Sensors and Encoders

Overview

Sensors provide feedback about your robot's state. This guide covers essential sensors from REV Robotics and CTRE Electronics.

REV Sensors

Common REV sensors used in FRC:

NEO Built-in Encoder: Internal encoder on NEO motors (42 counts/rev). Useful for velocity and basic position control.
Color Sensor V3: Detects color (RGB) and proximity. Connects via I2C (Onboard or MXP).
2m Distance Sensor: Time-of-Flight sensor measuring distances up to 2 meters with millimeter resolution.
Through Bore Encoder: Rotary sensor measuring both relative and absolute positions via ABI quadrature output.
Touch Sensor: Digital button input or mechanical limit switch.

REV Sensor Examples

Common REV sensor usage:

package frc.robot.subsystems;

import com.revrobotics.spark.SparkMax;
import com.revrobotics.spark.SparkLowLevel.MotorType;
import com.revrobotics.spark.RelativeEncoder;
import com.revrobotics.spark.config.SparkMaxConfig;

public class Drivetrain extends SubsystemBase {
    private SparkMax sparkMax = new SparkMax(1, MotorType.kBrushless);
    private RelativeEncoder encoder = sparkMax.getEncoder();
    
    public void configureEncoder() {
        SparkMaxConfig config = new SparkMaxConfig();
        // Set conversion factor: 0.05 meters per rotation
        // Adjust based on your wheel diameter and gear ratio
        config.encoder.positionConversionFactor(0.05);
        config.encoder.velocityConversionFactor(0.05);
        sparkMax.configure(config, ...);
    }
    
    public void readEncoder() {
        // Get position in rotations (or meters if conversion factor set)
        double pos = encoder.getPosition();
        // Get velocity in RPM (or m/s if conversion factor set)
        double vel = encoder.getVelocity();
    }
}

CTRE Sensors

Common CTRE sensors used in FRC:

CANcoder: Absolute magnetic encoder. Retains position after power cycles. Essential for Swerve modules.
Pigeon 2: IMU/Gyroscope. Provides Heading (Yaw), Pitch, and Roll. Used for Field-Centric driving.
CANrange: Time-of-Flight distance sensor for obstacle detection and autonomous navigation.
SRX Mag Encoder: Rotary position and velocity sensor for precise motion control.

CTRE Sensor Examples

Common CTRE sensor usage:

package frc.robot.subsystems;

import com.ctre.phoenix6.hardware.CANcoder;
import com.ctre.phoenix6.configs.CANcoderConfiguration;

public class SwerveModule extends SubsystemBase {
    // Create CANcoder on CAN ID 10
    private CANcoder encoder = new CANcoder(10);
    
    public SwerveModule() {
        // Configure magnet offset (calibrate for your module)
        CANcoderConfiguration config = new CANcoderConfiguration();
        // Offset in rotations to align zero position
        config.MagnetSensor.MagnetOffset = 0.25;
        encoder.getConfigurator().apply(config);
    }
    
    /**
     * Get absolute position from encoder
     * @return Position in rotations (0.0 to 1.0)
     */
    public double getPosition() {
        return encoder.getAbsolutePosition().getValueAsDouble();
    }
}

Product Documentation

REV ION Documentation REV Color Sensor V3 REV 2m Distance Sensor REV Through Bore Encoder CTRE Phoenix6 Documentation CTRE CANcoder CTRE Pigeon 2 CTRE CANrange

Resources

REV Setup CTRE Setup Motor PID Pose Estimation

Open full interactive app