There is a lot of split flap designs but this one is a bit different. Most use a magnet in one section of the drum to home the device. Due to backlash and play in the gears this can lead to skipped letters and inaccuracy. Rather than a magnet at the edge and a hall effect this device uses a magnet with a digital encoder. No matter what happens the drum knows where it is so it is not possible to get the wrong position. 

The motor is enclosed in the drum itself reducing overall size.