Re: [CAD_CAM_EDM_DRO] Re: Before I make a mistake, what do I need to know?

> The stepper motors that I was going to use where Nema 34, 2
> degree/step unipolar ones. Since 1.8 degree/step is more common and
> since I don't want to have to change motors in the near future, I was
> wondering what would be a better choice for motors. Should I go to
> the larger Nema 42 size. Would that give me more power plus speed and
> what about the cost.

Nema 42's would up your cost per axis substantially, unless you find a
surplus source that the rest of us have overlooked. Unless you are
building a very large heavy machine that needs to move fast, they are
probably not necessary. But if unsure, look up the mounting bolt
patterns and make brackets that can take either. If your machine is
small I think it really is worth trying your existing motors before
you spend more money.

> And should I buy a true bipolar motor as opposed
> to the unipolar ones.

If you are buying new, yes, get 8 wire with the low phase
resistance/voltage.

> Is 2 motors necessary for the X axis for accuracy and no binding, or
> is 1 motor enough

Depends on the design of your machine. If you have a bearing surface
for the lower axis that is as long as it is wide, you can probably
drive it with one motor and a screw in the middle. Gantry routers
which use two widely spaced rails typically need two screws for the
lower axis, and either a long belt to link them which can vibrate or
two motors which must be kept in sync.

> Also, will a commercial controller, such as from Geckodrives, make a
> lot of difference in preformance compared to a "home made" one.

The better commercial drives will get the maximum performance from
your motors. For small motors they are overkill, but you still
benefit from the carefull engineering and of course they help preserve
the upgrade path to bigger motors. The Gecko's will set you back
about three times as much as building your own 2 amp drivers, but they
are worth it for things much bigger than a sherline and may save you
quite a bit of time and frustration.

Chris

--
Christopher C. Stratton, stratton@...
Instrument Maker, Horn Player & Engineer
22 Adrian Street, Somerville, MA 02143
http://www.mdc.net/~stratton
NEW PHONE NUMBER: (617) 628-1062 home, 253-2606 MIT