[Andy Baker]

There is alot of good advice here.

We have considered using more bushings as Gui does. The weight and cost savings would be worth the effort, if rotating friction can be kept to a minimum.

Along with Gui's advice on making the hole placements accurrate, the surface condition of the shafts are very important when using bushings. The rougher the shafts are, the more friction they will generate while turning in the bushing. There are different ratings of "surface texture". From what I have heard, a roughness average of 0.1-0.08 micrometers is good for a bushing. This sort of surface texture can be achieved by polishing the shaft on a lathe until imprefections (grooves, etc.) have vanished.

Needless to say, it takes a while to get this sort of finish. But, once this finish is achieved, then friction is low and the need for a ball bearing is diminished.

We have not done this on our robot or on gearboxes, 'cause we don't spend the time to get the shafts' surfaces to this degree of polish... but it is tempting to try.

Andy B.