Technical Breakdown: Our Next-Generation Gearboxes
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Introduction
Since their debut on DeV17, our gearboxes have been some of the most quietly influential components on the car, hidden from plain sight within the upright and working in harmony with the electric motors. These gearboxes supported one of the most significant transitions in our team’s history: the move from a tubular chassis with rear-wheel drive to a carbon fiber monocoque with fully independent four-wheel drive. This design architecture enabled the performance leap we saw in DeV17 compared to what we achieved with DeV16, and it simply wouldn’t have been possible without the compact and reliable gearboxes which carried us through multiple seasons of competition. Our chosen powertrain configuration has been essential in delivering the performance targets that we had set ourselves the past few seasons.
After several years of intensive use, our gearboxes are nearing the end of their useful life cycle, which means that replacements are required. This need coincides with a new list of goals for our future powertrain design that demand more than what the current design can possibly provide. The existing gearboxes have gradually become a bottleneck in terms of size and packaging, and we have also seen smaller issues arise, such as constraints on suspension geometry due to packaging. With new performance targets emerging for our upcoming cars it became clear that a successor was needed, rather than just making copies of what we already had. These realizations are not just about improving the gearboxes for the sake of it, but rather to ensure that our future cars continue to remain at the cutting edge of performance.
This article serves as a summary of Ludvig Danström’s Master’s thesis while also highlighting the significant contributions of project sponsors and contributors. His work focused on enabling the switch to new, smaller tires, which helps reduce the overall mass of the wheel package while also addressing the limitations of the previous system. The result is a next-generation in-wheel transmission design that is significantly more compact, lighter, and designed to give the suspension engineers the freedom they needed to push the car’s handling even further.
Project Objectives
The primary objective of this project is to design a compact, lightweight gearbox capable of withstanding the high-performance demands of an electric powertrain. The gearbox plays a crucial role in transmitting torque from the electric motor to the wheel, and its design must balance efficiency, strength, and packaging constraints. With drivetrain efficiency and vehicle dynamics being critical in electric Formula Student competitions, the gearbox is continuously optimized for both mechanical performance and seamless integration within the vehicle architecture. The main packaging constraint set for this project was that the motor package should not extend further than 30 mm from the wheel package. The 30 mm reference distance, which represents a reduction from the previous 65 mm, was decided upon due to the impact that our current gearbox and motor package design has had on the design of the suspension as to avoid collisions and the general aerodynamics of the car. This reduced protrusion distance should make the impact that the motor and cooling jacket has on the design of other systems significantly smaller and therefore provide greater design freedom to improve parts of the car that have been limited by the previous gearbox and motor package.
A central aim of the project is to ensure that the gearbox transmits the required torque loads in combination with remaining as small and light as possible without sacrificing reliability. Reducing mass is essential not only for improving vehicle performance but also for maximizing efficiency.
Development Process
Early in the project, a comprehensive concept study was conducted to identify the most suitable gearbox configuration. Several design alternatives were developed and evaluated against a predefined set of criteria, including mechanical efficiency, manufacturability, durability, mass, and compatibility with surrounding systems. The selected concept demonstrated strong performance across all critical areas and integrated effectively with both the electric motor and the wheel assembly. In parallel, packaging constraints and mounting strategies were carefully considered to ensure the gearbox could be accommodated within the limited available space without compromising functionality or serviceability, when compared to the current system.
Following the concept selection, the detailed development of the gearbox began with defining the overall layout and the integration of all components. A key design objective was compliance with the 30 mm reference volume extending outward from the inner edge of the wheel rim and tire sidewall. Since the electric motor is mounted directly to the wheel assembly through the gearbox, this 30 mm envelope effectively defines the total allowable space for the gearbox and all associated structural interfaces between the motor and the wheel. To satisfy these constraints, the gearbox architecture was fundamentally revised by reversing the internal layout used on the previous gearbox as well as adopting a ring gear output configuration. This change enabled a more compact power transfer from the motor to the wheel while meeting the strict packaging requirements.
Throughout the development process, both internal and external knowledge resources were actively leveraged. These included alumni, academic staff, and industry experts. Former team members proved to be a particularly valuable resource, as many had previously designed similar systems and could contribute relevant experience and design insight. One notable example was a recommendation from the alumnus who led the development of the DeV17 gearbox to study the transmission used on EV12. This ultimately led to the adoption of a sun gear mounting solution of a similar design, which allowed for improved compactness and a reduced overall transmission size. Several other critical suggestions were also received from alumni and industry professionals, alongside extensive reviews of previous internal designs.
Once the conceptual architecture and manufacturability aspects were clarified, a MATLAB script was written with the goal of choosing the correct gear combination for the gearbox. More than three million potential gear combinations were generated using this MATLAB script that varied tooth counts and module sizes across two stages. From this dataset, 110 viable combinations were identified based on predefined requirements. This list was subsequently narrowed down to 70 total candidate solutions.
The overall design parameters of the gearbox were adjusted based on the selected materials, which will be discussed in more detail later on in this article. The chosen material increased allowable bending and contact stresses which led to adjusted values that were used to determine minimum required face widths and finalize gear dimensions, both of which had a major impact on the final design choices.
To dimension the gearbox for fatigue life, comprehensive load cases were derived from internally developed point-mass vehicle dynamics simulations. These results were converted into torque–speed histograms representing the expected operational life of the gearbox. The gearbox’s calculated load spectra was reduced to a single equivalent load case, significantly reducing computational effort during fatigue simulations in KISSsoft.
