Birdbrain RC Cranefly 2.5

By CarbonRain on Jan 02, 2020

23  383  2

I keep coming back to cinewhoops despite my limited success at designing them - the Goshawk ended up for all intents and purposes a heavier, harder to build, more complicated Squirt, and the Hoverfly is a very specialist tiny quad limited by flight time and motors that almost cook themselves in seconds. Having picked up a new GoPro Hero 6, I decided to go back to square one and hope it was a case of third time lucky.


Coming into the design process, I knew I wanted to go for a bottom mount design. I also wanted to make sure to add plenty of mounting points for accessories - too many times I've designed a frame then discovered during the build that adding the HD camera was a huge pain!

The design process was fairly quick, after realising at the start that an inverted layout would let me raise the centre of mass relative to the centre of thrust, keeping the stack height down and also letting me run taller ducts to maximise their effect. I went for 2.5" props as a sweet spot between the proven Shendrones Squirt and Nutmeg platforms, which also left me with a body that nicely fitted a 1000mAh 6S pack (the largest I planned to use on this little quad).

For a quad this size, I didn't feel comfortable running a unibody top plate purely in terms of the amount of material waste, and the cost of material - I opted for 4mm arms and 2mm carbon for everything else, which keeps it nice and rigid. Press nuts were used in the top plate to retain the arms; I added extra holes for accessory mounting, with 9 threaded and 7 unthreaded M3 holes, and a trio of SMA connector sized mounts at the tail.

The bottom plate is similarly laden with mounting points; in addition to the top plate's central 20x20 M3 mount, the bottom plate can take a central single 20x20 or 30.5x30.5, or a pair of 20x20 stacks.

The ducts were designed again following the formulae on this blog post and 3D printed mounts were made for a micro camera up front, and an R9 dipole antenna at the rear.

Alt Tag


For once I picked out some nice components rather than raiding the parts bin for a build, mostly because I wanted to go 6S on this one and didn't have anything suitable on hand! The Aikon ESC is a delight, though the Matek F722's connector has a different pin order which necessitated some reworking of the cable. I ran the VTX on the rear baseplate mount, and decided to try making my own pigtail for it (a right angle MMCX to right angle SMA) - turned out to be easier than expected! In fact the whole build went fairly smoothly, just building the quad upside down, then setting it up with the FC rolled 180 degrees in Betaflight.

Props are cut down Azure 5150s, which look great; I did find with the Goshawk that prop choice made a huge difference on a ducted quad though, much more so than a regular build. Next step will be to fly it - I'm limited to 1000mAh LiPos at the moment but suspect a smaller LiPo will be needed to really draw out the potential of this strange little creation.

Update: flies OK!


Part List

Flight Controller

Matek F722 Mini 2-8S 20x20 Flight Controller (10 builds)


Aikon AK32PIN 32Bit 35A 2-6S 20x20 4in1 ESC (50 builds)


4 x RCINPower GTS-V2 1506 3000KV 4300KV 4-6S Brushless Motor for RC Drone FPV Racing (10 builds)


Azure Power 5150 Tri-Blade 5'' Prop 4 Pack - Choose Your Color (31 builds)

FPV Camera

1200TVL Foxeer Micro Razer FPV Camera PAL NTSC Switchable 1.8mm lens 4ms Latency (4 builds)

FPV Transmitter

Matek Mini VTX 5.8Ghz Video Transmitter


2pcs Foxeer 5.8G Lollipop 3 2.5DBi Omni FPV Antenna RHCP SMA/RP-SMA for RC Drone Airplane (13 builds)


FrSky R9MM Long Range 915MHz RC Receiver - Get Yours Today! - RMRC (78 builds)


Rhino 1000mAh 6S 50C Lipo Pack w/XT60 (5 builds)


FrSky R9M 900MHz Long Range Transmitter Module (2 builds)


FrSky Taranis Q X7S Radio w/ Upgraded M7 Hall Sensor Gimbals (Carbon Fiber) (19 builds)


FrSky TARANIS X-Lite (Black) (67 builds)


FrSky R9M 868MHz Long Range Module
See Site


FatShark Dominator HD 2 Hydro-Dipped Urban Cam Grey and White FPV Goggle
See Site

HD Camera

Hawkeye Firefly 6S 4K WiFi Sport HD DV Camera - $75.31 |

HD Camera

HawKeye Firefly Q6 4K 120 Degree Angle Action Camera - $59.14 | (2 builds)

HD Camera

GoPro HERO6 Black - Waterproof Digital Action Camera for Travel with Touch Screen 4K HD Video 12MP Photos (5 builds)

HD Camera

GoPro HERO5 Session (197 builds)

HD Camera

GoPro Protective Lens (GoPro Official Accessory)
See Site

Video Receiver

Furious True-D V3.5 Diversity Receiver System Firmware 3.8A (FatShark Attitude Version)SKU: FPV-RX-TRUD3.8A (27 builds)


MultiStar Premium Multirotor Travel Backpack


TrueRC True-MOX 868MHz Antenna
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i-man   Jan 03, 2020  

Interesting build.
Do you have some photo of the inside please?
Need to see the maiden.
Will you share the frame?

itsyaboi29   Jan 02, 2020  

Who cut the frame for you.

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