Project Noctis: Biomimetic Bat
DESIGNATION: TACTICAL AERIAL OBSERVATION PLATFORM
Unlike fixed-wing aircraft or multi-rotor drones, bats (Chiroptera) utilize highly articulated, multi-jointed wings covered by an anisotropic membrane. This allows for unparalleled agility, silent flight, and the ability to operate safely in confined spaces (like caves or buildings).
For a college spyware project, a biomimetic bat provides three distinct advantages:
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Acoustic Stealth: Flapping wings generate lower-frequency, less recognizable noise compared to the high-pitch whine of quadcopter propellers.
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Energy Efficiency in Loitering: By mimicking a bat's ability to hang inverted from ceilings, the drone can achieve a zero-power observation state for days at a time.
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Visual Deception: At night or dusk, the silhouette and flight pattern are easily dismissed by human observers as local wildlife.
Materials & Architecture
Wings (Skeleton & Membrane)
- Bones/Spars: 1mm Carbon Fiber Rods [~$10]. Extremely stiff and lightweight, used for the main leading edge (the "arm" and primary "finger").
- Joints: 3D Printed TPU (Thermoplastic Polyurethane) [~$25/roll]. Allows for passive bending during the upstroke to reduce drag.
- Membrane: Ultrathin Silicone Elastomer (approx 50-100 microns thick) [~$15]. It stretches linearly, allowing the wing to billow on the downstroke for lift, and snap back flat.
Fuselage / Body
- Chassis: SLA 3D Printed Tough Resin or SLS Nylon [~$30]. Standard PLA is too brittle. You need a chassis that can absorb the continuous vibration of the flapping mechanism.
- Weight Distribution: The battery and main motor must sit exactly at the center of gravity (the "chest" of the bat) to maintain flight stability.
Power & Compute
- Microcontroller: ESP32-S3 [~$12]. Built-in WiFi/Bluetooth, dual-core for handling sensor data and motor control simultaneously, and supports low-power deep sleep.
- Battery: 150mAh - 300mAh 1S LiPo [~$8]. You must trade flight time for weight. Flight time will be short (3-5 mins), which is why the inverted hanging feature is critical.
- Coreless DC Motor & Gearbox: 8520 Coreless Motor w/ Micro Gears [~$15]. Provides the central flapping torque.
Feet (Hanging Tech)
- Actuator: Nitinol SMA (Shape Memory Alloy) Wire [~$15]. Instead of heavy servo motors, heating a tiny SMA wire with electrical current causes it to contract, opening the claws.
- Structure: Spring-Steel wire hooks [~$5] with passive tension locks.
Fuselage / Body
- Chassis: SLA 3D Printed Tough Resin or SLS Nylon. Standard PLA is too brittle. You need a chassis that can absorb the continuous vibration of the flapping mechanism.
- Weight Distribution: The battery and main motor must sit exactly at the center of gravity (the "chest" of the bat) to maintain flight stability.
Power & Compute
- Microcontroller: ESP32-S3. Built-in WiFi/Bluetooth, dual-core for handling sensor data and motor control simultaneously, and supports low-power deep sleep.
- Battery: 150mAh - 300mAh 1S LiPo. You must trade flight time for weight. Flight time will be short (3-5 mins), which is why the inverted hanging feature is critical.
Feet (Hanging Tech)
- Actuator: Nitinol SMA (Shape Memory Alloy) Wire. Instead of heavy servo motors, heating a tiny SMA wire with electrical current causes it to contract, opening the claws.
- Structure: Spring-Steel wire hooks with passive tension locks.
Flight Mechanics
Flapping vs. Hovering
True hover is incredibly difficult for a flapping wing of this size (hummingbirds achieve it via rigid, incredibly fast figure-8 flapping). Bats achieve near-hovering via a slow, high-angle-of-attack forward flight. For your drone, you should aim for slow forward flight with agile turning rather than perfectly stationary hovering.
The Flapping Mechanism: Spatial Crank-Rockers
Using individual servo motors for flapping is too slow and heavy. Instead, use a central Coreless DC Motor attached to a gearbox.
- The DC motor spins a central gear.
- Connecting rods attached to the gear convert rotary motion into the up-and-down plunging motion of the wings (Crank-rocker mechanism).
- Asymmetric Stroke: The upstroke must create less drag than the downstroke. By implementing passive, flexible joints mid-wing, the wing folds slightly inward as it goes up, and snaps fully extended on the way down, generating net positive lift.
