A flexure battery latch in three prints
· Builds · 3d-printing, cad
The battery on our robot was held in by velcro, which is a polite way of saying it was held in by hope. After it walked out of its bay during a match, I spent an evening designing a printed latch with a living hinge — a flexure — so the battery clicks in and pulls out with one finger, no fasteners.
Print one snapped at the hinge root on the fourth cycle. Classic mistake: I'd modeled the flexure with a sharp internal corner, which is a stress concentrator, and printed it with the layer lines running across the hinge instead of along it. Print two fixed the fillet but I got greedy and thinned the beam to make the click softer; it survived exactly eleven cycles.
Print three is the keeper: 0.8 mm beam, 3 mm fillet, printed flat so the hinge bends along the extrusion direction, PETG instead of PLA for the fatigue life. It has been through a few hundred cycles on the bench and the click is still crisp. The whole part is 14 grams and replaces a strap, two screws, and an apology.
The real version of this post gets the CAD screenshots and the beam-bending arithmetic; this placeholder exists so the cover image and the build tab have something to show.