The Rolling Stone

Tension Wheel

This spring loaded plunger pushes the spherical wheel into the drive rollers, providing necessary friction between the rubber o-rings and the polyurethane ball. A metal roller bearing on the end provides negligible rolling friction between the sphere and the plunger.

Exploded View of the tension wheel system

Isometric view of tension wheel system

Details and Photos of Tension Wheel Build (Click on the pictures for a larger view)

	Tensioner: This shows the tensioner block with its bronze sleeve (pressed into the aluminum block), and separately the tensioner shaft, with the 3/8in ball bearing already mounted, springs, and retaining clip
	Bronze Sleeve: Here's the bronze sleeve that was press fit into the main block. Bronze was used for its self lubricating properties and because aluminum on aluminum moving parts is a recipe for destruction. You can see the tensioner rod, the bearing is held in place with a 3/16th brass shaft which was press fit through holes in the head of the tensioner.
	Tensioner Retainer: Here you can see the retaining ring and the e-clip that hold the assembly together.
	Bearing Shaft: A good shot of the brass bearing shaft, for a snug press fit without too much stress, the holes must be about 0.0005in smaller than the shaft!
	Tensioner Assembly: here is the whole tensioner assembly. The bearing maintains contact with the wheel, the spring keeps the tesnion in the system. Yet the entire mechanism can rotate (around the bearing axis AND around the shaft axis) and translate (back and forth along the shaft axis). This single mechanism keeps the proper friction between the ball and the drive motors, while absorbing any irregularites.