Re: [CAD_CAM_EDM_DRO] gearmotors,encoders

jmw@... wrote:

> Are gearmotors more or less verboten as axes motors in CNC
> applications? Seems like the answer has gotta be "yes" for the same
> backlash reasons that have landed acme screws and nuts in scrap bins.

Ordinary gear motors would not be acceptable for this use, for
exactly that reason.

> But a 90 deg gearmotor sure would make a neat X-axis installation on
> a Bport-class machine. It'd be fine on Y too, and no messing with
> wheels and belts.

There ARE special worm drives that have backlash that can be adjusted
down to about zero. They use a 2-piece worm. It has two halves
that can slide together or apart just a little, on a keyed shaft.
The worm wheel has to be very accurately centered for this to
allow almost all the backlash to be taken out.

There are also recirculating ball worm drives that have been used,
mostly to rotate cranes and other massive loads.

> I've never heard of a no backlash gearset, except when someone messes
> up the shim pack rebuilding their diff ...

The approved motion-control speed reducer is the harmonic drive,
which I don't want to describe here. There are a bunch of outfits
making them. They can be made to have no backlash. There are also
ways of preloading the gears in a planetary drive to make them
free of backlash.

Jon