Quadruped Robot

I agree, but for position control the motor cogging is also important.
I’d rather pick a motor with more poles and lower kV. That results in higher voltage, but lower current for the same torque-output. Which is a much healthier setup IMHO.

Does anyone know the cause of cogging? Of the several drone motors I tests, one was unusable with SimpleFOC. People here seggested all kinds of things I might try. But repalcing the motor fixed it. I think in general I’ve found that for simpleFOC, ‘more poles is better’ but you’d think 7 should be emough

I also notice that some moters have only one more magnet on the rotor then coils on the stator and some have two more magnets. what effect does this have?

The cause of cogging is simply because the permanent magnets are attracted to the coils of the motor, there will be a place in the motors rotation where the motor prefers to be. This is why you can feel the cogging even when no power is being delivered to the motor.

If you think of the torque of the motor as having two components 1) this cogging force which is like a sine wave that repeats every pole pair and 2) the force caused by permanent magnets to electromagnet attraction which FOC algorithm attempts to keep constant.

To build a motor with low cogging is challenging and adds to cost e.g, increasing pole count and number of coils, reducing air gap, changing shape and arrangement of stator, coils, magnets. So if the application doesn’t need it, the simpler motor design is selected.

I think there is an element of buddhist acceptance that we need to do with cogging. It looks worse at low speed and no load, you have to ask yourself is it affecting what i need the motor to do under real world load and speeds.

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