Using and Creating a Drivetrain

A Drivetrain is an Attachment that houses your Robot’s drive logic.

Volt currently provides one pre-built Drivetrain type: MecanumDrivetrain.

MecanumDrivetrain

MecanumDrivetrain is an abstract Drivetrain class for four wheel mecanum drive robots. It has one method: setDrivePowers.

setDrivePowers takes a PoseVelocity2d that can be used to power each motor.

Implementations of MecanumDrivetrain are designed to work with RobotWithMecanumDrivetrain.

Choosing RoadRunner vs PedroPathing

There are two pre-built implementations of MecanumDrivetrain:

• MecanumDriveWithRR: A MecanumDrivetrain implementation using RoadRunner
• MecanumDriveWithPP: A MecanumDrivetrain implementation using PedroPathing

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Using MecanumDriveWithRR

MecanumDriveWithRR constructor parameters:

• hardwareMap: HardwareMap: Used to get drive motors
• pose: Pose2d: Used to set the Robot’s initial pose
• params: MecanumDriveWithRR.DriveParams: Used to configure RoadRunner

trajectory Builder

MecanumDriveWithRR provides a trajectory builder that composes Actions using RoadRunner’s TrajectoryActionBuilder.

Example

Kotlin

class ExampleRobot(
    hardwareMap: HardwareMap
) : RobotWithMecanumDrivetrain<MecanumDriveWithRR>(
    hardwareMap,
    MecanumDriveWithRR(hardwareMap)
) {
    fun driveForwardAction() = drivetrain.trajectory {
        strafeTo(Vector2d(24.0, 0.0))
    }
}

Java

public class ExampleRobot extends RobotWithMecanumDrivetrain<MecanumDriveWithRR> {
    public ExampleRobot(HardwareMap hardwareMap) {
        super(hardwareMap, new MecanumDriveWithRR(hardwareMap));
    }

    public Action driveForwardAction() {
        return drivetrain.trajectory(builder -> {
            builder.strafeTo(new Vector2d(24.0, 0.0));
            return Unit.INSTANCE;
        });
    }
}

Using MecanumDriveWithPP

MecanumDriveWithPP constructor parameters:

• hardwareMap: HardwareMap: Used to get drive motors
• followerConstants: FollowerConstants: Used to configure PedroPathing’s path follower
• localizerConstants: DriveEncoderConstants: Used to configure PedroPathing’s drive encoder localizer
• pathConstraints: PathConstraints: Used to configure PedroPathing’s path following constraints
• driveConstants: MecanumConstants: Used to configure PedroPathing’s mecanum drivetrain logic
• initialPose: Pose: Used to set the Robot’s initial pose

Note

When using MecanumDriveWithPP with ManualModes startTeleOpDrive() must be called upon initialization.

path Builder

MecanumDriveWithPP provides a path builder that composes Actions using a custom FollowerActionBuilder (built on PedroPathing’s path builder).

Example

Kotlin

class ExampleRobot(
    hardwareMap: HardwareMap
) : RobotWithMecanumDrivetrain<MecanumDriveWithPP>(
    hardwareMap,
    MecanumDriveWithPP(
        hardwareMap,
        FollowerConstants(),
        DriveEncoderConstants(),
        PathConstraints(),
        MecanumConstants()
    )
) {
    fun driveAction() = drivetrain.path {
        lineTo(Pose(24.0, 0.0, 0.0))
    }
}

Java

public class ExampleRobot extends RobotWithMecanumDrivetrain<MecanumDriveWithPP> {
    public ExampleRobot(HardwareMap hardwareMap) {
        super(hardwareMap, new MecanumDriveWithPP(
                hardwareMap,
                FollowerConstants(),
                DriveEncoderConstants(),
                PathConstraints(),
                MecanumConstants()
        ));
    }

    public Action driveAction() {
        return drivetrain.path(builder -> {
            builder.lineTo(new Pose(24.0, 0.0, 0.0));
            return Unit.INSTANCE;
        });
    }
}

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Creating a Custom Drivetrain

Building a custom Drivetrain class is just like building an Attachment:

1. Extend Drivetrain (or MecanumDrivetrain)
2. Configure hardware
3. Write drive logic

Basic Example

Kotlin

class ExampleDrivetrain(hardwareMap: HardwareMap) : Drivetrain() {
    val leftFront: DcMotorEx = hardwareMap.get(DcMotorEx::class.java, "lf")
    val leftBack: DcMotorEx = hardwareMap.get(DcMotorEx::class.java, "lr")
    val rightBack: DcMotorEx = hardwareMap.get(DcMotorEx::class.java, "rr")
    val rightFront: DcMotorEx = hardwareMap.get(DcMotorEx::class.java, "rf")

    // Define drive actions here
}

Java

public class ExampleDrivetrain extends Drivetrain {
    public DcMotorEx leftFront;
    public DcMotorEx leftBack;
    public DcMotorEx rightBack;
    public DcMotorEx rightFront;

    public ExampleDrivetrain(HardwareMap hardwareMap) {
        super();
        leftFront = hardwareMap.get(DcMotorEx.class, "lf");
        leftBack = hardwareMap.get(DcMotorEx.class, "lr");
        rightBack = hardwareMap.get(DcMotorEx.class, "rr");
        rightFront = hardwareMap.get(DcMotorEx.class, "rf");
    }

    // Define drive actions here
}

Next Steps

• Create an OpMode that controls your drivetrain
• Learn more about Actions