Measure torque with a BLDC motor

Question

I'm trying to build a bench test in order to measure the torque required to put and keep in rotation a brake which function with friction. The rotational speed for this test is slow (15 RPM) to be sure not to cause any damages to the brake. The idea was to drive the current within the servo drive to calculate the torque. However as I need to be precise on my torque estimation I don't want to use directly the torque constant given by the motor manufacturer. I would like to calibrate the motor with a known torque and then read my current value to establish a link between torque and current.

Do you have any idea?

I tried to use a hysteresis dynamometer but it only function with higher rotational speeds. And I'm not sure at all that the constant linking torque and current will remains valid at lower frequencies.

Thanks for your help!

Answer 1

Seems like a BLDC isn't such a great choice for a dynamometer. For one thing, it won't have smooth commutation as the pole pieces rotate. At that slow speed this will be a liability. In this it has the same flaws as a brushed motor.

Maybe an induction motor dyno (since you’re supplying torque to the load) would be a better choice.

Answer 2

If you want to measure torque on a rotating shaft, I would recommend you have a look into the prony brake. There are plenty of articles and videos too explaining different DIY implementations.