Treadmill motor / G340

As an experiment, I used a Geckodrive 340 to run the spindle on my
little Emco CNC5. Took some fiddling with acceleration (pulse train
output under CNCPro control) but it ran just fine, thank you. THe G340
has a pulse multiplier, which may not be necessary in an axis where you
have mechanical drive ratio in place.

Once I learned enough to abandon G-code spindle control <grin>, I
used a KBIC DC controller on the same, ubiquitous tradmill motor;
this works great *except* that under very low loads, carbon tends
to build up on the commutator and the speed becomes erratic until I
apply a percussively significant event to the motor housing (bang it
with a screwdriver or something), which causes the brushes to make
better contact again.

Under higher loads, no problem, and it's a great combination.

I agree that under high power operation, cogging would be a problem.
In most cases, these motors will be operating under a fraction of their
potential, so at minimum torque portions of their rotation, there should
still be plenty to move to the desired encoder position.

The second point I'd make is that reversing these motors *could*
be a problem in an application like a spindle, where 99 percent of
the motion is in one direction... This allows brushes to develop a sharp
trailing edge which, upon reversal, can snag in a commutator gap and
cause a chunk of carbon to break off and *possibly* become lodged
somewhere it shouldn't be.

In an axis situation, motion will be bidirectional. Now, there is some
finite slop between the brushes and their retainers, so there will be some
effective deadband at reversal time, but I dont' think this will be a
problem
either.

My view - give it a try. The Geckos are totally reusable, the motors are
cheap and highly useful in other applications, and there's nothing to lose
if money' the object.

/mark F