Agile 3" with HDZero

Summary¶

Agile — formerly named SCRAP — is the small, printable 3-inch 4S FPV play/practice platform in the libdrone family. It runs Betaflight, not ArduPilot: manual acro flight, fast to build, cheap to crash. It uses a freely downloadable printable frame, a standard 20×20 FC/ESC stack, and the same ELRS and HDZero ecosystem as Cinematic. A pilot who builds and tunes Agile has directly transferable ELRS/EdgeTX/HDZero skills for Cinematic — firmware and flight model differ (Betaflight manual vs ArduPilot), but the radio and video ecosystem is shared.

Concept¶

What Agile is¶

Agile is the play/practice platform: small, throwaway-cheap to crash, built for stick-time and acro rather than any mission role. It has no payload interface and no defined sensor suite. Its sub-250 g design target has regulatory implications for where it may be flown — see legal-and-regulatory and decide for yourself. It will crash. It will crash again. That is its purpose.

The frame prints in an evening on a Prusa CoreOne+ in PETG-CF. The electronics cost roughly CZK 9,500 total. The build takes one afternoon. The first flight can happen within 30 days of the decision to build.

The printable frame¶

The Whifflepick 3" toothpick frame (Printables model 1207344) is the reference Agile frame. 3 perimeter walls, 3 top/bottom layers, 0% infill, no supports. PETG-CF is the correct material — carbon-fibre-reinforced PETG is abrasion-resistant, available on a standard 0.4 mm hardened nozzle, and stiff enough for 4S loads on 3-inch props. The arms are integral to the frame. When an arm breaks — and it will — the print time for a replacement is under two hours.

The 20×20 mm FC stack mounting pattern is the only dimensional constraint that matters. It is universal across every micro FC stack sold.

Ecosystem alignment with Cinematic¶

Agile shares the radio and video ecosystem with Cinematic, even though the flight firmware differs: - Radio: ExpressLRS 2.4 GHz UART (EP1 Dual or EP2) — same protocol as Cinematic's RP2 - FC firmware: Betaflight — Cinematic runs ArduPilot; this is the one real divergence - Video: HDZero ECO Bundle — same HDZero ecosystem as Cinematic, lighter weight - Transmitter: EdgeTX on TX16S — same as Cinematic

ELRS binding, EdgeTX model handling, and HDZero goggle operation all transfer directly between the two. Betaflight rate-profile and PID intuition built on Agile is manual-acro specific and does not transfer to ArduPilot's flight modes on Cinematic — that's a genuinely different skill, not a shortcut.

Reference¶

Procedure¶

Rationale¶

The decision to build Agile rather than buy a BNF tinywhoop (e.g. Happymodel M8 HDZero) was reached by analysing the actual use case: outdoor pilot practice in variable wind conditions. A tinywhoop at 80 mm wheelbase and 33 g is dominated by wind above 15 km/h and provides no crash resistance in grass. Agile at 130 mm wheelbase with 3-inch props and 4S power handles outdoor conditions while remaining buildable, repairable, and cheap enough to crash without concern.

The choice of HDZero ECO over analog video was made on ecosystem coherence with Cinematic: the same HDZero Goggle 2 works for both. Buying an analog VTX plus an analog receiver module for the goggles would have cost approximately the same as the ECO Bundle while creating a separate ecosystem with no skill transfer value.

The Whifflepick 3" was chosen over the PecaJosef 3" because it is actively maintained, requires no supports (fast reprints), and uses PETG-CF natively.

Naming note¶

This platform was called "SCRAP" (Simple Configurable Repeatable Aerial Platform) through v3.0. Renamed to "Agile" on 2026-09-26 alongside the drop of the Pro/Core/Bandit/Ghost/Wing institutional-tier catalog — the platform itself, the BOM, and the firmware are unchanged; only the naming and the framing (a role-based class rather than an institutional-tier "budget variant") changed.

Connections¶

requires: - [[print-profiles]] - betaflight-setup - lipo-batteries related: - digital-fpv - elrs-protocol - wire-gauge-selection - electronic-speed-controllers - brushless-motors leads_to: - sk-agile-3in-hdzero