Robotic Touch Using A DIY Squishy Magnetic Pad

September 22, 2024 by Donald Papp 5 Comments

There are a number of ways to give a robotic actuator a sense of touch, but the AnySkin project aims to make it an overall more reliable and practical process. The idea is twofold: create modular grippy “skins” that can be slipped onto actuators, and separate the sensing electronics from the skins themselves. The whole system ends up being quite small, as shown here.

Cast skins can be installed onto bases as easily as slipping a phone case onto a phone.

The skins are cast in whatever shape is called for by using silicone (using an off-the-shelf formulation from Smooth-on) mixed with iron particles. This skin is then slipped onto a base that contains the electronics, but first it is magnetized with a pulse magnetizer. It’s the magnetic field that is at the heart of how the system works.

The base contains five MLX90393 triple-axis magnetometers, each capable of sensing tiny changes in magnetic fields. When the magnetized skin over the base is deformed — no matter how slightly — its magnetic field changes in distinct ways that paint an impressively detailed picture of exactly what is happening at the sensor. As a bonus, slippage of the skin against the sensor (a kind of shearing) can also be distinctly detected with a high degree of accuracy.

The result is a durable and swappable robotic skin that can be cast in whatever shape is needed, itself contains no electronics, and can even be changed without needing to re-calibrate everything. Cameras can also sense touch with a high degree of accuracy, but camera-based sensors put constraints on the size and shape of the end result.

AnySkin builds on another project called ReSkin and in fact uses the same sensor PCB (design files and bill of materials available here) but provides a streamlined process to create swappable skins, and has pre-made models for a variety of different robot arms.

Multi-Material Printing Enables Low Cost Silicone Prototypes

September 4, 2024 by Tom Nardi 9 Comments

While it’s the ideal choice for mass production, injection molding is simply no good for prototyping. The molds are expensive and time-consuming make, so unless you’ve got the funding to burn tens of thousands of dollars on producing new ones each time you make a tweak to your design, they’re the kind of thing you don’t want to have made until you’re absolutely sure everything is dialed in and ready. So how do you get to that point without breaking the bank?

That’s not always an easy question, but if you’re working with silicone parts, the team at OpenAeros thinks they might have a solution for you. As demonstrated through their OpenRespirator project, the team has developed a method of 3D printing single-use molds suitable for large silicone parts that they’re calling Digital-to-Silicone (D2S).

In the video below, [Aaron] and [Jon] explain that they started off by simply printing injection molds in the traditional style. This worked, but the molds can get quite complex, and the time and effort necessary to design and print them wasn’t a great fit for their iterative development cycle. They wanted to be able to do from design to prototype in a day, not a week.

Eventually they realized that if they printed the mold out of a water-soluble filament, they could simplify its design greatly. They’ve documented the design process in detail, but the short version is that you essentially subtract the 3D model of the design you want to produce from a solid shape in your CAD package, and add a few holes for injecting the silicone. Once the silicone has cured, the mold can be dissolved away in warm water to reveal the finished part.

They then took this concept a step further. Thanks to the multi-material capabilities offered by some of the latest 3D printers, it’s possible to print structures within the mold. Once the silicone is injected, these structures can become part of the finished part. For the OpenRespirator, this lets them add PETG stiffening rings around where the filters to snap into the silicone mask body.

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3D Printing Silicone Parts

February 8, 2024 by Al Williams 6 Comments

Silicone is a useful material for many purposes. Traditionally, creating something out of silicone required injection molding. That’s not difficult, but it does require a good bit of setup. As [Formlabs] points out in a recent video, there are at least three other routes to create silicone parts that utilize 3D printing technology that might fit your application better, especially if you only need a few of a particular item. You can see the video below.

The three methods are either printing silicone directly, printing a mold, casting silicone, or using high-performance elastomers, which are very silicone-like. Of course, as you might expect, some of this is aimed at prompting some of [Formlab’s] products, like a new silicone resin, and you can’t blame them for that.

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An Adjustable High-Voltage Power Supply Built With Safety In Mind

January 6, 2024 by Dan Maloney 11 Comments

It’s not entirely clear why [Advanced Tinkering] needs a 50,000-volt power supply, but given the amount of work he put into this one, we’re going to guess it will be something interesting.

The stated specs for this power supply are pretty simple: a power supply that can be adjusted between 20kV and 50kV. The unstated spec is just as important: don’t kill yourself or anyone else in the process. To that end, [Advanced] put much effort into making things as safe as possible. The basic architecture of the supply is pretty straightforward, with a ZVS driver and an AC flyback transformer. Powered by a 24-volt DC supply and an adjustable DC-DC converter, that setup alone yields something around 20kV — not too shabby, but still far short of the spec. The final push to the final voltage is thanks to a three-stage Cockcroft-Walton multiplier made with satisfyingly chunky capacitors and diodes. To ensure everything stays safe in the high-voltage stage, he took the precaution of potting everything in epoxy. Good thing, too; tests before potting showed arcing in the CW multiplier despite large isolation slots in the PCB.