With gear selection, sealing strategy, material choice, and manufacturing routes largely established, the project entered the mass optimization phase. The primary focus shifted to structural components such as the hub and the planet carrier. Topology optimization was applied to minimize mass while ensuring manufacturability using conventional manufacturing methods. Additional weight savings were achieved by reducing planet pin diameters from 12 mm to 10 mm and implementing angular contact ball bearings from Schaeffler throughout the gearbox. In parallel, the 70 remaining gear combinations were systematically evaluated in KISSsoft to determine minimum face widths and approximate gear mass while meeting fatigue life targets. This process resulted in five final candidates that satisfied the primary project objectives, from which the solution with the fewest overall drawbacks was selected.
Another component that required a redesign relative to the previous gearbox was the thrust washer system. Traditionally, these washers were manufactured from steel and loosely fitted, allowing free rotation. While this solution was effective with a steel carrier, the introduction of an aluminum carrier led to increased wear concerns. Several ideas were evaluated, including hard anodizing of the aluminum carrier to improve surface hardness, improved lubrication to promote hydrodynamic separation, and replacement of steel washers with softer materials such as brass. Although brass offered favorable wear behavior by acting as a sacrificial element, the requirement to manufacture a large number of high-quality washers with tight surface finish tolerances posed significant logistical and manufacturing challenges, but was deemed preferable as it resulted in an overall simplification of the design.
Sponsor Contributions
This project relied heavily on extensive sponsor involvement throughout multiple stages of the design and development process. Sandvik Coromant, KISSsoft, Atlas Copco, Schaeffler, Leax, Eibers Edeby AB, LaserNova, Bodycote, TR Fastenings, Curtiss-Wright, Tibnor, Svartviks Svarvteknik, and Ovako all contributed through technical expertise, component supply, software, or manufacturing services. Each company provided specialized knowledge within its respective domain, including material production, machining, heat treatment, shot peening, superfinishing, fastening systems, sealing technology, and precision manufacturing. The close interaction between these partners reflects the highly interconnected nature of modern mechanical engineering development, where system performance depends on the coordinated contribution of multiple industrial disciplines.
The collaboration with these companies extended beyond simple component supply and played a critical role in shaping several key design decisions. Leax provided early-stage design feedback and manufacturing insight and ultimately committed to producing selected gears free of charge. Their early involvement enabled manufacturability concerns to be identified at an early stage, significantly reducing development risk. Complementing this, Eibers Edeby AB was selected to manufacture the more geometrically complex sun gear due to their high level of specialization in precision gear cutting. Their feedback led to important design modifications which transformed an otherwise impractical design into a fully manufacturable component without compromising structural integrity.
Material selection and fatigue performance were strongly influenced by industrial collaboration with Ovako and Atlas Copco. Ovako supplied fatigue data for candidate gear steels, which directly enabled the determination of allowable bending and contact stresses used during gear dimensioning. Based on discussions with both companies, 158Q steel was selected over 277Q due to its superior compatibility with case hardening and the availability of reliable fatigue data. This material choice directly influenced safety factors, face width selection, and the overall robustness of the transmission.
Surface treatment and durability enhancement were also supported through sponsor involvement. Curtiss-Wright contributed expertise related to shot peening. Bodycote contributed heat treatment capabilities, enabling access to industrial-scale case hardening processes essential for achieving the required surface hardness and subsurface stress resistance of the gears. Tibnor supported the project through material sourcing, while LaserNova provided laser welding services for joining the two stages of the planet gear.
Fastener selection and joint integrity were supported by TR Fastenings, ensuring that suitable high-strength fasteners with appropriate coatings and mechanical properties were available for the gearbox assembly. Schaeffler contributed bearing expertise and component supply, supporting the selection and integration of rolling element bearings for both radial and axial load cases within the transmission.
Collectively, the contributions of these sponsors were not limited to individual components but formed an integrated support structure that directly influenced design strategy, manufacturability, validation, and reliability. The continuous technical dialogue between the project and its industrial partners enabled early risk identification, design iteration grounded in real manufacturing constraints, and a final transmission concept that is both high performance and manufacturable. Which at this point in time means that this project has achieved, in comparison to the previous gearbox, a 50% reduction in gearbox mass and a 20% reduction of the vehicle’s combined wheel package mass, when additional design improvements of affected systems are accounted for.
Conclusion
In summary, the development of this planetary gearbox has been a highly complex and multidisciplinary engineering project, spanning from conceptual design to gear optimization, structural dimensioning, material selection, manufacturing planning, and system-level validation. Through the use of advanced simulation tools and iterative optimization, the gearbox has progressed from an early concept to a fully validated design, prepared for manufacturing and integration into the DeV20 car. As the project now moves into the production and testing phase, the focus shifts toward final component verification, assembly, and on-vehicle validation to ensure both high performance and long-term reliability under competitive conditions.
Beyond its technical outcome, this project clearly demonstrates the advanced level of mechanical system development that the team is capable of executing. The project’s close collaboration with Swedish and international manufacturing and drivetrain partners, including Sandvik Coromant, KISSsoft, Atlas Copco, Schaeffler, Leax, Eibers Edeby AB, LaserNova, Bodycote, TR Fastenings, Curtiss-Wright, Tibnor, Svartviks Svarvteknik, and Ovako, highlights both its industrial relevance and the confidence these partners place in the team’s engineering capability. Their involvement has elevated the gearbox from a purely academic exercise to an industry-supported engineering product, while also showcasing the strong connection between the team and Sweden’s advanced manufacturing ecosystem.