Open Loop vs. Closed Loop

Imagine walking with your eyes closed and hoping you’ll keep a straight line… Probably not the best thing to do in front of the officer that’s making you do a field sobriety test.

An open-loop system sends a fixed command to the plant and hopes for the best. There is no sensor, no feedback, no correction. If anything pushes the plant off course (wind, friction, payload changes) the system has no way to know and let alone respond.

Here, we’re trying to “go to 1”. But we’re not using feedback, so the actuator output is zero. The mass just sits where it starts (or drifts if you add a disturbance below).

Drag the d slider to push the mass around. No amount of commanding will bring it back. That’s the fundamental limitation of open-loop control, and the motivation for closed-loop control, which we start in Level 2.