MCU-less Analog Biomimetic Bat Flapping-Wing Robot
Three-segment independently-driven wings with pure analog control
Hsi Wu (西木 / Xī Mù), the Sky Demon of Jackie Chan Adventures.
The project name Hsiwu is derived from Hsi Wu (西木), the bat-like Sky Demon from Jackie Chan Adventures (《成龙历险记》). A fitting namesake: just as Hsi Wu ruled the sky with his segmented, morphing wings, this robot replicates the segmented membrane deformation of a real bat in flight.
Hsiwu — named after the bat-like Sky Demon — is a biologically inspired bionic bat flapping-wing robot. Unlike conventional single-segment rigid-wing drones, it replicates the segmented membrane deformation of a real bat in flight. Each wing is divided into three independently driven segments — leading edge, middle section, and trailing edge — each powered by its own DC motor.
The bionic design takes the Rhinolophus luctus (great woolly horseshoe bat) as its morphological reference. Through a crank-rocker four-bar linkage mechanism, the continuous rotary motion of each DC motor is converted into the oscillating reciprocating swing that drives the wing segments—faithfully reproducing the coupled flapping-and-stretching kinematics of a real bat wing membrane.
A defining characteristic of this project is its pure analog control architecture. The system uses no microcontroller (MCU) and no embedded software whatsoever. Instead, it relies entirely on discrete analog and digital logic circuits — NE555 timers, 74HC04 inverters, and L293D H-bridge drivers — to generate the synchronized periodic reciprocating motion that drives the wings.
The project spans a complete engineering stack: analog electronics design, digital logic, custom PCB layout, mechanical structure modeling (SolidWorks), FDM 3D printing, and hardware assembly and debugging.
Reference Paper: The aerodynamic and mechanical principles are adapted from "Design and Manufacture of Bionic Bat Aircraft" (Qi Jinhao, Zhang Weiping, 2020), published in Machine Design and Research, Vol. 36, No. 5. The reference prototype achieves a 205 mm wingspan, 17.81 g total mass, 70° flapping angle, ~10 Hz flapping frequency, and ~0.16 N lift under a 3.7 V power supply.
Figure 0 — Project Overview. Full-color 3D render of the complete Hsiwu assembly. The bilateral symmetric frame chassis (central support, head support, tail bracket), six independently-driven wing segments (three per side — leading, middle, trailing edges), linkage rods, lead-screw-driven scissor expansion mechanism, and custom-shaped PCB are all visible. This render corresponds to the final assembly state defined in final_assembly.SLDASM.
- Bio-inspired Wing Kinematics — Three independently-driven segments per wing (Leading, Middle, Trailing), each with its own DC motor, mimicking the stretching and bending of a real bat's wing membrane. The crank-rocker four-bar linkage converts continuous motor rotation into oscillatory flapping.
- Zero MCU / Zero Code — Pure analog control: NE555 astable multivibrators for timing, 74HC04 hex inverters for phase splitting, and L293D dual H-bridges for bidirectional motor drive. No microcontroller, no firmware, no programming required.
- Custom Shaped PCB — A specialized irregularly-shaped PCB designed in EasyEDA (LCEDA) and Altium Designer, contour-fit to the internal mechanical frame. Integrates power management, signal generation, and motor driving onto a single compact board.
- Modular Mechanical Design — Fully parameterized 3D models built in SolidWorks. Frame components are FDM 3D-printable, assembled with standard M2/M3 screws and hinge linkages for easy tuning and repair.
- Integrated Power Management — Single-cell 3.7V LiPo battery input with MT3608 boost converter (3.7V → 7.35V for motors), on-board LDO regulation (5V for logic), reverse-polarity protection, and power switch with indicator LED.
