Creating your first Attachment

Rapidly develop and test new attachments for your robot with the Volt library.

What is an Attachment?

An Attachment is anything that has a function on the Robot. This could be a motor, a servo, a sensor, or anything else that can be controlled. Attachments are used to control the Robot and interact with the environment.

There should be one Attachment per “interaction” your Robot can perform.

Creating an Attachment

Create a new Kotlin class in TeamCode/src/main/kotlin/org/firstinspires/ftc/teamcode/attachment that inherits the Attachment class.

The Attachment class contains:

A list of motors
A list of servos
A list of continuous rotation servos
A boolean that is true when the attachment’s ControlAction is running
The function update(telemetry: Telemetry) that is called every tick
The function stop() that is called when the robot is stopped

Kotlin
Java

class Example : Attachment() {
    init {
        // Initialize
    }

    override fun update(telemetry: Telemetry) {
        // Update
    }
}

Add a motor

Defining the motor

Add the parameters hardwareMap and name for initializing a motor. Create a new DcMotor.

Kotlin
Java

class Example(hardwareMap: HardwareMap, name: String) : Attachment() {
    val motor = hardwareMap.dcMotor[name]

    init {
        // Initialize
    }

    override fun update(telemetry: Telemetry) {
        // Update
    }
}

Setting up the motor

Set the motor’s mode to DcMotor.RunMode.RUN_USING_ENCODER to use the motor’s built-in encoder. Set the motor’s zero-power behavior to DcMotor.ZeroPowerBehavior.BRAKE so the motor holds its position when the motor’s power is set to 0.0. Add the motor to the motors list so that it can be managed by the Attachment class.

Kotlin
Java

class Example(hardwareMap: HardwareMap, name: String) : Attachment() {
    val motor = hardwareMap.dcMotor[name]

    init {
        // Set mode
        motor.mode = DcMotorSimple.RunMode.RUN_USING_ENCODER

        // Set zero power behavior
        motor.zeroPowerBehavior = DcMotor.ZeroPowerBehavior.BRAKE

        // Add to list
        motors = listOf(motor)
    }

    override fun update(telemetry: Telemetry) {
        // Update
    }
}

Add logic

Setup the ControlAction

Create a new inner class called Control that inherits ControlAction. This class will be used to define the Attachment’s logic.

The ControlAction class contains:

A function called init() that is called when the action is triggered
A function called update(packet: TelemetryPacket): Boolean that is called while the action is running and returns whether the action is complete
A function called handleStop() that is called when the action is stopped

Kotlin
Java

inner class Control : ControlAction() {
    override fun init() {
        // Start
    }

    override fun update(packet: TelemetryPacket): Boolean {
        // Logic
        return true
    }

    override fun handleStop() {
        // End
    }
}

Control the motor

Add parameters for a power and a targetPosition. Create an instance variable for whether the motor is reversing. Set the motor’s power in the init() function. Determine whether the motor has reached the targetPosition. Stop the motor in the handleStop() function.

Kotlin
Java

inner class Control(
    private val power: Double,
    private val targetPosition: Int
) : ControlAction() {
    private var reversing = false

    override fun init() {
        // Determine reversing
        reversing = targetPosition < motor.currentPosition

        // Set power
        motor.power = if (reversing) -power else power
    }

    override fun update(packet: TelemetryPacket): Boolean {
        // Get position
        val currentPosition = motor.currentPosition

        // Determine if at target position
        if ((currentPosition < targetPosition) xor reversing) return false
        return true
    }

    override fun handleStop() {
        // Stop the motor
        motor.power = 0.0
    }
}

Add a callable action

Create a function called goTo(power: Double, position: Int) that returns a new Action.

Kotlin
Java

fun goTo(power: Double, position: Int): Action {
    // Return Control
    return Control(power, position)
}

Log the position of the motor

Modify the update(telemetry: Telemetry) function to log the position of motor.

Kotlin
Java

override fun update(telemetry: Telemetry) {
    // Log motor position
    telemetry.addLine("==== EXAMPLE ====")
    telemetry.addData("Position", motor.currentPosition)
    telemetry.addLine()
}

package org.firstinspires.ftc.teamcode.attachment

import com.acmerobotics.dashboard.telemetry.TelemetryPacket
import com.acmerobotics.roadrunner.Action
import dev.kingssack.volt.attachment.Attachment
import com.qualcomm.robotcore.hardware.DcMotor
import com.qualcomm.robotcore.hardware.DcMotorSimple
import com.qualcomm.robotcore.hardware.HardwareMap
import org.firstinspires.ftc.robotcore.external.Telemetry

class Example(hardwareMap: HardwareMap, name: String) : Attachment() {
    val motor = hardwareMap.dcMotor[name]

    init {
        motor.mode = DcMotorSimple.RunMode.RUN_USING_ENCODER
        motor.zeroPowerBehavior = DcMotor.ZeroPowerBehavior.BRAKE
        motors = listOf(motor)
    }

    inner class Control(
        private val power: Double,
        private val targetPosition: Int
    ) : ControlAction() {
        private var reversing = false

        override fun init() {
            reversing = targetPosition < motor.currentPosition
            motor.power = if (reversing) -power else power
        }

        override fun update(packet: TelemetryPacket): Boolean {
            val currentPosition = motor.currentPosition
            if ((currentPosition < targetPosition) xor reversing) return false
            return true
        }

        override fun handleStop() {
            motor.power = 0.0
        }
    }
    fun goTo(power: Double, position: Int): Action {
        return Control(power, position)
    }

    override fun update(telemetry: Telemetry) {
        telemetry.addLine("==== EXAMPLE ====")
        telemetry.addData("Position", motor.currentPosition)
        telemetry.addLine()
    }
}