Motors and servos

A configured device name connects a program to hardware. The string in hardwareMap.get() must match the active Robot Controller configuration exactly. Motor direction, encoder scale, servo linkage, and travel limits belong to the assembled robot; tutorial values are practice values.

Motor power

DcMotor.setPower() accepts a normalized request from -1 to 1. It is not a speed in revolutions per minute. Battery voltage, load, gearing, friction, and run mode affect the motion produced by a given value.

Save this complete file as MotorPractice.java. Configure an unloaded motor as testMotor, support the robot, and verify direction at low power before connecting a mechanism.

package org.firstinspires.ftc.teamcode;

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

@TeleOp(name = "Motor Practice", group = "Practice")
public class MotorPractice extends LinearOpMode {
    @Override
    public void runOpMode() {
        DcMotor motor = hardwareMap.get(DcMotor.class, "testMotor");
        motor.setDirection(DcMotor.Direction.FORWARD); // Verify on your assembly.
        motor.setZeroPowerBehavior(DcMotor.ZeroPowerBehavior.BRAKE);
        motor.setMode(DcMotor.RunMode.RUN_WITHOUT_ENCODER);
        telemetry.addLine("Unloaded test. Left stick controls up to 0.20 power.");
        telemetry.update();
        waitForStart();
        if (!opModeIsActive()) return;
        try {
            while (opModeIsActive()) {
                double power = -gamepad1.left_stick_y * 0.20;
                motor.setPower(power);
                telemetry.addData("Requested power", "%.2f", power);
                telemetry.addData("Encoder ticks", motor.getCurrentPosition());
                telemetry.update();
                idle();
            }
        } finally {
            motor.setPower(0.0);
        }
    }
}

BRAKE resists coasting at zero power; FLOAT allows coasting. BRAKE is not an active position hold and cannot be relied upon to support a falling arm. Changing motor direction also changes the logical encoder sign. Establish direction first, then calibrate counts versus physical movement.

Power playground

This example applies the same power to all four motors of the simulator's tank drivetrain for one second. The hardware names and right-side reversal match that template. Its setDrivePower() helper writes the requested power to each motor.

Press Play at 0.25, then change power to -0.25 and run again. The sign changes direction. Try 0.5 and compare the travel over the same duration. Press Reset between trials so each run starts at the same position. Motor power is still a request, not a distance or a measured speed.

The simulated robot uses its own motor and physics configuration. Use your real hardware names and measured limits when adapting the program to a robot.

Encoder modes

For RUN_TO_POSITION, set the target before selecting the mode, then use a positive power magnitude; the target determines direction. Check stop state, both sides of a drivetrain, and a deadline. The encoder movement guide provides a complete example. Reaching an encoder target does not prove that a slipping wheel reached the intended field location.

A relative encoder needs a known physical reference before software travel limits are meaningful. Record a known reference or home against a suitable switch; do not zero an arm at an arbitrary angle and assume the bottom stop is zero.

Positional servos

A Servo receives a normalized position command, usually between 0 and 1. The mapping to shaft angle depends on the servo's configured range and model; 0.5 does not universally mean 90 degrees. Measure safe linkage endpoints before choosing open/closed values.

// Import com.qualcomm.robotcore.hardware.Servo.
// During setup:
Servo claw = hardwareMap.get(Servo.class, "claw");

// Inside an active loop after START, with measured safe positions:
if (gamepad1.a) claw.setPosition(0.35);
if (gamepad1.b) claw.setPosition(0.55);

These are fragments inside an OpMode, not a complete file. The command returns before the servo physically arrives. getPosition() reports the commanded position; it is not feedback proving arrival. A timed wait is an estimate unless a sensor confirms the mechanism state.

A CRServo is a continuous-rotation output controlled by power and direction. It does not accept a positional angle target like Servo. Choose the type that matches the actual device.

Testing

Check motor motion and reported encoder sign separately, then test STOP while the motor is running. For a servo, start with a disconnected or unloaded linkage, move through a small safe range, and watch for binding before widening it. A small power or position range reduces test exposure but does not establish that a mechanism is safe.