Re: gearmotors,encoders

Jon,

Musing about zero-backlash gearmotors today, I thought someone must
have come up with a workable ball worm drive. The split worm
solution ... well that just strikes me as clever. Inexpensive, too,
I'd guess, for those with a sizeable peasant class on their domains.

I was hoping to avoid the complications of belt drive motor setups--
but belt drive also resolves a number of complications. No fiendish
helical couplers, additional mounting locations for tachs and
encoders, a pretty fair chance of neatly tucking the Y motor along
the knee just under the Y screw, and although a 90 degree bend would
save some space on the X installation, a nice table extension like
you made has benefits of its own. (BTW, you must have done a _lot_ of
sweeping while carving that mount.) And freeing up an encoder
mounting position means that plain vanilla PMDC motors can be used,
which seem to be about 1/4 the price of servos, new or used.

--- In CAD_CAM_EDM_DRO@egroups.com, Jon Elson <jmelson@a...> wrote:
>
>
> jmw@c... 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