Believe it or not, a variation of the tracked vehicle is the 6WD (six-wheel -rive). Because of all the surface area that the wheels expose to the ground, 6WD bots function very much like tracked vehicles. The figure below shows both the traditional tracked and 6WD arrangements.
In both, a single motor on each side of the base propels a driver. For a tracked base, the track itself acts as a belt to drive the other wheels. For a 6WD base, a belt, gear system, or chain drives all wheel simultaneously.
If you’re looking to construct a large robot, say about 2 feet long or more, you’ll want to look for a 1:12 to 1:6 scale tank. These are occasionally available at the larger discount retailers, such as Walmart. The fall and Christmas seasons are ideal times to find these. The toys are physically large, and stores may not stock them year-round because of space considerations.
A relatively new source of tanks in this size range are intended for BB and paintball play, and you can find them at online retailers specializing in air guns for these sports. Prices vary from about $50 to over $200, depending on the size, brand, and quality of the tank.
These tanks are remotely controlled. Note that quality varies greatly in this genre, with users sometimes reporting “DOA” products when they receive them through the mail. Make sure to buy yours from a reputable dealer who offers free shipping for the return of defective merchandise. As these are quite large and heavy, shipping can get expensive.
Automotive and machine timing belts are another source of tracks. Don’t forget the matching sprockets for these belts. The typical timing belt has a cog on one side only. This cog engages with the drive sprocket. Some timing belts are double-sided and have cogs on both inside and outside.
These are often used in serpentine arrangements where the front and the back of the belt engage with various mechanical parts. Double-sided timing belts are preferred for use as tank tracks, because they have a cog on the inside for engaging with the drive sprocket and a cog on the outside that act as cleats for enhanced locomotion.
You can find timing belts at automotive shops, junkyards, and industrial supply outlets. They come in various lengths and thicknesses. Most are fiberglass-reinforced rubber, which means they are flexible, but they do not stretch.