derekhawkins wrote:
>>I'd expect the lab-built "digital motor" approach to be less
>>than the cost of a roughly equivalent stepper
>>solution as viewed by total system cost.
>
>
> A new shaft encoder can be had for $19.00 these days. Adding
> a "second shaft" to any surplus DC motor is a piece of cake if you
> have access to and know how to use a mini-lathe...Or buy a surplus
> motor with encoder.
For lead screw applications I'd keep the encoder on
the screw. Doing so allows the screw to be driven
indirectly and velocity/torque/rotational-precision
to be scaled via simple friction coupling without
introducing slippage error.
You can cut an encoder disk with a lathe but it would
be easier to print such on transparency film via laser
printer. Postscript programs to do so are floating
around. Tap Don Lancaster as he is a likely source
for such sundries.
Though I wouldn't bother initially. 36-segment photo
interrupter disks and associated dual element quadrature
IR detectors can be ransacked from a cast off PC mouse.
And two are employed for use in X and Y axis encoding.
While 36 segment seems rather coarse, it is quite usable
directly with a lead screw pitch of 24-28TPI.
Other sources for interrupter substitutes would be gears
reclaimed from defunct consumer items (mechanical clocks,
VCRs, walkmans, etc..). The more difficult thing to
scrounge is the dual channel IR photo-interrupter used
for quadrature detection thus my suggestion of using
a mouse.
> H-bridge ICs are around $5.00, microcontroller
> around $3.00...Here's what's missing....Good PID code for the
> micros....Right now it's under lock and key but will soon trickle
> into the public domain.
Don't hang onto that key too long. Experience has
proven the benefit of community development and
support
--
uhmgawa@... www.gnu.org