Measuring The Speed Of Sound With Science And Statistics

August 27, 2012 by 22 Comments

Despite what you may have heard elsewhere, science isn’t just reading [Neil deGrasse Tyson]’s Twitter account or an epistemology predicated on the non-existence of god. No, science requires much more work watching Cosmos, as evidenced by [Ast]’s adventures in analyzing data to measure the speed of sound with a microcontroller.

After [Ast] built a time to digital converter – basically an oversized stopwatch with microsecond resolution – he needed a project to show off what his TDC could do. The speed of sound seemed like a reasonable thing to measure, so [Ast] connected a pair of microphones and amplifiers to his gigantic stopwatch. After separating the microphones by a measured distance; [Ast] clapped his hands, recorded the time of flight for the sound between the two microphones, and repeated the test.

When the testing was finished, [Ast] had a set of data that recorded the time it took the sound of a hand clap to travel between each microphone. A simple linear regression (with some unit conversions), showed the speed of sound to be 345 +/- 25 meters per second, a 7% margin of error.

A 7% margin of error isn’t great, so [Ast] decided to bring out Numpy to analyze the data. In the first analysis, each data point was treated with equal weight, meaning an outlier in the data will create huge errors. By calculating the standard deviation of each distance measurement the error is reduced and the speed of sound becomes 331 +/- 14 m/s.

This result was better, but there were still a few extraneous data points. [Ast] chalked these up to echos and room vibrations and after careful consideration, threw these data points out. The final result? 343 +/- 9 meters per second, or an error of 2.6%.

A lot of work for something you can just look up on Wikipedia? Yeah, but that’s not science, is it?

Turning A Webcam Into A Spectrometer

August 27, 2012 by 22 Comments

If you want to find out what something is made out of, you’ll probably be using a spectrometer. These devices allow scientists to determine what something is made of by shining light through an object and recording what colors are absorbed. Professional spectrometers cost many thousands of dollars, but you can build your own using a simple USB web cam, an old DVD-R, and a VHS cassette case.

In this tutorial of Public Labs’ DIY video spectrometer, [Jeffery] takes us through the process of building a spectrometer. After cutting a small bit of plastic from a DVD-R and mounting it on the lens of a web cam, [Jeff] puts the webcam in a VHS case and shines a light through a small slit. The result is a rainbow pattern captured by the webcam, and by putting different translucent materials in front of the light source, the spectrum slightly changes.

Of course a DIY spectrometer is nearly useless without a library of materials and their associated spectra. [Jeffery] is working on this as well with a wiki-style app called Spectral Workbench.

There’s a video tutorial for making your own DIY spectrometer available after the break. It seems like an easy build, if you can find the requisite VHS cassette case in your basement and/or attic.

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Making A Spray Booth From An Old Dishwasher

August 27, 2012 by 11 Comments

For several years, [Randy]’s spray paint booth was a simple cardboard box. Sure, it kept the overspray contained to a small area, but there was a lot of room for improvement. Luckily, after replacing his dishwasher he had the makings of an excellent spray paint booth that can be put together in a few hours.

The build began by tearing apart the old dishwasher and getting rid of just about everything; the door, plumbing, and electrical were all discarded leaving [Randy] with a plastic husk. After installing a small fluorescent light, plugging the drain hole, and making a simple lazy Suzan, [Randy] had a proper spray booth on his hands.

[Randy] opted not to put in a ventilation system; he was, after all, working with non-toxic vapors. If you’re planning on gutting a dishwasher for use with some nasty chemicals, it might be a good idea to use the drain hole as a ventilation port.

Becoming Gallagher In Your Mind

August 27, 2012 by No comments

The folks at the Louisville hackerspace LVL1 created the handiest and the dandiest kitchen tool you’ve ever seen. It’s not a slicer, it’s not a dicer, or a chopper or a hopper; it’s… a Star Wars Force Trainer that blows up watermelons.

The project is called Mind Over Melon and was created by [Chris] and [Brad] at LVL1 for the CONNECT at Bernheim festival this past weekend. The idea behind the build is allowing people to explode a watermelon with their mind using a Star Wars Force Trainer EEG toy.

