Pete C. wrote:
Ignoramus21167 wrote:


I have opened up one of my servos to see the shaft. It is a 10mm
shaft.

For that size, US Digital has suspiciously cheap encoders E7P:


Well, on the back of the envlope calculation is: ball screw pitch 1/8"
(0.125"). Pulley ratio 1:2. So, 720 CPR results in

0.125"/2/720 = .0000868 inch per cycle
OR
0.002mm

That would be acceptable to me.

i


.0000868" per count * servo error tolerance of +/- 128 counts (256 count
window) = 0.0222208" error which is very significant and would not be
acceptable to me.

Where do you get this "servo error tolerance +/- 128?" That sounds like
you are assuming the Gecko 320 series of drives,
which Iggy will not be using.

But, anyway, the US Digital encoders have caused all sorts of problems
in a variety of applications, mostly due to a total lack of decoupling
capacitors in the encoder. I have worked with the CUI AMT102 encoders,
and they seem to work well. But, they only go up to 8 mm ID on the
wheel adaptor. They have a DIP switch inside to set the resolution,
and also have the index pulse. There is a cable adaptor that converts
the output to differential. They are available from Digi-Key, and quite
affordable, just over $30 with either the plain or differential cable.

Jon