This shows the longitudinal square driveshafts passing through bevel gears and held up on pillow blocks with bearings, and then the bevel gears at each wheel station and their pillow blocks. There's also a center drive section with straight-cut gears I'll get to in a minute.
You'll note that the gears on one side are forward of the side bevel, and aft of them on the other side. This makes it so that the drive shafts turn the same direction to turn the wheels, so that the center drive section need only be one gear; as you can see, there just isn't room to fit a second set of anything in there to reverse direction or the like. I spent a bunch of time rotating my fingers around in circles in the air saying "This one goes clockwise so this one goes anticlockwise..."
The center drive is also an amalgam of printed and off-the-shelf parts. While gears can be printed, fairly strong even, doing them SMALL enough to make a diff was ... well, ugly. When you can get a metal one on Aliexpress for pocket change, it's just not worth the hassle. The drive gears on the end of it are still printed, and oddly, the coupler from the pinion gear to the motor is also printed, as I couldn't find a shaft coupler of the right dimensions.
And it starts to take shape and look like a thing, save the Dr Seuss colors. Really looked forward to even just primering the thing!
Can't see the gear drive, but the silver thing is the motor. It's a gear-reduction motor rather than your typical RC type motor as I needed something in the hundreds of RPM, rather than thousands. Also needed a right angle drive as the bed goes RIGHT above this, and trying to fit a regular RC motor-transmission inline with the driveshafts just wasn't in the cards.
Again, HRH Duke Leto presides. You'll also note I finally painted just for my eyeballs' sake.
Despite my best efforts to design the steering in CAD, I only managed to get it close. Once the suspension has weight on it, the thing settled more than I had modeled and all the steering angles went to crap. Also, not having the sides coupled (remember, left is separate from right!) is hairy. I cheated a smidge there by having two servos mirrored, but it still took some trial and error:
There's several variations of the steering arm, to see what geometry worked best.