At the moment my idea is to make a car that can ride a mono rail, that is pretty much just a board.
A motor should the drive on 1 of the wheels and the wheels on one side should be spring loaded so they always "clamp" down on the board to provide tension.
There should then be a switch in either end the car hit, and that then flip the DV voltage so the car go the other way, by varying the voltage you can change the speed, though i do think at 50 M we plan to set up on, the speed should not exceed a brisk walking pace.
The motor / electronics should be on the back side of the mono rail protected by a steel plate, the hand over of power from the mono rail should be at the top of the rail / board so the "car" always press down on the connectors,,,,,,, connectors you like garden railway where you use track power probably need to clean,,,,, but this should only take a few minutes for a 20 - 30 feet long rail.
These power rails could be pieces of metal into a grove in the wood, it could probably also just be clean copper wire in a even shallower groove.