I'm trying to create a setup to transfer motion from a motor to a shaft that requires a much higher torque (bi-directional). The housing is about 6 inches long and the speed ratio needed will be around 1:10 or even 1:15 and I'm looking at using a GT3 belt with 14mm pitch. The reason for 14mm pitch is that the datasheet appears to suggest it is the GT3 that can achieve the highest speed ratio. However, according to the data sheet, the highest speed ratio specified is only 6.857 (28:192) - does that mean the belt isn't designed for running in setups with higher ratios? Also, the shortest centre distance between the pulleys is 27.9 inches:

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If the speed ratio was to be pushed to ~10 (16:168) and the sprockets were just 5 or 6 inches apart, could idlers be fitted in between to give the belt and the sprockets better contact? Are there tips to setup such high ratio sprocket combination inside a small housing?


  • $\begingroup$ A 2 or 3 belt system? $\endgroup$ – Solar Mike Jun 13 '20 at 18:14
  • $\begingroup$ @SolarMike Hopefully just one belt. $\endgroup$ – John M. Jun 13 '20 at 18:23
  • $\begingroup$ You haven't provided the power and rpm of the driver, or the load factors of the driven item. Simple worm gearboxes would be the norm here for bi-diretional low lash motion. Belt tensioners are troublesome items on bidirectional belt systems since you want to tension the slack side, and there are two of them. A second option would be to belt drive a simple reversing gearbox on the output shaft. The motor and belt run one way. the tranny ratio can be standard at ,say, 2.5:1 and the rest done with the belt. $\endgroup$ – Phil Sweet Jun 13 '20 at 23:34
  • $\begingroup$ ... And how are you going to buy a toothed sprocket in a size that doesn't exist? $\endgroup$ – Phil Sweet Jun 13 '20 at 23:36
  • $\begingroup$ @PhilSweet I'm thinking to machine my own sprocket if I can't find one off the shelf. About the driver, it's a 20V 2A brushless with a max rpm of around 350rpm. The load is about 2kg. I've thought about worm gears, but I'm also trying to make it backdrivable. $\endgroup$ – John M. Jun 14 '20 at 5:19

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