code: func (a *AdafruitMotorHatDriver) SetDCMotorSpeed(dcMotor int, speed int32) (err error) {
  	if err = a.setPWM(a.motorHatConnection, a.dcMotors[dcMotor].pwmPin, 0, speed*16); err != nil {
  		return
  	}
  	return
  }
docs: // SetDCMotorSpeed will set the appropriate pins to run the specified DC motor
  // for the given speed.