pic: Inverted CIM Gearbox V3

[Joey Milia]

Originally Posted by Jared

What about it seems like a bad idea?
EDIT: I just noticed theres only one bearing. This is a bad idea. If there was a second bearing, it would likely be okay for the following reasons.

Cantilevering the gear has no effect on torsional loads, and the gear/shaft has no significant axial loading, so we only need to worry about radial loading on shaft and bearings.

Three CIMs have a combined stall torque of around 1000 in-oz, and pinions have a pitch radius of around .3 inches, so the tangential force at the pitch circle is around 3000 oz or 190 lbs force. FRC gears have a pressure angle of 14.5 degrees, so the radial load is 190 x tan 14.5, which is 50 lbs.

50 lbs is less than a cantilevered wheel will experience on a WCD and these shafts do not commonly bend.

When calculating reaction loading of a shaft you can't ignore the tangental load. Assuming the tangental and radial load is what you calculated, the gear meshes in only one place, and the gear is in a static condition, the reaction load on the shaft would be sqrt(190^2+50^2). However this is a simplified analysis and this gearbox has gears with multiple meshes that need to be considered. Also, some of these shafts are smaller than the .5in hex that is commonly used on WCD wheels.

I'm not saying the cantilever will be a problem necessarily, I haven't done the math, just that the loading is potentially higher.

I also totally agree with everybody so far, that a single bearing (assuming it's a common FRC bearing not rated for moment loads) is totally insufficient for any of the shafts.