So I searched around my parts last night looking for a gear that would fit and lock down on the pinion shaft of the axle. I had several old TMaxx tranny gears but couldn't find anything compatible that would fit on the motor to drive it.
I came across a bag of broken Axial parts and pieced together the center trans dif, then drilled the center out to 5mm and installed a set screw. The other end I cut off flush with the gear. I was pleasantly suprised to find that I had drilled the holes straight! No wobble!
I then took the lathe motor mounts, drilled and tapped a couple of 3mm holes into the side and bolted it down to the chassis. Added a 18t pinion and set the mesh. Everything looked perfect.
One the second run it was obvious that I had lost some speed so I swapped pinions. The next run munched the plastic gear on the axle. :evil:
At this point I'm pretty well out of usable parts, so I decided to try belt drive. I grooved the plastic gear to hold a big o-ring, and swapped the pinion out for the spindle that drives the lathe. Got everything lined back up and tried it out.
It worked very well. The o-ring acted like a slipper, but I didn't want to make it too tight and put tons of sideload on the motor or axle. Still not very fast though.
I'm thinking I may have to call this one done. For everything I've gone through I could have just slapped a big motor and battery in my B4 and been faster.
I had the idea to do the micro switch thing but with two batteries and two switches to make it a dual stage kinda thing, but I'm thinking I've already reached the point of diminishing return with this drivetrain.