1:1 ratio - pulley sizes

[dsc]

This might be a daft question, but I'll fire away anyway. I'm using a 1:1 ratio on a motor (with a gearbox) to shaft transmission, using HTD5 15mm wide belt / pulleys. Does it matter how big the pulleys are, or can I go with whatever size I want? I know that with 1:1 ratio torque / speed transfers over to the driven end, but maybe there's a reason to use smaller pulleys rather than big ones? only thing I can think of is inertia and how fast the pulley can move / stop.

Regards,
T.

[irving2008]

Inertia is one key parameter. Another is how many teeth are engaged v the torque you want to transmit. Also consider belt radius and therefore flex which translates to belt life.

[dsc]

Thanks irving, didn't think about teeth engagement vs. torque. I'll be using a 400W servo (1.27Nm, peak torque of 3.82Nm) with a planetary gearbox, 12:1 ratio, this will then be coupled to a shaft via pulleys and 1:1 ratio. I doubt I will ever exceed 20Nm on the drive side, but I'd rather be sure the pulley arrangement can take the maximum 45Nm just in case. Ramp up / down speeds aren't a big issue here, so bigger pulleys should be fine, I just need to google for some teeth / torque calcs.

Regards,
T.

[EddyCurrent]

Don't forget Jonathan's spreadsheet too.

http://www.mycncuk.com/forums/machine-building-faqs-problems-solutions/5848-calculating-timing-belt-lengths.html