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Hi,
Did some reading, and its apparent that reduction ratio at the final stage is important as the torque required on the final driving shaft in a multistage reduction train is the total torque required to overcome the load's moment of inertia (dependent on radius of driven pulley), and is not dependent on preceding gear reduction stages.
so higher the reduction ratio at the final coupling stage, lower the torque required at the final driving shaft.
I was looking at your metal friction drive and my hypothesis on why slippage is not such a problem is because the ratio at that stage is very high and torque required is relatively low.
if the diameter of your driven metal wheel was say 1/4th the size and the driving wheel was twice the size, the torque required would be much higher even if reduction was added at preceding stages and slippage might occur.
sorry to brag on in this thread, but its just clearer to understand now.
I'm quite confident i'll be able to get the ratio needed which is around 700:1 just using timing pulleys and a planetary gearbox.
backlash was quite low, but will need to measure it later.
as you mentioned, balance will be critical. thats another aspect altogether.
Pies australia and powergrip have timing pulleys that use taperlock so can accomodate a range of shaft sizes.
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