My father always had his Lionel trains running under the Christmas tree when I was little. When I moved out, the new house had a fireplace mantle and I used to set up a winter scene on it with a train running thorough the town. Static, of course. It was just a fireplace mantle.
When we moved to this house, the fireplace mantle was twice as wide and 16ft long, so I got it in my head that I could put an actual working railroad on it complete with a lighted town, crossing gates, a skating rink and a rail yard at either end. The problem was, it’s still not wide enough to turn a train around on. Yes, I could run it backwards but that’s not very realistic and prone to derailments. The solution was to put a turntable at either end with a run-around track to pick up the train again and head back. My ultimate goal was to make this computer-controlled so it could just run in the background every 15 minutes.
My model-making skills suck and the wooden turntable kept binding or wobbling or failing to align itself properly so that never went anywhere beyond a static model or manually running the engine without cars.
The next logical solution would be to buy a commercially made turntable. There were three problems with this: 1) they’re meant for a hole cut into a standard height table ie. you can make them as deep as you want, whereas this needs to be shallow; 2) even the smallest ones are too large for the mantle, and 3) even the smallest motorized, computer controlled ones start at around $400 - and I’d need two of them.
Now that I have a 3D printer, I’ve revisited the problem:
Add a $7 Arduino, a $5 Stepper motor and a $20 Adafruit Slip Ring (to provide continuously rotating power lights, track, position sensors, etc.) and I’m in business. This project alone will pay for the printer.
As a bonus, the movement is very smooth and super quiet, unlike some of the turntables I’ve heard. The gear backlash can simply be programmed out. I was going to post a video of it, but that’s not supported, apparently, but you get the idea.