You Reply: the romeo`s working voltage is 5VDC, but the board `s external power supply range is 5-23V
there is a L298 chip on the board, its external power supply range is 2.5-46VDC.
the motor`s working voltage is 5V, but it also works on 12V. when you increase the work voltage ,the motor will turn fast. you only can revision code to lower the speed.