Ummagawd Acrobrat Duo - DJI HD - 3 Inch

By Jayembee67 on Jan 17, 2020

16  2,480  18

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:



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snick8467   Nov 07, 2020  

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

Jayembee67   Nov 07, 2020 

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

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! :-)

snick8467   Jan 01, 2021 

just realized i never followed up. my problem was my own creation. I'd put a spacer under the air unit tpu thinking i could route wires under it. once i removed the spacer, there's no more clearance issues. had many fun packs since then!

Jayembee67   Jan 02, 2021 

Excellent, glad to hear it! Yes, it's a nice frame, so I'm glad it all worked out.

Suicidejack941   Aug 23, 2020  

could you do a 1300mah on this setup with 1507 3800kv?

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Jayembee67   Aug 23, 2020 

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.

Suicidejack941   Aug 24, 2020 

thank you for the info! really helped I think I'm gonna look into the cinerat 3 then.

Suicidejack941   Aug 24, 2020 

thank you for the info! really helped I think I'm gonna look into the cinerat 3 then.

MakeitHappen   Jan 23, 2020  

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?

Jayembee67   Jan 25, 2020 

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... :-/

MakeitHappen   Feb 02, 2020 

Thank you for your reply and thoughts on this. I'm still new to this and trying to get the weight to thrust ratio thing.

Yourinnate   Jan 25, 2020  

Great build! Just put our curiosity, could you squeeze 4 inch props on this bad boy?

Jayembee67   Jan 25, 2020 

Thank you! Sadly no, 3" props only. And with the Air Unit where it is, there is barely clearance for 3".

ICARU5   Jan 19, 2020  

Looks great! 👍
Would you share the 3D parts pls?

Jayembee67   Jan 19, 2020 

Thank you! And of course, you can find them here:

ICARU5   Jan 20, 2020 

thanks a lot! :-)

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