Homebrew PCBs

derekhawkins wrote:
>>I'd spend some time looking at a DC motor approach
>>with shaft encoder positional feedback.
> 
> 
> Just like those fooling around with toner transfer now will someday 
> move on to photoetching so will those on steppers now move on to DC 
> servos. Seems to be a natural progression, at least it was for me.

Another benefit of closed loop control is the ability to
detect/correct positioning errors which isn't possible
with an open-loop stepper approach.  If the stepper-driven
drive mechanism hits a friction snag and misses a step(s)
you are going to be cutting somewhere you'd rather not.

Additionally it is possible (perhaps even preferable) to
avoid direct drive of the lead screw by the DC motor and
pick up low speed torque in the process.  This speed reduction
can be implemented as a "belt drive" from motor to lead
screw with no loss in positional accuracy when the encoder
remains on the lead screw.  Note depending upon the torque
required the "belts and pulleys" can be as low-tech as
those found in consumer electronic devices.  i.e.: scavenging
a few scrap VCRs will supply the needed prototype components.

-- 
uhmgawa@...        www.gnu.org