What about this idea
I got some rubber belts that I bought from Dick Smith a while ago. I found some plastic wheels with like tyre rubber on it at Bannings. This tyre has grooves so belt can sit in it safely. Now, there are different sizes of this wheels. The one I like is 125mm in diameter.
Thats 392.5mm circumference.
Encoder shaft I thought to put peace of thin car vacuum hose over the shaft for better grip. Not sure of dimensions of the shaft yet with the hose over it. But thinking this should work and rubber belt should not slip. I can always put 2 idlers close to encoder shaft so the belt "hugs" shaft better and give better grip this way.
Now, what I need to know is how to calculate ratio between this 2 shafts. Is it as simple as taking this 392.5 and dividing it with thickness of the encoder shaft?
Lets assume encoder shaft is 6mm. Thats 18.84mm circumference. 392:18.84=20 (approx)
20 turns of encoder shaft while big wheel turns once?
20x512=10240
In other words how many times will encoder shaft turn when big wheel turns once?
thanks