The core logic is distributed across five functional blocks integrated onto a single custom PCB:
Figure 1 — Full System Schematic. Complete circuit diagram showing four functional blocks: (left) MT3608 boost converter with Schottky diode reverse-polarity protection and power switch; (upper-middle) three NE555 astable multivibrator stages generating independent ~4.8 Hz square-wave timing signals; (right) 74HC04 hex inverter for complementary phase generation; (lower) three L293D dual H-bridge drivers, each using one half-bridge channel per motor to produce continuous forward/reverse reciprocation.
| Block | Components | Function |
|---|---|---|
| Power Supply | MT3608, LDO, Schottky diode | 3.7V LiPo → 7.35V (boost, motors) + 5V (LDO, logic). Reverse-polarity protection, on/off switch with indicator LED. |
| Timing Generation | 3× NE555 (astable) | Three independent, synchronized square-wave oscillators at ~4.8 Hz. Sets the flapping frequency. Each NE555's RC network can be independently tuned for per-segment timing adjustment. |
| Phase Inversion | 1× 74HC04 hex inverter | Inverts the three NE555 outputs to produce complementary logic levels for H-bridge direction control. Each NE555 output drives one inverter channel, yielding the inverted signal for the opposing half-bridge. |
| Motor Drive | 3× L293D dual H-bridge | Each L293D uses one half-bridge channel per motor. Complementary logic signals produce continuous forward/reverse reciprocation. Built-in flyback diodes protect against inductive kickback. |
| PCB Layout | Custom contour | Vertical modular layout; board outline shaped to fit the internal mechanical frame. Irregular board profile matches the central support chassis curvature. |
Figure 2a–2b — PCB Design Views (I). Left: 3D render showing component placement on the custom-shaped PCB — three NE555 (SOP-20, U1–U3), 74HC04 (SOIC-14, U5), three L293D (SOIC-8, U6–U8), MT3608 (SOT-23-6, U4), SMC Schottky diode (D1), SMD inductor (L1), XH-2A connectors (U9), 0805 passive components (R1–R11, C1–C8), and slide switch (SW2). Right: 2D top-layer copper routing with silkscreen overlay.
Figure 2c–2e — PCB Design Views (II). Left to right: Bottom copper layer with silkscreen; raw top-layer routing trace (no fill); raw bottom-layer routing trace (no fill). The Gerber fabrication files are available in electronics/output/gerber/.
The mechanical assembly is designed in SolidWorks (.SLDPRT / .SLDASM source files) and manufactured via FDM 3D printing. The kinematic principles are adapted from the reference paper "Design and Manufacture of Bionic Bat Aircraft" (Qi & Zhang, 2020).
The following kinematic schematics are reproduced from the reference paper. They illustrate the four core mechanisms that underlie the wing drive train:
Figure 3a–3b — Crank-Rocker Four-Bar Linkage. Left: Kinematic diagram of the crank-rocker mechanism that converts the motor shaft's continuous rotary motion into the rocker arm's oscillating up/down swing. The crank (driven by the geared hollow-cup DC motor) rotates continuously; the connecting rod transmits motion to the rocker, whose output angle determines the wing segment's flapping amplitude (~70° in the reference design). Right: Dimensioned linkage drawing with parameter table — key link lengths a/b/c/d/e/f/g/h/i/j/k and crank/rocker pivot angles α/β are dimensioned for the target 75° flapping stroke. The reference prototype uses linkage ratios optimized for a 205 mm wingspan.
Figure 3c–3d — Scissor Expansion & Leg Drive Mechanism. Left: Scissor mechanism controlled by a lead screw (P = 0.4 mm pitch, d₂ = 1.74 mm effective diameter). The motor-driven lead screw advances/retracts a traveling nut, which pushes/pulls a scissor linkage to control wing membrane expansion and contraction. The reference paper calculates a lead screw driving torque M = 0.0064 N·mm. Right: Leg/transmission mechanism showing the motor-to-linkage coupling geometry, with pivot points O–O′ and reaction forces FA, FB resolved through static equilibrium analysis. The overall mechanical advantage is designed to deliver ~0.16 N of lift from a 3.7 V supply.
