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 flips the logical coordinate system of the servo object. By passing Servo.Direction.REVERSE, the SDK ensures that 0.0 maps to the physical "far right" and 1.0 maps to the physical "far left" — the opposite of the default. This allows the programmer to use the exact same position value for both servos in a mirrored assembly.

This is architecturally identical to DcMotorSimple.Direction.REVERSE from Unit 8 — both exist so that your code can express intent cleanly (setPosition(1.0) always means "close the claw") without any manual inversion math scattered throughout the codebase.

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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Template Challenge

Robot Scenario: You have two servos for a double-gate. The "left_gate" is mounted normally, but the "right_gate" is mounted upside-down and needs its direction reversed. Both gates should open fully (1.0) when gamepad1.y is pressed, and close fully (0.0) when gamepad1.a is pressed.

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="Double_Gate_Challenge")
public class DoubleGate extends OpMode {

    private Servo leftGate;
    private Servo rightGate;

    @Override
    public void init() {
        leftGate  = hardwareMap.get(Servo.class, "left_gate");
        rightGate = hardwareMap.get(Servo.class, "right_gate");

        // INSERT CODE HERE: Reverse the direction of rightGate
        // INSERT CODE HERE: Set both gates to 0.0 initially
    }

    @Override
    public void loop() {
        if (gamepad1.y) {
            leftGate.setPosition(1.0);
            rightGate.setPosition(1.0);
        } else if (gamepad1.a) {
            leftGate.setPosition(0.0);
            rightGate.setPosition(0.0);
        }
    }
}

Show answer

@Override
public void init() {
    leftGate  = hardwareMap.get(Servo.class, "left_gate");
    rightGate = hardwareMap.get(Servo.class, "right_gate");

    rightGate.setDirection(Servo.Direction.REVERSE);

    leftGate.setPosition(0.0);
    rightGate.setPosition(0.0);
    telemetry.addData("Gates", "Initialized closed");
}

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