PID Control
PID Control - Precise Position Control
PID (Proportional-Integral-Derivative) control replaces imprecise voltage commands with accurate, feedback-driven position control. Essential for mechanisms that need to hit specific targets.
🎯 Key Concept: PID uses sensor feedback to automatically adjust motor output to reach and maintain target positions.
Understanding PID Components
P - Proportional
Definition: "The amount of output to apply per unit of error in the system"
Error = Target - CurrentP_Output = kP × ErrorBehavior: Larger error = stronger correction. Provides immediate response but may cause oscillation.
I - Integral
Definition: "The amount of output to apply per unit of error for every second of that error"
Accumulated_Error += Error × dtI_Output = kI × Accumulated_ErrorBehavior: Eliminates steady-state error by accumulating past errors over time.
D - Derivative
Definition: "The amount of output to apply per change in error over time"
Error_Rate = (Error - Last_Error) / dtD_Output = kD × Error_RateBehavior: Reduces overshoot by predicting future error trends and dampening response.
⚡ Feedforward Gains
Feedforward gains help the system by predicting the required output based on the target, rather than reacting to error.
kS - Static
Constant output to overcome friction and get the mechanism moving.
kG - Gravity
Compensates for gravitational forces acting on the mechanism.
kV - Velocity
Output applied per target velocity to maintain smooth motion.
kA - Acceleration
Output applied per target acceleration for responsive movement.
📚 Complete PID Tuning Guide
For detailed PID tuning instructions, step-by-step processes, and mechanism-specific guidance:
📖 CTRE Manual PID Tuning GuidePID Implementation in Code
🔧 PID Configuration Example
1// In your subsystem constructor
2public ArmSubsystem() {
3 TalonFXConfiguration config = new TalonFXConfiguration();
4
5 // PID Configuration for Slot 0
6 Slot0Configs slot0 = config.Slot0;
7 slot0.kP = 24.0; // Proportional gain
8 slot0.kI = 0.0; // Integral gain
9 slot0.kD = 0.1; // Derivative gain
10
11 // Feedforward gains
12 slot0.kS = 0.25; // Static friction compensation
13 slot0.kG = 0.12; // Gravity compensation
14 slot0.kV = 0.12; // Velocity feedforward
15 slot0.kA = 0.01; // Acceleration feedforward
16
17 motor.getConfigurator().apply(config);
18
19 // Create PID control request
20 positionRequest = new PositionVoltage(0).withSlot(0);
21}
22
23// Method to set target position
24public void setTargetPosition(double positionRotations) {
25 motor.setControl(positionRequest.withPosition(positionRotations));
26}
27
28Workshop Implementation: PID Control
🔄 Before → After: Implementation
📋 Before
- • Commands control Arm with voltage
- • No position feedback control
- • Imprecise, inconsistent movement
- • No automatic target reaching
- • Manual voltage adjustment needed
✅ After
- • PID position control with PositionVoltage
- • Automatic target position reaching
- • Precise, repeatable movements
- • Feedforward compensation for gravity
- • Tolerance checking for "at target"
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🔍 Code Walkthrough
PID Implementation:
- • PositionVoltage: Replaces VoltageOut for closed-loop control
- • Slot0 Config: PID and feedforward gains configuration
- • Target Setting: setTargetPosition() method for precise control
Gain Values Used:
- • kP = 24.0: Strong proportional response
- • kD = 0.1: Small derivative for damping
- • kS = 0.25: Static friction compensation
- • kG = 0.12: Gravity feedforward for Arm
💡 Next Step: PID gives us precise position control! In the next section, we'll upgrade to Motion Magic for smooth, profiled movements with controlled acceleration.