KUNHD3-X8 Caddx Vista 3" X8 Octocopter

By Jayembee67 on Jul 26, 2020

12  288  9

This is mostly @kwadekenstein's fault, of course... Having seen a couple of 3" X8 octocopters here, I almost felt obliged to give it a go myself. I could have gone the Shendrones route, but really preferred the idea of taking a more DIY approach - and having managed to pull off a couple of large scale X8 kit-bashing builds, I began to trawl the interwebs in search of a suitable frame.

I was looking for something with a dual stack configuration as there were going to be two ESCs, and I wanted to use Caddx Vista which whilst smaller than the DJI Air Unit, is hardly slim. In the end I happened across this Phisital KUN HD3 (yeah, I don't know, your guess is as good as mine) 3" frame on Amazon, and unexpectedly it looked like it would fit the bill. It has dual stack spacing and is actually designed to hold a full sized Air Unit on a little shelf, so I presumed there would be plenty of vertical height to get everything in there. And so ordered a couple of the frames...

(...This is the real problem with X8 machines; the doubling up of the frame, motors, ESCs... they are not cheap and cheerful builds, even using obscure import frames and middling motors. Ack, my poor bank balance. Any road up)

When the parts started to arrive I started to do layout and printing, and spent a week on that aspect of the build, by far and away the majority of the build time. But a build like this needs a lot of parts, and I tend to have to do a lot of trial-and-error printing and fitting, all of which takes aaaaaages. I did shortcut the bottom plate spacer though; I drew around one of the plates, scanned it and created an SVG, and then imported that into TinkerCAD. It wasn't very precise, but it was a lot quicker and easier than attempting to build that shape by hand in TC. And it printed right first time. So that is a technique I shall use more in the future.

Once I had everything printed well enough to pass muster, I set to with the actual soldering iron work, something I like less and less as my eyesight gets poorer and my hands shakier (Lesson for today kids: Don't Get Any Older!) particularly with 20x20 hardware. The ESCs are fine, nice big chunky pads, but those little FCs are getting less fun with each build. Still, having said that, the Matek F277 uses the edge-groove pads (I am sure there is a proper name for them) and that made soldering up the FC surprisingly easy. The 4 surface pads for motors 5-8 were an exciting challenge, but overall, the FC was a good deal less awful than I had feared.

Amazingly everything worked first time, this is pretty much unheard of with a normal build, let alone something nominally twice as complex. And this FC does indeed support DSHOT on all 8 signal pads, most excellent. So I got to build a proper contra-rotating X8 with proper DSHOT control. The only issue I have is that I used iFlight Succex ESCs which I was expecting to be BLHeli_32, but when I plugged in, they were BLHeli_S (maybe I was sent the wrong ones? Maybe I'm an idiot? Likely the latter...), so I can't try RPM filtering on 8 motors yet. Although that might be horribly ill-advised anyhow.

Regardless, it hovers, does all the video sending and receiving one expects, and was buzzed around the back garden successfully LoS. As with my other contra-rotating X8 machines, it makes a heck of a noise in flight, but it also looks like it has that locked-in thing going on. Hopefully I shall get to test it properly soon and find out for sure.

UPDATE 2020-08-06
I built this machine with the intention that it would be a Hero7 Hauler - and it does fit that bill, but with the H7 on board, it's a bit too heavy, a bit too power hungry, and bit too sluggish. Which is a shame, you could feel it champing at the bit, but when you opened it up, the battery drained fast. I was watching the throttle and the battery voltage all the time, which wasn't that much fun. I know I intended a small cruiser, but it had more to offer.

So I took the H7 off and replaced it with the much inferior but still stabilised, and most importantly much lighter, Insta360 GO just to see what it would do. And that's much more like it. I can now get 3:30-4:00min of vigorous flying out of a 1300mAh 4S pack, and the machine flies really well - all those props grip the air very nicely; you can throw it about in a very agreeable manner.

The Insta360 GO footage is low res, low frame rate and entirely mediocre looking, but the quality of the stabilisation and the CinemaScope-y aspect are great, so the trade-off for the weight saving is not a wash. I imagine this is how this setup will be flown going forwards. Because it's really good fun now!



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Jodie Froster   19 days ago  

This thing is stellar!

Jayembee67   19 days ago 

Thank you! Yes, it's been a good project, and because I took so much time, actually surprisingly painless, given all the wire stuffed into such a small volume. I'm pleased with it - now whether I will actually fly it much, that's another question. But it looks great on the shelf, at least. ;-)

Jodie Froster   18 days ago 

Why would you not fly it?

Jayembee67   18 days ago 

Actually, after testing it yesterday, I have shifted my opinion and now think I might be flying this quite a lot! It was really more fun than I had expected! :-D If I can just get a bit more battery life out of it... I put on some less aggressive props today, I might get to run some further tests this afternoon if I am lucky. I also just reprinted the GoPro mount - I had originally set it to 25º but the machine wants more of an angle than that, so 30º it is. More news when I have it to share.

DoubleJackOnTap   19 days ago  

Wow! Very nice. Im super impressed with the cable management.

Jayembee67   19 days ago 

Thank you! Yes, there was a lot of wire to wrangle, but ultimately a fun and satisfying build. And it flies too, which is always a plus! ;-)

kwadkenstine   20 days ago  

Good work , Im impressed!!!

Jayembee67   19 days ago 

Thank you! Although we shall have to see how well it actually flies, of course; although it does fly, which is encouraging. But yes, it came out pretty neatly and has a nicely chunky aspect - I kind of reminds me of one of those very colourful jumping spiders; kind of squat, sort of ugly-cute, and a little hydrocephalic.

kwadkenstine   20 days ago  

Its so cute

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