When my best friend gave me all his old Lego parts (as he found himself and his siblings never using them) I found a lone differential gear lying in the box. Back then I did not even know how to use that part; but I did know for sure that was one of the most useful pieces in Technic. For those of you already familiar with differentials, the following (up until the rover video) won't be necessary to read though.
To the right we have two examples of Lego differential gears. The kind I have right now is the one on the right. The one on the left can only be used in bevel gear configuration. By themselves, the gears are nothing, just cylinders with tubes through them. They're made to contain 3 separate 12-teeth bevel gears on the inside, as shown below:
This is what a fully functional differential looks like. The function of this gear isn't too complex; it basically allows variance in the speed of both ends of the axle. Say the differential was motorized and the red and blue axles had wheels. If you were to slow one of the wheels down by friction, the differential would somehow transfer the energy lost by friction to the other wheel. This is especially useful for cars when they steer, since one wheel always makes a bigger circle than the other, and therefore their speeds must vary in order to turn smoothly. If you were to hold say, the blue end so that it doesn't move at all, the red end would double in speed.
To the right we have a real image of the lego parts needed to have a working differential. This particular differential gear has a gear fused on both ends to allow more variety of possible connections. The gear would be motorized by another gear connected to either of the fused gears. If the central bevel does not move, the ends of the axle will have the same speeds. If one of the vertically placed bevels slows down, the central one will speed up and so cause the opposite vertical bevel to speed up as well. This is what creates the phenomenon described along with the previous image.
Now to the actual project at hand. The 6 wheeler was intended to be an optional chassis for the next generation Lego Battlebots. Unfortunately, because my schoolwork got in the way so much, the game was not completed that year (I did make it a year later; stick around for the blog post). I only made a few embryonic prototypes of chassis and weapons, but eventually I realized the amount of work needed to complete it and the other simpler projects I had in mind would overrule any possibility of further developing the game. Ironically, I have a video but no pictures of this project. I hope you enjoy it:
As you saw this thing had double steering to meet up with the project focus. I thought, if this chassis will go against a tank chassis (the Battlebots standard), it better have decent maneuvering ability, especially because tanks can change direction in one place. I tried my best to make the return-to-center function work flawlessly, and I came pretty close by using some small rubber bands. Initially, the differential was motorized by two clutch gears (they stop spinning if too much torque is applied) but when I put a load on top of the chassis platform the rover didn't move. Therefore I replaced the clutch gears with regular, 24-teeth gears. Another issue I noticed was that during battle testing (again, with embryonic prototypes) the chassis platform easily came off the rover and made the idea of completing the game even more intimidating.
6 Wheeler Rover
1 Battery Box
3 M Motors