[Backtracking][1].

1. Place a mechanism which aims at the goal from a random direction and a random distance. 
2. Then another one which aims at that mechanism, and so on. The number of iterations depends on the desired difficulty.
3. Place the start so it faces the last placed mechanism.
4. Then rotate each rotator into a random direction so the player has to guess how to rotate them.


  [1]: https://en.wikipedia.org/wiki/Backtracking