Lesson 7.5: Challenge — Keep Shared Hardware Classes Consistent Across OpModes

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Technical Context

As robots become complex, putting all hardware mapping in a single OpMode file leads to unmaintainable "spaghetti code." Creating a dedicated Hardware Class (or Mechanism Class) allows you to define your hardware once and share it across every Autonomous and TeleOp program on the robot. If a motor port changes, you update one file — not every OpMode.

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Why Shared Mechanism Classes Save Time

A mechanism class requires a custom init() method that accepts the HardwareMap from the parent OpMode as a parameter. This is the key architectural insight: the mechanism class cannot access hardwareMap on its own because that object belongs to the OpMode context. By passing it in, you allow the mechanism to perform its own registry lookups while remaining completely portable.

This pattern is known as dependency injection — the OpMode "injects" the hardware context that the mechanism class needs. The mechanism class encapsulates the hardware-specific details (names, directions, run modes), shielding the OpMode from them entirely.

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Annotated Code

The mechanism class (separate file):

package org.firstinspires.ftc.teamcode.mechanisms;

import com.qualcomm.robotcore.hardware.DcMotor;
import com.qualcomm.robotcore.hardware.HardwareMap;

public class IntakeSystem {

    private DcMotor intakeMotor;

    // The OpMode passes its hardwareMap into this method
    public void init(HardwareMap hwMap) {
        intakeMotor = hwMap.get(DcMotor.class, "intake");
        intakeMotor.setDirection(DcMotor.Direction.REVERSE);
        intakeMotor.setPower(0);
    }

    // Clean public interface — OpMode never touches the motor directly
    public void setIntakePower(double power) {
        intakeMotor.setPower(power);
    }

    public void stop() {
        intakeMotor.setPower(0);
    }
}

Using the mechanism inside a TeleOp:

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.OpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import org.firstinspires.ftc.teamcode.mechanisms.IntakeSystem;

@TeleOp(name="Intake_TeleOp")
public class IntakeTeleOp extends OpMode {

    private IntakeSystem intake = new IntakeSystem();

    @Override
    public void init() {
        // Pass the OpMode's hardwareMap into the mechanism
        intake.init(hardwareMap);
        telemetry.addData("Status", "Intake ready");
    }

    @Override
    public void loop() {
        intake.setIntakePower(gamepad1.right_trigger);
    }
}

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Fill-in-the-Blank Practice

1. To share hardware across files, we encapsulate the mapping logic into a __________ class.
2. The mechanism's init() method must accept a __________ object as a parameter so it can perform registry lookups.
3. Encapsulation is a best practice because it isolates hardware "quirks" (like reversed directions) from the __________ logic.

Show answers

1. mechanism (or hardware) class
2. HardwareMap
3. main OpMode (match / driving) logic

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Template Challenge

Robot Scenario: Create a separate LinearSlide class. It should map a motor named "slide_motor", set its ZeroPowerBehavior to BRAKE, and expose a move(double speed) method. Then use it inside a TeleOp.

Step 1 — The mechanism class:

package org.firstinspires.ftc.teamcode.mechanisms;

import com.qualcomm.robotcore.hardware.DcMotor;
import com.qualcomm.robotcore.hardware.HardwareMap;

public class LinearSlide {

    private DcMotor slideMotor;

    // INSERT CODE HERE: Write an init() method that accepts HardwareMap,
    // maps "slide_motor", and sets ZeroPowerBehavior to BRAKE

    // INSERT CODE HERE: Write a public move() method that takes a
    // double 'speed' and applies it to slideMotor
}

Step 2 — Using it in a TeleOp:

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.OpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import org.firstinspires.ftc.teamcode.mechanisms.LinearSlide;

@TeleOp(name="Slide_TeleOp_Challenge")
public class SlideTeleOp extends OpMode {

    // INSERT CODE HERE: Declare and instantiate a LinearSlide object

    @Override
    public void init() {
        // INSERT CODE HERE: Initialize the slide using hardwareMap
    }

    @Override
    public void loop() {
        // INSERT CODE HERE: Drive the slide with gamepad1.left_stick_y
    }
}

Show answer

LinearSlide.java:

public class LinearSlide {

    private DcMotor slideMotor;

    public void init(HardwareMap hwMap) {
        slideMotor = hwMap.get(DcMotor.class, "slide_motor");
        slideMotor.setZeroPowerBehavior(DcMotor.ZeroPowerBehavior.BRAKE);
        slideMotor.setPower(0);
    }

    public void move(double speed) {
        slideMotor.setPower(speed);
    }
}

SlideTeleOp.java:

private LinearSlide slide = new LinearSlide();

@Override
public void init() {
    slide.init(hardwareMap);
    telemetry.addData("Status", "Slide ready");
}

@Override
public void loop() {
    slide.move(-gamepad1.left_stick_y);
}

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