The project's mechanical assembly consists of the following sub-assemblies (all SolidWorks source files in mechanical/source/):
| Sub-assembly | Path | Key Parts | Description |
|---|---|---|---|
| Structural Frame | structural/ |
central_support, head_support, tail_bracket |
Left-right symmetric chassis; the central support forms the main body, with head/tail brackets anchoring the wing pivot points |
| Rod Linkages | rods/ |
rod_a, rod_bc, rod_d, rod_h, rod_ij, rod_kf |
Six linkage rod types forming the four-bar crank-rocker kinematic chains for each wing segment |
| Motor & Coupling | motor/ |
four-stage_geared_hollow_cup_motor, 2-to-3_coupling |
Hollow-cup DC motor with 4-stage planetary gear reduction; 2-to-3 shaft coupler for connecting to the lead screw |
| Lead Screw Assembly | structural/ |
lead_screw, head_drive_shaft, bearing, center_bearing_cap, head_bearing_cover |
Lead screw (P = 0.4 mm) drives the scissor expansion linkage; supported by miniature bearings at both ends |
| Pivot Hardware | structural/ |
head_pin, tail_pin |
Precision hinge pins for wing segment articulation at the leading and trailing pivot points |
| Fasteners | fasteners/ |
SCA_M2_L10/L12/L14/L18, SLMNA-M2, SLMNA-M3 |
M2 countersunk screws (10–18 mm lengths), M2/M3 lock nuts for frame assembly |
| Final Assembly | assembly/ |
final_assembly.SLDASM |
Master assembly file referencing all sub-components in their assembled positions |
Figure 4 — Lead Screw Transmission Animation. Dynamic demonstration of the lead-screw-driven scissor mechanism. As the motor rotates the lead screw, the traveling nut advances linearly, pushing the scissor linkage open to expand the wing membrane area — or retracting to contract it. This coupled expansion/flapping motion is a key biomimetic feature that replicates the bat wing's variable-camber aerodynamics.
Figure 5a–5b — Mechanical Drawings. Left: Top/plan view — reveals the motor placement, linkage rod routing, and overall wingspan geometry. Right: Isometric wireframe view — a line-drawing render showing the complete kinematic skeleton with all linkage pivot points, rod connections, and structural frame members visible in a single perspective. The front elevation view is shown in the project banner above.
HSIWU/
├── electronics/ # PCB design files
│ ├── source/ # LCEDA project (.eprj2) + Altium Designer source files (.schdoc, .pcbdoc)
│ └── output/ # Gerber files, BOM, pick-and-place (.csv/.xlsx), PDF schematic
├── mechanical/ # 3D CAD models (SolidWorks)
│ ├── source/ # Native SLDPRT/SLDASM files
│ │ ├── structural/ # Frame, lead screw, bearings, pins, brackets
│ │ ├── rods/ # Six linkage rod types (a, bc, d, h, ij, kf)
│ │ ├── motor/ # Geared hollow-cup motor + shaft coupler
│ │ ├── fasteners/ # M2/M3 screws & lock nuts
│ │ ├── pcb_3d_models/ # PCB with all component 3D models placed
│ │ └── assembly/ # Master assembly file
│ └── output/ # Export files — STEP (3D printing), STL (laser cutting)
├── docs/ # Technical documentation
│ ├── en/ # English docs — theory of operation, mechanical design, assembly guide
│ └── zh-CN/ # 中文文档 — 工作原理、机械设计、组装指南
├── BOM/ # Bill of Materials spreadsheet (.xlsx)
├── media/ # Project media assets
│ ├── photos/
│ │ ├── project/ # Renders, PCB views, mechanical drawings, test photos
│ │ └── reference/ # Reference paper figures and the original paper (PDF)
│ └── videos/ # Demonstration videos (.mp4)
├── .github/ # GitHub community files
│ ├── CODEOWNERS # Code ownership definitions
│ ├── PULL_REQUEST_TEMPLATE.md # PR template
