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Lesson 10.4: Maintaining Speed Consistency with RUN_USING_ENCODER

The Problem with Voltage-Based Speed Control​

Picture this: your autonomous routine drives the robot perfectly in practice at full battery. Then in the second match of the day, the battery is at 80% and the robot underdrives every segment by a few inches. You change nothing in the code -- the issue is that RUN_WITHOUT_ENCODER sends a fixed fraction of whatever voltage the battery currently has. Less voltage means less speed, and by the end of a competition day the robot is driving noticeably slower than it was at the start.

RUN_USING_ENCODER eliminates this problem by making the Hub treat setPower() as a velocity command instead of a voltage command.

What Velocity Control Actually Does​

When this mode is active, the Hub monitors how fast the encoder is actually ticking and compares it against a target speed derived from your setPower() value. If the motor slows down because the battery dropped or the robot hit a bump, the Hub automatically increases the voltage to compensate and bring the speed back to the target. If it speeds up, the Hub backs off the voltage.

The result is that setPower(0.5) always means approximately 50% of the motor's maximum achievable speed, regardless of battery state. This makes your autonomous distances far more consistent match over match.

One trade-off worth knowing: RUN_USING_ENCODER cannot use setTargetPosition(). If you need to move to a specific tick position, you want RUN_TO_POSITION from Lesson 10.3. These two modes serve different purposes -- velocity consistency versus positional targeting.

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="Run_Using_Encoder_Demo")
public class RunUsingEncoderDemo extends OpMode {

    private DcMotor leftDrive;
    private DcMotor rightDrive;

    @Override
    public void init() {
        leftDrive  = hardwareMap.get(DcMotor.class, "left_drive");
        rightDrive = hardwareMap.get(DcMotor.class, "right_drive");

        // Enable velocity PID on both drive motors
        leftDrive.setMode(DcMotor.RunMode.RUN_USING_ENCODER);
        rightDrive.setMode(DcMotor.RunMode.RUN_USING_ENCODER);

        rightDrive.setDirection(DcMotor.Direction.REVERSE);

        telemetry.addData("Status", "Velocity control active");
    }

    @Override
    public void loop() {
        // setPower now commands velocity, not raw voltage
        double drive = -gamepad1.left_stick_y;
        leftDrive.setPower(drive);
        rightDrive.setPower(drive);

        telemetry.addData("Commanded Velocity", drive);
        telemetry.addData("Left Ticks",  leftDrive.getCurrentPosition());
        telemetry.addData("Right Ticks", rightDrive.getCurrentPosition());
    }
}

Fill-in-the-Blank Practice​

  1. RUN_USING_ENCODER uses internal __________ logic on the Control Hub to maintain motor speed.
  2. This mode improves drivetrain consistency because the robot travels at a fixed __________ rather than a fixed voltage.
  3. In this mode, the setPower() method effectively sets the motor's targeted __________.
Show answers
  1. PID
  2. velocity
  3. velocity (speed / ticks per second)

Template Challenge​

Robot Scenario: You have a four-motor drivetrain stored in an array named motors. Configure every motor to use RUN_USING_ENCODER for consistent velocity during TeleOp using a for..each loop.

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="Consistent_Drive_Challenge")
public class ConsistentDrive extends OpMode {

    private DcMotor leftFront, rightFront, leftBack, rightBack;
    private DcMotor[] motors;

    @Override
    public void init() {
        leftFront  = hardwareMap.get(DcMotor.class, "left_front");
        rightFront = hardwareMap.get(DcMotor.class, "right_front");
        leftBack   = hardwareMap.get(DcMotor.class, "left_back");
        rightBack  = hardwareMap.get(DcMotor.class, "right_back");

        motors = new DcMotor[]{ leftFront, rightFront, leftBack, rightBack };

        // INSERT CODE HERE: Use a for..each loop to set every motor to
        // RUN_USING_ENCODER
    }

    @Override
    public void loop() {}
}
Show answer
for (DcMotor motor : motors) {
    motor.setMode(DcMotor.RunMode.RUN_USING_ENCODER);
}

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