Birdbrain RC SKEW_R 5

By CarbonRain on Jan 14, 2019

12  282  3

Hadn't flown the Mahou Shoujo prototype for a while (been doing more freestyle than racing over the past 7 or 8 months), so when I cracked it out for some circuits last weekend I fell in love with how it flew all over again. Planning on doing more race events in the 2019 season, so I decided to revisit the design and whip up something a bit more race-day friendly.

The Mahou Shoujo is a great quad, but its main advantage is also its main disadvantage - it's a very low maintenance build, which makes it difficult to damage but if you do damage it, it's practically impossible to fix on race day. Last race I flew with them, I broke a baseplate in a big crash and had to write off the quad for the day, as fixing it would have required desoldering and resoldering all the motors from the 4-in-1 ESC board, and with only 4 groups at the event it didn't leave enough time for that sort of work between spotting and flying.

As a result, I decided to whip up a frame with the same stretch plus geometry, but in carbon rather than HDPE, with individually replacable arms to make field repairs easy. I also decided to stick with the skinny arm and cross brace layout of the plastic equivalent. Fitting it all together with those constraints was a bit of a challenge until I realised I could make it work if the arms were all rotationally skewed, making the frame asymmetrical. In terms of flying this shouldn't make any difference, as stretch plus quads are already technically asymmetric in nature, having uneven yaw due to the front/back motors being further apart than the left/right pair, something you never notice in the air.

The pod went through a few design iterations, starting with a plain pod I found the FPV camera would foul on the pigtail at the max 60 degree notch (up from the 30/45 degrees on the Mahou Shoujo pods, not that I expect I'll be using it much!) Whilst tweaking that, I added a fin to help protect the antenna by deflecting impacts from close to the connector. What's probably hard to see in the photos is that directly under the pod is a printed shelf for the VTX and RX (both fastened down with velcro), and I incorporated a little V shape for the RX antennas too.

Build was a straight swap from the Kittilyt 6 (excluding the ESC which was new, old one finally called it quits after 6 months of abuse). Happy with the result, it looks pretty tidy and is 40g lighter than the identically built Mahou Shoujo. Time will tell as to how the frame holds up to crashes, but I'm cautiously optimistic (and already have files prepped for slightly stronger parts if required. Just need some good flying weather now!

Photos

Part List

Flight Controller

OMNIBUS AIO F4 V5 Flight Control (16 builds)
Store.myairbot.com
$29.99

ESCs

Anniversary Special Edition Racerstar REV35 35A BLheli_S 3-6S 4 In 1 ESC Built-in Current Sensor for RC Drone (94 builds)
Banggood.com
$34.05

Motors

4 x Motor 2305-2550KV (2-6S) AMAXinno (3 builds)
Eu.amaxshop.com
See Site

Propellers

EMAX Avan S 5042 Bi-Blade 5” Prop 20 Pack - Choose Your Color (6 builds)
Racedayquads.com
$9.99

FPV Camera

RunCam Swift 2 CCD 600TVL NTSC Mini Camera FOV 130/150/165 IR Blocked w/ OSD MIC For FPV RC Drone (404 builds)
Banggood.com
$31.99

FPV Camera

RunCam RC25G FPV Lens 2.5mm FOV 140 Degree Wide Angle for Split Swift Swift2 Mini Gopro Hero2 Split2 (9 builds)
Banggood.com
$12.99

FPV Transmitter

ChaosFPV VTX[T] Video Transmitter (25-800mW, 7-24V, BetaFlight Telemetry) (6 builds)
Unmannedtechshop.co.uk
$18.40

Antenna

Foxeer Lollipop V2 5.8GHz SMA Antenna 2 Pack - RHCP - Choose Your Color (76 builds)
Racedayquads.com
$19.90

Receiver

Frsky XM+ Micro D16 SBUS Full Range Mini Receiver Up to 16CH for RC FPV Racing Drone (1146 builds)
Banggood.com
$13.99

Batteries

Turnigy Graphene 1300mAh 4S 65C Lipo Pack w/XT60 (8 builds)
Hobbyking.com
$20.99

Radio

FrSky R9M 900MHz Long Range Transmitter Module (2 builds)
Taco-rc.com
$59.99

Radio

FrSky Taranis Q X7S Radio w/ Upgraded M7 Hall Sensor Gimbals (Carbon Fiber) (32 builds)
Getfpv.com
$187.99

Radio

FrSky TARANIS X-Lite (Black) (63 builds)
Hobbyrc.co.uk
$132.60

Radio

FrSky R9M 868MHz Long Range Module
T9hobbysport.com
See Site

Goggles

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

HD Camera

Hawkeye Firefly 6S 4K WiFi Sport HD DV Camera - $75.31 |GearBest.com
Gearbest.com
$75.31

HD Camera

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

HD Camera

GoPro HERO5 Session (189 builds)
Getfpv.com
$199.99

HD Camera

GoPro Protective Lens (GoPro Official Accessory)
Amazon.co.uk
See Site

Accessories

TrueRC True-MOX 868MHz Antenna
Hobbyrc.co.uk
$21.43
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Discussion

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Mellowme17   Jan 17, 2019  

curious about this i love plus frames not manh out there can you fit race wire on the arm? looks like fullsize cam... nice work

Mellowme17   Jan 17, 2019  

curious about this i love plus frames not manh out there can you fit race wire on the arm? looks like fullsize cam... nice work

QU|(K_F0X   Jan 15, 2019  
1

Looks like a really well designed frame, good job!

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