Lesson 10.5: Developing a Precise Drive and Stop System for Linear Navigation

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Why Encoder Resets Matter More Than You Think

Suppose an autonomous move ends near 1000 ticks and the next command should advance another 500 ticks. Calling setTargetPosition(500) requests the absolute encoder position 500, which is behind the current position. The controller may correctly drive backward toward that absolute target even though the programmer intended a relative move.

STOP_AND_RESET_ENCODER establishes a known software zero, but it is not required before every segment. A routine can reset once and use cumulative absolute targets, or compute a relative target such as drive.getCurrentPosition() + deltaTicks. Re-zero only at an intentional reference point because resetting the count does not correct the robot's physical field pose.

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Putting the Full Sequence Together

A basic encoder-based move after establishing a known zero has six steps:

1. Reset the encoder with STOP_AND_RESET_ENCODER
2. Set the target position with setTargetPosition()
3. Switch to RUN_TO_POSITION
4. Apply power with setPower()
5. Wait for the move to finish with isBusy()
6. Stop and restore RUN_USING_ENCODER for the next normal drive command

The isBusy() method reports whether a motor in RUN_TO_POSITION is still outside its configured target tolerance. Combining it with opModeIsActive() is a useful loop condition. A timeout and multi-motor completion policy may also be needed so a stalled or lagging motor cannot hold autonomous indefinitely.

One thing to remember: after STOP_AND_RESET_ENCODER, the motor is stopped. You must switch to a movement mode before calling setPower() or nothing will happen. RUN_TO_POSITION also remains active after arrival, so cleanup must restore RUN_USING_ENCODER. Otherwise the next TeleOp-style power command can continue targeting the old position instead of behaving like a velocity request.

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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="Drive_And_Stop_Demo")
public class DriveAndStopDemo extends LinearOpMode {

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

        waitForStart();

        // Step 1: Zero out any accumulated ticks from previous runs
        drive.setMode(DcMotor.RunMode.STOP_AND_RESET_ENCODER);

        // Step 2: Define the absolute target from zero
        drive.setTargetPosition(1000);

        // Step 3: Activate position control
        drive.setMode(DcMotor.RunMode.RUN_TO_POSITION);

        // Step 4: Apply power. The Hub starts moving now.
        drive.setPower(0.5);

        // Step 5: Block until the Hub reports arrival
        while (opModeIsActive() && drive.isBusy()) {
            telemetry.addData("Target",   drive.getTargetPosition());
            telemetry.addData("Position", drive.getCurrentPosition());
            telemetry.update();
        }

        drive.setPower(0);
        drive.setMode(DcMotor.RunMode.RUN_USING_ENCODER);
        telemetry.addData("Status", "Move complete");
        telemetry.update();
    }
}

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Fill-in-the-Blank Practice

1. To zero out accumulated ticks before a new move, you apply the DcMotor.RunMode.__________ mode.
2. After a reset, the motor must be switched to a movement mode because the reset command also __________ the motor shaft.
3. After the move, restore __________ so later drive commands no longer target the old encoder position.

Show answers

1. STOP_AND_RESET_ENCODER
2. stops (halts / disables)
3. RUN_USING_ENCODER

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Simulator Practice

Use the simulator below to complete the precise autonomous slider routine. Fill in the missing reset, target, run mode, power, busy-loop telemetry, stop logic, and RUN_USING_ENCODER restoration, then press START to move the game element.

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 10.5 Simulator

Loads the lesson-specific Telemark encoder challenge with incomplete starter code for students to finish.

Includes live mechanism feedback, telemetry checks, and encoder-state validation for each lesson concept.

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