re: RE: need axis design idea

Thanks for all the good ideas for a long linear axis.

They break down into three camps of linear to rotary conversion:
1. using a wire wrapped around a shaft
2. using a rack & pinion
3. using friction drive

angle position is measured with a rotary encoder or a mouse.

Any of these schemes can have decent sensitivity, some of them good
precision.
I'm worried a bit about accuracy; perhaps a calibration would be enough to
take care of that.
The idea of a wire wrapped around the shaft of a encoder should be pretty
uniform along any length, but a rack could have pitch changes that would
affect accuracy considerably.

For the rail a box made of plywood could work, or better a piece of square
tubing. Tubing is pretty inexpensive at the welding shop.

In this group people have discussed using skate bearings, this should be a
good way to make the carriage run easily on the rail.

Another plan might be to have a PC board made with the pattern for a digital
caliper on it; the pattern could be repeated a lot of times across the width
of the board, then cut up into strips and assembled end to end to make a
long travel. If this works I'll report back here.

The mill scales made like that aren't long enough for my project. I wonder
if the scales are limited in how far they'll read?
The external readout boxes for them might read the internal values, and so
would have the same limit in travel.

regards-
Elliot
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