DC Motor Friction resistance 1

[Katy1163]

Does anyone know how I can find the friction resitance of a motor assembly from performing measurements?

 

[davidbeach]

It depends. What measurements do you have available? Does friction need to be determined separately from windage or can you lump friction and windage together?

 

[Katy1163]

Well, I have the motor available to me as well as any of the equipment I would need. So basically, I can take any measurements that would not include taking the motor apart. And yes, the friction resistance has to be determined separately from the winding resistance.

 

[davidbeach]

Windage is not winding resistance, it is the wind resistance to the rotor as it spins. You'd pretty much have to run the motor in a vacuum to sort out the windage and the mechanical friction; generally they are lumped in together.

You'll have to know all of the electrical losses in the motor, for which you will need a good motor model. Lots of electrical tests to determine the model. Once you have your model, so for any given current into the motor you can calculate all of the electrical losses. Then run the motor on a dynamometer. Electrical power into the motor less motor electrical losses, less less mechanical power out gives friction and windage. Up to you to sort it all out.

 

[ijl]

What about rotating the motor with another motor, and measuring the torque and rotating speed. Does probably not work, if there are magnets in the motor, however. The contribution of drag (air resistance, windage) can be estimated by rotating at different speeds.

 

[burnt2x]

ijl,
Very nicely said! Thinking out of the box, I guess. Star to you.
Katy1163,
By driving your motor with another "known" motor, you took out the copper and core losses.