Autonomous UGV Hinge Bracket Structural Optimization

Structural optimisation of the central hinge bracket connecting the front and rear chassis of an autonomous mountain-mowing UGV. The original bracket carried significant non-load-bearing material; the goal was to strip that material out while keeping every safety margin intact and preserving the vehicle's full steering capability across Alpine terrain.

The optimised design was validated across three governing load cases — maximum braking, maximum acceleration, and a static 45° slope — confirming a substantial weight saving with safety factors well beyond target.

The optimisation started from a clear hypothesis: the original bracket geometry carried "lazy" material that wasn't contributing meaningfully to load transfer. Rather than a wholesale redesign, the approach targeted identifying and removing that non-structural material while holding stress and displacement within a 2.0–3.0 safety factor target and maintaining weldability. S355J2/S355MC steel was retained as the material of choice over a lighter aluminium alternative (6082-T6/6061-T6): despite steel's roughly 3× higher density, its substantially higher tensile strength and bending endurance limit, straightforward weldability with standard electrodes, and materially lower cost made it the better fit for a cost-sensitive structural component, even before optimisation began.

The result was a 16 kg mass reduction — from 43 kg to 27 kg, a 37% saving — achieved purely by removing non-load-bearing material from the bracket's geometry. A hard functional constraint ran alongside the mass target throughout: the vehicle's full ±73° turning angle, essential for manoeuvring in Alpine meadows, had to be preserved. The narrower optimised geometry met this requirement without compromise, confirming the mass saving came without any loss of core vehicle manoeuvrability.

Both the original and optimised geometries were then validated under three governing load cases — maximum braking, maximum acceleration, and a static 45° slope, the most demanding of the three — tracking global chassis displacement and stress alongside local stress at the hinge itself, the most safety-critical location on the part. Global displacement and stress increased modestly across all three cases, as expected from removing material, but remained far below yield throughout. Critically, stress at the hinge — the component's single point of failure risk — was reduced or held essentially unchanged in every load case despite the lighter structure, evidence that the optimisation redistributed load more efficiently rather than simply trading away margin for mass.

Safety factors, calculated against the S355 bending endurance limit, remained above 6 for every component and load case on the optimised design — comfortably clearing the 2.0–3.0 target. A sensitivity check on the vehicle's mass distribution (an alternate 50/50 front-rear split against the design baseline) showed hinge loads would only decrease under that scenario, confirming the safety margin holds robustly across plausible loading conditions and that the 37% mass reduction stands on solid ground.