Planetary gearheads
 

Thinking of earlierthreads, I wonder what their planetary gearboxes are like.
http://motioncontrolproducts.co.uk/i...hp/cPath/27_28

http://www.mechmate.com/Forum/messages/12/3335.gif

We need to understand what 5 arcmin of backlash will mean to a 25mm [1.0"] pinion on a rack....
A full turn (360 degrees) will cause a travel of 78mm [3.1"]. There are 360 degrees x 60minutes in a full circle = 21600 minutes. If 5 of these minutes are rattling loose, then that equals..
5 ÷ 21600 X 78mm are loose = 0.018mm [0.0007"]
...which is okay for a CNC router.

When folk mischievously want to show how bad their competition's gearboxes are, they will talk of the backlash on the input shaft. That 216:1 gearbox with 15 Arcmin on the output will have 3240 Arcmin backlash on the input, which is about 54 degrees movement of the input shaft, but still only a tiny amount on the output shaft.