How-To: Work with Shape-Memory Alloy

We’re very pleased to have Jie Qi on MAKE for our Advanced Materials month (which has been extended until Feb 6). Her bio is so impressive, I thought I’d post the entire thing:

I was born in China and moved to the US when I was 6… Fast forward to college at Columbia University. I started out a pre-medical/biomedical engineering major and spent a semester and summer doing tissue engineering research in the MBL group. That same summer, I got an internship in Brooklyn building sculptures out of bottles for Aurora Robson, through which I fell in love with art again. So I changed my major to mechanical engineering (because they get access to the machine shop!) and discovered new media art. At this point, I got started on the littleBits project with Ayah Bdeir and learned to design and build electronics. She introduced me to the Media Lab, and I immediately fell in love with the place. So I got a summer internship in Leah Buechley’s group. That summer, I discovered the Arduino and the joys of paper + electronics. After I went back to Columbia for my senior year, I continued working on littleBits and spent a semester attempting to make microscale artwork using photolithography and microfluidics in the LMTP research group. Turns out it’s really hard to make art when you can’t see it! After graduating (with a BS in mechanical engineering), I came straight to the Media Lab and started my masters in the High-Low Tech group. I’m still here, now in my second year, and learning tons every day!

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).

Because SMAs are silent, lighter than traditional actuators, and can be set to create many kinds of motion, there are a ton of cool things you can do with them that are hard to achieve with other actuators. Marcelo Coelho has experimented with combining custom-set nitinol with textiles to create actuated fashions as well as responsive and soft interfaces like the Shutters Project:

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:

Animated vines:

I/O self-folding paper:

SMA Primer
If you’re using SMAs for the first time, I recommend starting with Flexinol muscle wire (which is available on Robotshop, or directly from Dynalloy). It is reliable and simple enough to hook up to a circuit. When you run current through, the resistance of the wire causes it to heat up and the wire will contract about 10% of its original length. Since there is a layer of oxidation around the wire, you cannot solder directly to the wire itself. To attach the flexinol wire to a circuit, simple fold the end of the wire into a “u” and use a jewelry crimp bead around the ends. The crimp bead holds onto the wire mechanically and also makes it possible to solder the ends for robust electronic connections.

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.

Happy making!


What is the World’s Strongest Plastic?

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:

  1. What do you mean by “plastic?” Do thermosetting materials like epoxy count? What about polymers that are reinforced with glass or carbon fiber infill?
  2. What do you mean by “strong?” Are you talking about wear resistance? Compressive or tensile strength? Temperature resistance? Chemical resistance?

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.


The Modular Electronic Drums of Nick Yulman

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.



Plywood Table is All Secret Compartment

Artists Naoki Hirakoso and Takamitsu Kitahara built this wooden surface called the Kai Table, complete with a bunch of “secret” compartments — probably more accurately described as storage compartments; they don’t seem too secret. [via Dornob]


Last Weekend’s Betaspring Hackathon: Netduinos, Arduinos, and Hungry Hippos

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:

  • Matt Gillooly’s Hungrypotamus. He hacked a Hungry Hungry Hippos game to be played over the Internet. Matt’s project was the Hackathon Champion. The project was controlled by the Arduino-compatible Teensy.
  • Chris Meringolo’s connected kegerator (pictured above). This system embedded an RFID tag into pint glasses, allowing you to control who gets beer, and keep an eye on how much they have (the Betaspring folks saw potential for a leaderboard there). Chris used an Arduino-compatible Freeduino USB Host Board as the brains.
  • Chris Perez and Simon Norridge engaged in a variety of LED experiments: an epoxy glow stick and LED-illuminated tip jar.
  • Ramsey Abouzahra, Damian Ewens, and Pat DeSantis worked on a scalable system for turning a building into a dancer-controlled (Kinect-enabled) light wall. They received the Most Ambitious Project award.
  • Betaspring (excluded from the competition) designed a Netduino Plus-based Internet enabled doorbell. Hackathon partner GreenGoose supplied some sensors for the hackathon. Betaspring used one in their project.
  • Ryan Rogowski and Rob Sanchez used an Arduino and a RedPark Serial Cable for iOS, along with a LED fretboard accessory they developed in partnership with KippKitts, to start work on an iOS app that would teach you to play guitar.
  • Topher Brown (winner of the Hardcore Prize) stayed all night and worked on an Internet-connected taillight (it fell off the back of a car). He’ll use it to indicate the status of various server devices at work.

Hacktastic Days(and Nights) at Betaspring

Flickr set


Tool Review: NWS Ergonomic Long-Nose Pliers


NWS Ergo-Grip Long-Nose Pliers Size

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.

NWS Long-Nose Pliers Hand Grip

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.

NWS Ergo-Grip Long-Nose Pliers Hand Angle

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.

NWS Ergo-Grip Long-Nose Pliers Jaws Closeup

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.

NWS Ergo-Grip Long-Nose Pliers Grip Closeup

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.


New in the Maker Shed: Membrane Matrix Keypad

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!


  • Weight: 7.5 grams
  • Keypad dimensions: 70mm x 77mm x 1mm (2.75″ x 3″ x 0.035″)
  • Length of cable + connector: 85mm
  • 7-pin 0.1″ pitch connector
  • 7-pin 0.1″ male headers included.
  • Compatible with the Matrix Keypad Arduino Library


EMSL Weighs in on Power Dissipation

I loved this fascinating post by Windell of Evil Mad Scientist Laboratories, all about managing power in electronics projects:

An ever-present challenge in electronic circuit design is selecting suitable components that not only perform their intended task but also will survive under foreseeable operating conditions. A big part of that process is making sure that your components will stay within their safe operating limits in terms of current, voltage, and power. Of those three, the “power” portion is often the most difficult (for both newcomers and experts) because the safe operating area can depend so strongly on the particulars of the situation.

In what follows, we’ll introduce some of the basic concepts of power dissipation in electronic components, with an eye towards understanding how to select components for simple circuits with power limitations in mind.

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.


Heirloom Quality Capacitive Touch Stylus

Check out this heirloom quality capacitive touch stylus from Talking Rock, Georgia maker Stephanie McLaughlin. Each stylus Stephanie makes is hand-turned on a lathe and made from quality materials.


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