R/C helicopter - DIY hatcam Doppler speed-trap

Video tutorial - how to speed-trap 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 http://en.wikipedia.org/wiki/Doppler_effect http://en.wikipedia.org/wiki/Speed_of_sound

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

Category:

Science & Technology

Tags:

• helifreak
• r/c
• helicopter
• hatcam
• Doppler
• speed
• trap

[johnfranks]

Hmm... I could not come up with a feasible calculation using this method with one of my rc car videos. Does the model need to approach/depart at 90° to a fixed camera (no pan) with unidirectional stereo microphone? YouTube Video: RKaTikVXbUo if you care to check out the shot im referring to. Cheers!

-john c.

[xeeded]

@johnfranks, the vehicle needs to approach and depart relatively straight on while maintaining a fixed speed for a couple of seconds on both sides of the pass. If you're getting strong frequencies on the gram they should flatten out at both ends of the pass, which is correct. Some drive trains are harder to pick out than others, so if you don't have strong frequencies then try attaching a loud buzzer to the vehicle.

You can also do constant big circles (away from the recorder) at fixed speed.

[xeeded]

Glad to hear you've been finding it helpful and having some fun with it. Cheers!

[Deucetrinal]

Good instructions, thanks!

[grnbrgb]

I tried this against the video "Funjet 6S Cobra Speed Drive 285 km/h" and got 288.79 km/h (assuming 20C) where the reported speed in the video is 285.12 +/-3 km/h!

Excellent tutorial, and great idea.

[HeliEye]

Excellant instructional video 5*

Steve

[henrikolsen5]

Very nice demonstration and explanation. Thanks.