Ummagawd Acrobrat Duo - DJI HD - 3 Inch
By Jayembee67 on Jan 17, 2020
I have an original Acrobrat frame built out with SD gear and stacked cameras, and I have really liked that machine; the way it flies and how robust it is.. So when I was thinking about another 3" HD rig (it might well be the only thing we get to fly very soon), I was of course interested to see the new Acrobrat Duo, which made the claim of being compatible with the DJI Air Unit. So I decided to see if that was true.
And it is indeed possible to get an Air Unit and everything else into the frame, but It has taken a good deal of time in TinkerCAD, and then printing multiple iterations of parts, to get it all to fit tidily and securely. It's pretty cramped, but at least these DJI HD builds don't require much soldering, or masses of leads to fit in someplace.
I am a bit unsure about the placement of the video antennas; there is quite a lot of carbon in the way of the prop wash as it is, so putting more stuff down there might not be the best of plans as far as maintaining thrust and minimizing turbulence goes. I'll see how this thing flies, but I might need to move the antennas to the top of the frame. But then they won't have that nice wide separation... Still, on to the next thing for now; tuning, I bet this will need some tuning. These little, heavy, quick machines don't seem to do so well with BF 4.1.x defaults, apparently.
UPDATE 2020-01-18
In the end, I decided to move the video antennas to the back of the frame rather than under the arms. Likely getting a poorer signal, but much cleaner and less obstruction to the rotor wash.
UPDATE 2020-02-05
Final Evolution. This machine been a difficult child. At first it was a mass of rattles and shakes, and once I solved that, it became a battery vampire; voltage sag warnings within 1 minute. And the video feed was poor. Boo.
The battery issue was motors that were too fast for such a heavy quad, 1408 4100kv, were not what was needed. I tried lower pitch props, and got better flight times but at a cost of speed and grip. So I bit the bullet and ordered new motors; 1507 3300kv, a fairly major change inspired by @TaterrsFPV. But it solved my problem and now I am getting 3:30 of perfectly acceptable flying out of an 850mAh pack. Huzzah.
I also moved the DJI antenna back down under the rotor arms; on the back, whilst tidy, they didn't have enough separation and were too much in the battery shadow. And that helped a lot, the video is now much better.
And finally, as the new motors were purple they clashed horribly with the orange TPU parts, so as I needed to reprint a bunch of parts anyhow, I redid the colour scheme. It's finally the machine I had hoped it would be, which is good, you don't want to waste a DJI build, far too expensive...
Maiden Flight of the final setup. Quite acceptable considering it was blowing a gale out there:
Photos
Part List
Frame |
Ummagawd Acrobrat Duo 3" Micro Frame by Tommy Tibajia
(5 builds)
Racedayquads.com
|
$44.99 |
Flight Controller |
SucceX-D Mini F7 TwinG 2-8S TwinG Flight Controller (ICM20689)
(4 builds)
Iflight-rc.com
|
$49.99 |
ESCs |
SucceX Mini 40A 2-6S 4-in-1 ESC Dshot1200
(3 builds)
Iflight-rc.com
|
$42.99 |
Motors |
iFlight 4pcs XING 1408 4100KV 2-4S Brushless Motor for 130-180mm FPV Racing Drone Micro Quadcopter (Unibell)
Amazon.com
|
$68.99 |
Propellers |
GemFan Flash 3052-3 (2CCW-2CCW) Choose Color
(13 builds)
Pyrodrone.com
|
$2.99 |
FPV Camera |
DJI Digital FPV Camera
(164 builds)
Racedayquads.com
|
$59.00 |
FPV Transmitter |
DJI Digital FPV Air Unit Video Transmission Module
(121 builds)
Racedayquads.com
|
$99.00 |
Antenna |
DJI Digital FPV Air Unit Elbow MMCX Antenna 2 Pack
(44 builds)
Racedayquads.com
|
$15.00 |
Receiver |
TBS CROSSFIRE NANO RX (SE) - FPV LONG RANGE DRONE RECEIVER
(412 builds)
Team-blacksheep.com
|
$29.95 |
Batteries |
Tattu R-Line 850mAh 4s 95c Lipo Battery
(27 builds)
Getfpv.com
|
See Site |
i just converted my acrobrat to dji, and find the props barely hit the air unit. did you encounter this at all? i might have to make an 1/8" riser to get the motors up so the props don't hit
The clearance is tight for sure, but I think that you might be right. The XING motors I have used are tall, and so I have about a 2mm clearance both vertical and horizontal - so even when bending the props, they still just miss the Air Unit
https://photos.app.goo.gl/kH1aBLSpGt9567gh6
Yes, motor risers might be your best bet, I'm afraid, but a pretty small modification at least. Print them in TPU and they can be soft mounts, just like back in the good old days of a few years ago! :-)
could you do a 1300mah on this setup with 1507 3800kv?
Hrm. Well, I have to say, this is a great frame, it's robust, there is just loads of room in there, and the finished machine flies very nicely. It's pretty big for a 3", you can get 3 20x20 boards in a row in there if that is what you wanted. But unfortunately, that's the thing, this frame is designed for 20x20 boards. You could likely attach 30x30 with adapters, but with your battery requirement, I'm not sure this is the best choice.
How is the flight time with XING 1408 4100KV? Having a hard time on which motors to use, since I keep reading this frame is on the heavy side. Would higher kv be better on 3inch props vs lower kv?
To be honest I am no expert with 3" machines, and so I am sort-of-guessing myself. And in truth, were I to do this build again, I think I would go with 3600kv XING 1408 motors.
The problem I am experiencing with this machine is that it is absolutely brutal on my batteries. I'm using 850mAh Tattu 95c packs, which are fine on my other 3" builds, but if I don't fly conservatively, I can get voltage warnings after 1min of flight with the Acrobrat; it's horribly saggy. I can get over 3:30 of decent flight, but I have to be careful. I just checked, and my voltage meter was a little off, but I think it's mostly the weight and higher-draw motors.
All of which is a shame as it flies nicely. I had gyro issues with the first FC, but once that was replaced, it's been flying very well. But it feels like I have this upper range to the throttle that I just can't use, so I think that the 3600kv motors might have been better. But, caveat emptor, I haven't had the chance to test with 3600s... :-/
Great build! Just put our curiosity, could you squeeze 4 inch props on this bad boy?
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Were you able to get it tuned out to get rid of the oscillations and prop wash with the new motors? Am looking to build one of these myself like slope
Mostly. The final hardware setup worked out better, and I did manage to get it better tuned, but in truth, it was always a bit on the rattly side and I never quite got it flying as well as I wanted it to. Maybe the geometry with the stack so far forward was a bit of an issue? In the end I actually recycled the hardware into another frame - but that build was also a bit rattly, so there is a danger the stack was the issue, not the frame.
So the bottom line is that for me it was a nice frame, but I never quite got the thing flying as I wanted it to fly - but I suspect that might have been an issue with me, not with the frame.