What is PID?
Proportional-Integral-Derivative (PID) control is a fundamental algorithm used in UAV flight controllers to maintain stability and achieve desired flight behaviors. PID operates as a feedback mechanism, continuously adjusting motor speeds based on deviations from the target state. It consists of three components:
- Proportional (P): Corrects the error in proportion to its magnitude. A high P gain results in aggressive corrections but may cause oscillations.
- Integral (I): Addresses accumulated past errors to eliminate drift over time. Excessive I gain can lead to slow response and instability.
- Derivative (D): Predicts future errors based on the rate of change, damping oscillations and improving responsiveness.
Importance in Quadcopters
PID controllers are essential for stabilizing a quadcopter’s:
- Roll and Pitch: Lateral and forward/backward tilts.
- Yaw: Rotational movement around the vertical axis.
- Altitude: Vertical position, particularly for maintaining hover or controlled ascents and descents.
Without well-tuned PID controllers, a quadcopter would struggle to maintain stable flight, leading to erratic or uncontrollable behaviour.
Tuning the PID
Tuning the PID involves adjusting the P, I, and D gains to achieve optimal performance. This process is typically iterative:
- Set P Gain: Start with a low value and gradually increase until oscillations occur. Then reduce slightly for stability.
- Adjust I Gain: Introduce I gain to correct for drift. Too much I gain can cause overshoot and instability.
- Fine-Tune D Gain: Add D gain to dampen oscillations and improve response time. Excessive D gain can lead to sluggish control.
Software tools and real-world testing are often used in conjunction to refine PID values. Each axis (roll, pitch, yaw) may require separate tuning to account for asymmetries in the UAV’s design.
