Build Helios - 3.5” Sub-250g (Sub 160g possible) DJI O3 Drone – Frame/Build Thread

[Recursion]

I’ve been working on designing/developing/testing this since the early Spring after the DJI O3 system was released and the V2 Goggles supported it. My personal challenge was to create a 3.5” O3 build that flew as well as my Scythe (3.5” as well) does on the O2/Vista. I’ve enjoyed the journey, but I am enjoying flying the result even more, which is a sub-160g (including GPS) 3.5” O3 build with an 11 : 1 thrust to weight ratio.

I’ve made a video to outline the requirements, design, build process which you can view here:

I had more than 20 minutes of content, but I cut it down to something reasonable. Feel free to ask any questions if you have any here. Many years ago I used to post giant build threads so doing it after the fact still feels a bit foreign to me. 

When building this I assumed few if any would follow suit given it’s a naked build given the cost of an O3, but the design ended up allowing for an very easy mounting of a stock O3 Airunit, which would still be the lightest full Airunit build you could make on 3.5”. The camera will need to be naked, but taking it out and putting it back in the case is extremely simple, where the Airunit is a one-way journey.

If you’re interested in building one yourself, remember that the magic of this unique class of quad is to have the highest thrust to weight ratio you can reasonably pull off. They are more fun than any 5” I’ve had when you nail it.

I strongly recommend unless you have something in mind already that you’re set on making that you use the same motors, propellers, and battery I have. I’ve done a ton of research over the past few years, and have done a lot of testing to try and find the perfect combination for this type of aircraft. I've published a lot of my test results on these forums, which you can reference here: https://intofpv.com/t-recursion-labs-sub...er-testing. You usually find motors cheaper on Aliexpress if it’s about price, although they are not expensive at most local stores. I am not sponsored by anyone.

Pics




Frame

To get your own frame cut:  https://www.cncdrones.com/recursion-heli...frame.html
Print your own 3D printable parts (camera housing required): https://www.printables.com/model/555727


Recommended Build:

• Motors: T-Motor F1404 3800Kv (supports any motor with 9mm mounting holes)
  
• Propellers: HQProp T3.5x2.5x3
  
• Flight Controller: 20x20 or 25.5x25.5 AIO, with a 9.5mm maximum clearance between the center of the 20x20 mount hole and the stand-offs.
  
• Battery: 4s 550mah Tattu or equivalent low internal resistance high quality lipo or greater. A larger battery may be required if you don’t go with the recommended motor/propeller combination.
  
• Video: DJI O3 System, Stock or Naked (Required)
  
• 60cm DJI O3 Camera cable (Stock cable will work)
  
• 10x130mm Battery Strap (For 4s 550mah. Longer for larger)
  
• 2x5.8GHz Whip Antennas (only if you’re not using the DJI FPV controller)
  
• Capacitor: Panasonic Low ESR 25VDC 470uf Capacitor - Mfr: EEU-FR1E471Y (High quality 8mm diameter to fit out the back between the stand-offs. If you put them on the battery leads it doesn’t matter).
  

[Lemonyleprosy]

I’m tempted to build one of these, but with a 1s walksnail vtx and the HD Pro cam.

I don’t run dji so I’m not aware of its camera dimensions and whatnot- do you think I’d be able to get a Pro cam in the canopy without major modifications?
https://caddxfpv.com/collections/walksna...6178551086

As a side note, I really enjoy your content. You put time into making quality content that’s also entertaining, and it shows.

[brandonstreet]

Man this thing is a little powerhouse. Looks awesome! Love the video and all the testing that went into it. Covering all your bases with the thermo testing and such. Great job!

[MomoBrut]

Well, a lot of work ... Thanks for it. The result is great. That just has to be appreciated. And everyone will say that it is good to move forward, but lately I feel that forward is not always forward.

Someone says about me that I am a bit skeptical in my views, I only see it realistically, not everyone likes my views, hah ...
I have been condemning the O3 from the very beginning, my realistic view of this device has not changed all this time, I published it the very day the O3 came out, I was not wrong. I won't go into the technical details here, which I previously posted on IntoFPV in that thread about the new O3. After all this time, I understand this from DJI's side not as an effort to bring some technical solution that moves things forward. It's mainly a money trap, a ruse for rookies. The O3 video recording simply does not have the necessary quality to make the video worth something, the benefit is only a higher resolution of the FPV feed at the cost of its greater delay, in addition to a poor dynamic range. The video taken without the ND filter will never be good, and at the same time the FPV feed with the ND filter will always be much harder to use for controlling the quad ... It's just a trap, you have to pay money for something you don't really need or, more precisely, it's actually worse. For me, it's not a technically or economically better way, I definitely don't plan to convert my 10 quads to O3.

