On Mon, 03 Oct 2005 15:42:08 -0400, Brian Lawson
wrote:

On Mon, 03 Oct 2005 10:56:34 -0700, Eric R Snow
wrote:

On Mon, 03 Oct 2005 13:33:52 -0400, Brian Lawson
wrote:


Brian,
The mirror is about 1/2 inch on a side and .09 thick. The laser is 1.5
inches dia and 8 inches long. With wires coming out. I feel it may
have more influence on shaft movement if mounted directly to the shaft
than the mirror will. Direction is determined by only one encoder. It
has two readheads out of phase with each other. So A leads B turning
one direction and B leads A in the other.
Thanks,
Eric

Hey again Eric,

I must be missing something about using the mirror. Maybe I should
just shut up and see what you do, or the results anyway, but that's
not me!!

My lack of understanding is in/with the deflection of this mirror. As
I understand it, you are going to

1 - fasten a mirror to the shaft,
2 - shine a laser beam on the mirror,
3 - note the point this reflected beam contacts a wall 132 feet away,
4 - make a "mark" on the wall at that point
5 - rotate the encoder one pulse (by turning or stepping the shaft to
create a single "output" pulse of the encoder)
6 - repeat step 5 for ten or more "pulses", and then reverse the
. step direction for the same number, and see if there is a
. difference between the start point and the end point.

To me, that should work, but if you are going to measure the distance
the beam "moves" from pulse to pulse, then the mirror will cause a
"doubling" deflection type error with each pulse. That was the
reason I suggested fastening the laser direct to the shaft.

Am I wrong about your intent, or the error?

Take care. Watch the laser in the eyes.

Brian Lawson.
Actually Brian, I want to do both, watch for change AND measure
movement. I did not realize the mirror would double the movement until
it was pointed out to me. Then it clicked and I remembered. The laser
is 3mw, 632 nm. Still, I'm always careful with lasers since I saw a
hole burned through a wall at a lab at UW in Seattle.
Eric