About dunkermotoren gr63x55 torque


My project is to add some support to my bicycle by adding 100 watt silent motor.(dunker motoren gr63x55)

The problem is the torque of the motor is not enough to turn the wheel by friction. (I am using 8s lipo battery)

I will be really happy if you could give an advise to increase of the torque of this motor. ( by pwm frequency, or adding magnets… without adding gears to slow rpm)

Thank you in advance

Image from Original Post so we don't have to download it. See this Simple Image Guide


You need to provide a link to the datasheet for the motor.


How will the motor be mounted in relation to the tire? Surely not the way you are holding it in the picture. :slight_smile:

Hi. Specifications are given below

It will be mounted with brackets. I am inspired by some examples on youtube

Nominal voltage V 24
Nominal current A 4.9
Nominal torque Ncm 27
Nominal speed rpm 3350
Friction torque at no load Ncm 2
Peak stall torque Ncm 257
No load speed rpm 3650
Maximum output power W 245
Nominal power W 94.7
Torque constant Ncm/A 6.4
Terminal resistance Ohm 0.6
Terminal inductance mH 1.5
Starting current A 40
No load current A 0.4
Demagnetisation current A 33
Rotor inertia gcm^2 750
Weight kg 1.7

Your spec says the motor's normal speed is over 3000 RPM. When you calculate the gear-ratio between your tyre and the motor, how fast will the motor be turning?

Clearly if the wheel is not moving, then neither will the motor move and you will be relying on the stall torque and the stall current.

First, I suspect the motor is not designed to withstand 40 amps for more than a few seconds.

Second, I have no idea if your batteries are capable of safely delivering 40 amps.

Third, you need to calculate whether the 257 Ncm stall torque is sufficient to achieve what you need. If it is not then maybe you need additional reduction gearing. Which brings me back to my first paragraph.


Thank you very much Mr Robert :slight_smile:

0.27Nm with approx 1cm radius drive dog is about 3kgf on the tyre, plenty to overcome friction I’d have thought.