I recently bought the OWI 3 in 1 ATR (all terrain robot) kit from Amazon. What got my attention was its potential for hacking and re-use of its components. In the “Rover” mode the unit is pretty tightly packed. There does not seem to be much space to add electronics, or batteries inside, but they can be added on top. The front of the robot seemed a good spot to put the extra stuff, so I taped a 4 full AA battery pack as a test. The results were pretty good – the motor handles the extra load without a problem and the additional weight at the front actually helps the bot to climb over fairly tall obstacles with a vertical wall:
Here is the Rover next to an Arduino Uno to provide an idea of the size:
And here is box with a cool view of the three “robots” that you can make with the kit.