Beating Human Heart - Gears, Crank

Video! A fun anatomical desktop fidget. Twist the handle to get a full 'lub-dub' heartbeat. Almost like a manual mechanical animatronic.

Included is the ZIP files of STLs to illustrate where they are in the mechanism, as well as the entire print plate as a single STL to show the recommended print orientation. You can use PLA or any rigid material to print the mechanism, and it should print easily without brim or supports. The skin has to be a flexible filament - I used 87a harness TPU. (If you don't want to use TPU, you might be able to redesign the skin using a voronoi pattern or other cutout to get the required flexibility - but I will leave that as an exercise to the reader)

The only hardware required is some M3 screws:

• 5x 14mm
• 12x 6mm No glue or anything else

Some fun design tips I learned from this:

• A screw makes a great pivot, especially if you have it 'bottom out early' in the anchored part, thus forcing the correct amount of tolerance between the screw head and the rotating part
• TPU can be sewed using hooked leather needles
• In OnShape: make a sketch of circles in the shape of gears you like, derive the diameters to variables, then use GearLab to build out the gear train. Then, building a frame around it is far easier.
• Chat-gpt can help greatly with designing your gear train to have the proper spacing and final ratio (though it is not perfect)

You can also tweak the design in CAD in my OnShape. You could, say, retolance the parts to work better for your printer slicer, or change it to use a different screw size, or redesign it into something else entirely - up to you!

Category: Mechanical Toys