It's a very simple robot which I have programmed to draw. I hacked 2 micro servos so they continuously rotate, and attached to jam jar lids as wheels. The bot can be programmed to run the wheels for different amounts of time making a spirograph type shape. The wheels were very smooth and I knew they'd need to be more grippy. Sugru is great for this. I rolled a sausage of sugru and rolled it around the wheel smoothing it down. I then used a plastic?spatula?to carve the treads. Works perfectly. Dominic.