java.lang.IllegalArgumentException: Unable to find a hardware device with the name "leftFront"

The java.lang.IllegalArgumentException: Unable to find a hardware device with the name "leftFront" error means that the program could not find a hardware device named "leftFront" in the robot's configuration .

This error typically occurs because the name used in the code for a hardware device does not match the name configured in the Robot Controller's hardware map .

To fix this, ensure that the string passed to hardwareMap.get() exactly matches the name of the device as it is entered in the Robot Controller configuration . For example, if you are trying to instantiate a DcMotor named "leftFront", the code should look like this: DcMotor leftFront = hardwareMap.get(DcMotor.class, "leftFront"); . If the device is a DigitalChannel, the code would be DigitalChannel digitalDevice = hardwareMap.get(DigitalChannel.class, "digital device"); .

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Reading and Writing to Hardware

Game Manual 0·CC BY-NC 4.0

When using the FTC® SDK, there are a variety of built in hardware classes which can be used to communicate with hardware on the robot such as DC Motors, Servos, and Sensors.

The first thing required to properly create an object is to import its class. In Android Studio, if the class is referenced without being imported Alt+Enter can be pressed to automatically import it. After it is imported, the next step is to create the object:


private DcMotor liftMotor;

After the object is created, it must be instantiated. Part of the OpMode superclass is something called hardwareMap. hardwareMap is used in the FTC SDK to instantiate objects rather than calling a constructor.

It contains all of the information entered into the configuration on the Robot Controller, such as names of hardware and what port it is plugged into. Here is an example of instantiating the motor we created above:


liftMotor = hardwareMap.get(DcMotor.class, "Lift Motor");

Whatever sensor you are using, you will pass that class into the spot where DcMotor.class is. For example, if liftMotor was a Servo, Servo.class would be passed instead.

For the second argument, you pass whatever the device is named in the Robot Controller configuration. hardwareMap will then go find what port the device with that name is plugged into, which allows the hardware to be accessed.

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Common Issues > Exceptions

Game Manual 0·CC BY-NC 4.0

Note that LinearOpMode already contains a shorthand sleep() (https://github.com/OpenFTC/Extracted-RC/blob/f47d6f15fa1b59faaf509a522e0ec04f223ec125/RobotCore/src/main/java/com/qualcomm/robotcore/eventloop/opmode/LinearOpMode.java#L96) method that does this under the hood. (And you shouldn't be using sleeps in OpMode since they're more strictly controlled. Read next sections for further information)

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Gamepad Usage

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PS4/Etpark Note: L1 is left_bumper, L2 is left_trigger, R1/R2 are the right-hand equivalents.

Since both PS4-style and Xbox-Style controllers are FTC® legal, there are aliases in the FTC SDK (https://github.com/OpenFTC/Extracted-RC/blob/c960dd7de34d49a66c00a345636175392f936b9e/RobotCore/src/main/java/com/qualcomm/robotcore/hardware/Gamepad.java#L892) between PS4-style and Xbox-style button naming.

+--------------+-----------+ | PS4 | Xbox | +==============+===========+ | circle | b | +--------------+-----------+ | cross | a | +--------------+-----------+ | triangle | y | +--------------+-----------+ | square | x | +--------------+-----------+ | share | back | +--------------+-----------+ | options | start | +--------------+-----------+ | ps | guide | +--------------+-----------+

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Reading and Writing to Hardware > Examples of Using Common Hardware Components > Digital IO

Game Manual 0·CC BY-NC 4.0


DigitalChannel digitalDevice = hardwareMap.get(DigitalChannel.class, "digital device");

A DigitalChannel has a couple main methods. setMode() is used to set the port as either an OUTPUT or INPUT port, getState() returns the current state of the port (only works in INPUT mode), and setState() sets the state of the port (only works in OUTPUT mode)

Tip: Digital ports start by default in INPUT mode

Danger: Digital ports are pulled UP to prevent floating. This means that there is a resistor between the port and 3.3V so the port reads HIGH by default when nothing is connected. As a result digital devices MUST connect the digital pin to ground when closed, then leave it unconnected when open. For limit switches, this means connecting one lead to ground and the other to the digital port. Connecting this wrong (connecting 3.3V to the digital port) may cause instability and can cause your expansion hub to crash

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Encoders > Programming Encoders > Reading Encoders

Game Manual 0·CC BY-NC 4.0

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.hardware.DcMotor;
@TeleOp
public class EncoderOpmode extends LinearOpMode {
    @Override
    public void runOpMode() throws InterruptedException {
        // Find a motor in the hardware map named "Arm Motor"
        DcMotor motor = hardwareMap.dcMotor.get("Arm Motor");

        // Reset the motor encoder so that it reads zero ticks
        motor.setMode(DcMotor.RunMode.STOP_AND_RESET_ENCODER);

        // Turn the motor back on, required if you use STOP_AND_RESET_ENCODER
        motor.setMode(DcMotor.RunMode.RUN_WITHOUT_ENCODER);

        waitForStart();

        while (opModeIsActive()) {
            double CPR = [Your Counts Per Revolution Here];

            // Get the current position of the motor
            int position = motor.getCurrentPosition();
            double revolutions = position/CPR;

            double angle = revolutions * 360;
            double angleNormalized = angle % 360;

            // Show the position of the motor on telemetry
            telemetry.addData("Encoder Position", position);
            telemetry.addData("Encoder Revolutions", revolutions);
            telemetry.addData("Encoder Angle (Degrees)", angle);
            telemetry.addData("Encoder Angle - Normalized (Degrees)", angleNormalized);
            telemetry.update();
        }
    }
}

Open Game Manual 0

Encoders > Programming Encoders > Running Motors With Encoders

Game Manual 0·CC BY-NC 4.0

package org.firstinspires.ftc.teamcode.Tests;

import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.hardware.DcMotor;

@TeleOp
public class ArmOpMode extends LinearOpMode {
   @Override
   public void runOpMode() throws InterruptedException {
      // Position of the arm when it's lifted
      int armUpPosition = 1000;

      // Position of the arm when it's down
      int armDownPosition = 0;

      // Find a motor in the hardware map named "Arm Motor"
      DcMotor armMotor = hardwareMap.dcMotor.get("Arm Motor");

      // Reset the motor encoder so that it reads zero ticks
      armMotor.setMode(DcMotor.RunMode.STOP_AND_RESET_ENCODER);

      // Sets the starting position of the arm to the down position
      armMotor.setTargetPosition(armDownPosition);
      armMotor.setMode(DcMotor.RunMode.RUN_TO_POSITION);

      waitForStart();

      while (opModeIsActive()) {
            // If the A button is pressed, raise the arm
            if (gamepad1.a) {
               armMotor.setTargetPosition(armUpPosition);
               armMotor.setMode(DcMotor.RunMode.RUN_TO_POSITION);
               armMotor.setPower(0.5);
            }

            // If the B button is pressed, lower the arm
            if (gamepad1.b) {
               armMotor.setTargetPosition(armDownPosition);
               armMotor.setMode(DcMotor.RunMode.RUN_TO_POSITION);
               armMotor.setPower(0.5);
            }

            // Get the current position of the armMotor
            double position = armMotor.getCurrentPosition();

            // Get the target position of the armMotor
            double desiredPosition = armMotor.getTargetPosition();

            // Show the position of the armMotor on telemetry
            telemetry.addData("Encoder Position", position);

            // Show the target position of the armMotor on telemetry
            telemetry.addData("Desired Position", desiredPosition);

            telemetry.update();
      }
   }
}

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