Pirx Seven – The ultimate custom 7-inch FPV frame, part 1

Do you know this old saying “If you want something done right, do it yourself”? I do and sometimes I just live according to it. Not always, I’m not crazy, but at least from time to time!

I fly 7-inch FPV drones a lot. To be honest, they are my favorite flying devices. There are a few good 7-inch frames, like TBS Source One for example. There is a difference between good and great tho. I do think that Source One is a good frame, there are a lot of things on it that do not make me very happy tho! The list might not be very long, but it is relevant:

  • props in the view
  • limited space to install split-like hybrid cameras
  • no very convinient place to install VTX
  • it’s not that big inside as one might imagine…

Because of that, and because I think I know how to do it (I’m an engineer) I’ve devided to design and manufacture my of 7-inch FPV drone frame that would fix what I do not like in Source One.

This is how Pirx Seven was born!

Pirx Seven - 7-inch FPV drone frame

  • Dead Cat configuration
  • Plenty of space inside for everything you want! There is even a place in the back to fit the whole 30x30mm stack!
  • Place for Split-like hybrid camera in the front
  • Attachable mounts for antennas, GPS and other accessories
  • Clear, unobstructed view for HD camera like GoPro on the front deck

So far, I was able to mill a prototype unit to test it in flight. So far so good, I really have to say that I like what I designed.

Pirx Seven - 7-inch FPV drone frame

Fully assembled frame weight 205g with steel screws and aluminium standoffs.

Pirx Seven - 7-inch FPV drone frame

What next? Test flight and some changes. The full list consists of 12 points in total and basically means that I will have to redesign almost everything…

If you want to know why the name and what does Pirx stands for, here is the answer. It’s a tribute to Polish writer StanisÅ‚aw Lem and his book Tales of Pirx the Pilot.

Your first 7-inch FPV drone

I love 7-inch FPV drones and during the last year, they were my most used FPV gear. For freestyle, cinematic, cruising and long-range. I currently own 3 7-inch FPV drones and 4th one in the assembly process.
I think of myself as a 7-inch expert. I’ve wasted enough money and equipment to know what works and what does not work well with 7-inch propellers.

TBS Source One 7-inch FPV drone

If you are thinking about building your own 7-inch FPV drone, here are some tips that might save you a lot of time and a lot of money on wrongly chosen equipment.

The Frame

Of course, the frame is the most important part of a build. No matter if you will be building a freestyle or long-range rig, there is one thing that you have to know: Horizontally scaling 5-inch frame by making arms longer is a no-go. Longer arms require more stiffness and they also have to be thicker! The sweet spot is 6mm thick good quality carbon fiber. 5mm thick might work too but forget about 4mm or thinner arms. They will be too flexible and the whole quad will be in a state of a constant wobble!

Alfa Monster 7-inch FPV Frame

If you are looking for 7-inch frame recommendations, here are my choices: Team BlackSheep Source One with 7-inch arms, Alfa Monster and AlfaRC Fighter.

Propellers

Kind of obvious, right? The choice of good 7-inch propellers is not that big as one might imagine. Sure, you can buy some “inventions from 4 years ago for cheap” but believe me, they are not worth it. There are 3 types of modern 7-inch propellers that I find worth looking at in late 2019:

  • DAL T7056C – good for freestyle and thanks to aggressive pitch they are very dynamic. Can be used no longer flight, but this is not where they really shine.
  • HQProp Durable 7x4x3 V1S – a more aggressive version of 7×3.5×3 that in my opinion works much better than original. Slightly more pitch only helps during steady flight. They are rather for cruising than for freestyle.
  • GemFan FLASH 7042 – kind of good propeller, but don’t get me wrong, you should try 7042 only if DAL or HQProp are too heavy for your motors. So if you have 2207 or 2306 you might try FLASH. If you have bigger motors, just go with DAL or HQProp.

Motors

Brotherhobby Avenger V2 2507

Probably the most often made mistake by the “7-inch virgins” are too small motors. Beginners think that putting the same motors that work great with 5-inch propellers on a 7-inch frame is a good idea. OK, maybe sometimes they lower the KV. This will not work. I know. I tried that by myself and only wasted some money and a lot of time and nerves.

What you need are big motors. In a size of 2506-2507. 2208 might work as well and 2508 is rather the max size that makes sense.

On the KV size, the rule of thumb is that on 4S you should aim at 1500-1500KV and on 6S at 1200KV. Those values give a nice compromise between efficiency and raw power. Of course, this is only a rule of thumb and when needed you might choose higher KV. For example, my 7-inch freestyle drone uses 1700KV on 4S motors.

My recommendation is rather simple: for now, there is only one motor that comes is wide enough KV range and it’s called BrotherHobby Avenger v2 2507.

