Jie put together this wonderful introduction to shape-memory alloys (SMA) for us. Thanks, Jie! Great to have you aboard. -Gareth
You’ve likely heard about shape-memory alloys (SMAs), metals that change shape when heated to an activation temperature. When cool, they are malleable and can be shaped like a typical metal. However, when heated to activation, they return to their preset shape. At the atomic level, the crystalline structure of an SMA changes with heat from one regular structure to another. However, while all metals will change shape with heat (i.e. melt), SMAs change shape all in solid phase and this change is reversible. For example:
The most commonly used SMA is nitinol (nickel titanium). Commercially it can come in unset form, meaning it has no “memory” yet, as well as pre-trained shapes like muscle wire which contracts when heated (hence the name).
Hylozoic Soil, a sculptural installation by Philip Beesley, uses muscle wire to actuate portions of this “living” architecture.
Yet another magical sculpture is the Robotany project by Jill Coffin, John Taylor, and Daniel Bauen in which the branches of a living tree are made to sway when someone walks by. Since the SMA wire is completely silent and hidden, the tree appears to be moving to a virtual breeze.
In my projects, I’ve found that SMA wires are perfect for actuating papers, which are rigid enough to hold interesting structures but soft and light enough to be moved by tiny SMA wires. Some examples are:
Venus fly trap pop-up page:
I/O self-folding paper:
The hardest part about using muscle wire is controlling the amount of current running through the wire. You want to give it enough for a dramatic effect, but not so much current that the wire burns out (and stops contracting). Flexinol wire has a consistent resistance per length and an optimum current as specified in the flexinol technical data.
One simple technique is to look at the target current from the data sheet and then use Ohm’s law (voltage = current x resistance) to calculate the length of wire that is needed to maintain this amount of current based on the power supply you have. Since these wires generally require hundreds of milliamps, I recommend getting a strong lithium-ion battery or use a wall power supply. For example, if I were using the 0.006″ diameter wire, which needs 0.400 Amps, and I have a 5V power supply, I would need a total resistance of 5/0.4 = 12.5 ohms. Since the resistance of this particular wire is 1.3 ohms/in, I would need 12.5/1.3 = 9.5 inches.
In general, always test your mechanism using low power and turn on the wire in short intervals. If you see a jerking motion, chances are the wire has gotten too much power and might in fact have burned out. If you have an Arduino, you can hook up the wire using a transistor and PWM the power. Start with a low duty cycle and work your way up until you get a strong enough movement. Note that once the metal is getting enough power to change shape, adding more power won’t make the movement more dramatic, it will only make the shape change more quickly.
Now that you have the basic electronics, here are some simple mechanisms you can use to get various motions out of your wire. One of the most dramatic mechanisms is the curling mechanism where you simply sew nitinol to the paper. In this case, when the wire contracts, the paper must curl around it to make up for the shorter length of wire.
To make a self-folding flap, anchor the ends of wire on the main side of the crease and attach the center of the wire very close to the crease on the flap. This mechanism uses the wire as a tendon to pull the flap.
By adding simple folds, you can change a mechanism completely. For example, going from curling to flapping only takes a couple of curved folds to each side of the curling mechanism.
You can add extra flaps to the folding mechanism to make a parallelogram, which makes surfaces rise off the page.
For these and other mechanisms, check out these projects from a recent paper electronics workshop
If you’re looking for a simple beginner project, try this flapping origami crane tutorial.
It’s a simplistic question, possibly even naive. Put it to a chemical engineer or a materials scientist, and she or he will almost certainly not come back with a single answer, but with (at least) two questions:
But say you limit your question to thermoplastic materials that can be melted and molded, extruded, spun, and/or drawn into various shapes. And that you exclude composite materials of any kind—just pure polymers without any reinforcement or infill.
Given those answers to question 1, a single material begins to stand out almost regardless of how you answer question 2.
That material is polybenzimidazole (PBI), marketed as a bulk polymer under the trade name Celazole. It is commonly reported to have the highest compressive strength of any unfilled plastic material, and also has the highest tensile strength, highest shear strength, and highest Rockwell hardness rating of any plastic that I have been able to find. It maintains its mechanical properties at high temperatures better than any other unreinforced polymer, and can reportedly survive short-term exposure to 1400°F, which is 200° above the melting point of aluminum. Phrases like “the highest performing engineering thermoplastic available today” are commonly used to describe Celazole in plastics industry literature.
NASA identifies PBI as a space program spinoff technology, and maintains an informative page describing its history, which, in fiber form, includes astronaut flight suits used on Apollo, Skylab, and numerous space shuttle missions.
Nick Yulman, of NY Soundworks, recently debuted debuted his Index Boogie performance piece at PS1. The piece consists of various solenoid-powered noise makers, which Yulman calls either “Surface Poppers” or “Drum Beaters”. They’re designed to be modular music devices that can easily be mated to virtually any inanimate object.
