I've made this as an assembly you can take, and put in your vehicles. It's a seat that starts in one position, and if you sit in it, rotates 180 degrees.
It locks itself in both orientations using a gripper, because it's a velocity motor, so it wouldn't keep position otherwise.
I've built it for when I have a steering space too narrow to walk around the seat, and have no space on walls to put a door/hatch there. When you want to get off, just crouch on the seat, it'll spin back to the original orientation.
The microcontroller is timed in ticks, I haven't tested the mechanism in extreme conditions, or at extreme speeds, so I can't guarentee that the timing required won't be slightly different in those conditions, but it should work fine.
