Okay, I'll bite. Here is something I ran across a year or so ago...http://digitizeit.de/heli/
my friend aceisback did this:http://www.freemansgarage.com/tach.html
it works great but the cost of doing it. More of a winter I'm bored project. Not cost effective unless you already have most of the parts.
rather the first works well or not.....?????? I really cannot fathom how you would be accurate without knowing exactly what the engine rpm's are doing. If you knew for certain you were at (x)RPM's you probably know how simple the math is to get headspeed. (maingear_toothcount/pinion_toothcount)=gear_ratio then (RPM's/gear_ratio)=headspeed but without some type of shutter, optical pickup or hall effect sensor. I don't really see how you would know for sure. I have in the past without anything around just set a flat curve on idle up 1. Then slowly moved it up while I was doing fairly aggressive climb outs. When I was satisfied that the heli was performing okay I used that flat curve number as my baseline. I was very close to the expected rpm range I was hunting for. You might post and see if anyone has a spare governor that you can get cheap and install. I use a Zero Alpha that came with my Raptor and RedLine 53 and it works fantastic.
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