Based on this photo [1], I'm guessing they use a system much like a cog railway. There would be a continuous ring of teeth along the tracks and a small motor on

Based on this photo [1], I'm guessing they use a system much like a cog railway. There would be a continuous ring of teeth along the tracks and a small motor on the platform with a few inch gear to engage the cog. Or vice versa. The cog ring would probably be made up of several smaller segments.