I've listed on Ebay a set of parts to make a pair of tracks for a small tank-drive type robot.
Included are 2 toothed belts 525mm circumference (flat timing belt),10mm wide. 4 toothed sprockets 42mm dia. And 4 bushes for the sprockets to run on.
The belts are flexible polyurethane (steel wire reinforced) and have two fingers which give the ability to climb over small steps and other obstacles. These fingers can be shortened or cut off completely if required depending on your design and weight of robot.
Item no. 5961028871
I also have some small gearmotors with good torque suitable for driving these, they come with an attached toothed pulley to match the belts:
Nos. 3879562130 & 3878034033
And some larger high-torque gearmotors suitable for medium sized robots: No. 3879562314
All are new or new old stock with low start price and no reserve. I have quantities of these and will be relisting the items as they sell.