Physical AI Lab // Episode 1.2 // One-pager

Control: PID and control rate

Getting the motors to catch up with the target, steadily

Three key points

  1. Closed loop: measure what actually happens, compare with the target to get the error, then act on the error, round and round; not measuring is open loop, which can't cope with disturbances.
  2. Three flavours of PID: P does the heavy lifting (too big and it swings), I fills in the tail of steady-state error, D brakes to hold down shaking; tune all three together (about nine in ten industrial controllers are PID, R).
  3. Control rate: how many times a second this loop goes round; too slow and even the best PID can't hold steady. One force-controlled arm, the Franka Research 3, has a maker-stated low-level control rate of 1 kHz (O).

Evidence: O official · R research · M media

RNine in tencontrollers in industry are of the PID kind (one study's estimate, quoted in a review)
O1 kHzlow-level motion control rate of Franka Research 3, a force-controlled robot arm, about 1 kilohertz (about 1000 times a second)

Further reading