I have to comment on the dwell subject....

Somone mentioned that distance from the prop hub center will effect dwell times? I'm sorry but this is not correct... regardless of how far from the center of the prop hub it is, it will take EXACTLY the same amount of time to make one full revolution... I think what you are thinking about is the speed of the magnet travels slower the closer it is to center and faster the farther out from center it is... but... it will still complete one full revolution in EXACTLY the same amount of time....

So... regardless of how large your prop hub is, dwell time is an accurate way to time the module... I can see why they used it... I could also see using a "counter" to measure rpm's to set the timing... but evidently they chose dwell as the better choice for them....