Motor dedent torque

[Eelco]

Im working on a project to minimize motor noise; part of motor noise is due to the torque ripple caused by dedent torque, but Im having a hard time finding any information whatsoever on what is a typical or 'good' dedent torque value for a direct drive bike hub motor.

Generic info cited for dedent torque is that it tends to be around 5% of the rated torque; though thats in the context of comparatively low pole count, say 12 pole motors; not the 40-ish poles that you see in direct drive hub motors; where id expect it to be lower, all else equal.

Curious if anyone here knows of any information, or has ever measured a hub motor and could post the result to get an impression of what is out there.

 

[neptronix]

I have never heard this term before.

But first let me ask you, are you using a FOC controller? these produce the quietest drive possible.. and would be an easy slam dunk.

 

[aae34]

Detent torque, i guess?

 

[A-DamW]

dedent torque

I am going to guess this means "Cogging torque":

Cogging torque - Wikipedia

en.wikipedia.org

Perhaps similar to "Detent":

Detent - Wikipedia

en.wikipedia.org

 

[ZeroEm]

To my knowledge "Detent" has not been an issue for me. Taking off at max power Detent is less than 5 and cruising speed around 15mph it would be less than 1, not sure it is worth trying to measure. So it's has not affected my riding pleasure. When I tried to ride with regen on to make free energy that was a pain in the legs and don't do it anymore.

 

[A-DamW]

Curious if anyone here knows of any information, or has ever measured a hub motor and could post the result to get an impression of what is out there.

Can you share the project you are working on? maybe with pictures?
It may help diagnose the noise you are trying to minimize.

 

[Eelco]

I have never heard this term before.

But first let me ask you, are you using a FOC controller? these produce the quietest drive possible.. and would be an easy slam dunk.

Yeah im using an FOC controller and a high bandwidth encoder. Its theoretically understood that this leaves detent (excuse the typo) torque as one of the dominant source of noise.

Detent is what gives the motor the tendency to snap to certain preferred positions. It occurs at multiple harmonics of the pole and tooth count, giving noise frequencies that scale with rpm.

 

[Eelco]

I am going to guess this means "Cogging torque":

Cogging torque - Wikipedia

en.wikipedia.org

Perhaps similar to "Detent":

Detent - Wikipedia

en.wikipedia.org

Im intentionally avoiding the term 'cogging' since cogging seems to be used to refer to any kind of motor friction effect in the ebike community. Detent is a more specific term that does not carry that baggage (or any connotation at all with many people it would seem).

Also interesting to note that detent is not a friction effect; its a conservative force; there is no proportionality between how 'notchy' your motor is and how much drag it produces.

Anyway... Im still half expecting there to be a thread on this forum by justin measuring detent torque for a bunch of motors... but if not I guess ill have to collect my own data.

The problem with that is im not so much interested in the detent torque of any specific motor; but rather an understanding of what the range of possibilities is. In industries where people care more about detent you can see 10x variations between motors of similar specs; so it will take a bunch of datapoints to answer that question.

 

[Eelco]

To my knowledge "Detent" has not been an issue for me. Taking off at max power Detent is less than 5 and cruising speed around 15mph it would be less than 1, not sure it is worth trying to measure. So it's has not affected my riding pleasure. When I tried to ride with regen on to make free energy that was a pain in the legs and don't do it anymore.

Not sure we are talking about the same thing, but I always like it when people have numbers. So when you say 'Taking off at max power Detent is less than 5'; what are you referring to with that number 5?

 

[ZeroEm]

Was trying to figure out what you were talking about? maybe dedent() in Python?

We call it cogging but you don't want to! It was my lack of understanding and fell into a trap that was not intended but never the less there. Realized my mistake as A-DamW posted. People have used stronger magnets but don't think you want to discuss that.

detent (noun) · detents (plural noun)

1. a catch in a machine which prevents motion until released:
   "a system of detents is used to ensure that gears are held in whatever position is selected" · "a detent spring"