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Lesson 9.4: Using CRServos for Intake-Style Mechanisms

Technical Context​

Continuous Rotation (CR) servos are used for high-speed intakes or spinning mechanisms where positional precision is not required. They provide a compact, lighter alternative to a full DC motor when you need continuous rotation but don't have a free motor port — or when the mechanism is small enough that a servo's current draw is acceptable.

How CRServos Differ from Standard Servos​

Unlike standard positional servos, a CRServo does not have a target angle. It has no concept of "position" — instead, it spins continuously at a speed determined by its power value. For this reason, the SDK exposes it through the setPower() method, exactly like a DcMotor:

  • 1.0 — full speed forward
  • 0.0 — stopped
  • -1.0 — full speed reverse

Because it uses setPower() instead of setPosition(), you must also remember that a CRServo will not hold any position when set to 0.0 — it simply stops spinning. There is no equivalent of ZeroPowerBehavior.BRAKE for a CR servo.

The hardware must be instantiated using CRServo.class — not Servo.class. Attempting to cast a CR servo as a standard Servo will compile successfully but crash at runtime when setPosition() is called on an incompatible device type.

Annotated Code​

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.OpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.hardware.CRServo;

@TeleOp(name="CRServo_Demo")
public class CRServoDemo extends OpMode {

    // Must declare as CRServo — not Servo
    private CRServo intake;

    @Override
    public void init() {
        // Must get as CRServo.class from the hardwareMap
        intake = hardwareMap.get(CRServo.class, "intake_servo");
        intake.setPower(0);
        telemetry.addData("CR Intake", "Ready");
    }

    @Override
    public void loop() {
        // Trigger directly drives the servo speed — 0.0 to 1.0
        intake.setPower(gamepad1.right_trigger);

        // Left trigger runs it in reverse for ejecting
        if (gamepad1.left_trigger > 0.1) {
            intake.setPower(-gamepad1.left_trigger);
        }

        telemetry.addData("Intake Power", intake.getPower());
    }
}

Fill-in-the-Blank Practice​

  1. A CR Servo is commanded using the __________ method instead of setPosition().
  2. To stop a CR Servo, the power must be set to __________.
  3. If a CR Servo rotates the wrong direction for an intake, you can invoke the __________ method to flip it without changing your power logic.
Show answers
  1. setPower()
  2. 0.0
  3. setDirection()

Template Challenge​

Robot Scenario: Your robot uses a CRServo named "spinner" to move game elements into a scoring container. Run it at 60% power forward when the driver holds the B button, and at 60% reverse when they hold the X button. It should stop otherwise.

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.OpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.hardware.CRServo;

@TeleOp(name="CR_Spinner_Challenge")
public class CRSpinner extends OpMode {

    private CRServo spinner;

    @Override
    public void init() {
        // INSERT CODE HERE: Map "spinner" as a CRServo
    }

    @Override
    public void loop() {
        // INSERT CODE HERE: If B is pressed, set power to 0.6
        // INSERT CODE HERE: Else if X is pressed, set power to -0.6
        // INSERT CODE HERE: Otherwise set power to 0.0

        telemetry.addData("Spinner Power", spinner.getPower());
    }
}
Show answer
@Override
public void init() {
    spinner = hardwareMap.get(CRServo.class, "spinner");
    spinner.setPower(0);
    telemetry.addData("Spinner", "Ready");
}

@Override
public void loop() {
    if (gamepad1.b) {
        spinner.setPower(0.6);
    } else if (gamepad1.x) {
        spinner.setPower(-0.6);
    } else {
        spinner.setPower(0.0);
    }
    telemetry.addData("Spinner Power", spinner.getPower());
}

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