Armattan Gecko 3" DJI Build

By Jayembee67 on May 17, 2020

14  250  13

I had seen a couple of successful DJI builds with the Gecko frame, and as I am fully committed to building a 3" fleet at the moment it seems, this was the next obvious choice.

It was a surprisingly clean and easy build, given the very limited space, the side-by-side stack mounting holes mean this is possible. I could have just about got everything in there without modification, but in the end I added a couple of top-plate shims to give a bit more room between the Air Unit and the flight controller. Party to reduce heat transmission, but mostly to reduce vibrations.

And it's a great little flier, quick, agile, responsive, crisp video... BUT! It suffers from the same problem as my 3" DJI-F5 build; when the throttle gets beyond a certain point, I start to see fast yaw oscillation; you see it in the video, and I can see it in the blackbox traces on both gyro and PIDs. Which is really annoying as at lower speeds it's flying delightfully, and to be honest its low speeds are quite high. I have partly solved the problem by dropping the 4.1.x PID gain sliders way down, which has helped a good deal, but I am still seeing those oscillations when I push too hard, and by reducing the PIDs so much, I am losing some crispness in the handling. I did up my TPA breakpoint value, but I'm not sure if that helped very much, and I swapped the motor direction to props-out, which also seems to help some.

But if anyone has any suggestions as to how to tune out those higher-throttle yaw oscillations with 4.1.x, I would be very grateful!

Anyhow, for now this is flying acceptably, and it's actually lots of fun to throw around, but it's more ragged than I would like. And I can't get better prop-wash handling without making the yaw oscillations more pronounced. Here's a flight at the end of the first tuning session:

Photos

Discussion

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DoubleJackOnTap   10 days ago  

Are you using RPM filtering?  My Gecko also suffered from terrible vibes at mid to high throttle.  RPM filtering significantly reduced it.   I'm going to try BF 4.2 next.  4.2 is amazing at default values on my Rooster.

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DoubleJackOnTap   6 days ago 

I installed 4.2.0 on mine today. Huge improvement. Default pids and cut / pasted the CLI from the HD quick settings from the Tuning Notes (https://github.com/betaflight/betaflight/wiki/4.2-Tuning-Notes). I also adjusted the notch filter settings as recommended for rpm filtering. This is the best my Gecko has ever flown. I ran without a ND filter and pretty low jello. I was even running some pretty beat up props. More testing tomorrow, but this was very exciting for me.

Jayembee67   6 days ago 
1

Excellent news. Alrighty, that's where I go next. Thanks for the update!

DoubleJackOnTap   6 days ago 

I may also try emuflight.  The new release is getting great reviews for cinewhoops and micros.   Seems like the Gecko is pretty finicky, maybe it is more like a micro for tuning than a 5"?

miromir237   11 days ago  
1

Nice a clean build. I like it.

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