RXUF|RotorX Ultra Fox

By Minichado on Nov 20, 2018

16  819  7

I was super excited to get this build done, even though I don't have all of the planned parts yet!!! the PL below is what the final form will be, at the moment I'm short a nano RX crossfire receiver and my GPS module. I also had ordered another flight controller I was hoping to use but I had some available hardware on the bench so I went with it. I had some 2407 2500kv motors that could have turned the 7' props but were a touch too aggressive KV wise, I decided to pick up some 1700kv 2207 from zerocool (thanks man!) and I feel like that was the best choice.

The goal of this is to be an ultra long range cruiser. This is entirely new territory for me. I fly racers that weight 400gm AUW, like a bat out of hell, from full to dead in 2:30. This setup has a battery that weighs 436gms on it's own!!!! We ended up clocking close to 950 grams, which is over 2lbs, in the air!!! With that I expected it to feel like a boat. a very slow boat. I didn't really know what to expect w.r.t. throttle response from the maiden flight. more on that later.

Thoughts on the Build
The frame is just long enough that you are going to have to extend motor wires to reach a 4-1 ESC, which is what I prefer these days. So I ended up using race wire not for ease of motor swapping, but for a clean and simple method of extending the motor wires. it got the job done!

While the frame does have a cutout where you can drop a stack down into a pocket (7mm carbon + Ti plate so it's roughly an 8-10mm pocket) my particular ESC did not fit down in there well. That worked out OK, as I was still able to raise up the stack and build on top of that and had room to spare underneath the pod. There are a number of tricks and various component choices you could make to maximise the space available inside of this pod, I did not make those choices. but even choosing poorly matched components I was able to make it work. That said, an ESC or stack that has a square footpring is 100% fine. Anything with a tab sticking out for main battery leads (like a PDB or 4-1ESC) might run into fitment issues. Be aware and plan accordingly.

Maiden flight was in 40 F weather, which is starting to get into voltge drop due to cold weather territory, but even so I was able to clock a 20:34 maiden flight. in flight (under load) the voltage was sitting around 3.55v/cell when I landed. It settled up to 3.67v as soon as I landed (in the cold). I' could have pushed a few more minutes of flight out and even then in warmer weather you might get a bit more still. Essentially it has far exceeding my expectations. 20 minutes is so long of a flight that you can wear out a spot pretty well.

Thoughts on setup
I did not push throttle too hard, but 2207/1700kv on 7056 felt adequate enough that you could respond and change direction in a bind as needed. I cruised straight towards a tree then punched out over it late to see how quickly it could change direciton. When you ask it to go, it goes.

The cruising speed was much higher than I anticipated. This is my first time flying 7" props, so yea, no previous datapoints, but 30-40% throttle it felt like I was cooking it 40-50mph (will verify later with gps).

I am running a 20-25 cam angle with what I think is a 20 gopro angle at the moment. even at the relatively high cruising speed, she felt easy to control, and manouverable. I resisted all urges to split S and punchout. It was very difficult :D

Final note is betaflight 3.5.5. freshly flashed on an f4 board, I did not have any noticeable bobbles/propwash/nada. I'm still reviewing goprofootage and will likely update the PID tune some, but if you didn't know any better watching the footage you might think it's just another 5" rig.

&

Photos

Discussion

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n_dietz88   Nov 23, 2018  

how/where do you get the 7" version!? thanks and nice build!!

Minichado   Nov 23, 2018 

rotorx sold them as a limited release, it was announced on the FPV show and they sold out pretty quick. they also sell a 5" RX Atomix fox (which I put as the frame link, there is no current link for the 7" frame) and they sold arm upgrade kids for that. You can try and shoot them a message on fpv slack or instagram and they can let you know if it's possible to get something together for you. great group of guys!

jdmkramer   Nov 22, 2018  
1

I watched the maiden when I saw it in slack and I knew that hum sounded familiar! The resonance of 7" I thought, but in fact it was the same motor and prop as well. I love that setup on my Ragu. Awesome build!

FrenchB   Nov 20, 2018  
1

nice build and maiden

Minichado   Nov 22, 2018 

thanks!

Showusflight   Nov 20, 2018  

A new Texas neighborhood is a good place to fly. Looks like it anyway. Great build.

Minichado   Nov 20, 2018 

lol not texas but yea wanted to maiden in a familiar location

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