Ghost variant

Summary¶

libdrone Ghost is the quiet, long-endurance variant of the libdrone family. Two engineering decisions define it: large low-KV motors driving 12-inch props at low RPM reduce acoustic signature substantially compared to any other family member, and Li-Ion 18650 batteries replace Li-Po for energy density over peak power, yielding 30–45 minutes hover endurance. Ghost reuses the complete Bandit electronics stack — ArduPilot, ELRS MAVLink, QGroundControl, mandatory ESP32-S3 IFF bridge — with a new laser-cut CF plate arm architecture scaled to the 12-inch prop class.

Concept¶

The acoustic argument¶

The dominant noise source in a multirotor is propeller tip speed. Tip speed equals RPM × π × diameter divided by 60. A larger disc area moving the same mass of air requires less RPM for the same thrust — and lower RPM means lower tip speed, which means substantially lower acoustic emission. A standard 6-inch drone at 50 m produces approximately 65–70 dB(A) at the ground. Ghost at the same altitude produces approximately 50–55 dB(A) — roughly half as loud to the human ear. For operations where the drone's presence should not be obvious to casual observers, this reduction is operationally significant.

This is not stealth in a technical sense. Ghost can still be detected by attentive observers at close range. It is a meaningful reduction in the passive acoustic detection range — the distance at which a drone's sound is the first cue that it is present. See → acoustic-signature-design for the physics derivation and design rationale.

The Li-Ion choice¶

Ghost uses a 4S2P pack of 18650 cells rather than a LiPo pouch. Li-Ion cells carry more energy per kilogram than LiPo at the cost of lower peak discharge current. For a survey platform carrying large props at low RPM, peak current demand is low — this is exactly the operating profile where Li-Ion's energy density advantage materialises without the discharge rate becoming a constraint. The result is 30–45 minutes of hover endurance from an ~436 g battery pack. See → li-ion-batteries for chemistry and construction detail.

CF plate arm architecture¶

Ghost's 12-inch prop class requires arm stiffness that 3D-printed PETG or TPU cannot provide at the required span. Arms are laser-cut 2 mm carbon fibre plate sandwiches — two plates per arm, clamping onto the existing 3 mm CF rod system. This makes Ghost arms non-printable by the community but field-repairable without tools: unclamp, slide, reclamp in under 15 minutes. See → cf-plate-arms for the DXF geometry and fabrication detail.

IFF and ESP32-S3¶

The ESP32-S3 companion board is mandatory on Ghost. It runs three concurrent firmware tasks: MAVLink-to-CoT bridge (feeding position and attitude to ATAK), EASA Remote ID broadcast (WiFi NAN + BLE 5.0), and IFF GPIO interface for future allied hardware modules. An EMCON kill switch on the body cuts all ESP32-S3 RF emissions simultaneously — flight operations and the independent IR strobe are unaffected. See → esp32-s3-companion and → iff-architecture.

Reference¶

Shared SKUs with Bandit: Matek H7A3-SLIM, SpeedyBee BLS 50A, EP2 Nano, Foxeer Predator Nano, Foxeer Reaper Nano V2, Matek M8Q-5883, 3 mm CF rods.

Procedure¶

Rationale¶

Ghost was designed to answer the question: what does the threat sound like from eighty metres? The awareness curriculum (Bandit) teaches operators to detect drones by sound. Ghost was designed to be the hardest platform in the family to detect acoustically. Flying Ghost and then measuring its own detection range using the Bandit awareness exercises closes the loop: the student learns to detect it, then builds and flies it, and measures what they built. The platform is both the answer and the instrument.

Connections¶

requires: - platform-overview - bandit-variant - ardupilot-copter related: - platform-selection - acoustic-signature-design - li-ion-batteries - cf-plate-arms - esp32-s3-companion - iff-architecture - operational-security leads_to: - acoustic-signature-design - li-ion-batteries - cf-plate-arms