A Refrigerator Cooled by Rubber Bands

Ever noticed that a rubber band gets warmer when it’s stretched? The bands also get cooler when allowed to snap back to relaxed length? [Ben Krasnow] noticed, and he built a rubber band cooled refrigerator to demonstrate the concept. The idea of stretching a rubber band to make it hotter, then releasing it to make it cooler seems a bit counter intuitive. Normally when things get smaller (like a gas being compressed) they get hotter. When pressure is released the gas gets cooler. Rubber bands do the exact opposite. Stretching a rubber band makes it hot. Releasing the stretched band causes it to get cooler.

No, the second law of thermodynamics isn’t in jeopardy. The secret is in the molecular structure of rubber bands. The bands are made of long polymer chains. A relaxed rubber band’s chains are a tangled mess. Stretching the band causes the chains to untangle and line up in an orderly fashion. By stretching the band you are decreasing its entropy. The energy of the molecules in the band don’t change, but entropy does. All the work one does to stheatwheelretch the band has to go somewhere, and that somewhere is heat. This is all an example of entropic force. For a physics model of what’s going on, check out ideal chains. If you’re confused, watch the video. [Ben] does a better job of explaining entropic force visually than we can with text.

To test this phenomenon out, [Ben] first built a wheel with rubber bands as spokes. Placing the wheel in front of a heater caused it to slowly rotate. [Ben] then reversed the process by building a refrigerator. He modeled his parts in solidworks, then cut parts with his Shaper handheld CNC. The fridge itself consists of an offset wheel of rubber bands. The bands are stretched outside the fridge, and released inside. Two fans help transfer the thermal energy from the bands to the air. The whole thing is hand cranked, so this would make a perfect museum or educational demonstration. Cranking the fridge for 5 minutes did get the air inside a couple of degrees cooler. Rubber is never going to displace standard refrigerants, but this is a great demo of the principles of entropic force.

For more thermodynamic fun, check out [Al Williams] recent article about building a DIY heat pipe.

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Hackaday Links: April 17, 2016

There have been really cool happenings in the CNC world for the past few years. There is a recent trend of portable, handheld CNC machines. Yes, you read that correctly. This SIGGRAPH paper demonstrated a handheld router with a camera and a few motors that would make slight corrections to the position of the router. Load in a .DXF or other vector file, and you become the largest CNC machine on the planet. We saw it at one of the Maker Faires, and about a year ago the team soft launched. Apparently, the Shaper router is gearing up for production and [Ben Krasnow] got the first look with a full 17-minute demonstration of [Ben] fabricating parts out of aluminum. It looks like a great tool, and we can’t wait to see this thing in production.

Octoprint is the best way to give a 3D printer a web interface. The dev for Octoprint, [Gina Häußge] used to have a sponsor for developing Octoprint. They’re gone now, which means it’s time for [Gina] to start a Patreon. If you use Octoprint, you know it’s worth more than a dollar a month.

Really bad USB power supplies are nothing new around these parts. There are cheap USB supplies that don’t have any fuses, don’t have any circuit protection, and are noisy as hell. This is the worst USB power supply the Internet has to offer. It’s from one of the relatively new designs of USB power supplies that steps down mains voltage to five USB A ports. [bigclive]’s teardown revealed this was passing half wave mains voltage to the USB ports. It can light up a light bulb. It can kill your phone. The fault? A pinhole in the insulation between the windings of the transformer.

Electronic conference badges are getting excessive, but they can be so much cooler. Here’s Atmel’s take on a high-end conference badge. It has a display, sensors, WiFi, Bluetooth, runs Android, and has 512MB of RAM, 4GB of Flash. It’s a freakin’ mini tablet meant to last for three days.

Speaking of Atmel, they’re having a few growing pains in the merger with Microchip. Employees coming to Microchip from Atmel are getting their severance benefits cut in half. Apparently, the severance benefits given to Atmel employees were not communicated to Microchip before the merger.

Raspberry Pi Zeros are back in production. There’s also going to be a mysterious new feature. Is it WiFi? No, it’s confirmed not to be WiFi. How about Ethernet? Bluetooth? an RTC? Full size HDMI port? Actual pin headers? Audio port? Improved CPU / RAM? No, children. It’s none of these.

