Run to Position

In the previous lesson, you learned how to read encoder values. Now you will learn how to use them to command a motor to go to a specific position. The FTC SDK has a built-in run mode called RUN_TO_POSITION that handles this for you -- you tell the motor where to go, and it drives itself there.

What is RUN_TO_POSITION?

RUN_TO_POSITION is a motor run mode that turns the motor into a position-controlled actuator. Instead of saying "run at this power," you say "go to this tick count," and the motor's internal controller does the rest.

This is incredibly useful for:

• Autonomous driving -- Move forward exactly 1000 ticks
• Arm positioning -- Raise the arm to a specific height
• Intake mechanisms -- Rotate a mechanism a specific number of degrees

The Correct Sequence

Setting up RUN_TO_POSITION requires a specific sequence of steps. Getting the order wrong is one of the most common mistakes in FTC programming:

// Step 1: Reset the encoder
motor.setMode(DcMotor.RunMode.STOP_AND_RESET_ENCODER);
// Step 2: Set the target position (in ticks)
motor.setTargetPosition(1000);
// Step 3: Set the run mode to RUN_TO_POSITION
motor.setMode(DcMotor.RunMode.RUN_TO_POSITION);
// Step 4: Set the power (this is the maximum speed the motor will use)
motor.setPower(0.5);

The order matters. Here is why:

1. Reset first -- You want to start counting from zero, so reset the encoder.
2. Set target before mode -- The motor needs to know where to go before you tell it to start going there. If you set RUN_TO_POSITION before setting a target, the motor may briefly try to go to position 0 (or whatever the last target was).
3. Set mode before power -- Setting the mode to RUN_TO_POSITION changes how the motor interprets the power value. The power becomes a maximum speed, not a direct power command.
4. Set power last -- This starts the motor moving toward the target. The motor will accelerate up to this power level and decelerate as it approaches the target.

Understanding Power in RUN_TO_POSITION

In RUN_TO_POSITION mode, the setPower() value works differently than in normal mode:

• The value you set is the maximum power the motor will use.
• The motor automatically adjusts its actual power to reach the target smoothly.
• The power should always be positive in RUN_TO_POSITION mode, even if the target is behind the current position. The motor figures out which direction to go on its own.
• Setting power to 0 stops the motor even if it has not reached the target.

Checking if the Motor is Done

After commanding a motor to a position, you often need to wait until it gets there. The isBusy() method returns true while the motor is still moving toward its target:

while (motor.isBusy() && opModeIsActive()) {
    telemetry.addData("Position", motor.getCurrentPosition());
    telemetry.addData("Target", 1000);
    telemetry.update();
}
// Motor has reached the target (or opMode was stopped)
motor.setPower(0);  // Stop the motor

The opModeIsActive() check is important -- it ensures the loop exits if the driver presses Stop on the Driver Station.

A Complete Example

Here is a full example that drives a motor to position 1000:

DcMotor motor = hardwareMap.get(DcMotor.class, "driveMotor");
motor.setMode(DcMotor.RunMode.STOP_AND_RESET_ENCODER);
motor.setTargetPosition(1000);
motor.setMode(DcMotor.RunMode.RUN_TO_POSITION);
motor.setPower(0.5);
waitForStart();
while (motor.isBusy() && opModeIsActive()) {
    telemetry.addData("Moving to", 1000);
    telemetry.addData("Currently at", motor.getCurrentPosition());
    telemetry.update();
}
motor.setPower(0);

Common Mistakes

• Forgetting to reset the encoder -- The motor remembers its position from the last run. Always reset if you want to start from zero.
• Setting power before mode -- If you call setPower(0.5) while still in RUN_USING_ENCODER mode, the motor will just run at 0.5 power instead of going to a position.
• Using negative power -- In RUN_TO_POSITION, always use positive power. Negative power can cause unexpected behavior.
• Not checking isBusy() -- Without a wait loop, your code will immediately move to the next command while the motor is still moving.

Your Exercise

In this exercise, you will set up a motor to drive to a target position of 1000 ticks using RUN_TO_POSITION.

Your task (follow this exact sequence):

1. Get the motor "driveMotor" from the hardware map.
2. Reset the encoder using STOP_AND_RESET_ENCODER.
3. Set the target position to 1000.
4. Set the run mode to RUN_TO_POSITION.
5. Call waitForStart().
6. Set the motor power to 0.5 to start moving.