Re: [CAD_CAM_EDM_DRO] machine inaccuracies fixed by software compensation

actually with the way steppers are built the tolerances
don't have to be all that tight to get within 5%/step
check
http://www.doc.ic.ac.uk/~ih/doc/stepper/kp4m4/
for a better explanation than I can give on it

also these motors are machined 'mass production style'
on dedicated tools and they've had almost a hundred years to
work the bugs out
so that 5% is the max ALLOWABLE error for full stepping
if the production realy gets that sloppy you can bet someone
is in for a royal @$$ chewing

Brian

> I got yelled at over this calculation. Several people
> said this was 5% of ONE STEP, not per revolution!
> I find it pretty hard to believe that is actually the case,
> though, as it implies extremely careful matching of
> tolerances inside the motor. it seems to me a VERY
> slight imbalance in the force of magnets on the
> A and B phases in the motor's rotor could easily
> cause MUCH more error than 5% of that one step.
> If it is really per step, that implies an accuracy per
> revolution of .025% for the whole revolution, which is
> awfully good. On the other hand, 5% of one revolution
> is 10 steps, which sounds quite a bit too much.
> Assuming the mechanical part is completely accurate
> (poles on the rotor and stator) and the only variation
> was magnetics, then an error of 1% of a revolution
> equals 2 steps, and the motor would have no reason
> to go one way or the other, in other words, it would have
> lost a step. So, the magnetic error has to be less than
> 1% of a full revolution. But, adding mechanical tolerances
> back in, it could add up to close to 1% of a revolution.