I really like how you solved the camera attachment and its protection, your solutions always have a head and a heel, that's how it should be. There were more than enough problems to solve. I understand that due to the durability of the solution it is not possible to put an ND filter there, but that is unacceptable to me. There is noticeable jello in the part of the peaceful cinematic flight, such a video is basically unusable for further editing. And even if the ND was usable, to date I haven't seen any O3 video that is really smooth and shake-free (I'm not even talking about colors and dynamic range, 10b colors don't work very well either).
It's nice to see how you solved quite a few technical problems to get O3 to use. But it's not the way for me, luckily not everyone is like me. I'll stick with Nebula Pro Nano and Scythe, it's the golden grail for me and fulfills everything I think is good. And a naked GoPro Hero 8 or 11 will take care of the rest.

[Recursion]

I’m tempted to build one of these, but with a 1s walksnail vtx and the HD Pro cam.

I don’t run dji so I’m not aware of its camera dimensions and whatnot- do you think I’d be able to get a Pro cam in the canopy without major modifications?
https://caddxfpv.com/collections/walksna...6178551086

As a side note, I really enjoy your content. You put time into making quality content that’s also entertaining, and it shows.

I really appreciate that. Thank you

This was designed specifically for the O3 for both the camera and the top plate mounting, and will not work with anything else. 

I remember that the Walksnail system used to have a camera that looked like it was the same size as the Nebula Nano Pro that looked like it was the same shape/size with the same mounting holes. If that's the case then it should work perfectly on the Scythe, which would weigh and fly the same as the Helios.

[Recursion]

Well, a lot of work ... Thanks for it. The result is great. That just has to be appreciated. And everyone will say that it is good to move forward, but lately I feel that forward is not always forward.

Someone says about me that I am a bit skeptical in my views, I only see it realistically, not everyone likes my views, hah ...
I have been condemning the O3 from the very beginning, my realistic view of this device has not changed all this time, I published it the very day the O3 came out, I was not wrong. I won't go into the technical details here, which I previously posted on IntoFPV in that thread about the new O3. After all this time, I understand this from DJI's side not as an effort to bring some technical solution that moves things forward. It's mainly a money trap, a ruse for rookies. The O3 video recording simply does not have the necessary quality to make the video worth something, the benefit is only a higher resolution of the FPV feed at the cost of its greater delay, in addition to a poor dynamic range. The video taken without the ND filter will never be good, and at the same time the FPV feed with the ND filter will always be much harder to use for controlling the quad ... It's just a trap, you have to pay money for something you don't really need or, more precisely, it's actually worse. For me, it's not a technically or economically better way, I definitely don't plan to convert my 10 quads to O3.

I really like how you solved the camera attachment and its protection, your solutions always have a head and a heel, that's how it should be. There were more than enough problems to solve. I understand that due to the durability of the solution it is not possible to put an ND filter there, but that is unacceptable to me. There is noticeable jello in the part of the peaceful cinematic flight, such a video is basically unusable for further editing. And even if the ND was usable, to date I haven't seen any O3 video that is really smooth and shake-free (I'm not even talking about colors and dynamic range, 10b colors don't work very well either).
It's nice to see how you solved quite a few technical problems to get O3 to use. But it's not the way for me, luckily not everyone is like me. I'll stick with Nebula Pro Nano and Scythe, it's the golden grail for me and fulfills everything I think is good. And a naked GoPro Hero 8 or 11 will take care of the rest.

You're assessment is fair. The O3 has a lot of positives but also has negatives over the O2 system (Vista). The two main ones is cost, and the way it handles light changing, and low light, as you pointed out. The fpv image quality is absolutely fantastic though, so for chill flying during the day, or flying where I just want to sight see and experience the thrill of flight, I'm extremely satisfied. The latency increase is minor when on the V2 Goggles where you can retain 120fps. I think I made up for the difference when I moved to ELRS from the DJI controller (though I switched them on the Scythe as well). For recording your own flying having the quality this has on board is absolutely fantastic, but it does not replace a GoPro if that is the quality you want/need, but not having the weight for fun flying while getting some really decent footage is amazing. The new video algorithms they have is really good at maintaining quality, but on the Goggles 2 you can get that on the Vista since it updates the firmware to be O3 Lite (you only get 100fps though).

