Lesson 8.4: Choosing Between Coasting and Stopping with setPower(0.0)

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Technical Context

Precision in autonomous and TeleOp benefits from predictable stops. If a programmer relies on mechanical friction alone to stop a robot, the stopping distance can vary with field tile material, mechanism load, and the robot's speed when power is cut. Using setPower(0.0) with an intentional ZeroPowerBehavior makes the response more repeatable, but it does not eliminate mechanical variation.

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How Zero Power Changes the Way a Mechanism Settles

setPower(0.0) is a deliberate command that tells the Control Hub to cease applying voltage to the motor port. Its physical effect is entirely determined by the ZeroPowerBehavior established in Lesson 8.3:

ZeroPowerBehavior	Effect of setPower(0.0)
FLOAT (default)	Motor terminals disconnected, so the robot coasts to a stop via friction
BRAKE	Motor terminals electrically brake rotation, so the mechanism usually decelerates faster; this is not active position holding

In a high-speed drivetrain, switching to 0.0 power with FLOAT behavior can let the robot travel beyond its target. BRAKE often reduces that coast distance, although the result still depends on mass, speed, traction, gearing, and motor-controller behavior.

A common pattern is to set BRAKE on drive motors in init(), then send setPower(0.0) at the end of an autonomous step. Closed-loop position or velocity control is needed when the robot must settle to a measured target rather than merely resist coasting.

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Annotated Code

package org.firstinspires.ftc.teamcode;

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

@Autonomous(name="Coast_vs_Stop_Demo")
public class CoastVsStopDemo extends LinearOpMode {

    private DcMotor driveMotor;

    @Override
    public void runOpMode() {
        driveMotor = hardwareMap.get(DcMotor.class, "drive");

        // BRAKE resists coasting after setPower(0.0); it is not position hold.
        driveMotor.setZeroPowerBehavior(DcMotor.ZeroPowerBehavior.BRAKE);

        waitForStart();

        // Drive forward for 2 seconds
        driveMotor.setPower(0.6);
        sleep(2000);

        // Command zero power; BRAKE resists continued rotation.
        driveMotor.setPower(0.0);

        telemetry.addData("Status", "Stopped at target position");
        telemetry.update();

        sleep(1000); // Hold stopped state briefly for visibility
    }
}

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Fill-in-the-Blank Practice

1. Sending a power value of __________ is the standard way to stop a motor in the SDK.
2. Relying on __________ alone to stop a robot is inconsistent because it varies with the battery voltage and field surface material.
3. To stop a motor currently running at full reverse speed, you would change its power from -1.0 to __________.

Show answers

1. 0.0
2. mechanical friction (or coasting / FLOAT behavior)
3. 0.0

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Simulator Challenge

Use the simulator below to practice an emergency stop that combines BRAKE mode with an immediate setPower(0.0) cut.

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 8.4 Simulator

Loads the lesson-specific Telemark motor challenge with starter code instead of a completed solution.

Includes live hardware feedback, telemetry checks, and gamepad input for each motor-control concept.

Best for practicing power, direction, braking, stopping behavior, and limit-switch safety in context.

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