Re: [CAD_CAM_EDM_DRO] Re: Bridgeport servo motors

Re the brush angle
I could be wrong, been out of school for a long time, but
the brushes might be placed at this angle in order to reduce the affects of
armature reaction which is an 'S' shaped distortion of the main field flux
due to current flowing in the field windings. Armature reaction varies
directly with the current flowing through the field windings and causes the
nuetral plane of the brushes to shift in the same direction as the rotating
armature. The motor will rotate in the opposite direction but there will be
excessive sparking at the brushes, the commutator will take a real beating,
and the output power will be reduced. The brush angle may have been shifted
optimally away from the nuetral plane so that the motor application will
handle a constant load in that rotation direction and also deliver maximum
power, because the affects of armature reaction also impact slightly on
output power.
If you were to remove the end bell and shift the brushes back to the nuetral
plane you might find it would deliver the same performance in both directions
with minimum sparking.
cheers,
Denis Casserly

On February 4, 2005 10:44 pm, Jon Elson wrote:
> braidmeister wrote:
> >Scott,
> >Unfortunately...It is correct...they ARE CCW...#$^%^(*()&$!!!!
> >
> >I just called them and the tech opened up the motor and looked at the
> >brushes. He said that it did sound different running it forwards or
> >backwards...BUT the brushes were angled...and there is no easy way to
> >get them timed for both directs.
> >
> >WHAT A HUGE DISAPPOINTMENT!!!
> >
> >So now...back to freakin' square 1. I would be interested in other
> >types of motors than these or the Ameteks (too slow). Anybody got a
> >source for 3 that will work at a decent price? (Decent meaning better
> >than $400 ea)
> >
> >SO here's a question for you people: Since Surplus Center advertised
> >the motors as bi-directional, who pays for the shipping up and back?
> >Why should I have to pay shipping on something that was falsely
> >advertised?
>
> No doubt the brushes are run in in one direction, due to the intended use
> of the motors. But, that doesn't mean they CAN'T be run the other
> direction.
> You might have slightly faster brush wear with this setup, but it may be
> almost
> insignificant. If you run it both directions, the brushes will likely
> change their
> fit slightly, and the difference in sound will stop. It might be a good
> idea to adjust
> the brush holders (I'm guessing these are cheaply made motors, with stamped
> brass brush holders riveted to a phenolic card or something similar.)
> If the
> brushes rock in the holders when you reverse direction, this will make
> for poor
> fit between the brush and commutator, So, you might want to make sure
> the brush holders grip the sides of the brush well enough to minimize the
> rocking. Other than that, they most likely will work OK.
>
> As for return, if you lean on them, they might agree to a UPS "call tag"
> where they pay the shipping to return the items. You've probably got a
> couple days to research it and see if anyone is using them in reversing
> operation
> without trouble.
>
> Why are the Ameteks too slow? Given a suitable power supply, I think
> they can
> do OK.
>
> Jon
>
>
>
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