Originally Posted by Azjulian
I wonder how difficult it would be to build something like that, looking at some videos on prop balancing I see that they are using a laser trigger (which run about $250) and a single axis accelerometer. Then you are just looking for the "phase" between the two signals, I'm going to have to stick an accelerometer on my engine and see how messy the signal is and if it can be converted in software to a straight frequency and ignore the noise using a frequency domain algorithm. It would be kind of cool to do all of this on a raspberry pi.
You probably don't need a laser trigger either, just pick up the alternator output and trigger on the highest peak, or magneto grounding signal, or perhaps heat-shrink a teensy antenna onto one of the spark plug wires. It's easy to find electrical noise synchronized to the engine--we usually take extra steps to fight it. From there all it takes is a little bit of trial and error with washers to find out at what angle that electrical peak occurs.
A few months ago I picked up a MEMS accelerometer breakout board from Sparkfun with the idea bolting it to the front of the engine permanently. From the specs it looks like these things are quite rugged, wonder why Lyc doesn't bolt one to all their engines at a few bucks a pop now that we all have data acquisition systems built in on the Dynons and Garmins.
Will report back when I find some time to play with it.