Hi 
TurtleBot3 has sprockets that enable anyone to easily change from general wheels to caterpillars.
If you want to replace it, you would just pull rubber wheels out of the sprockets and assemble pieces of caterpillars on it.
It makes to efficiently drive on piled woods or books rather than using general wheels.
Furthermore, TurtleBot3 can ride on the off-road conveniently. (e.g. debris, grass, bushes and even rocks!!)
This example is made of two Dynamixels (XM430-W210-R), two Dynamixels dummy and 72 pieces for caterpillars. (The One side of caterpillars needs 36 pieces)
Thanks.