The open-loop heating system has some advantages, including design simplicity and ease of maintenance. With only voltage applied to a heat source, this method does not require an elaborate control ...

The biggest improvement is that AR2 had a closed-loop control system, and AR3 is open-loop. If something bumps the arm or it crashes, the bot will recover its previous position automatically.

Self-regulating systems with feedback loops, i.e., the routing back of the output of a system to its input, have existed since antiquity and have since become an integral part of modern technology.