This model is based on the Tumbler batmobile from Christopher Nolan's series of Batman films. It uses the parts from two NXT kits (1.0 and 2.0) plus a differential and accompanying bevel gears. Originally, I'd planned to cover it in black plates for a more authentic look but in the end, I thought I'd see what I could do with just the NXT parts (plus differential)
It uses one motor to drive the rear wheels and two motors for the steering. Each steering motor runs a pair of 24 tooth gears, the second of which has a cam mounted on it which presses a touch sensor when the wheel is facing forward. A small routine in the program calibrates the steering using this. The shaft of the second gear moves an axle connector with a ball joint, which moves a linkage to another ball on the actual front wheel assembly to turn it.
The trickiest parts of the build were making a working steering mechanism and keeping the model compact with the right shape. Also, I learnt a lesson in this build: keep the NXT easily accessible! By the time I'd finished building it, the batteries were going and I couldn't replace them without disassembling a large proportion of the model, so the final program was rather simpler than I'd intended. Also, because there was very little clearance beneath the model, it didn't tend to work too well on carpet, so I should have made the rear wheels lower. all in all, though, I'm reasonably pleased with how it came out.
Please feel free to comment and let me know what you think/what I could have done better.