Like I said in the video, I'm not replacing my Scythes. I have 4 of them (plus a bunch of spare parts) and like 6 naked GoPros I bought for cheap damaged and fixed up. I'm still very happy to fly them. It's not like that time when I tried an old analog 3" build. The system isn't even that much different from a technical standpoint. The main difference is the quality of the new camera and improved local recording. The truth is that if it wasn't for the V2 support with 120fps where I can use both systems, I don't think I would have jumped on this.

[MomoBrut]

The O3 can be set up to be usable for an acceptable fpv feed, but the video will be essentially unusable for further processing. It can be used on larger quads and the video can be taken on a more dignified camera that is capable of higher quality recording. The way I see it, it's actually about getting the pilot drunk with a better image. However, the price of such intoxication is brutal, together with the current increase in prices, quads with O3 are already really expensive.

I know from my experience that if I am flying in an unknown place, at a greater distance, in a limited time window, with the possibility of flying at most twice, getting a quality flawless shot is quite stressful requiring absolute concentration and also monitoring a large number of telemetry parameters in order not to screw something up, is maybe just do it well and without incident, there's really no time to get drunk on the image. These times I appreciate an fpv feed that has dynamic range, the dynamic changes quickly with the light level and it just eases my stress, I don't care if the image is a lower resolution 720p or over-sharpened, and this is what the Nebula Pro and O2 give me.

It is simply necessary to live only with the O3 on Helios, you cannot put another camera there. Such a solution is only good for a certain type of use, basically flying around for fun, freestyle, etc. What I like about my Scythe LR is that I can fly very far and at the same time capture video quality that until recently I was only able to capture with significantly larger quads. And most importantly, it weighs up to 250 g and I can fly it almost anywhere, which is not possible with large quads. And if it's all well-tuned and therefore quiet, people won't even notice. That's the power...

[Recursion]

So you were not the only one who said they would want an ND Filter MomoBrut. Someone locally who is going to build one wanted to be able to put on the Avata ND Filters he has the other day, and he donated one to me to try and design around. I have not flown it but it looks like it'll fit well and stay in place. Since this one is mine now when I'll test it eventually and see what I think about having one on my FPV feed.

[MomoBrut]

Great. I will be very happy if you send some flight video, sunny day around noon, ND16 or ND32, 4K 60 fps, manual settings - Shutter 1/120, ISOlimit 400, WB 5500, D-Cinelike, EIS off, Sharpness -1, Noise Reduction -2 . And especially with the O3 automatic transmission mode turned off, which is jerky, as you yourself wrote earlier. And I would also be interested in how it is possible to fly with this setting and the ND filter from the pilot's point of view.

That ND filter seems to be perfectly integrated on that mount. If it turns out to be a viable alternative, I'll give it a try.

[Recursion]

One project I've taken on is to design/build some modular race gates I can quickly setup in various configurations quickly to practice my technical skill. Still have more TPU connectors to print, but I ran the Helios threw the first track I whipped up to practice maneuvers I struggle with on weekend to try them out. Since the sun is setting this is a perfect example of where the O3 struggles with change of brightness.

[bakedFPV]

Is there a preset tune I can dump into beta flight when I’m done? I’m in the process of building one. Any advice would be spectacular

[Recursion]

Is there a preset tune I can dump into beta flight when I’m done? I’m in the process of building one.  Any advice would be spectacular

What setup did you end up with? If it's the same then absolutely, if it's close then I can provide what should be relevant.

[Recursion]

Since there was nothing 'new' I wanted to build, I decided to make another Helios this year, but try to see if I could make it better. I've managed to get the flight/video stack 4mm shorter (which is huge), and shave off even more weight. Still doing testing (recent snow has put a dampener on it), but quick test flights definitely feels even more agile, and I'm converting my other one over. Carbon plates are the same, so it's just different stand-offs (18mm) and build.

[FloppyFish]

Since there was nothing 'new' I wanted to build, I decided to make another Helios this year, but try to see if I could make it better. I've managed to get the flight/video stack 4mm shorter (which is huge), and shave off even more weight. Still doing testing (recent snow has put a dampener on it), but quick test flights definitely feels even more agile, and I'm converting my other one over. Carbon plates are the same, so it's just different stand-offs (18mm) and build.

Hello!

I would love to build this! May I ask what FC/ESC stack you used for this new 18mm Standoffs?

---

Hello!

I would love to build this! May I ask what FC/ESC stack you used for this new 18mm Standoffs?