Limelight 3A Vision Training

Helping FTC Robots See the Field

The Limelight 3A is a smart vision camera used in robotics to help your robot detect objects, find targets, and line up automatically. It uses LEDs, a fast processor, and built‑in software to track things on the field.

1. What Is the Limelight 3A?

The Limelight 3A is a small green‑glowing camera that helps your robot “see.” It can detect:

• AprilTags
• Game elements
• Targets or markers
• Objects you train it to recognize

FTC teams use it mostly for Autonomous to help the robot know where it is and what it should do next.

2. Why Teams Use Limelight

• It finds AprilTags very accurately
• It works even in bright or dark lighting
• It gives your robot real‑time position data
• It reduces guesswork in autonomous
• It’s easier than writing your own vision code

3. How Limelight Connects to Your Robot

The Limelight 3A connects to your FTC robot using:

• USB (for power)
• Ethernet (for data)

Your robot reads the Limelight’s data using a network table or JSON output.

4. What the Limelight Sends to Your Robot

The Limelight gives your robot important information such as:

• tx – horizontal offset (left/right)
• ty – vertical offset (up/down)
• ta – target area (how big the object looks)
• AprilTag ID – which tag it sees
• Robot pose – where the robot is on the field

Your robot can use this to turn, drive, or align automatically.

5. Simple FTC Java Example

This example shows how your robot might read Limelight data. (This is simplified for teaching.)

// Example: reading Limelight values
double tx = limelight.getTX();  // left/right offset
double ty = limelight.getTY();  // up/down offset
double ta = limelight.getTA();  // target area

// If the target is left, turn left
if (tx < -2) {
        leftDrive.setPower(-0.2);
        rightDrive.setPower(0.2);
}

// If the target is right, turn right
else if (tx > 2) {
        leftDrive.setPower(0.2);
        rightDrive.setPower(-0.2);
}

// If centered, drive forward
else {
        leftDrive.setPower(0.3);
        rightDrive.setPower(0.3);
}
            

6. Using Limelight for AprilTags

The Limelight 3A can detect AprilTags automatically. This helps your robot:

• Know which side of the field it’s on
• Choose the correct autonomous path
• Score more accurately

Example: reading the AprilTag ID

int tagID = limelight.getAprilTagID();

if (tagID == 1) {
        // left spike mark
} else if (tagID == 2) {
        // center spike mark
} else if (tagID == 3) {
        // right spike mark
}
            

7. Practice Challenges

• Use Limelight to center your robot on a target
• Use AprilTags to choose between 3 autonomous paths
• Make the robot stop when it gets close to the target
• Print Limelight values on telemetry

8. Limelight 3A Reference Link

Official Limelight Website:
https://limelightvision.io

Limelight 3A Product Page:
https://limelightvision.io/products/limelight-3