High speed with low torque

developement
1

Hi all,

how can I achieve a very high speed with very low torque?
At the moment I am controlling my motor with current sensing and set the motor speed to a very high number and limit the torque by limiting the current.
This works fine, however, limiting the current also decrease the speed of the motor.
I assume this is normal but is there a way to get better results? I only achieve very low speed with low current. Does this depend on the motor I am using?

Thank you and best,
Alex

1 Like
2

You need a motor with the minimal count of poles ( 2 ).
The rotor diameter needs to be small, so you need an inrunner.
All friction must be minimal, so you need high quality ballbearings and smooth finish, and the rotor needs to be well balanced.

In short : pay a lot of money.

Next problem is simplefoc may not be fast enough.

3

Thank you for your reply! As I understood correctly, the only thing I can do is to buy another motor? There is no way to optimize it via code, for example another PID configuration?

Thanks!

4

Hi @Alexander992 ,

I’d like to understand better what you’re trying to achieve… generally speaking, if things are set up correctly, you can use closed loop velocity control mode (with a sensor) to set a desired speed. There is probably a much better way to express it, but in my simple mind this then means SimpleFOC will use only the current needed to set the desired speed. Of course if you then load the motor the current will increase in order to try to maintain the speed you set, but as long as the motor is unloaded or lightly loaded, the current should stay very low.

If you then check the current needed to set the speed you want for the expected load, and then set the current limit to just above this value, then you should have a system that applies just the torque required to attain your desired speed, but doesn’t increase the torque beyond this point even if you load the motor (of course the motor will then slow down).

Note that I think you can try this with any BLDC motor, any pole number. It doesn’t have to be a special one, even though I am sure Jan is right that there would be advantages to picking just the right motor.