Lesson 15.2: Controlling a Pedro 3 Follower

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Why Use a Path Follower?

Encoder-only autonomous routines often drive to one tick target, stop, turn, and repeat. Wheel slip, battery variation, and contact with field elements make every step start with a little error from the step before it.

Pedro Pathing continuously estimates the robot's field pose and corrects its drivetrain while following a geometric path. Pedro 3 combines localization, drivetrain control, and its Foresight following algorithm inside a Follower.

Path Following Feedback Loop

1

Path geometryA Pedro 3 Path contains one or more line and curve segments.

2

Target poseThe Follower chooses where the robot should be on the path now.

3

Pose errorCurrent odometry pose is compared against the target pose.

4

Motor correctionDrive powers are recomputed, the robot moves, and odometry updates again.

Pedro 3 setup comes first

Use the Pedro Pathing Quickstart or complete the official installation and tuning guides before running these examples. In Pedro 3, your generated Constants.create(hardwareMap) method constructs the correctly configured Follower; new Follower(hardwareMap) is an older API and is not valid Pedro 3 setup.

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The Pedro 3 Follower Lifecycle

The important calls are:

• Create: Constants.create(hardwareMap) assembles the drivetrain, localizer, and algorithm configured for your robot.
• Locate: follower.setPose(startPose) establishes the robot's field pose before it moves.
• Follow: follower.follow(path) begins direct path following.
• Update: follower.update() must run every active loop so localization and motor commands continue to advance.
• Observe: follower.pose() returns the current Pose; use x(), y(), and heading() to read it.

Pedro 3 reports four follower modes through follower.mode(): FOLLOW, HOLD, MANUAL, and IDLE. follower.following() tells you whether it is actively tracking a path. follower.isBusy() is a stricter completion signal that also accounts for the follower's end conditions.

Diagnose hardware before retuning software

If the plotted path looks right but the robot oscillates or cuts corners, first check odometry mounting, wheel offsets, motor directions, and whether follower.update() runs every cycle.

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Poses and PoseFactory

A Pose stores X and Y in inches and heading in radians. Pedro 3 recommends a PoseFactory so headings can be written in degrees and common transformations, such as alliance mirroring, can be applied consistently.

private final PoseFactory poseFactory = PoseFactory.degrees();

private final Pose startPose = poseFactory.of(12, 12, 0);
private final Pose parkPose  = poseFactory.of(60, 12, 0);

poseFactory.of(x, y, heading) uses the factory's angle unit. A raw new Pose(x, y, heading) always expects radians.

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Is Ivy Required?

No. Pedro can follow a path directly:

follower.follow(parkPath());

while (opModeIsActive() && follower.following()) {
    follower.update();
}

That is reasonable for a one-path experiment. For a real autonomous routine, Pedro's documentation recommends a command framework instead of a hand-written state machine. Ivy is the simplest choice because it includes Pedro-aware follow() and hold() commands.

Use this rule of thumb:

Situation	Good choice
One path while learning or tuning	Direct follower.follow(path)
Several paths plus mechanisms	Ivy commands
Team already uses another command framework	Keep it and write one tested Pedro follow command
Existing, reliable state machine	It can remain, but do not start a new one just to sequence Pedro paths

Ivy is a separate dependency and is not required by the follower itself:

implementation 'com.pedropathing.ivy:pedro:1.1.1'

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Annotated Pedro 3 + Ivy Example

package org.firstinspires.ftc.teamcode;

import static com.pedropathing.api.Paths.line;
import static com.pedropathing.ivy.Scheduler.schedule;
import static com.pedropathing.ivy.pedro.PedroCommands.follow;

import com.pedropathing.api.PoseFactory;
import com.pedropathing.follower.Follower;
import com.pedropathing.ivy.Scheduler;
import com.pedropathing.math.Pose;
import com.pedropathing.paths.Path;
import com.qualcomm.robotcore.eventloop.opmode.Autonomous;
import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode;
import org.firstinspires.ftc.teamcode.pedro.Constants;

@Autonomous(name="Pedro_3_Intro")
public class Pedro3Intro extends LinearOpMode {

    private Follower follower;
    private final PoseFactory poseFactory = PoseFactory.degrees();

    private final Pose startPose = poseFactory.of(12, 12, 0);
    private final Pose parkPose  = poseFactory.of(60, 12, 0);

    private Path parkPath() {
        return line(startPose, parkPose).linear(startPose, parkPose);
    }

    @Override
    public void runOpMode() {
        Scheduler.reset();
        follower = Constants.create(hardwareMap);
        follower.setPose(startPose);
        follower.update();

        waitForStart();
        if (isStopRequested()) return;

        schedule(follow(follower, parkPath()));

        while (opModeIsActive()) {
            follower.update();
            Scheduler.execute();

            telemetry.addData("X", "%.2f", follower.pose().x());
            telemetry.addData("Y", "%.2f", follower.pose().y());
            telemetry.addData("Mode", follower.mode());
            telemetry.update();
        }
    }
}

The follower and scheduler are separate systems, so both require one update per loop. Ivy's follow() command starts the path and handles its completion condition; the OpMode does not need to poll and advance a custom state variable.

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Fill-in-the-Blank Practice

1. Pedro 3 creates the configured follower with Constants.__________(hardwareMap).
2. The current pose is returned by follower.__________().
3. Ivy is __________ for direct path following but recommended for multi-step autonomous routines.

Show answers

1. create
2. pose
3. optional (not required)

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Simulator Challenge

Complete the Pedro 3 lifecycle. Create the follower with Constants.create(hardwareMap), create a degree-based PoseFactory, set the starting pose to (8, 60, 0°), call follower.update() before waiting for Start and on every active loop, and report follower.pose().x(), .y(), and .heading().

The simulator remains on the DECODE field so new members can focus on the API without learning a second game layout.

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 15.2 Simulator

Loads the lesson-specific Telemark advanced autonomous challenge with incomplete starter code for students to complete.

The simulator editor contains the starter code; use the answer below only after trying the challenge.

Show answer

PoseFactory poseFactory = PoseFactory.degrees();
follower = Constants.create(hardwareMap);
follower.setPose(poseFactory.of(8, 60, 0));
follower.update();

waitForStart();

while (opModeIsActive()) {
    follower.update();

    telemetry.addData("X",       "%.2f", follower.pose().x());
    telemetry.addData("Y",       "%.2f", follower.pose().y());
    telemetry.addData("Heading", "%.4f", follower.pose().heading());
    telemetry.update();
}

Connects to the mechanical track

The follower is only as good as the localization under it, and that is also a mounting problem.

See Lesson 7.4: Mounting Odometry Pods for Reliable Localization.

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