Thanks to some encouragement from the followers of this blog, I gave Lego a shot for driving the turntable. We have a house full of the stuff, although one of our collectors likes mostly the Friends and Elves Lego, which is sadly not conducive to turntable manufacture. Fortunately, the Boy like Star Wars and Technic and other Lego that is full of gears and whatnot.
The first port of call was to replicate the Tamiya gearbox in Lego. Predictably, this worked better than the Tamiya version because the shafts are cross-shaped, rather than round. I tried two different ways to tie the Lego into the rest of the mechanism, both based around a T-shaped end to the central shaft of the turntable.
Then, on Saturday evening, Gary Hinshaw hosted a test operating session on his Tehachapi BC layout. It was a fun low-key get-together, designed purely to shake down the mechanical aspects of the layout. I brought the turntable mechanism along for comment, which is yet another benefit of not being a lone-wolf modeller.
Toward the end of the evening, Mark Dance, came up with the brilliant suggestion of abandoning the worm drive altogether, and driving the turntable with a rubber wheel running along the outside of the PC board plate. There is nothing like a fresh perspective to get you out of a rut!
So, today, the Boy and I raked through the Lego some more and came up with a simple wheel mechanism along with some universal couplings that can be used to drive the turntable out near the edge rather than at the centre where the torque is felt the most (lead photo). It works! The springs enable us to be imprecise about the exactly location of the supporting tray in the benchwork.
The thing I like most about this idea is that it is remarkably simple, and could probably be self-aligning. I may even be able to make the whole thing out of wood. The only downside is that the wheel would have to be very small indeed to have the same driving ratio as a worm drive. The PC board is about 7.5 inches in diameter. So, if I wanted a 1:20 ratio, I would need a wheel of only 3/8″, substantially smaller than the Lego wheel shown above.