│ ├── ISSUE_TEMPLATE/ # Bug report & feature request templates
│ └── FUNDING.yml # Funding/sponsor configuration
├── .gitignore # CAD/EDA/3D-printing-aware ignore rules
├── .gitattributes # Binary/text handling & diff configuration
├── CHANGELOG.md # Version history (Keep a Changelog format)
├── CONTRIBUTING.md # Contributor guidelines (English)
├── CONTRIBUTING.zh-CN.md # 中文贡献者指南
├── LICENSE.md # MIT License
├── README.md # Project overview (English)
└── README.zh-CN.md # 项目概览（中文）
See BOM/ for the complete component spreadsheet. Key components:
| Category | Item | Qty | Notes |
|---|---|---|---|
| Frame | 3D-printed parts (ABS/PLA) | — | Central support, head support, tail bracket, bearing caps; 0.2 mm layer height recommended |
| Fasteners | M2 countersunk screws (10/12/14/18 mm) | — | SCA series |
| M2/M3 lock nuts | — | SLMNA series | |
| Bearings | Miniature ball bearings | — | For lead screw and pivot joints |
| Motors | DC hollow-cup geared motors | 3 | Four-stage planetary gear reduction; one per wing segment |
| Power | 3.7V LiPo battery | 1 | Single-cell |
| ICs | NE555 timer (SOIC-8 equiv., on SOP-20 carrier) | 3 | Astable multivibrator configuration |
| 74HC04 hex inverter (SOIC-14) | 1 | Six NOT gates; three used for phase inversion | |
| L293D dual H-bridge driver (SOIC-8 equiv.) | 3 | One half-bridge channel per motor | |
| MT3608 boost converter (SOT-23-6) | 1 | 3.7V → 7.35V step-up | |
| Passives | Resistors, capacitors (0805) | — | Timing RC networks, decoupling, filter |
| Schottky diode (SMC) | 1 | Reverse-polarity protection | |
| Power inductor (SMD, 7.3×6.8 mm) | 1 | MT3608 boost inductor | |
| Adjustable resistors (SMD trimmer) | 3 | Per-segment frequency fine-tuning | |
| Connectors | XH-2A 2-pin header (P2.50) | — | Motor wire connections |
| Slide switch (SS12D07VG4) | 1 | Power on/off | |
| Indicator LED (0805) | 1 | Green power-on indicator |
Open electronics/. The schematic is documented in PCB_Base.pdf and PCB_Base_doc.png (see Figure 1). The board can be manufactured directly from the Gerber files in electronics/output/gerber/, or you can re-export from the EasyEDA (LCEDA) project in electronics/source/JLC/. The pick-and-place file (electronics/output/pick_and_place/PCB_BASE.csv) and BOM (electronics/output/bom/PCB_Base_BOM.xlsx) are ready for SMT assembly services.
Find the 3D models in mechanical/. Export the parts to STL and print them on a standard FDM 3D printer (0.2 mm layer height recommended; ABS for structural durability or PLA for ease of printing). The STEP files in mechanical/output/3dp/ are ready for direct slicing and printing. For laser-cut parts (rods), use the STL files in mechanical/output/laser/. To modify the design, open the native SolidWorks source files in mechanical/source/ — all parts are fully parameterized.
- Solder all components onto the custom PCB according to the schematic (Figure 1). Refer to the PCB layout views (Figure 2a–2e) for component placement.
- Connect the three motor wires to the XH-2A headers on the PCB.
- 3D-print the structural frame parts:
central_support,head_support,tail_bracket,head_bearing_cover,center_bearing_cap,head_drive_shaft,head_pin,tail_pin. - 3D-print or laser-cut the linkage rods:
rod_a,rod_bc,rod_d,rod_h,rod_ij,rod_kf. - Assemble the frame using M2/M3 screws, lock nuts, and miniature bearings as specified in
final_assembly.SLDASM. Refer to the mechanical drawings (Figure 5a–5b) and the front elevation banner for assembly reference. - Mount the PCB onto the central support chassis.