Index Boogie uses these devices to play drums, books, and a glass beaker, allowing the user to quickly switch between various objects with different tonal characteristics. The devices are controlled by preset midi compositions that can be switched when Nick flips a book to different pages.
I spent the last weekend as an advisor to Betaspring‘s Digital Meets Physical Hackathon. The participants arrived Saturday morning and organized into teams. I stayed until about midnight, and returned around 10am Sunday morning, where I was able to help a couple teams get unstuck. It wasn’t that I was any smarter than them; I just had more sleep!
After Allan Tear of Betaspring kicked things off, he turned the stage over to James Rutter of AS220 Labs, who explained that the labs would be open all day for hackathon participants. AS220 is an unjuried, uncensored, all-ages arts center in Providence, and AS220 Labs combines a fab lab, community access to those tools, and other programs. AS220 Labs made their tools (such as a laser cutter and a couple of MakerBot 3d printers) available to participants that day.
After James gave an overview of the labs, Chris Walker from Netduino spoke. Chris had brought a bunch of Netduinos for participants to make things with. A Netduino plus became the heart of Betaspring’s own hackathon project: an Internet-connected doorbell. After Chris spoke, Kipp Bradford of KippKitts spoke; he brought some recently-created kits and parts (motor shields, driver boards, LEDs), and some other unusual items that proved useful.
After that, hacking began, and participants completed a number of projects:
You probably have never heard of NWS before, have you? They’re a German hand tool manufacturer that produces some really sweet pliers and cutters. Today I’d like to focus on the NWS ergonomic electrician’s pliers (angled long-nose pliers), which are designed to be held and used with a straight wrist.
Ergonomic and pistol-grip pliers can offer a number of advantages over traditional-styled pliers. As you can see in the following photo, regular pliers point up at a 45° angle when held naturally with a straight wrist. Ergonomic pliers, on the other hand, are angled forward by about 45° such that the jaws are oriented in line with one’s arm.
As slight a difference as it might seem, straightening your wrist results in greater twisting and pulling power, easier tight-quarters access, and improved user comfort.
I first learned about NWS pliers a couple of months ago and promptly purchased a few pliers and cutters to try out. Since then, these ergonomic long-nose pliers have become one of my favorite tools to use. Actually, I have become quite fond of all of the NWS pliers now in my toolbox, but perhaps that’s a story for another time.
The spring-action long-nose pliers feature a straight-grooved gripping area, crimping anvils, two-size wire strippers, and a hard/soft wire cutter. The handle has a three-material composition with medium-hard plastic, soft and textured grip zones. There’s also a built-in spanner (box-end wrench) and a lock to keep the jaws closed during storage or transport.
Quality-wise, these pliers are absolutely fantastic. The black-PTFE (Teflon-like) coating shows no sign of chipping or peeling, the jaws are perfectly formed and grooved, and the cutters meet with zero gaps. I would have preferred a knife-anvil cutter profile rather than knife-knife, but there’s no sign of misalignment or premature dulling.
These pliers are usually the first I reach for when working inside of a computer case or project box, where a high density of components and wires requires a completely straight angle when installing or removing parts. The NWS pliers have large jaws and are not designed for precision work, so my hemostats still see a fair bit of action.
Although the ergo pliers are great for general purpose and even heavy-duty usage, they do have limitations. While they are incredibly comfortable to use, certain tasks are best accomplished with traditional-styled pliers. It all depends on the task at hand and grip angles needed to access the parts awaiting manipulation. As such, pliers like these will complement but not replace ordinary styled ones.
The model number for these long-nose pliers is 1406-69-200. If you’re not a fan of the PTFE coating, there’s also a matte chrome option – 1406-49-200. Ergo-style pliers with wider combination jaws are also available (1096-69-200 and 1096-49-200). The pliers are priced at $35-40 and are currently only carried by two USA distributors – German-Hand-Tools and Chads ToolBox. Both vendors are highly recommended, but be sure to ask if the pliers are in-stock and not back-ordered before you place an order.
Stuart Deutsch is a tool enthusiast, critic, and collector. He writes his passion at ToolGuyd.
The Membrane Matrix Keypad, available in the Maker Shed, has 12 buttons arranged in a telephone-line 3×4 grid. It’s made of a thin, flexible membrane material with an adhesive backing (just remove the paper) so you can attach it to nearly anything. The keys are connected into a matrix, so you only need 7 Arduino pins (3-columns and 4-rows) to scan through the pad. Every time I look at this keypad I can’t help but imagine it being used to open a door to a secret lair or as the only way to disarm an evil device. Have other uses in mind? Put them in the comments!
I loved this fascinating post by Windell of Evil Mad Scientist Laboratories, all about managing power in electronics projects:
Windell goes into the math in choosing the right components to ensure that, for example, your resistor can take all the current going through it.
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