Head Bangers

prusaprinters

<figure class="image image-style-align-center image_resized" style="width:72.28%;"><img src="https://media.printables.com/media/prints/316656/rich_content/279ec4f3-814a-49f0-b3bf-fff73361af3a/headbangers.gif#%7B%22uuid%22%3A%2273591dcd-41c4-4c08-ab8e-ce2af6b39df3%22%2C%22w%22%3A690%2C%22h%22%3A305%7D"></figure><p>These guys are always butting heads, especially when debating Newtonian physics. They're an inverted version of the classic Newton's Cradle demonstration of conservation of momentum and energy. &nbsp;</p><p>But why is the middle spring so much stiffer? Because of imperfections in the collisions (energy loss, misalignments, etc.), the motion can devolve into a 'sway' mode, where all the heads sway together. With the center spring stiffer, the middle guy acts as a steadying moderator, keeping the debate going back &amp; forth in a more regular manner. (Sorry, I've gone off the rails with my metaphor.)<img></p><p>The secret to making this work is that all the 3 heads need to be touching at the time of impact, otherwise, they just kind of chatter. (Sorry, that metaphor again.) Because the heads need to print with a small gap between them, after printing you have to flex the convolutions of the outer springs (gently) so that the heads actually press against each other slightly.</p><p>Printing is simple with built-in supports underneath the springs. Use PLA and 0.2mm layers. The more massive the heads are, the longer they will bang. I used 5 perimeters and 50% infill, but you can try more or less.</p>