**6. Discussion**

The work presented is focused on the design and development of a front single-sided swingarm used on a new three-wheel electric motorcycle. To the best of our knowledge there is no literature for front single-sided swingarm analysis, since most of the research found is related to rear swingarms. Comparing a front and a rear swingarm, loading conditions are di fferentiated. One di fference is the effect of loads from the motor through the chain on a rear swingarm and on the other hand higher braking forces applied on the front wheel of a motorcycle.

The main targets set for the development of this part, are structural safety and low weight. A dedicated CAE software was used for the modelling of loads, constraints and materials applied, in order to evaluate a front swingarm design through series of finite element analysis simulations. Results of stresses and displacements were calculated and presented. A review of braking conditions was also presented, in order to identify the braking forces applied and investigate their e ffects on the structural strength of the part under consideration. In the simulations conducted, two loading scenarios were performed. The first scenario included weight distribution forces, while the second scenario investigated the e ffect of braking forces, considered as the worst-case scenario. At first, an initial swingarm design was evaluated. In the worst-case scenario, the maximum stress calculated was 98.6 MPa, far lower than the yield stress (503 MPa), corresponding to a safety factor of *N* = 5.1. Displacement results showed a maximum value of 1.27 mm on this design. A swingarm redesign and material replacement was decided, targeting lower weight and production cost. A topology optimization procedure was used, so as to assist the redesign of the swingarm and obtain valuable results regarding specific areas of material removal. The final form was also a ffected considering our production capabilities, targeting manufacturing with CNC machining. In the final swingarm design,

exactly the same modelling process was followed and only the worst-case scenario (second loading scenario—braking) was used in the simulations. A direct comparison of results for the initial and final swingarm design revealed that, the maximum stresses are 19% higher in the final design (117.2 MPa), as well as displacements were raised by 25% (1.59 mm). Safety factor was reduced to *N* = 1.95, which is normal for these type of structures (as related to rear swingarm literature) and ensures structural rigidity. The main target was of course to lower weight, which is accomplished since a 23.2% reduction was achieved, resulting in a weight of 4.35 kg.

The main contribution of this work was to present valuable results and insights, based on finite element analysis simulations, revealing stress and displacements that are calculated for various versions of a new front single-sided swingarm design. The results presented indicate strongly that the proposed structure is effective and promising for actual prototyping. For a future work, the modelling of suspension and tires could be applied, in order to obtain more refined results and target further weight optimization.

**Author Contributions:** Conceptualization, P.S.; Methodology, P.S. and E.C.; Software, E.C.; Validation, P.S. and N.C.T.; Formal Analysis, N.C.T.; Writing—Original Draft Preparation, P.S. and E.C.; Writing—Review and Editing, P.S., E.C. and N.C.T.; Visualization, E.C. and P.S.; Supervision, N.C.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work has been partially funded by the TUC's internal project "TUC Eco Racing team".

**Acknowledgments:** The authors would like to acknowledge the DEADALUS/TUC team's members who contributed and helped in the development.

**Conflicts of Interest:** The authors declare no conflict of interest.
