The first step in building your mobile robot is to pick your tracked vehicle platform. There are several manufacturers that make preassembled, tracked units. Here's an image of a preassembled, inexpensive tracked platform, made by Dagu. It's called the Dagu Rover 5 Tracked Chassis.

Once you have chosen your mobile platform, you'll need to hook up a motor controller, a battery, and the BeagleBone Black.