Hi,

I have a 1kW 48V electric bike brushless motor and its controller. The throttle controls the speed of the motor, but I want to control the torque rather than the rpm.

Basically the motor should be set to certain speed, let's say 20rpm, and then controlling the torque (measured on the shaft) regardless the speed (i.e. 20Nm from 0 to 20 rpm)

I know that I need a current control loop, but I don't know how to do it.
Should I make it modifying the current speed controller or make it from scratch?
Is there anything off the shelf for this purpose?

Thank you

 

May not be understanding what you are asking, but that kind of thing is usually done by gearing the output of the motor. Electric motors of any type don't like to be run much under their designed RPM's. They tend to heat up too much. A small amount of speed regulation is OK, but a motor designed for many 1000RPM won't last long when run at 20 RPM.

 

Try monitoring the current and as it increases above a set value, have the circuit back off the throttle control voltage.