[frizzen]

I'm just going by what the thread says, but it sounds like you're right. Three servos are gutted of the pot and circuit board with the motors hooked up direct to the input wire making it into a gear-motor. The geartrain has been modified to open up to full rotation. They're then run in parallel off an esc.

If you like that route, i would ask him what servos were used and if he would be willing to share the 3D printer file, and any other details like making outputs or steering axle. There's probably someone fairly near you with a 3d printer, ask around your computer friends. Someone on this board might also, or you can have someplace like shapeways do your run.

If he doesn't want to share the file, you might check out 'thingiverse' for other 3D printable options.

Durablity of those axles is probably not as good as it would be with a normal diff, but it's not like you're going for speed or rock crawling.

I'll get some instructions posted on how to scale it, been a while since i had to do it.

If your copy or print shop is worth going to, they should be able to do the scaling of your blueprint to whatever you like. I would still take a dial caliper with me to verify they got it correct since i'm more comfortable working in thousandths vs pica. Have them print atleast 10-12 copies so you've got some to destroy for the build.