Lesson 9.3: Fixing Inverted Servo Setups with Direction Settings

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Technical Context

Dual-servo grippers often have servos mounted mirrored to each other on opposing sides of the mechanism. Without software inversion, a "close" command would move one servo inward and the other outward, causing the gripper to splay open instead of grip. Correcting this in init() allows identical position commands to drive both sides symmetrically.

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When Servo Direction Is the Cleaner Fix

The setDirection() method reverses the servo object's logical coordinate system. With Servo.Direction.REVERSE, logical 0.0 and 1.0 exchange endpoints. The physical directions depend on the servo mounting and linkage, so verify them on the actual mechanism.

This serves the same basic purpose as DcMotorSimple.Direction.REVERSE: it lets code use one logical convention for mirrored hardware instead of repeating inversion math.

Setting	setPosition(0.0) result	setPosition(1.0) result
Direction.FORWARD (default)	Physical far-left	Physical far-right
Direction.REVERSE	Physical far-right	Physical far-left

The default direction for all servos is Servo.Direction.FORWARD.

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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.Servo;

@TeleOp(name="Servo_Direction_Demo")
public class ServoDirectionDemo extends OpMode {

    private Servo leftServo;
    private Servo rightServo;

    @Override
    public void init() {
        leftServo  = hardwareMap.get(Servo.class, "left_claw");
        rightServo = hardwareMap.get(Servo.class, "right_claw");

        // Invert the right servo so both respond identically to "close" commands
        // Without this, setPosition(1.0) would open one side and close the other
        rightServo.setDirection(Servo.Direction.REVERSE);

        leftServo.setPosition(0.5);
        rightServo.setPosition(0.5);
        telemetry.addData("Claw", "Both servos at center");
    }

    @Override
    public void loop() {
        if (gamepad1.a) {
            // Both servos move inward: claw closes
            leftServo.setPosition(1.0);
            rightServo.setPosition(1.0);
        } else if (gamepad1.b) {
            // Both servos move outward: claw opens
            leftServo.setPosition(0.0);
            rightServo.setPosition(0.0);
        }
    }
}

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Fill-in-the-Blank Practice

1. To flip the orientation of a servo, we use the parameter Servo.Direction.__________.
2. The default direction for all servos in the SDK is Servo.Direction.__________.
3. Reversing a servo's direction is typically performed during the __________ method of the OpMode lifecycle.

Show answers

1. REVERSE
2. FORWARD
3. init()

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Simulator Challenge

Use the simulator below to practice reversing the mirrored "right_gate" servo so both double-gate flaps open and close symmetrically.

1.Complete the codeWork in fullscreen when you need more room for the editor and visualizer. Where file tabs are available, hover over the tab strip and choose + to create a file or reuse saved code.

2.Run the lifecyclePress Init, then Start. Use the available gamepad or scene controls.

3.Debug the behaviorCheck telemetry, motion, requirements, and hints before opening the answer.

Telemark Unit 9.3 Simulator

Loads the lesson-specific Telemark servo challenge with starter code for students to complete.

Includes live mechanism feedback, telemetry checks, and gamepad input for each servo-control concept.

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