How a Desktop CNC and a Single Lithium-Ion Battery Fixed Tiny FPV Drones

Most tiny 1S FPV quads promise fun in a pocket-sized package and then land after ten or twelve minutes. Battery weight climbs fast once you chase real flight time, frames snap on the second or third hard landing, and the video link rarely reaches beyond a couple of kilometers. One builder decided those limits were optional.

Mediocre Nerd set a high bar for his new project by outlining three specific goals. He wanted a camera that could produce sharp, clean digital footage instead of the soft, analog mess that existed before. He wanted a range of at least five kilometers and an airframe that could sustain a few accidents. As a result of his efforts, he developed a tough three-inch quad dubbed Swift after the little birds that can remain airborne for months without landing.

He began with the frame, which would serve as the foundation for the rest of the structure. Off-the-shelf parts, such as the Crux 3, are extremely lightweight, but they provide little room for mounting gear and crack easily. Rather to go that route, Mediocre Nerd opted to cut his own frames from carbon sheet using a Makera Z1 desktop CNC. Early versions, at 3mm thick, felt unbreakable, but they weighed a ton. Slender frames from common suppliers, which he cut by hand, were as brittle as glass. Finally, he came up with a design that uses 2.5mm professionally made carbon in a tidy deadcat arrangement, with the front arms sticking straight out so the propellers don’t block the camera’s view. To keep the frame from becoming too heavy, sturdy aluminum standoffs and light nylon fittings are used. As it happens, frame kits are now available for anyone else who wants to try this out, saving you from the trial and error.

Instead of the customary tiny LiPos, power is provided by a single, basic lithium-ion battery. There is a cylindrical 18650 that weighs less than 45 grams and provides a full 20 minutes of cruise time. A 5,000 mAh 21700 extends that to 27 minutes, whereas a higher-capacity 21700 kept the motors running long after 30 minutes and was still going strong at 34 minutes before the voltage dropped below 2.4 volts and the telemetry kicked in, which is where the energy density really starts to show. Three small LiPo packs with a similar total weight can only manage around 2,000 mAh combined, thus employing a single cell is a significant advantage.

It wasn’t only an issue of selecting the appropriate cell, as the link was equally crucial. Using standard BT2.0 and XT30 plugs, as well as commercial holders, resulted in a considerable voltage loss under load. So Mediocre Nerd designed a 3D printed tray including huge copper strips and 18-gauge wire, which demonstrated to sustain the highest voltage even after a full-throttle 10-second run. You may swap batteries on the same airframe: there are separate slots for the 18650 and 21700, making it simple to transfer between the two.

When it came to electronics, he understood he needed to match the endurance he’d built into the aircraft. So he went with the Flywoo Goku F405 HD 1S all-in-one board, which has some decent 12-amp ESCs and a built-in ExpressLRS receiver. The video was captured with a DJI O4 Air Unit, which he chose for its great image quality and impressive claimed range. A TPU canopy sits atop the camera and a small HGLRC GPS module, and he added an ND filter directly in front of the lens to prevent blurring from vibrations and to preserve the glass. Assembly did expose a short at first, between a metal camera tab and a negative lead, but a simple coat of liquid electrical tape cured it almost fast.

During testing, motors demonstrated that they were still a work in progress. The earliest flights had GEPRC 1202.5 motors spinning at 15,000 KV on Gemfan Hurricane 3018 props, which powered the thing but guzzled electricity, so low-end torque was limited at reduced throttle. Things really started to improve once he upgraded to RCinPower 1303 motors at 11,500 KV, which were only four grams heavier. They provided him with the desired low-end oomph while also running significantly cooler and more efficiently. The quadcopter can now hover at little around 30% throttle, even with a heavier 21700 cell on board.

Flight testing pretty much confirmed everything. Local short flights on the 18650 cell would typically last twenty minutes. The 21700 cells, on the other hand, required endurance for well over half an hour, and then came the main test: open water with nearly seven kilometers of clear line of sight. He was fortunate to have a tailwind on the outbound leg, which allowed him to travel five kilometers before the video feed and GPS telemetry stopped working.
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