Homebrew PCBs

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