The build features the Force Trainer attached to an XBee module, wirelessly connected to the ground zero of watermelon destruction. When the operator of the device concentrates very hard, a series of LEDs light up and a solenoid dumps a shot of compressed CO2 into a watermelon.

[Brad] tells us instructions to build your own mental Sledge-O-Matic will be available on the LVL1 wiki shortly, but until then enjoy this video of the Mind Over Melon being featured on WHAS11 news.

Multicolor Print Head Allows RepRap To Print Rainbows

August 27, 2012 by 29 Comments

Multicolor 3D printers have been around for a while, but most of these machines – like the Makerbot Replicator – suffer from alignment problems and the inability to mix colors on the fly. [RichRap] came up with an interesting solution to this problem by having three filament extruders feed into a single hot end, allowing him to change and mix colors on the fly.

To print in multiple colors, [RichRap] developed a three-extruder x carriage that sends colored filament to a single hot end. Unlike the Makerbot Replicator, [Rich]’s extruder can mix and blend different colors into each layer of a print.

The electronics portion of the build, [RichRap] controlled the X, Y, and Z axes of his printer with a RAMPS board, but used a slightly modified Sanguinololu board for the extruder motors. A single motor driver for the extruders is connected to a trio of toggle switches, allowing [RichRap] to switch between filaments on the fly.

[Rich] has a very cool build on his hands, but it’s far from a perfect solution. Right now, any one of the three colors can be used to print, but printing with two or three colors simultaneously requires a change in the firmware. We expect someone to solve this problem in the near future, allowing the holy grail of a CMYK print head to come to fruition.

You can see a demo video of [RichRap]’s tri-color print head after the break.

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3D Printed Guns, Laws And Regulations, And Philosophical Discussions On The Nature Of Printed Objects

August 26, 2012 by 237 Comments

For as long as they’ve been banded about, 3D printers were regarded as the path to a new economy, a method of distributed manufacturing, and a revolution for the current consumer culture. With every revolution, a few people need to get angry and the guys at Defense Distributed are doing their part to make that happen. They’re designing a handgun able to be printed on a hobbyist-level 3D printer

This isn’t the first time we’ve seen a 3D printable weapon; this 3D printed AR-15 lower receiver is the only part of an AR-15 that contains the ID markings and serial number. Legally, the AR lower is the gun, and requires a background check to purchase (with the footnote that this varies from state to state and country to country – long story short, the BATFE probably isn’t happy about a 3D printed AR lower). The one drawback of a 3D printed AR-15 lower is that every other part of the gun must be purchased elsewhere. This is where Defense Distributed comes in: they propose designing a gun that is 100% printable on a hobbist-level 3D printer such as a RepRap or Makerbot.

Right now, Defense Distributed is looking for funding to produce two gun designs. The first design, WikiWep A will serve as a research build, allowing Defense Distributed to answer a few questions on what can be built with a RepRap. WikiWep B will have moving parts for the firing action and very nearly all the parts will be printable on a RepRap or Makerbot.

In the video Defense Distributed put up for their now cancelled IndieGoGo campaign (available after the break), the guys talk about the distribution of a CAD file of completely 3D printable weapon being a threshold of a new economy where laws and regulations cease to apply. We’re not sure we agree with that statement; after all, anyone with some metal forming tools can build an excellent weapon to acquire another weapon, but we’re interested in seeing what governments and regulators will make of Defense Distributed’s project.

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Visualizing Water Droplets And Building A CT Scanner

August 26, 2012 by 9 Comments

Since his nerves were wracked by presenting his project to an absurdly large crowd at this year’s SIGGRAPH, [James] is finally ready to share his method of mixing fluids via optical tomography with a much larger audience: the readership of Hackaday.

[James]’ project focuses on the problem of modeling mixing liquids from a multi-camera setup. The hardware is fairly basic, just 16 consumer-level video cameras arranged in a semicircle around a glass beaker full of water.

When [James] injects a little dye into the water, the diffusing cloud is captured by a handful of Sony camcorders. The images from these camcorders are sent through an algorithm that selects one point in the cloud and performs a random walk to find every other point in the cloud of liquid dye.

The result of all this computation is a literal volumetric cloud, allowing [James] to render, slice, and cut the cloud of dye any way he chooses. You can see the videos produced from this very cool build after the break.

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