Pin Not Exported Error While Doing Stepper Motor Control on BeagleBone Black

[Jeremy Wright]

BeagleBone Black, Debian 9.5 2018-10-07 image - Go 1.10, installed Gobot using go.

I'm new to Gobot and Go. I've adapted the stepper example here to work with the BeagleBone Black using the information about the adapter here. I ended up with this code:

package main

import (
        "fmt"

        "gobot.io/x/gobot"
        "gobot.io/x/gobot/drivers/gpio"
        "gobot.io/x/gobot/platforms/beaglebone"
)

func main() {
        beagleboneAdaptor := beaglebone.NewAdaptor()
        stepper := gpio.NewStepperDriver(beagleboneAdaptor, [4]string{"P8_13", "P8_14", "P8_15", "P8_16"}, gpio.StepperModes.DualPhaseStepping, 2048)

        work := func() {
                //set spped
                stepper.SetSpeed(15)

                //Move forward one revolution
                if err := stepper.Move(2048); err != nil {
                        fmt.Println(err)
                }

                //Move backward one revolution
                if err := stepper.Move(-2048); err != nil {
                        fmt.Println(err)
                }
        }

        robot := gobot.NewRobot("stepperBot",
                []gobot.Connection{beagleboneAdaptor},
                []gobot.Device{stepper},
                work,
        )

        robot.Start()
}

I get the following error when trying to run the code from inside the Cloud 9 IDE on the BBB.

write /sys/class/gpio/export: operation not permitted
pin has not been exported

I have checked to make sure that the GPIOs that I'm using are in /sys/class/gpio, and they are. I can run an equivalent example in Python and it works fine.