Choosing the tracked platform
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.