Lesson 8.1: Using setPower() to Control Motor Speed

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Technical Context

The Robot Controller manages motor output by sending pulse-width modulation (PWM) signals to the Expansion Hub or Control Hub. Sending power levels allows for variable speed control; however, providing too much power to a stalled mechanism — such as an arm pressed against a hard stop — can lead to motor burnout or stripped gears from sustained high-current draw.

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What setPower() Is Really Doing

The setPower(double power) method is the primary tool for commanding hardware motion. It accepts a double parameter ranging from -1.0 (full reverse) to 1.0 (full forward), where 0.0 signifies a stop command.

Important behaviors to understand:

• Values above 1.0 or below -1.0 are automatically clamped by the SDK — passing 1.5 is treated as 1.0.
• The method does not directly control velocity — it controls the PWM duty cycle (effectively the voltage fraction). Actual speed depends on battery voltage, load, and the motor's run mode.
• The command is held until another setPower() call overrides it — if you never call setPower(0), the motor keeps running after your code finishes that loop cycle.

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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.DcMotor;

@TeleOp(name="SetPower_Demo")
public class SetPowerDemo extends OpMode {

    private DcMotor intake;

    @Override
    public void init() {
        intake = hardwareMap.get(DcMotor.class, "intake");
        intake.setMode(DcMotor.RunMode.RUN_WITHOUT_ENCODER);
        intake.setPower(0); // Safe known state before match starts
        telemetry.addData("Status", "Intake ready");
    }

    @Override
    public void loop() {
        // Capture joystick input and pass it directly to the motor
        double powerRequest = -gamepad1.left_stick_y;
        intake.setPower(powerRequest);

        telemetry.addData("Power Sent", powerRequest);
    }
}

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Fill-in-the-Blank Practice

1. The setPower() method accepts a __________ data type as its parameter.
2. To command a motor to rotate at half-speed in the reverse direction, you would pass the value __________ to the method.
3. If the motor power is set to 1.2 in code, the SDK will clamp the value and treat it as __________.

Show answers

1. double
2. -0.5
3. 1.0

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Template Challenge

Robot Scenario: You need to map a motor named "intake" and run it at full speed forward whenever the driver holds gamepad1.right_trigger past 50%, and stop it 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.DcMotor;

@TeleOp(name="Intake_Power_Challenge")
public class IntakePower extends OpMode {

    private DcMotor intake;

    @Override
    public void init() {
        // INSERT CODE HERE: Map "intake" and set its RunMode to RUN_WITHOUT_ENCODER
    }

    @Override
    public void loop() {
        // INSERT CODE HERE: If right_trigger > 0.5, set power to 1.0
        // Otherwise, set power to 0.0
    }
}

Show answer

@Override
public void init() {
    intake = hardwareMap.get(DcMotor.class, "intake");
    intake.setMode(DcMotor.RunMode.RUN_WITHOUT_ENCODER);
    intake.setPower(0);
}

@Override
public void loop() {
    if (gamepad1.right_trigger > 0.5) {
        intake.setPower(1.0);
    } else {
        intake.setPower(0.0);
    }
}

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