After testing the Flat-Pack Camera Arm I built, I was pretty happy with the results. Happy, except for one detail: the joint at the base of the arm would creep down over time. This wasn’t a problem while taking shots of projects at the bench, given how often I’d have to reposition it anywhere. The big breakdown was trying to capture time lapses. The creep was just too noticeable, and it would never stay in place long enough to keep the action of a day’s hacking in frame.
So, I set out to make some locking plates for the arm, and I think people could find some interesting uses for the process I came up with. The broad strokes of the method are that you design the part you’d like at the end in CAD, design a floor under your part with walls around it (I call this a bathtub), print the bathtub mold you designed, cast the mold using 2-part silicone (making sure it’s nice and level), and cast your final material into that mold. Once you’ve got the knack of replicating parts using 1-part molds, you can get fancier: adding vent holes for letting air escape or labels for your parts or building multiple parts for your molds for even more precise geometry.
Below you can find more information on the whole project:
This will be an update on the things I’ve learned molding quadrupeds over the last couple of months and some previews of the new robots I’ll be experimenting with in the next few weeks. To start, I’ve had the chance to run a gaggle of design experiments ranging from small changes to the particular silicone I’ve been casting, to more radical changes to how the whole plionics manufacturing process comes together.
I’ve discovered that molding complex channels of tubing can be extremely difficult, and the CAD equally infuriating. I’m discovering some automatic routing tools in SolidWorks that could streamline the process, but there might be another solution that sidesteps that whole mess entirely. It’s possible to cast around silicone tubing that’s already connecting up all the interior geometry. So, what I’d have to do to get the design working is build the cores with little fastenings for plugging in tubing and make sure all the tubes have enough clearance to get past one another. I’m anticipating the world of reality doesn’t let me off the hook that easily, but it’s a start. Continue reading →
Quadrupeds. I’ve been dreaming about quadrupeds. I’ve been hunting for challenges to test my methods and improve the engineering on the whole “print and cast a soft robot” thing (I really need to come up with a name for this… “Borgatronics?”). I started with tentacles because they were easy to design, easy to test, and symmetrical.
They’ve made a lot of progress, but it’s time to turn to other designs. I’ve produced a few prototypes along one main design, and have discovered many things. I’m going to try and explain my logic behind the design and some of the major changes I intend to make in the next version. I’m also going to tell you all the myriad ways I went wrong in this design and the things I’ve done to try and make it right.
This is going to be a pretty dry technical post on the industrial design aspects of the robots I’ve been developing. I promise you entertainment and levity aplenty in the future. For now, we grump about casting flaws, mold design, and process control. Continue reading →
Mold making and casting has been a huge part of my life for years. It started in the SFX industry, making molds and cleaning up parts for robotic snakes on Snakes on a Plane (really), and has become an even more significant factor with the recent soft robotics project. However, one thing has plagued me this whole time: buckets.
There are lots of elegant methods for prepping a mold, squaring away your shop space, keeping everything all clean and science-y, but no matter how you slice things (unless you’re dealing with 50 gallon drums), pouring out gooey slimy liquid rubber always ends up being a mess. I often end up going through several sets of stirring sticks and dipping disposable cups into my material in the hopes of keeping everything quarantined and safe from contamination. Still I end up feeling like a Dickensian orphan, dipping a ladle into what amounts to $200 of runny goo. Continue reading →
Last week I headed up to Viridis3d for some more hacking. We got some beautiful results using some vaccuum casting with the trefoil design, parts printed for both the internals and outer shell of the quadruped, and schemes for tempting new mechanisms. All in all it’s been really exciting seeing the progress. Also, I have some updates on controlling the trefoil tentacle with an arduino powered set of air solenoids.
One of the confounding factors in getting this flavor of robot moving predictably has been how difficult it is to control wall thickness and bubble inclusions when casting the final silicone pieces. Like almost every mold, you do the best you can, try to create a nice, sterile, well ordered universe, and hope. Although Dragon Skin has performed really well as a durable, flexible silicone, it has the nasty habit of trapping bubbles in inconvenient spots when curing. Many silicones have a thin, pancake syrup consistency when mixed, but Dragon Skin is much more like honey or molasses, meaning it’s really easy to trap bubbles in the mix while stirring and have them set in place when everything’s curing. A good solution for the problem is pulling them back out with a vacuum chamber. Continue reading →
I’ve finally gathered my wits after a whirlwind tour of Europe, starting at CCC, giving some talks and connecting up with potential collaborators, to Berlin to meet hackers I hadn’t seen in years, to Brussels to play with some material science experiments in impact resisting plastics. While at CCC I gave three talks, two lightning talks on digital fabrication and the strange world of news advertisement, and a 15 minute talk on the methodology and philosophy behind my soft robots. I’ll be uploading the short talks sometime soon, but for now please see my soft robots lecture after the jump. Continue reading →
I have lots of updates to share. First, there’s a new video of the latest tentacle prototype in action below the fold. Second, We’ve made some excellent progress on the method of manufacture, reliability, and repeatability of the designs we’re producing. It’s almost at the point where we need to figure out a good real-world experiment to test our ideas against. I’m currently torn between creating a grasper and something that walks. Jim and I have been working out ways of getting a self contained power source inside of a soft robot, and it seems like we might be able to use a canister of compressed gas to do everything from timing movements to articulating valves. I’m working out ways of integrating peristaltic pumps and timing mechanisms that will be simple to prototype… which is a pretty tall order. However, I think a combo of laser cut bits and creative molding can have this one solved. Continue reading →
After only six actual work days, a few afternoons spent on CAD, and a lot of tweaking, I’ve got a working robotic tentacle prototype! I used the hand pump off of a sphygmomanometer and a lot of sil-poxy, but it’s working in a rough and ready way. There’s video after the jump below.
I had to cut this one open to fully remove all the core and then sealed it back up. I think the next version will evacuate the core cleanly due to the powder tweaks we made, though. It could also use some revisions to the way it interfaces with the air supply. In the future I’m going to have to run some tests on adhering silicone to various plastics to see what will make for the most solid fittings. The sil-poxy infosheet says polyurethanes are a good candidate, so I might start there. Continue reading →
I just arrived back from a second session of hacking and casting with Jim Bredt over at Viridis3D, and I have to say I’m pretty excited. The biggest result of the most recent round of mold making is a successful method for getting soluble cores into printed molds and casting silicone around them reliably and repeatably. I ended up doing a lot of revisions to the casting method and industrial design based on the results of last month’s experiments. The mold goes together in new ways with changes to accommodate pouring the mold, reusing the outer shell, aligning the cores, printing the cores, and how it will get hooked up to pneumatics once everything’s cast and functioning. I’m especially proud of the design behind the base of the soluble core, which is tapered so that it can align and center itself within the mold even if its dimensions shrink by a few percent. The little ears on this base are both to align it rotationally (which doesn’t matter much as far as the tentacle is concerned, but could matter in other more complex molds) and to prevent the core dropping down further into the mold and mucking up the wall thickness if it shrinks more than spec. Continue reading →