Aside from the potting, some really interesting details went into this build, especially on the high-voltage side. The 3D-printed and epoxy-filled HV connector is pretty cool, as is the special wire needed to keep arcs at bay. The whole build is nicely detailed, too, with care taken to bond each panel of the rack-mount case to a common ground point.

It’s a nice build, and we can’t wait to see what [Advanced Tinkering] does with it. In the meantime, if you want to get up to speed on handling high voltage safely, check out our HV primer.

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3D Printed Cookies, Sort Of

January 5, 2024 by Kristina Panos 1 Comment

Are there any cookies that taste better than the ones you make yourself? Well, maybe, but there’s a certain exquisite flavoring to effort. Just ask [jformulate], who created these custom chocolate-topped butter cookies using a mixture of 3D printing, silicone, and of course, baking and tempering.

[jformulate] did this project along with a makerspace group, and the first thing they did was decide on some images for the cookies. Once a hexagon-shaped mold was created in Fusion360, the images were added in. Some had to be height-adjusted in order for the detail to come out.

Once these positives were printed, it was time to make the food-safe silicone molds that would form the custom chocolate toppers. If you don’t have a vacuum de-gasser, [jformulate] recommends pouring a thin stream from a high place to avoid air bubbles. You can always tap the mold several times on a flat surface as well to bring trapped air to the top.

Finally, it’s time to make cookies. [jformulate] has good instructions for tempering chocolate, as well as a recipe for the butter cookies that support the designs. As a bonus, [jformulate] shows how to make a fish-shaped hot chocolate bomb, and made Jolly Rancher (sadly not Wrencher) medallions using the silicone molds and a microwave.

For the semi-disappointed, directly 3D printing cookies is definitely a thing.

Nuke Your Own Uranium Glass Castings In The Microwave

April 26, 2023 by Dan Maloney 20 Comments

Fair warning: if you’re going to try to mold uranium glass in a microwave kiln, you might want to not later use the oven for preparing food. Just a thought.

Granted, uranium glass isn’t as dangerous as it might sound. Especially considering its creepy green glow, which almost seems to be somehow self-powered. The uranium glass used by [gigabecquerel] for this project is only about 1% U₃O₈, and isn’t really that radioactive. But radioactive or not, melting glass inside a microwave can be problematic, and appropriate precautions should be taken. This would include making the raw material for the project, called frit, which was accomplished by smacking a few bits of uranium glass with a hammer. We’d recommend a respirator and some good ventilation for this step.

The powdered uranium glass then goes into a graphite-coated plaster mold, which was made from a silicone mold, which in turn came from a 3D print. The charged mold then goes into a microwave kiln, which is essentially an insulating chamber that contains a silicon carbide crucible inside a standard microwave oven. Although it seems like [gigabecquerel] used a commercially available kiln, we recently saw a DIY metal-melting microwave forge that would probably do the trick.

The actual casting process is pretty simple — it’s really just ten minutes in the microwave on high until the frit gets hot enough to liquefy and flow into the mold. The results were pretty good; the glass medallion picked up the detail in the mold, but also the crack that developed in the plaster. [gigabecquerel] thinks that a mold milled from solid graphite would work better, but he doesn’t have the facilities for that. If anyone tries this out, we’d love to hear about it.

A Soft Soldering Jig For Hard Projects

April 5, 2023 by Matthew Carlson 21 Comments

We’ve seen some absolutely gorgeous freeform circuit sculptures. There’s a mystic quality to taking what has normally been hidden away for safety and reliability reasons and putting it on display for everyone to see. Of course, creating these unique circuit sculptures takes considerable time and effort. [Inne] created several silicone soldering jigs to help with these tricky joints.

While a vice or helping hands is crucial for many joints, when dealing with tiny SMD components and exacting angles, you need something a little more specialized. Double-sided tape is often recommended, but heat ruins the adhesive and SMD components like to stick to soldering iron tips. Since silicone tends to be heat resistant, it makes a decent material for soldering on. [Inne] uses a city analogy with the cups for soldering called plazas, each with a hole (called a manhole) leading to a foot-switch vacuum pump to keep parts in place. The OpenSCAD code is available on GitHub under a GPLv3 license. It generates a two-part mold that you can cast in A-8/A-15 silicone.

It’s a clever project that makes it far easier to assemble gorgeous circuit sculptures. We love the design and thought that went into it, particularly the naming scheme as we often find appropriately naming variables in OpenSCAD quickly becomes difficult.