hi sacher! welcome to pf!
let's start with the simplest case … a wheel with one cylindrical hole across a diameter, and a rod we can slide along it
with the rod horizontal and with the brake on, we slide the bar to the left, then we release the brake …
the wheel turns 180°, until the rod is at the right …
now we apply the brake again, slide the rod through, release the brake, and so ad infinitem
i] this assumes no friction … in practice, because of friction, the rod won't quite
return to horizontal
ii] even if we add more rods (at different angles), pushing them out when they're exactly horizontal
, the same thing will happen: the wheel will turn to the point where the centre of mass is at the original height
(and if we push a rod out when it's above
the horizontal, then we're supplying energy by doing so
, aren't we?