Sensors and Encoders

intermediate40 min

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

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

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