Like many drone enthusiasts, I sometimes push my equipment to its limits, and occasionally, things break. In my case, it was the AIO board on my trusty 4″ Rotorama build. This mishap, coupled with some less-than-perfect arm modifications (user error, definitely!), led me to retire that frame and embark on a new project: a 3.5″ build centered around the popular AOS 3.5 frame, known for its lightweight design and suitability for 3D printed parts and efficient power setups, often utilizing an XT30 connector.
My goal was to salvage the still-functional components from the 4″ build and create something nimble and fun. Key criteria for the new frame were compatibility with FPV Cycle 16mm motors (size 1606) and flexibility in stack options – either a 30.5mm stack or an AIO. However, learning from my recent AIO board failure, I decided to steer clear of another AIO for this build. The thought of potentially scrapping an entire board due to a single component failure pushed me towards a more modular 20mm or 30.5mm stack setup.
After extensive browsing through designs on CNC Madness and other platforms, the AOS 3.5 frame truly stood out. The latest O3 iteration seemed particularly appealing, and the fact that it was available in different colors sealed the deal! Aesthetics matter, right?
For the electronics, I was torn between the SpeedyBee F7 mini stack and the Diatone Mamba F405 Basic Mini Mk IV stack. Ultimately, availability in Europe (I’m based in Sweden) led me to choose the Diatone Mamba.
The camera was already in my parts bin – a Foxeer T-Rex 1500 TVL. Despite limited reviews, the positive feedback I found convinced me to give it a try. And I’m glad I did – the image quality is fantastic!
The motors were also readily available: FPV Cycle 16mm white motors. Unfortunately, the wires were a tad short from their previous life on the 4″ build, especially for the rear arms. While two motors had sufficient wire length, the other two needed extensions. I considered TinyLED racewire, but it felt a bit too thin for my liking on the AOS arms. Cutting the motor wires so close to the motor also made me uneasy. So, wire extensions it was.
Soldering isn’t my strongest skill, but I can handle basic tasks. I opted for 20 AWG battery wires for the extensions, as I had them on hand. The original FPV Cycle motor wires are 24 AWG, which I didn’t have readily available. Using my Omnifixo soldering helping hand, I carefully aligned the wires and created a stable solder joint. Two layers of shrink tubing provided robust protection against flexing and fatigue at the solder points. I’m quite pleased with how clean the wire extensions turned out.
Alt text: Close-up of a cleanly soldered motor wire extension on a white FPV Cycle motor for an AOS 3.5 drone build, showcasing robust shrink tubing.
For video transmission, I reused a TBS Triumph stubby antenna from the 4″ build. I fashioned a simple antenna bracket to mount it securely. The Sixty9 Crossfire receiver was also carried over and mounted on the aft 20×20 location on the frame. The standard Immortal-T antenna for the Crossfire was zip-tied to the front arms, tucked neatly underneath. I haven’t rigorously tested the link quality at distance yet, but if it performs reliably out to my usual 500-meter range, I’ll be satisfied.
The dry weight of the build came in at 188 grams. Switching to 1404 motors might shave off 12-15 grams, but I’m a big fan of the FPV Cycle 16mm motors, so they were an easy choice for this AOS 3.5 XT30 project.
After the build was complete, a quick maiden flight confirmed that everything worked as expected. Since that initial test, I’ve addressed a minor issue with link quality, adjusted the camera angle, and ordered more 850mAh batteries to extend my flight times. This AOS 3.5 frame is proving to be a fantastic platform for a lightweight and agile 3.5″ FPV drone.
Alt text: In-flight shot of a custom-built AOS 3.5 inch FPV drone during its maiden flight, highlighting its compact size and agility.
Maiden Flight:
