Mechanical Transmission for a Biomimetic Wind Turbine

Context & Objectives

As part of the PJT "Project" course at Arts et Métiers Bordeaux, we developed a small-scale wind turbine concept inspired by nature and based on the preliminary work of ADV Tech. Our team's role was to focus on the mechanical transmission system, particularly the design and validation of a compact gearbox and shaft assembly.

This project fits within the broader context of France’s energy transition, aiming for:

Carbon neutrality by 2050
40% renewable energy in the national mix by 2030
Doubling installed wind power capacity within the next decade

In this framework, domestic wind turbines are a promising solution thanks to their compactness, low environmental footprint, and local production capacity. Our contribution focused on turning biomimetic principles into mechanical reality through systems thinking, functional analysis, and simulation.

Functional Decomposition

At the early design stage, we defined the main function of the wind turbine as: “Convert wind energy into usable electrical energy for domestic applications.” To structure the system design, we broke this down into sub-functions based on the APTE methodology and supported the process with a CDCF and a FAST diagram.

Function	Description
Main Function	Convert wind energy into electrical energy
Capture wind	Via a rotor with biomimetic blades
Transmit mechanical power	Through a gear system to the generator
Regulate rotation	To adapt to variable wind conditions
Support components	Ensure structural integrity and accessibility
Enable maintenance	Allow disassembly and part replacement
Facilitate end-of-life	Promote recycling and material separation

These functions were constrained by technical and economic specifications, notably:

Max rotor diameter: 1.5 m
Power output: ≥ 500 W nominal
Wind resistance: up to 25 m/s
Assembly constraints: standard workshop tooling

Gearbox Architecture

While the rotor and blades were inspired by biomimetic studies from ADV-Tech, our team focused on designing the mechanical transmission responsible for torque conversion and power delivery to the generator.

The gearbox is composed of three coaxial shafts — input (e), intermediate (i), and output (s) — coupled via a two-stage spur gear system. This arrangement allows for efficient speed multiplication while maintaining a compact layout compatible with the wind turbine nacelle.

Gearbox layout sketch — Sketch of gearbox architecture: shafts, gear meshes, and housing alignment in the nacelle.

Gear meshing schematic — Topological representation of gear meshing and direction of rotation.

Particular care was given to the axial and radial positioning of bearings, the load paths between gears, and the mechanical clearance needed for both assembly and future maintenance. The gearbox casing was modeled to host all components and allow smooth transmission of forces.

Mechanical Sizing & FEA Validation

The shafts were dimensioned based on torsional load calculations derived from the rotor power and gear ratio requirements. Classical analytical methods provided initial diameters, which were then refined to accommodate keyways, bearings, and geometric constraints within the housing.

Once modeled in CAD, each shaft was integrated into a full transmission assembly that includes the spur gears, ball bearings, and mounting interfaces. The goal was to ensure dimensional coherence and ease of assembly.

Input shaft geometry showing dimensional sections adapted to torque and key constraints.

CAD of full transmission — Full CAD assembly of the gearbox: shafts, spur gears, ball bearings, and structural casing.

To ensure the structural integrity of the transmission system, we conducted a Finite Element Analysis (FEA) using Abaqus. The output shaft, as the most loaded component, was analyzed under nominal torque and boundary conditions representative of gear contact and bearing constraints.

Von Mises stress: 47.7 MPa — well below the steel yield strength (≈250 MPa)
Displacement U2: 0.136 mm — mainly bending in the Y direction
Displacement U3: 0.0078 mm — very limited out-of-plane deformation
Displacement U1: ~10⁻⁷ mm — negligible axial deformation

These results confirm that the design is mechanically robust, with deformations constrained within safe limits. The shaft is primarily subjected to bending along the Y-axis, with a safety factor >5.

Displacement U2 FEA — FEA — U2 displacement field showing bending deformation under torque.

Displacement U3 FEA — FEA — U3 displacement field confirming minimal lateral deformation.

FEA — Von Mises stress distribution across the shaft, well within allowable limits.

Gearbox Integration & Global Architecture

Once the shafts were dimensioned and validated through FEA, the full gearbox was assembled in CAD and integrated into the wind turbine nacelle. The mechanical transmission was designed with a focus on compactness, alignment, and ease of manufacturing.

The gearbox follows a two-stage spur gear configuration, enabling a significant rotational speed increase between the rotor and the generator. It includes:

Input shaft linked to the rotor hub
Intermediate shaft carrying the idler gears
Output shaft connected to the generator flange
Ball bearings to support radial and axial loads
Aluminum housing with structural ribs for stiffness

Gearbox sketch layout — Gearbox architectural sketch showing shaft alignment and bearing placements along X, Y, Z axes.

Gearbox positioning in the nacelle — Gearbox integration in the wind turbine frame, aligned with the rotor and generator positions.

Full gearbox CAD model — Complete gearbox CAD model — input/output shafts, gear stages, bearings, and casing structure.

Particular attention was given to mounting constraints, gear clearance, and shaft support spacing to ensure proper meshing and minimal backlash. The model was also designed for easy assembly with standard tools, in accordance with the project's functional requirements.

My Role

Within our 4-member team, I was in charge of several critical aspects of the project, both at the system level and in detailed mechanical design.

I led the functional analysis during the early conceptual phase, producing the decomposition logic through FAST and CDCF methodologies.
I contributed to the mechanical sizing of the shafts, including hand calculations and design recommendations based on torsional theory.
I carried out the Finite Element Analysis (FEA) using Abaqus to validate the output shaft’s structural integrity under operating loads.

My contributions focused on ensuring that the internal mechanical components of the wind generator were functionally sound, structurally reliable, and aligned with manufacturability goals.

Acknowledgments

I would like to thank my teammates Justin Cabe, Thomas Barrau, Bixente Bengochea, and Lilian Cassou-Leins for their collaboration and strong commitment throughout the project.

I am also grateful to Prof. Elise Gruhier and Dr. Mathilde Zeni (ENSAM - I2M) for their guidance, encouragement, and technical support during this entire year.

Conclusion

This project validated the mechanical feasibility of a 5 kW turbine, combining biomimicry, simulation, and systems thinking.

Biomimicry leveraged for aerodynamic efficiency
Gearbox and structural elements dimensioned and verified
Project structured using Systems Engineering and functional logic