Soft Robotic Quadruped - First Draft
by gianteye, published
These files are designed to make a simple soft robotic quadruped. The process may seem complex, but it's pretty easy once you have a handle on the basics. Essentially the goal is to get a robot you design in CAD popped out into the real world as a seamless silicone part, ready to be piloted with air pressure. The way this shakes out is to use molding to get waxes that form the interior air channels, and print shells to form the exterior surface. I've been using powder printing over at http://viridis3d.com (they've been excellent research partners) to achieve this, but it should work equally well using FDM as long as you acetone smooth it and check for cracks.
This prototype didn't function as planned, but the next revision (due out late April) should correct the design oversights.
You'll want to check here http://har.ms/blog/print-your-own-robot-part-8/ for details, as the process is pretty involved.
First, to make the wax interior parts, print out all of the left hand and right hand wax molds. I believe I made a measurement error on the walls of one of these, so that when it's poured the silicone won't reach up to the top of the model. I corrected this with some clay, but it could just as easily be done by dragging some points around in the DXF. Acetone smooth the molds and check for cracks/delaminations. If everything's solid, pour all the molds up in silicone. When the molds cure, pop them out and use a razor blade to relieve the undercuts. I designed these molds to be pressure injected with wax, but found a workaround so they could be cast at home. Check the post above for details on how I adjusted these molds for gravity pouring wax.
Print both sides of the shell, smooth them, and check for cracks. These get bolted together with 1/4-40 screws. When you've cast your waxes, slide them together, place them into the mold, and cast your silicone. The best silicones I've found for these bots have been Smooth-On Dragon Skin (which ideally should be vacuum cast) and a 50/50 mix of Dragon Skin and Smooth-On Eco Flex.
When the silicone is cured, boil the quadruped in soapy water to melt out the wax. This takes some time and a few changes of water as the wax makes a huge mess. I've been experimenting with water soluble materials for forming the interior bladders, and will update my site ( http://har.ms ) with the results.