AOS 3.5 EVO - 250g O3 freestyler

By sascha on Jul 31, 2023

5  0  12

I wanted to look into DJI's O3 system and still had some electronics lying around that would do the job. I only needed new motors and a frame, so I thought: why not go with the new AOS 3.5 EVO which was made for the O3 system.

The frame looks nice. Corners and edges are slightly chamfered which makes them feel really nice. But then came the build and it somewhat stopped being nice. If you want to go DJI digital, you only have one option: Stack in the front, O3 unit in the back. You could move the O3 unit to the front by replacing the stock antenna though. The center position only makes sence if you have an AIO and HDZero or go analog. Otherwise there's not enough space.

Then there's another really annoying issue and I'm not (yet) sure if it's the designer's or the manufacturers fault. Every position allows to either use 20x20 or 25x25, but for whatever reason, there are press nuts in the front 25x25 positon making it impossible to use screws at the 20x20 position because either the screw head is blocked by the pressnut or a the counter-nut hits the press nut. A thing that was actually recommended by the frame's designer to use to reduce vibrations. Chris' response to this was to simply pop out the press nuts ... better said than done.

So, using a 20x20 Fettec AIO was not an option neither was a standard 20x20 stack unless I wanted to replace the O3's antenna. So I went with an 25x25 AIO instead...

Anyway, rest of the build went pretty nice and straight forward. With 4S 550-650 mAh it could actually still be below 250g.


Part List


See Site

Flight Controller

Mamba MK4 F740 AIO 40A 6S 32bit ALL IN ONE AIO FC&ESC 25.5mm/M2


4 x T-Motor F1404 - 4600kv motors (2 builds)
See Site


Gemfan Hurricane 3520 Durable Tri-Blade 3.5" Propeller (2CW+2CCW) - Choose Your Color (45 builds)

FPV Camera

DJI O3 Air Unit (79 builds)


TBS Crossfire Nano Rx - FPV LONG RANGE DRONE RECEIVER (1488 builds)
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QCumberCool   Mar 27, 2024  

nice build and very clean! i'm trying to decide if i want to build a sub250 with the sacrifices you have to make. what did your AUW end up being? do you have any flight videos you could share?

adv.andrei   Aug 31, 2023  

can you share the pids?

unganga   Aug 10, 2023  

hi i'm confused! does mamba aio f740 support dji o3 it has bec on 5v 2A.
I want to collect on this fc and o3
thanks for the answer!

sascha   Aug 10, 2023 

The AIO is rated for 6S (up to ~26 V) and so is the O3 Air Unit (7.4 - 26.4 V). The voltage pin inside the connector is simply a VCC pin, so the AU is provided with whatever voltage your battery provides. So you actually don't need a 9V BEC if you use this AIO with an O3 AU

In theory, you can also run this AIO with a Vista/Link (rated for 7.4 - 26.4 V) but no OG DJI Air Unit since that one is only rated for 4S.

unganga   Aug 10, 2023 

thanks a lot for the explanation!

BaSS   Aug 04, 2023  

Hey, nice build! The bottom plate with the lock nuts is supposed to be the other way around and fc on top of that.

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BaSS   Aug 04, 2023 

the press nut is the nut on the other side of the bolt, it locks the bolt in as Chris intended, you tighten the bolt in the press nut, fc on top, nut on top of that and done, right?

so, press nut flange towards the top, screw comes from underside into press nut until tight (instead of lock nut) and then flight controller followed by another nut to lock the fc.

sascha   Aug 04, 2023 

The press nut is in the 25x25 hole. I wanted to use a 20x20 stack though. Wanting to put a screw into the 20x20 hole causes the screw head bumping into the press nut. Turning around the plate would instead cause the counter nut to bump into the press nut. Chris himself recommended to use a counter nut for stack screws. So whatever configuration I use, it won't work for a 20x20 stack in the front position.

This is the reason I switched over to a 25x25 AIO as mentioned in my description above.

BaSS   Aug 05, 2023 

Hah, I see now, thanks for indulging me :) My flight controller is actually 25.5 where I was thinking 20x20... You are right, he offers both 20 and 25, it is weird you cant really use both then.. a (printed) 25.5 to 20 adapter for the o3 would also have been nice if included.

Thanks for the replies, enjoy the flying :)

BaSS   Aug 04, 2023  

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