consumes 200W and only produces an output of 160W, its efficiency would be 160/200*100 = 80%

Alan
 

[MasterCATZ]

P1 is the measured power consumed by the motor in Watts. (Input)
P2 is the measured power produced by the motor in Watts. (Output)


finally the answer I am been trying to find