Steering & Yaw
Because you only have one central flapping motor, you steer by altering the shape of individual wings, just like a real bat.
- Place two micro-servos (e.g., 1.7g linear servos) on the "shoulders".
- To turn left, the left servo retracts slightly, partially folding the left wing membrane. This decreases lift and increases drag on the left side, causing the bat to bank and turn.
Spy Payload & Sensory Array
To keep weight strictly under 80 grams, you cannot use heavy optical lenses. You must rely on micro-sensor arrays that feed data back via the ESP32's WiFi connection.
Ultrasonic (Echolocation)
Hardware: 2x MEMS Ultrasonic Transducers
Mounted in the "ears". Used strictly for collision avoidance during autonomous flight. They pulse sound out and measure return time to prevent the drone from crashing into walls in the dark.
Thermal Imaging
Hardware: FLIR Lepton Micro-Camera
A traditional camera is useless in the dark and requires too much bandwidth. The FLIR Lepton is smaller than a dime, sees body heat through light foliage/smoke, and provides the ultimate "predator" surveillance feed.
Infrasonic Audio
Hardware: I2S MEMS Microphone
Capable of picking up extreme low-frequency vibrations. When hanging from a ceiling, it can detect the vibration of footsteps down a hallway or the hum of hidden machinery long before a visual line of sight is established.
Optical Stereoscopic (Eyes)
Hardware: 2x Micro CMOS Pinhole Cameras
Positioned perfectly at the anatomical "eyes". Provides standard optical video feed for well-lit environments. Using two allows for stereoscopic depth perception algorithms to assist the ultrasonic sensors.
Inverted Hanging Mechanism
This is the defining feature of your spy drone. Flight consumes immense battery; a spy device needs to loiter and observe. By hanging, power consumption drops by 98%.
The "Passive Lock" Concept
A real bat's tendons are arranged so that the weight of the bat pulls its claws closed. It requires zero muscle energy to hold on. We replicate this using mechanical leverage and Shape Memory Alloys (SMA).
- The Approach: The drone flies upwards toward a rough ceiling or rafter. An upward-facing ultrasonic sensor detects proximity.
- The Impact: As the feet strike the ceiling, the physical upward force triggers a bistable spring mechanism, snapping the curved micro-claws (hooks) inward, grabbing the surface.
- The Hang (0 Power): The motor turns off. The drone's gravity pulls down on the leg shafts, mechanically pulling the claws even tighter into the wood/plaster.
- The Release (Active): To fly away, the ESP32 sends a 3V pulse through a Nitinol (SMA) wire. The wire heats up instantly, contracts, and pulls the release pin. The claws spring open, the drone drops, and immediately initiates flapping.
SMA ACTUATION CYCLE
Claw: Mechanically Locked
Power Draw: 0 mAh
Claw: Forced Open
Power Draw: High (Brief 1s pulse)
Bill of Materials (BOM) & Estimated Cost
| Component | Category | Est. Cost (USD) |
|---|---|---|
| Carbon Fiber Rods (1mm) | Structure | $10.00 |
| TPU Filament (Roll) | Structure | $25.00 |
| SLA Tough Resin / SLS Nylon | Structure | $30.00 |
| Silicone Elastomer Membrane | Structure | $15.00 |
| ESP32-S3 Microcontroller | Compute | $12.00 |
| 1S LiPo Battery (150-300mAh) | Power | $8.00 |
| Coreless DC Motor & Gears | Mechanics | $15.00 |
| Nitinol SMA Wire | Mechanics | $15.00 |
| Spring-Steel Wire Hooks | Mechanics | $5.00 |
| MEMS Ultrasonic Transducers (x2) | Sensors | $5.00 |
| FLIR Lepton Micro-Camera | Sensors | $180.00 |
| I2S MEMS Microphone | Sensors | $8.00 |
| Micro CMOS Pinhole Cameras (x2) | Sensors | $20.00 |
| Estimated Total Project Cost: | $348.00 | |
* Note: Prices are estimates and vary based on supplier/retailer. The FLIR Lepton thermal camera is the most expensive component. It can be omitted to bring the total cost down to ~$168.00 if you want to rely purely on the optical eyes and echolocation.
Schematic Data
MACHINE DRAWINGS: VECTOR GRAPHIC OUTPUT