code: func (a *AdafruitMotorHatDriver) SetStepperMotorSpeed(stepperMotor int, rpm int) (err error) {
  	revSteps := a.stepperMotors[stepperMotor].revSteps
  	a.stepperMotors[stepperMotor].secPerStep = 60.0 / float64(revSteps*rpm)
  	a.stepperMotors[stepperMotor].stepCounter = 0
  	return
  }
docs: // SetStepperMotorSpeed sets the seconds-per-step for the given Stepper Motor.