RE: [CAD_CAM_EDM_DRO] Digest Number 1912

Another thing to look for is the brush timing. Some times the timing of the
brushes relative to the field magnets, is optimized for one direction of
rotation. If the motor is then run backwards it will pull a lot more amps
for a given load.

Andre' B. andre_54005@...
If something cannot be defined, it does not exist.
Isaac Newton

-----Original Message-----
Message: 9
Date: Wed, 02 Jan 2002 18:25:30 +0000
From: Jon Elson <elson@...>
Subject: Re: DC Treadmill motor for servo?

mark wrote:

> In response to below...
> 1. Agree with the brush observations - this is an issue that becomes
> serious
> when brushes are worn-in; it's wear that creates the bad angles. Result
> can
> be a chunk of brush material chipping off when reversing (sharp edge
> catches
> a commutator groove) and doing damage.

Some motors designed for one direction operation have brushes that are
canted to the shaft centerline. This improves brush life for that
direction, but can cause very rapid brush wear if the motor is run
in the other direction.

> 2. Don't agree with lumpy operation statement for "real" DC motors and
> controllers. The earlier-available GE units were, like the early
> Sherline
> motors, triac-based (or whatever) and had badly reduced torque at lower
> speeds. The more modern, pulse-width type of controllers (new Sherline,

This has nothing to do with the controller. I am talking about reluctance
ripple, torque ripple and velocity ripple. The first has to do with
magnetic
design of the armature, the other two have to do with the design of the
armature windings. These do not cause a problem at high speed, and
may be done intentionally to improve brush life, but they cause problems
at low speeds with variation of motor torque or speed.

Jon




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