Sensors in FRC

Banner Sensors

Banner sensors are small optical sensors used for object detection.

• Digital output (true/false)
• Fast and reliable
• Detects if something is in the way - super simple

Example (Digital Input)

private DigitalInput banner = new DigitalInput(0);

public boolean hasPiece() {
    return banner.get();
}

Encoders

Encoders measure rotation accurately and are used to know how many times a motor has rotated.

Types of Encoders

• Integrated encoders: Neo/Kraken built-in sensors
• External encoders: SRX Mag, Through-Bore
• Absolute encoders: Gives the true angle at startup
• Relative encoders: Counts movement from zero, wherever it was when it powered on is "0 rotations"

Example (SparkMAX Built-In Relative Encoder)

private RelativeEncoder encoder = sparkMotorController.getEncoder();

public double getPosition() {
    return encoder.getDistance();
}

Absolute vs Relative Encoders

Absolute Encoders

• Know angle on startup
• Used particularly on swerve, helpful in other places if precision is absolutely needed
• Not affected by missed counts

Relative Encoders

• Start at 0 on boot
• Require homing
• Used for mostly everything that doesn't need to be ultra-precise or can't be reasonably put in a home position

Limit Switches

Limit switches detect endpoints of travel and protect mechanisms.

• Not as common anymore
• Digital input (true/false)
• Often used for homing

Example (Limit Switch)

private DigitalInput limit = new DigitalInput(1);

public boolean atHome() {
    return limit.get();
}

Homing a Mechanism

Homing establishes a known zero position for a mechanism.

Common Homing Methods

• Drive into a limit switch → reset encoder
• Move slowly until hard-stop → reset encoder
• Put the mechanism in the right place before powering on the robot

Example (Homing using a limit switch)

if (limitSwitch.get()) {
    encoder.setPosition(0);
}