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AOS 3.5


The latest version of this frame is the AOS 3.5 EVO. It soft mounts the FPV Camera, supports ND filters with DJI O3 and fits 14-20mm FPV cams (14mm uses a 3D printed mount, STL provided below).


Built to go toe to toe with 5" Freestyle quads. Smooth, responsive, and able to carry an Insta360 Go (or similar) and still come in under 250g.

  • Approx. 50g with all hardware

  • Designed for up to 3.5 inch props

  • 160mm wheelbase

  • 4 mm Arms

  • One 25.5x25.5 or 20x20 mm stack in the front and one 25.5x25.5 or 20x20 mm stack in the rear OR

  • One 25.5x25.5, or 20x20 mm stack in the centre

  • Fits the Caddx Vista, WS Avatar or DJI O3 Air Unit perfectly

  • Fits both 20mm (DJI camera) and 19mm (Micro sized) cameras

  • Motor mounting 9x9 up to 12x12 (1404, 1504, 1505 recommended)

  • Standoffs, carbon and hardware included

AOS 3.5 EVO XT30 Mount

VTX Antenna Mount M2

AOS ELRS Antenna Mount

AOS EVO Camera Mounts

M2 SMA VTX Antenna Mount

AOS 3.5 Arm Bumper

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WHY 3.5"

Maximum flight performance under 250g


3.5" Props give you the maximum performance
for freestyle flying under 250g

The AOS 3.5 was born from an analysis of quadcopter weight against prop size. The result was the identification of disc loading as a key parameter that could be compared between quads of different sizes and was a strong predictor of flight performance for freestyle flying.

By looking at the flight performance of a large number of quads it was possible to identify the ideal disc loading for a freestyle drone and thereby calculate the ideal prop size for an FPV freestyle drone of a given weight.

When that analysis is performed for 250g the ideal prop size turns out to be very close to 3.5" and several good 3.5" props are available.


In that moment the AOS 3.5 was born!

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Understand the design methodology behind the AOS 3.5 V2

Harmonic analysis, topology optimisation. 

I used Blackbox logging and harmonic analysis to visualize the vibrations of the AOS 3.5 during the design process. I combined this with topology optimisation to tune the geometry of each part of the frame, moving the frame resonances up and away from the motor frequencies and separating them as far as possible. This avoids, as far as possible, the situation where the motor frequencies match a frame resonant frequency and so amplification is minimized.

As a result, you can run less filtering. Every layer of filtering adds delay that’s mathematically related to how effectively it removes vibrations. This delay prevents the flight controller from responding rapidly enough to propwash leading to poor propwash handling. Reducing the amount of filtering is the best way to improve propwash handling. With the AOS 3.5 you’ll be in the best possible position to reduce your filtering to an absolute minimum.

Another advantage of lower noise is the ability to run higher PID gains. Higher PID gains allow the quad to track your stick movements with less delay and more precision. The result is greater confidence, particularly when flying tight lines where fast reactions are vital.

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See the key features of the frame

Key Features

Top and bottom plates

The 2mm thick main plate supports a central full-sized 25.5 or 20mm stack. Alternatively you can run two 25.5 or 20mm stacks, one in the front and one in the rear. The M2 20mm holes are designed to be easily drilled out to M3 if required.

The cut outs in the top and bottom plate of the AOS 3.5 are optimized to preserve as much of the bending and torsional stiffness of the plate as possible whilst minimizing weight.

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The AOS 3.5 uses a topology optimized truss design for the arms. This truss design provides enormous torsional stiffness, resolving a key source of vibration in traditional frames. It also allows two particularly harmful resonant modes to be individually modified to separate them in frequency.

Truss structures are inherently very strong as they convert bending loads into compression and tension in the individual members. Carbon is much stronger in pure tension and compression than in bending. The 3 screw motor mounting reduces weight and removes the motor hole that can be a stress riser for compressive failure in hard crashes. 


Y-shaped motor protectors minimize the risk of damage to those expensive components. Should you ever need to replace an arm, there are only two screws to undo and neither are shared with your electronics.

Camera Protection

The AOS 3.5 uses 2mm Carbon Plates to hold and protect the camera. These are stiffer, lighter and cheaper to replace than aluminum or titanium.


The camera plates include 2 standoffs to maximise durability and a cutout pattern that supports DJI O3 and all typical19-20mm FPV cameras.

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Go Pro Mount

The AOS 3.5 has 32x32 mm M2 mounting holes for 3D printed mounts for your HD camera.

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