Heh, for a while I was working on LEGO swerve drive but without the turntable piece, and I found it is hard but not impossible, if you drill out the center of large LEGO gears it is possible. I had two working modules made in fact I still have them. Lost interest in finishing it though. I might post a pic if I can find my camera.
OK found camera, it was in it's case.
So I took 4 pictures with my cat partially in some. I know it currently has the worst gearing system ever, yet it was 2:30am and I just wanted a working system before I went to bed. I woke up the next morning with ideas on how to get it working right, correct gearing but got distracted and was too lazy to pull out all the LEGO boxes from LEGO camp. There is 6 boxes and 2 bins. Stack attack bins. All in my small cramped room.