OT Soft or pneumatic 6" diameter narrow wheels?

(they list a whole bunch, starting at about 5 bucks).

Also try your local lawnmower shop.

For free, maybe! You might try your local hospital maitenance department. I've salvaged wheels from broken/disfunctional gurneys and was given other wheels, already removed by the maintenance men. These are pretty nice wheels.

Sonny

Yeah, that sounds good.

Also wheelchair wheels, small front or anti-tip wheels. And maybe walker wheels. I found some online that might work.

If the stick could flex - essentially a shock absorber - it would keep the drive wheel in better contact with the ground.

This is what it looks like.

That bouncing is less problematic with more experience. A larger wheel might help, but weight is my primary concern. Besides upgrading the batteries to lithium-ion, I will reduce the structure weight. Some functional improvements can be made, but increasing its weight is extremely undesirable.