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devilbug (nighthawk mod) - fftunes - 11-07-2016

About the name

When goog'ling the name "devilbug" you'll mostly come across pictures of fishing lures (is that the right word?) which look awesome, but nothing like a quad. I like this one though: Smile

I got the idea for the name because of the shape of the quad's top-plate, which looks a bit like a bug with horns.

Old build

Main goal of the old build was to make a low-profile go-pro carrier out of a basic nighthawk frame. I made this quad when betaflight 2.1.6 was out, which, in multirotor time scale, is ages ago. This is what i came up with then:

I fear i won't quite reach the same weight with a new build:

With the light 1806 motors its power was limited, but it gave me some flights which i still like, even after this long time (disregard my flying skills, as i said, this was ages ago): Wink

Though, all in all, it didn't get too many flights - only because it quickly got outdated by newer quads with stronger motors etc pp. But i always liked its flight characteristics, which i think were mostly given by its low weight and the somewhat special aerodynamics (low profile, kind of front 'spoiler' and the wide top-plate). Hopefully with my new build i can recreate the "feeling" this quad got me, but regarding motors, and 4mm arms vs 3mm arms, it will pretty surely end up a bit heavier. We're doing this for science, right?

New parts list
  • frame: nighthawk clone, 6" version 4mm arms
  • motors: rcx 2206/2400kV
  • esc: Aikon 30a 2-4s
  • props: hq5045bn
  • fc: Revo F4
  • rx: Lemon Diversity sat w/ long antennas
  • vtx: hawkeye 32ch with pigtail, aomway antenna
  • pdb: flyduino micro 5V/12V
  • filter: small one from rtfquads, reinforced with a cap

First wanted to use the micro PDB on the left, but as i don't need 12V i can finally make use of this old, big one: Smile

Flanged aluminum lock nuts vs. what came with the rcx motors:

Not yet sure about the camera, either i'll use a spare one with typical 28x28mm footprint, or i'll get a newer, smaller one, like the mini version of the runcam owl, for example. Also i was thinking about having the top-plate made of carbon by a friend, but this might take a while. Maybe i'll make another wood piece first.

New build

I didn't get far yet, as i only just got the escs & motors a few days ago, and i'm not in a hurry.

Motors and escs soldered to an old pdb i use for testing. Man they run smooth and slow on 2s. Big Grin
Blheli_s 16.4 flashed (thanks Oscar), adjusted min/mid/max throttle and disabled heat protection.
It's the first time i'm using blheli gear. Are there any other important settings i need to change from defaults?

First time trying some cord to secure wires and gear, instead of the usual zipties.

Litterally stitched together: since i secured everything else with cord, i thought why not try it for the FC.
It is not really soft though, that urethane-type foam is pretty stiff. But at least it's light. Big Grin
This is not final, i'll change the wiring after the filter so the camera gets 12V. Just have no cam yet.

Like on the old build, a simple vtx-antenna holder made with instamorph:

Starting a simple top plate to figure out where the rest belongs, like cut-outs for battery straps etc.
I might make a carbon plate some time thanks to sloscotty's guide, but for now i'm working with this:

Cut off the FC pins and direct soldered everything. Some of the wires glued to the FC. Now it is low enough:

FPV camera mount is a bit of a hack job made from 2mm aluminum plate, thick double-sided foam tape in between:

Finished & works

Did a short test LOS with half-empty battery, debug_mode=notch & disabled gyro notch filters.

Yeah... no. But yeah... still not bad since it could even run 6" props if needed. Big Grin

RE: devilbug (nighthawk mod) - fftunes - 11-29-2016

Setting up the new bird

There was quite some noise. Pitch axis is a bit worse, not sure yet if i should quench that peak at 180Hz instead.
This is how pitch axis looks after the filters - considering it's fully zoomed in, i think it's not so bad:

As far as i could test LOS in my backyard, it sounds and behaves pretty clean. Roll and pitch seem fine with low P&D.
Need to experiment more on yaw with high P / lower accel limit. But hope for an FPV maiden flight tomorrow.


Maiden day was great. Have not done these half-flip-roll-half-flips before so got a bit excited. Big Grin
Also fun to play with the Xiaomi Yi again. Recorded in 1600x1200 and resized in editor:

Upped P and D a tiny bit during first flights. Yaw is still not very good, but it's not always noticeable in FPV.

In the first fpv flights i noticed it was quite easy to push into propwash situations (for example above video @0:51).
At first i thought i would try reversed motor direction for direct comparison back to back, but i'll keep that for later.
I readjusted the filters after reading that too low notch filters can increase prop wash. D-term looks clean: Smile

Only using 1 gyro notch filter for now. More filtering seemed to increase D-noise, maybe due to phase shifting?
Anyway, after some changes in yaw, the quad is pretty much set up. What's left to improve is the pilot. Smile

Next session, in colder weather and strong wind, it felt uncomfortably loose again, so will go over PID once more.
Also on large screen i think i see some vibration in the video. Maybe will have to go over Yaw PID too, again.
Still has normal motor direction. Will try to do a video to directly compare normal and reversed motors eventually.

RE: devilbug (nighthawk mod) - fftunes - 12-10-2016

Custom carbon top plate

Thanks to sloscotty's guide i plan to let make a carbon top plate eventually. This post will be updated by time.

Played around a bit more with QCAD. Probably not doing everything right, but that what it looks like so far:

A bit more rounding, and done:

Gave that version to my friend from smartshapes and he said it shouldn't be a problem.

Any comments, questions, suggestions welcome.

RE: devilbug (nighthawk mod) - fftunes - 01-07-2017

Update. Custom top-plate basically ordered (not from Armattan service like in sloscotty's guide but from smartshapes).

RE: devilbug (nighthawk mod) - Grisha0 - 01-11-2017

one concern, your arms are held by 2 screws, and there is not a lot of meat on overlap.
arent' you affraid it will snapoff?

RE: devilbug (nighthawk mod) - fftunes - 01-11-2017

(01-11-2017, 10:01 AM)Grisha0 Wrote: one concern, your arms are held by 2 screws, and there is not a lot of meat on overlap.
arent' you affraid it will snapoff?

Not really... until you mention it, lol. Wink

The 1st version of this build endured quite some crashes. Ok it was a bit lighter too, about 54g.
The new arms are 4mm thick, bottom plate 2mm. Middle plate with 1.5mm is probably the weak spot now.
But the plates are cut in a way that makes the whole frame a bit flexible. Better for crashing.

It's more that the frame is almost too soft for the stronger motors / heavy props, there's some resonance.

It sounds buttery smooth but it's easy to get propwash. Maybe PID are still too soft. Not finished yet. Wink