The output performance of an energy harvesting backpack critically depends on its velocity amplifying mechanism. While conventional designs often employ a gearbox, extensively studied in vibration harvesting, these approaches face some limitations. The substantial weight of metallic gearboxes and amplified electrical damping often impede optimal power output. To address these challenges, a lightweight and flexible energy harvesting backpack incorporating an ejection velocity-increasing mechanism was modeled, analyzed, and tested. Given the piecewise linearity of this proposed mechanism, the crucial connections between its different stages were investigated using a detailed flowchart. Numerical simulations, guided by this flowchart, were conducted to validate the velocity amplification design, compare its effectiveness against mechanical motion rectifiers, analyze the nonlinear characteristics of the ejected mass, and identify optimization strategies for the mechanism. Experimental validation confirmed theoretical analyses, demonstrating that this design can amplify the input frequency by threefold compared to a linear backpack. Furthermore, parameter experiments revealed that optimal performance is achieved with a large energy storage spring and a high ejected force threshold.