C.H.I.P., the nine dollar computer that made some waves last summer, has on-board Flash storage. That means you don’t need to put an image on an SD card. The folks behind C.H.I.P. have recently improved the method for flashing a new OS onto their tiny board: a Chrome plugin. Yes, this sounds completely bizarre, but Chrome plugins are becoming increasingly popular for USB gadget wizardry. You can program an Arduino with Chrome and log USB power profiles with a USB tester and Chrome. You will ride eternal, shiny and chrome.

Crazy Whirlwind Pre-Hackaday Prize Launch Tour

The Hackaday Prize was about to launch but the date wasn’t public yet. I decided to do a pre-launch tour to visit a few places and to drop in on some of the Hackaday Prize Judges. It started in Chicagoland, looped through San Francisco for a hardware meetup and Hardware Con, then finished with visits to [Ben Krasnow’s] workshop, [Elecia White’s] studio, and the Evil Mad Scientist Laboratories.

The Prize is now running and it’s time for you to enter. Look at some of the awesome hacking going on at the places I visited and then submit your own idea to get your entry started. Join me after the break for all the details of the adventure.

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How to Zip, Stick, and Screw Stuff Together

One of the first problems every new hacker/maker must solve is this: What’s the best way to attach part “A” to part “B”. We all have our go-to solutions. Hot glue, duck tape ( “duct tape” if you prefer) or maybe even zip ties. Super glue, epoxy, and if we’re feeling extra MacGyver-ish then it’s time for some bubble gum. For some Hackaday readers, this stuff will seem like old hat, but for a beginner it can be a source of much frustration. Even well versed hackers might pick up a few handy tips and tricks presented in this video after the break.

In part one of this series, [Ben Krasnow] shows us the proper use of just a few of the tools and techniques he uses in his shop. [Ben] starts out with a zip-tie tool which he loves in part because of a tension setting that ensures it’s tight but not overly. He moves on to advice for adhesive-vs-material and some tips on using threaded fasteners in several different circumstances. He also included a list of the parts and tools he uses so you don’t have to go hunting them down.

[Ben] is no stranger to us here at Hackaday. He does some epic science video. You can subscribe to his channel or follow his blog if you enjoy what you see.

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Celebrating the Omnibus Launch

On Thursday night Hackaday hosted an event in San Francisco to commemorate the launch of the 2014 Hackaday Omnibus. Our first print edition, compiled to commemorate some of the finest original content which we published last year should begin shipping as early as today. To celebrate the occasion, we were graced by a full house of amazing guests. Is it lame to say some of the people I respect most in the world were there?

Lightning Talks

Whenever you get a lot of people together, a good rule of thumb is to seize the opportunity to have them speak about what they’re doing. It’s not a big “ask” either; 8-minutes on what you’re passionate about is pretty simple.

[Jonathan Foote] gave a talk on generating RGBY colors from Hue. The project is ongoing but explores the concept of mixing colors of light with one additional source added to traditional red, green, and blue. [Priya Kuber] recently moved to San Francisco. She recently concluded more than a year of standing up the Arduino office in India (relevant but unrelated video). Her talk covered the emerging maker/hacker hardware scene in India which is showing amazing growth. [Chris McCoy] demonstrated his Raver Rings which began a Kickstarter on the same day. [Elecia White] of embedded.fm spoke about the educational opportunities that podcasts and other delivery medium provide and the responsibility we all have to guide our continued learning. [Emile Petrone] talked about an upcoming feature for his site Tindie which will add manufacturer information and ratings to the mix. And rounding things out [Dave Grossman] gave a talk on his Virtual Carl project which used video footage of his grandfather, combined with a Raspberry Pi and peripherals to create a remembrance of the man in virtual form.


[Ben Krasnow] shows off the chamber containing supercritical carbon dioxide.
During the rest of the evening there were a few spectacular demos going on. First, [Ben Krasnow] who is well known for his Applied Science series (among a million other accolades), brought at least two demos with him. The first was a pressure chamber made out of two massively thick discs of acrylic separated by a metal ring. Inside the void he had pumped and pressurized CO2. When the chamber is heated it, the contents become Supercritical Carbon Dioxide and the visual transition between liquid and gas disappears.

