Single Use Mechanisms

Ball-Based

Nov 2023

I developed a mechanism that allows a slider to move forward and backward once and then prevents the slider from moving forward again. When the slider moves forward, a spring-loaded ball snaps forward. When the slider is moved back, the spring pushes the ball into a window in the slider. This ball then blocks the slider from moving forward again. A light spring is preferable because if the slider doesn’t have sufficient friction or some other holding force, the spring automatically pushes the slider forward.

Cantilever-Based

Mar 2024

After designing the ball-based mechanism, I wanted to see if I could design a mechanism with even fewer moving parts. The slider in this mechanism has a cantilever built into it, and it has a dowel pin on one side of the cantilever. When the slider moves forward and backward once, the dowel pin is forced to the other side of the cantilever. Now, if the slider moves forward again, the slider strikes the dowel pin and cannot move any further without breaking something. The cantilever also acts like a spring, ensuring that the dowel pin cannot escape even if the mechanism is used in an arbitrary orientation. For future reference, I suspect that any single use mechanism requires some sort of biasing force (such as gravity, springs, or magnets) or holding force (such as friction) in its design, especially if it needs to work in any orientation.