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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:
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.
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):
Though, all in all, it didn't get too many flights - only because it quickly got outdated by newer quads with stronger motors etc pp.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
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:
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.
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.
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?
Also, 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.
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.
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.
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:
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.
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.
Update 30.1.2017: Yay, got my own plates! ... I think 1mm should be fine to carry the battery.
Ordered 1x1mm, 1x1.5mm because i was not sure how stiff it's gonna be with the cuts and holes.
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.
Not really... until you mention it, lol.
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.
RE: devilbug (nighthawk mod) - fftunes - 01-30-2017
Update, got my custom plates today, yay!
Added a pic in post #3, will mount them soon.
RE: devilbug (nighthawk mod) - sloscotty - 01-30-2017
(01-30-2017, 04:10 PM)fftunes Wrote: Update, got my custom plates today, yay!
RE: devilbug (nighthawk mod) - fftunes - 02-17-2017
Increased p-term a bit, but it's still loose enough that i-term can go all over the place, resulting in the sticks feeling unreliable during or after somewhat medium changes in attitude or under load (fast turns etc), or even causing drifts if worst comes to worst.
Thanks to Boris himself i know now that d-term transition setpoint set to max will improve center stick stability. So that's next to try, but as i already have it at around 0.6-0.7 (max. is 1.0) i don't expect much improvement. However, Boris also said that he might increase the max value for transition setpoint in the future as he also found that the range is relatively small.
PS: Didn't mount the cfk plate yet. Hmmm, also might try soft-mounting motors on this bird...
EDIT: lol i had transition setpoint at 0.35 - increasing it to 0.55 basically fixed all the misbehaviour. New videos in the works