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 - Current
P_Output = kP × Error

Behavior: 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 × dt
I_Output = kI × Accumulated_Error

Behavior: Eliminates steady-state error by accumulating past errors over time.

Note: The integral term can lead to "windup," which may make your mechanism unstable. In most FRC applications, you can leave the integral term at zero.

D - Derivative

Definition: "The amount of output to apply per change in error over time"

Error_Rate = (Error - Last_Error) / dt
D_Output = kD × Error_Rate

Behavior: 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.

When to use:
Always

kG - Gravity

Compensates for gravitational forces acting on the mechanism.

When to use:
Arms/Elevators

kV - Velocity

Output applied per target velocity to maintain smooth motion.

When to use:
Flywheels/Intakes

kA - Acceleration

Output applied per target acceleration for responsive movement.

When to use:
High Inertia Mechanisms

📚 Complete PID Tuning Guide

For detailed PID tuning instructions, step-by-step processes, and mechanism-specific guidance:

CTRE Manual PID Tuning Guide

📹 PID and Feedforward Tuning Tutorial

Watch this comprehensive tutorial on PID and feedforward tuning techniques, practical tuning steps, and optimization strategies:

PID Implementation in Code

🔧 PID Configuration Example

PID Setup in Subsystem ConstructorJAVA

Workshop 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

PID gives us precise position control! In the next section, we'll upgrade to Motion Magic for smooth, profiled movements with controlled acceleration.

Previous: Mechanism Setup Next: Motion Magic