I started building this vehicle the way so many of my projects start; trying to learn about and build a new mechanism. In this case, I started with the front drive train.
I am quite impressed by the frame strength. Even with enough weight over either axle to make the tires go flat (maybe 2+ kg), the frame has almost no flex, and shows no signs of stress.
The only weak area I have found so far, is the drive train. There is no gearing after the differentials. Because of this, the 12 tooth gears shatter under significant load (I already broke two on this project).
The way I transfer torque to the front segment would normally try to twist the frame at the turntable, but I have it geared 6x the speed of the wheels. Due to the higher RPM, it needs less g/cm, which would twist the frame. It would obviously be a lot more efficient to have one of the drive motors on the front, but I didn’t want the weight, bulk, and wires; I also like the look of the UJ in there.
The overall drive gear ratio is 2:1. I get decent power, and fair speed. Efficiency isn’t great, being that I gear up for the center transfer.
All that limits the frame from twisting infinitely is the wire that connects the steering motor to the NXT.
For the code that runs the steering motor, I use the new NXC functions called APR (Absolute Position Regulation). It allows the steering motor position to follow that of the controller analog stick, a very nice feature.
It is remote controlled by a PlayStation 2 controller using the Mindsensors PSP-Nx interface.
Here are some pictures: