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.