Re: [femm] Cogging torque

[dcm3c@xxxxxxx]

In a message dated 11/25/2001 10:16:29 AM Eastern Standard Time, robin.cornelius@xxxxxxxxxxxxxxxxxxx writes:


> Dear group,
>
> I am trying to calculate the cogging torque for a brushless rotor, 
> but I am having some fundimental problems (this is not my area of 
> expertiese !).
>
> What intergral should i look at ? . I have tried a line intergral 
> around the air gap between stator and rotor (with a reasonable dense 
> mesh) and looked at the torque from stress tensor. (I am then steping 
> the rotor around to see the value at different pole pitches).But the 
> magnitude of the results is too large and the pitch/value graph is 
> not quite what i would expect. I remember that David M. mentioned 
> coenergy in a past email in relation to cogging torque? if this is 
> good to use over what areas should this be evaluated (iron,air,magnet 
> all?)
>
> Any advice greatly appreicated.
>
>
> Robin Cornelius
>
> robin.cornelius@xxxxxxxxxxxxxxxxxxx


Evaluating the torque from the stress tensor along a line that runs through the middle of the air gap ought to give you a reasonable result.  Also, make sure that your rotor is centered at (0,0) -- otherwise, you can get results that might not be what you expect.  Alternatively, you can do the coenergy approach.  This is a volume integral that you evaluate over the entire problem domain.  The torque is then the change in coenergy with respect to angle for where current is kept constant.

If you send me a copy of your problem, I might be able to say more.

Dave.