I only learned what a syncro drive was last week, but as soon as I heard about it, I wanted to see if I could build one. I was surprised how easy it all came together. The syncro drive was built and functional in about 2 hours, figuring out how to mount the motors and NXT was about 2 hours, then building a rudimentary avoidance program was another hour.
I'm pretty sure I could get this down to 1 motor using the bidirectional locking differential design, but that'll take a little more time to figure out.
A total afterthought on this model, that's turned out to be very cool is mounting the proximity sensor on the 3rd motor and setting it up to sweep 350 degrees back and forth like a radar tower. The program is currently very rudimentary: If the prox-sensor every reads lower than 15 inches, turn the syncro drive about 45 degrees, that actually allows it to avoid most obstacles.
Not much to note here except getting a general idea for the size of the thing
Here you can see the big gears that drive the wheel-assemblies (I cheat a little and only drive 2 of them)
Drive Motor Closeup
Closeup of how the motor connects to the driving gears.
The motor is connected to the 8t geat, which drives the 40t gear which drives the 4-knob geat down by the wheels. It is also connected to the other side via the 40t geats visible in the previous photo.
Steering Assembly Closeup
Here you can see the gear train that connects the steering motor to to the turntables on the bottom of the bot.
Syncro Assembly Closeup
Here are closeups of the syncro assemblies. The key to everything of course is the turntable part. I've got 3 here, one came with my NXT, one came with the firetruck set, and I borrowed one from my roommate.
The first part of the whole design was building a platform that could mount the 3 turntables with a standard gear in the middle. The fit here is pretty tight, you actually have to flex the base a little to get that middle gear into place. But once it is in, it is very solid. The problem is that the alignment of the turntables is off by one-half of one tooth. The end result is that the robot rotates a little when the syncro drive turns. (on a perfect syncro drive, the robot body never turns). I'd like to try with 4 turntables to see if I can alleviate that problem.
The 2nd picture is a closeup of the wheel assembly. I was really happy with the compactness of this design, but I'd really like to figure out a single-wheel-per-base design someday. Maybe after I get 2 more turntables. :-)
Closeup of Syncro Assembly #2
Here is a detailed pic of how I got the wheels to turn. It's really quite strong and stable.