He also showed off a lens that can be focused electronically. This is not mechanical, there are zero moving parts. Instead a droplet of oil floating in water is the lens. A 75V, AC power supply pulls on the droplet, altering the meniscus to focus the lens. He didn’t fabricate the device from scratch, but the concept is completely new to us and quite interesting.

[Brian Benchoff] poses with Othermill hardware
[Brian Benchoff] poses with Othermill hardware
Othermill is located in the SF area. They produce a desktop milling machine which is spectacular at routing PCBs. The little wonder isn’t limited to that though. Above you can see [Brian] holding up a milled wooden plaque which has milled mother-of-pearl inlays. The table is also strewn with other examples in wax, metal, wood, and more.

Cocktail Hour

The rest of the evening was devoted to conversation on all topics. Get enough hardware geeks in one room and they’ll solve the world’s problems, right? That’s a conversation for another post.

Couldn’t make it to this one but still in the San Francisco area at least occasionally? We held this at the Supplyframe office. They host a ton of great events like the Hardware Developers Didactic Galactic.

[Thanks to Richard Hogben for the photos!]

This Message will Self Destruct… as You Read It?

A group of Harvard chemists have come up with a novel use for fire. Through experimentation, they have been able to build what they call an InfoFuse. As the name implies, it’s essentially a burning fuse that can “transmit” information.

The fuse is made from flash paper, which is paper made from nitrocellulose. Flash paper burns at a relatively constant speed and leaves no smoke or ash, making it ideal for this type of project. The chemists developed a method of conveying information by changing the color of the flame on the paper. You might remember from high school chemistry class that you can change the color of fire by burning different metal salts. For example, burning copper can result in a blue flame. This is the key to the system.

The researchers dotted the flash paper with small bits of metal salts. As the flame reaches these spots, it briefly changes colors. They had to invent an algorithm to convert different color patterns to letters and numbers. It’s sort of like an ASCII table for fire. Their system uses only three colors. The three colors represent eight possible combinations of color at any given time. Just two quick pulses allow the researchers to convey all 26 letters of the English alphabet as well as ten digits and four symbols. In one test, the researchers were able to transmit a 20 character message in less than 4 seconds.

[Ben Krasnow] found the Harvard project and just had to try it out for himself. Rather than use colors to convey information, he took a more simple approach. He started with a basic strip of flash paper, but left large tabs periodically along its length. As the paper burns from end to end, it periodically hits one of these tabs and the flame gets bigger momentarily.

[Ben] uses an optical sensor and an oscilloscope to detect the quantity of light. The scope clearly shows the timing of each pulse of light, making it possible to very slowly convey information via fire. Ben goes further to speculate that it might be possible to build a “fire computer” using a similar method. Perhaps using multiple strips of paper, one can do some basic computational functions and represent the result in fire pulses. He’s looking for ideas, so if you have any be sure to send them his way! Also, be sure to check out Ben’s demonstration video below. Continue reading “This Message will Self Destruct… as You Read It?”

The Platinum Catalyst Use in a Vintage Lighter

[Ben Krasnow] has an inimitable knack for choosing the most interesting concepts for his experiments. We’re sure it’s a combination of base knowledge and epic-curiosity. This time around he’s showing off a vintage cigarette lighter whose quirk is not needing to be “struck” to produce a flame. It’s a catalytic lighter that uses platinum to ignite methanol vapors.

The concept shown in the video below is platinum’s catalyst properties with some types of flammable gasses. The image above shows the cap of the lighter which includes a protective cage around a hunk of fine platinum powder known as platinum black. It is suspended by platinum wire and as the hydrogen passes by the reaction causes the platinum black and wire to glow red-hot.

This simple, quick experiment fills in our own knowledge gaps. We were already familiar with the role that catalytic converters play in automobiles; consuming any unburned hydrocarbons before they exit a vehicle’s exhaust system. We also know the these devices are targets for thieves seeking the platinum (and other metals like palladium and rhodium) found inside. Now we know exactly how catalytic converters work and the integral role that platinum plays in the process. All thanks to [Ben’s] demonstration of how this lighter works.

Now, if you wear a platinum wedding band and your hand passes a jet of hydrogen are you likely to get burned?

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