Featherlight 190 - 245g AUW 5 inch

By Cheredanine on Sep 21, 2017

20  3,391  16

New frame from Aeronaut FPV, 28grams for a 5 inch frame! Built based on previous tests with 5 inch racers, to be honest I could cut some more weight off this by using a lighter vtx, and I used titanium bolts and locknuts for the stack, could also have tried it without the cap, but 245gram AUW with a tattu 850mah 4s lipos is just fine.
Thoughts based on prototypes of this sort of frame-
Weight is very important, there is a temptation to get bigger, more powerful motors, but then you need a bigger lipo and you lose the benefit and may as well have just built another traditional 5 inch quad, stick to 1407 motors at 2800kv-3200 max, use light ones, (there is a variation of about 4 grams between the heaviest and the lightest, doesn't sound much but that is 16grams for 4, that is a 10% increase in weigh ignoring the lipo)
I have tried several props, pure nylon didn't fly that well, Carbon or glass-nylon were much better, 5030 work well, 5045 are a little faster flying but heavier on the lipo, 5040 are the fastest.

first 2 mins of first lipo below, guessed at pids, they can probably go up a bit, think it needs more rc rate and less s rate to reduce expo (you really need more incline than a normal 5 inch to prevent altitude gain) but very nice

Some thoughts if you are considering building one of these:

  1. It is a racer, it is fast, it doesn't do slow (because of the physics involved). It has massive agility but see point 2.
  2. It has far more agility than a heavier quad. But to get it to work it needs to be canted over hard. You fly with a very steep camera angle and you really need to throw the stick into pitch and roll, hence my statements above about removing some expo from what I would normally fly, particularly on pitch and roll. It is a bit like formula 1 cars where you have to go fast round corners to get enough down force to actually make the corner, the more aggressively you fly this, the better it responds
  3. I can't stress this one enough. There is a temptation to think "ooo I could put efaw 1806 or pyroflip 2204 3022kv on it". Don't. You put those motors on, you need a bigger lipo, then you think more aggressive props, your lipos gets bigger still and you are back to a conventional racer. Stick to light 1407 motors, the rotorgeeks 7075 are great, if I could have easily got my hands on the cobra 1407 3200kv readily I would have tried those but as per thread below, 3200kv is possibly a little too high for 4s. If t-motor ever do an F20ii at 3000kv, take their hand off

all the parts I used in the frame came from my previous sub 250 gram 5 inch build. Which I spent a lot of time testing parts on, those thoughts, particularly points 2 and 3, are the most important thing to get your head around. I am sure some of the serious race set will try and develop this style of quad further and give far more relevant advice in time

Edit : motors - having tested a lot, the best performers for 4s are the cobra champion 3200kv, the actually kv of these is closer to 3000 which is about the sweet spot


Part List


Aeronaut Fpv (2 builds)
See Site

Flight Controller

Asgard V2 Flight Controller (integrated Omnibus F4 FC, 4x 24A Dshot ESC, OSD) (2 builds)
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4 x Rotorgeeks 7075 Series 1407 2800kv


HQ 5x4 (4 pack) (2 builds)

FPV Camera

RunCam Micro Swift 2 600TVL Cam with OSD (3 builds)
See Site

FPV Transmitter

TBS Unify Pro HV Race (10 builds)
See Site


TBS 5.8GHz Linear Antenna (U.FL) (6 builds)
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FrSky XM+ Receiver (EU) (9 builds)
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Tattu 75C 850mAh 4s 14.8V Li-Po Battery with XT60 connector
See Site
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tykkah   May 25, 2018  

I have a choice between BH1407 2800kv and t-motor 1408 2800kv. Which you think would work better on this frame?

Cheredanine   May 25, 2018 

i would take the t-motor, should have slightly more torque

IvanNik   Mar 12, 2018  

I'm very impressed by your Featherlight build!!!

Recently I did light build https://rotorbuilds.com/build/8126 but it's so heavier than yours :))

I have several questions/ideas:

  • What do you think about stretch-X layout with the same weight/frame factor?
  • What do you think about mounting battery on top?
  • Could you compare Featherlight 190 with your latest PROton build (speed, maneuverability, which do you prefer)?
Show 5 more comments
IvanNik   Mar 27, 2018 

What do you think about my mock: https://rotorbuilds.com/build/10851
already ordered carbon cut.. I'm interested to compare side by side..

Cheredanine   Mar 27, 2018 

hard to tell from the mock up how mach carbon is in the middle, but concenrs would be too much (adding weight) or two littoe allowing twisting or breakage, but as i say cant tell from the mock up

IvanNik   Mar 27, 2018 

agree, main plate is 4mm + additional bottom plate 1.5mm. Let's see the final frame.

Carbon_Rob   Sep 21, 2017  

Have to ask the obvious question, how does it crash?

Cheredanine   Sep 22, 2017 

It's a fair question, and I will have to give it more crashes/time to give a definitive answer. However, it is 5mm carbon, it has less flex than racers with 3mm carbon plates, it is under 250grams AUW and the forces in a crash are directly proportional to the mass, your average 5 inch goes for about 400grams to 600, this being half that, the forces involved when it crashes are halved. My previous sub 259gram 5 inch has the same width of arm. I have crashed that a fair amount, without counting the damaged props, it has twice wrecked motors in crashes and the frame, other than scuffs on the carbon, has survived completely intact

Carbon_Rob   Sep 22, 2017 

That's impressive! I'm continually shocked at how well my light weight crafts take crashes. Like you said, force is proportional to mass. I didn't realize that was 5mm carbon.

Querk   Sep 21, 2017  

I see you ended up going with the lower kv variant of the rg 1407s, how do they compare to the 3200kv? Do you think this setup has an advantage over a 4in quad?

Cheredanine   Sep 21, 2017 

Hi mate, rotorgeeks kindly sent me both to test (3200 and 2800kv). It was very prop dependent, on both 5030 and 5045 the 3200 were slightly faster although there was a bit of a plateau at the top end on 3200 with 5045, 5040 were the fastest props but the 3200kv at WOT were again plateauing and kicking the hell out the lipo, with dramatic voltage sags. On 3s you get a fast agile quad with good flight times with either so would probably run 3200 for that extra bit of speed, if you want the fastest though with viability for racing on 4s then 2800kv with 5040 props is the sweet spot.
The best quads I have (and I have a lot) are my kinetic aerial air-ro running F20ii, they match most of my 5 inch for speed but have the agility of micro due to the low weight. Thirs sort of 5 inch have the same agility but more speed. Hence for freestyle/acro an ultralight 4 inch with F20ii is, imho, pretty unbeatable, but this has an advantage for racing (assuming the track allows you to use the speed)

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