A PID-controlled robot joint with well-tuned gains (K_p = 10, K_i = 0.5, K_d = 1) reaches its setpoint accurately for small setpoint changes but oscillates severely and overshoots for large step changes. The most likely cause is:
AThe proportional gain K_p is too high
BThe derivative gain K_d is not large enough to damp the oscillation
CThe actuator saturates during large transients, causing integrator windup that keeps the joint overshooting even after reaching the setpoint
DThe control loop frequency is too low to handle large transients
Ziegler-Nichols is valuable because it relates the tuning gains to the plant's actual behavior (its critical frequency and gain), not arbitrary parameters. The resulting PID controller is typically slightly underdamped (some overshoot) but stable, providing a good baseline for manual fine-tuning. Variations like Ziegler-Nichols for no overshoot (K_p = 0.2·K_u) or quarter-amplitude damping (K_p = 0.45·K_u) offer different trade-offs between speed and overshoot.