Insert the 3.7V LiPo battery and flip the power switch (SW2). The onboard green LED (LED1) should illuminate, and the wings should begin flapping at the designed ~4.8 Hz frequency. The flapping rate can be fine-tuned by adjusting the three trimmer resistors (R4, R10, R11) that set each NE555's RC time constant.
During the powered-on test, the onboard green indicator LED illuminates and the 3D-printed robot executes the full flapping motion. A Tektronix TDS1001B-SC oscilloscope is used to monitor the ~4.8 Hz square-wave output from the NE555 oscillator stages and verify signal integrity.
Figure 6a–6b — Assembly & Fabrication. Left: Bench assembly setup — third-hand tool with magnifying glass holding the partially assembled mechanical frame; PCB, motors, and linkage rods visible on the work mat. Right: PCB soldering station — the custom-shaped board undergoing manual SMT soldering of 0805 passives and ICs.
Figure 7 — Live Oscilloscope Test. Tektronix TDS1001B-SC digital storage oscilloscope probing the NE555 output waveform during a powered-on test. The scope displays the ~4.8 Hz square wave (period ≈ 208 ms) with voltage swing from 0 V to VCC (5 V logic rail), confirming correct astable multivibrator operation. Multiple channels allow simultaneous monitoring of all three motor drive signals for phase verification.
| Parameter | Value | Source |
|---|---|---|
| Bionic Reference | Rhinolophus luctus (great woolly horseshoe bat) | Reference paper |
| Wingspan | 205 mm (reference) | Qi & Zhang, 2020 |
| Total Mass | 17.81 g (reference) | Qi & Zhang, 2020 |
| Flapping Frequency | ~4.8 Hz (this project) / ~10 Hz (reference) | NE555 RC network / paper |
| Flapping Angle | ~70° (reference target) | Crank-rocker geometry |
| Power Supply | 3.7V LiPo single-cell | This project |
| Motor Supply | 7.35V (boosted) | MT3608 converter |
| Logic Supply | 5V (regulated) | On-board LDO |
| Motor Type | Hollow-cup DC, 4-stage planetary geared | ZWPD006006-26 (reference) |
| Lead Screw Pitch | P = 0.4 mm, d₂ = 1.74 mm | Reference paper |
| Gear Ratio | 1:4 (motor output : lead screw) | Reference paper |
| PCB Design Tools | EasyEDA (LCEDA) + Altium Designer | This project |
| CAD Software | SolidWorks (native .SLDPRT/.SLDASM) | This project |
| Manufacturing | FDM 3D printing (frame) + FR-4 PCB | This project |
Distributed under the MIT License.
- Reference Work — "Design and Manufacture of Bionic Bat Aircraft" (Qi Jinhao, Zhang Weiping, 2020), published in Machine Design and Research (Vol. 36, No. 5, pp. 38–43), Shanghai Jiao Tong University. This paper provides the theoretical foundation for bat flight kinematics, four-bar linkage design, scissor mechanism force analysis, and prototype validation methodology upon which this project's mechanical design is based.
- Name Inspiration — The character Hsi Wu (西木, the Sky Demon) from the animated series Jackie Chan Adventures (《成龙历险记》), whose iconic bat-like form inspired the project's name and its tribute to segmented-wing biomechanics.
- Tools — SolidWorks (mechanical CAD), EasyEDA / LCEDA (PCB design), Altium Designer (schematic capture), Tektronix TDS1001B-SC (test & measurement).
- Inspiration — FESTO BionicOpter and Bat Bot B2 (Caltech/UIUC) for demonstrating the feasibility of bio-inspired bat flight; the broader bat flight biomechanics literature (Swartz et al., Tian et al., Wolf et al.) for wing membrane mechanics and flapping kinematics research.