Everything else

For the rest of the equipment, you can choose whatever you want. Any equipment will work and you do not have to match it to the propeller size. My choices are:

Armattan Marmotte Schmarmotte

This is my second adventure with Armattan frames. The first one was Rooster. And it would be great if not moving arms. I yielded again and got me an Armattan Marmotte this time. I recorded this video before flying it. When I write those words I already know how it flies. It flies good, but I still have to tune and update motors to something more modern and not beaten up. In other words: Armattan Marmotte is great in the air but some of the design elements are extremely bad!

7″ FPV frames – window shopping on Aliexpress

7-inch FPV quadcopter drones are getting more popular and because of this, Chinese manufacturers are finally putting new frames on the market. While even 6 months ago the choice of 7-inch frames was very limited, now you have at least a half-dozen choices when you want to buy cheap from China. Let’s go to Aliexpress and do some window shopping (not licking 😉 )…

Frames from this video:

First glance at Armattan Rooster FPV quadcopter drone frame

After flying chinesium (XMR250, Reptile X4R 220, Martian II) and frames from DemonRC I’ve decided to switch to completely different brand. My choice is Armattan Rooster, the newest freestyle frame from Armattan.

Armattan Rooster FPV quadcopter drone frame

Armattan Rooster FPV quadcopter drone frame

Armattan Rooster FPV quadcopter drone frame

Armattan Rooster FPV quadcopter drone frame

Armattan Rooster FPV quadcopter drone frame

Armattan Rooster FPV quadcopter drone frame

Armattan Rooster FPV quadcopter drone frame

Armattan Rooster FPV quadcopter drone frame

Rooster arrived few days ago, and this is what I can say about it before putting all the stuff into it:

  • sunken nuts you have to install by yourself are a very idea. It’s hard to do without tools and skills. It would be much much better is they were preinstalled. Armattan, please, fix it!
  • additional pair of standoffs between plates would not hurt
  • it is tight inside and I will have to be creative to fit X4R and TBS Unify Pro in the back of the frame
  • frame itself looks good tho. I might even say it is pretty

3D printed racing drone, part 3

It is done. It is alive. My 3D printed FPV racing drone works. A few weeks ago I finally flight tested my design and it works! Even better than expected, since I survived the experience without a scratch. OK, I did not crash it yet, but give me some time for that too….

3d printed fpv racing drone

And I have a cool name for it: Isando which means hammer in Zulu. Kind of fits, right?

Ah, STL files are available on Thingiverse of course.

3D printed racing drone, part 2

My 3D printed racing drone is done. More or less. I was able to finish it a few weeks ago and even perform a maiden flight. It survived the experience, but I also discovered few problems I will have to solve before officially calling this project a success.

3D Printed Racing FPV Drone

3D Printed Racing FPV Drone

First of all, the decision about hard mounting a flight controller and not installing a capacitor on mains was a bad one. Not only motors are “twitching” from time to time, a video is very noisy. I hope big low ESR capacitor will solve that, since there is no way for soft mounting for this frame.

3D Printed Racing FPV Drone

Besides that, it worked just fine. I will try to prepare a video from the maiden flight in a few day, for now only a few pictures and final specification:

  • Frame: PLA 3D Printed, 220mm motor-to-motor diagonal
  • Motors: EMAX RS2205S 2300KV
  • ESC: Racestar RS30A BLHeli_S
  • Flight controller: FrSky XSRF3O running Betaflight 3.2
  • VTX: TS5823 200mW
  • Camera: RunCam Swift
  • Total weight, no battery: 380g

Total build is, of course, heavy, but not that heavy as I feared. I was expecting something way above 400g. The frame is also quite stiff. I wonder how much beating it will be able to take….

3D Printed Racing FPV Drone

EXUAV Y120S drone racing frame: go home designer, you are drunk

Chinesium is amazing. Well, to be precise, not only chinesium manufacturers will do anything just to stand off a little. Just like this little (120mm) quadcopter frame called EXUAV Y120S. Why do I even bother to write about it? Simple: I love crazy designs. Just look at those pictures below:

EXUAV Y120S 120mm Mini racing frame

No, it’s not a tricopter. It is a quadcopter. But where is the 4th arm and where 4th motor goes? Below rear motor! It’s a Y with 2 motors on arms in the front and 2 motors on one arm in the back. Rear motors are counter-rotating! Read More

3D printed racing drone, part 1

I've been pretty busy last 2 weeks. Among other things, I've started to design 3D printed racing drone frame. I'm fully aware there are plenty designs available on Thingiverse, but almost all of them forgets that plastic filament is not carbon fiber laminate and what works well with carbon, will fail with filament. So, I came up with this:

3D Printed Racing Drone

3D Printed Racing Drone

  • suitable to 220x and 230x motors with 19x16mm hole spacing
  • fits PCB and 36x36mm flight controller (30.5mm hole spacing)
  • size: 220mm motor to motor (diagonal)
  • fits "standard size" FPV camera

It is heavy for sure. It has thick arms and a lot of M3 nuts and bolts connecting all the parts together. I hope it will be enough to survive at least some beating… First flight in a few weeks since I'm still waiting for motors.