R/C helicopter - DIY hatcam tachometer

Video tutorial - how to tach your r/c heli using a hatcam video and a computer.

Program available at http://audacity.sourceforge.net

Technical details can be found at http://en.wikipedia.org/wiki/Spectrogram

Also works for planks, cars, crotch rockets, and (many) other things.

Category:

Science & Technology

Tags:

• helifreak
• hatcam
• audio
• tach

[moschetto58]

Very interesting. It would be nice if you could provide some more detail on how to identify the correct peak: I tried the method and found 3-4 peaks in the 59-101 Hz range.

[xeeded]

@moschetto58,different gear trains come up noisier than others. Protos is a nice clean signature, Trex-450 not so much. When you've got a mess you need to get an assist from the tail rotor - so check your main rotor to tail rotor ratio and ensure that you have a strong peak on both frequencies before you accept the main blade rate.

For example, 5:1 main-to-tail ratio on Blade 400, with peaks at 87 Hz, 93 Hz, 98 Hz, and 465 Hz would pretty much guarantee 93 Hz or 2790 RPM.

[xeeded]

I don't fly nitro and haven't investigated nitro videos, but the idea certainly can work. In that case you will likely find the cylinder firing rate becomes the dominant part of the spectrum and, if your clutch isn't slipping and the gearing is known, then you should be able to work out head speed.

[DerickZ316]

@DerickZ316 One thing, though. My spectogram doesn't look remotely like yours! Maybe I'm just getting a bad sample or my camera has poor audio? It's awfully fuzzy and though I can occasionally see some of the higher harmonics fairly easily, the main rotor itself is completely lost in the static. I can only pick it out in the plot, and even than it's sort of an educated guess. Any thoughts?

[DerickZ316]

I just used this method to estimate my headspeed at 2370 RPM. I was between 70 and 85 percent throttle, and after taking out 10% for efficiency, a popular online calculator places my headspeed at 2357 RPM. Great method!

[stellablade]

I've tried this method and a couple of other headspeed recorders such as Heli-Headspeed and Heliport and never get accurate results. I tried my T-rex 250 using the Audacity method and it told me the headpseed was around 8,000rpm! I've no idea why these methods do not work for me. Puzzling. The only method I've found to work is the Helitach app for the iphone.

[sbranik]

Will it work with nitro powered helis? Have you done any testing?

[rcflyair]

Brilliant! I've just estimated my headspeed at 2880 rpm without spending a nickel. Close enough! Thanks heaps....

rcflyair

[pommesschranke2]

thank you very much!

I love free & open source software like audacity.

[liamandchad]

Fantastic video and very well exsplained.