The roller mechanism are simple brass wheels on a music wire axle soldered to supports made from printed circuit board. How do you switch the power to all those tracks. Once upon a time, we had a typical 12 position rotary switch, but then we rebuilt the yard and ended up with 20 tracks. The turntable rotates like our switch, so get rid of the redundancy and let it do the switching. It's shown in green in our sketch.
Spring loaded brushes wipe on the copper.
This it what it looks like on the new 48 track table. The bottom bearing is in place and the switch mounts below that. There is also a phosbronze wiper on the shaft to carry power to one rail on the table. The other rail gets it's power from the ring rail. Track power is selected at one end only of the table, so that end usually points to the roundhouse and garden tracks.