AtomRC Swordfish: Building With 21700 Li-ion Cells
Why I picked the AtomRC Swordfish over the Volantex Ranger 2400, the flight controller I'm using, and the high-energy 21700 Li-ion battery setup for long endurance flights.
Why the Swordfish (and not the Ranger 2400)
I built a Volantex Ranger 2400 first and ran into three things that bugged me:
- Wing connectors carry the flap and aileron servos directly — every wing remove/install stresses tiny pins.
- Tight internals — there's very little space to lay out a clean FPV / INAV stack.
- Wooden centre plate — fine for stock electronics, awkward for a modern flight controller. I designed and printed a replacement plate; happy to share the STL — DM me.
After watching a few build comparisons on YouTube I switched to the AtomRC Swordfish.
The Plane
1200 mm twin-motor EPP fixed wing — light, robust, FPV-ready out of the box.
AtomRC Swordfish 1200 mm — Banggood
Flight Controller
I already had the Matek F722-WPX from another project, so I'm using that:
Note: Matek lists this board as End-of-Life. For new builds in 2026, look at the H743-WING family or the newer WING-FC-405; my reasoning here is purely "use what I already own".
Battery Pack — Why 21700 Li-ion (Not LiPo)
For long-range fixed-wing, energy density per gram beats peak C-rating. A 4S2P or 4S3P pack of high-drain Li-ion cells gives:
- ~250 Wh/kg vs ~150 Wh/kg for typical LiPo → roughly 40–60% more flight time for the same weight.
- Much longer cycle life.
- Safer storage and transport.
The trade-off: you have to respect the lower max current rating and design the pack to never sag below ~3.0 V/cell.
Cells
I'm going with the Molicel INR21700-P45B — 4500 mAh, 45 A continuous, the current sweet-spot for high-drain Li-ion in the FPV/long-range community.
Reference Video
The build/cell choice was inspired by this video: YouTube — long-range cell comparison
Pack Holder
To keep the cells together cleanly without spot-welding mistakes:
21700 Battery Pack Cap Holder 6S & 4S by wrong17 — Thingiverse
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