MACH-0 — Wearable Hip Protection Device for Fall Prevention

MACH-0 is a novel deployable mechanical hip protection device designed for elderly fall prevention. Falls are the leading cause of death among the 65+ population, contributing to 58.1% of all deaths in 2020 — and hip fractures are involved in approximately 1 in 3 fall-related fatalities. Current market solutions are either passive foam pads with limited effectiveness, or expensive airbag devices (starting at $750) requiring gas cannister replacements after each use.

Inspired by the Phlat Ball toy, the device uses three 1075 spring steel leaf arches arranged in a hexagonal pattern on a 3D-printed baseplate. In the stored state, the leaves are held flat by a buckling rod release mechanism held just past the unstable equilibrium point. A solenoid pushes the mechanism through equilibrium, releasing the leaves to deploy into their protective arch configuration in milliseconds — fully reusable with no consumables.

Testing was performed using the Instron Dynatup 9250 HV drop tower for impact characterization and a custom inverted pendulum jig to simulate a sideways fall. Angular position, velocity, and acceleration were captured at 1000 FPS using the OptiTrack 120X Prime motion capture system. The device achieved a 50 ± 20% peak force reduction — 2.5× the 20% target — and the spring constant can be tuned simply by swapping leaf thickness, allowing the design to scale to real-world body weights.

Testing was conducted in the USC Quan Lab using a custom inverted pendulum jig with rigid aluminum framing and an OptiTrack reflective marker mount. These photos document the physical setup — the pendulum arm, baseplate fixture, solenoid wiring, and drop-release rig used to capture the 50 ± 20% peak force reduction result.

The OptiTrack 120X Prime system captured pendulum arm kinematics at 1000 FPS, tracking reflective markers to extract angular position, velocity, and acceleration throughout the drop event. Trials were run with and without the spring steel device to isolate the device's contribution to impact attenuation. The combined plots directly compare spring vs. no-spring conditions across all three kinematic channels simultaneously.

To select the optimal spring steel geometry, multiple leaf configurations were tested on the Instron Dynatup 9250 HV drop tower at a controlled impact energy of 10 J. Variables included arch angle (60° vs. 79°) and strip thickness (10 thou vs. 15–20 thou of 0.025" 1075 spring steel). Force-time traces show the attenuation bandwidth and peak force for each configuration — the 79°, 15-thou strip at 10 J produced the best balance of deployment reliability and force reduction for the final design.

The 3D-printed slotted baseplate was modeled in Siemens NX and iterated through multiple revisions to optimize slot geometry for secure spring steel retention while minimizing print mass. The slot angle and depth were tuned to ensure consistent arch deployment angle across all three leaves, and the central boss was sized to interface with the buckling rod release mechanism. The native .prt CAD files are available in the project archive.