The Rolling Stone

These move the sphere through the friction provided by the black rubber o-rings (3). They are driven by the geared 12V motors attached to them. The drive wheel system also includes the encoders. These relay information back to the DSP about how fast the drive rollers are turnings so that corrections can be made in real-time, making sure the system goes in the correct direction at the correct speed.

Exploded View of the drive wheel system

Isometric view of drive wheel system

Details and Photos of Friction Drive Build (Click on the pictures for a larger view)

	Friction Drive Assembly: Here you can see the motor, bearing blocks, axle, setscrews, friction wheel, and encoder that make up one of the two friction drive assemblies
	Motor Mount: Here you can see the motor, bearing blocks, axle, setscrews, friction wheel, and encoder that make up one of the two friction drive assemblies
	Encoder Bearing Mount: Here you can see a similar mount for the encoder side of the assembly. I had to make four of these before I could get the tolerance right for the press fit on the bearings.
	Axle with Friction Wheel: this is the axle, turned down on the lathe to fit the roller bearings with a spot left in the middle for the friction wheel (double seal o-ring). the o-ring sits in a groove left in the raised portion of the axle. the axle is hollow t accept the motor and encoder shafts , and a tapped hole accepts a 4-40 setscrew to further secure the shafts. The length of the shaft and position of the friction wheel needed to be extremely precise, as there is no lateral positioning for this component, and it must contact the wheel EXACTLY in the center for smooth operation.
	Encoders: here you can just barely make out the flat that had to be cut into the encoder shafts. They were originally perfect cylinders, but i needed a flat spot for the setscrews to bite into, so I ground down a flat with a file.