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March 16, 2008

Art Bots 2008

The fifth international ArtBots exhibit is being held on September 19-21 in Dublin Ireland. Whether you're interested in creating a robotic work of art, or a robot capable of producing its own works of art, you have till May 1st to submit an entry.

I've seen the output from this robot talent show / art fair for a few years now, and I'm really excited to see what happens this year. Are any of you folks planning on entering or attending?

Shown above: One of Bruce Shapiro's "Ribbon Dancer" robots. When activated, the robots are able to perform intricate dance routines by moving a ribbon through the air in choreographed patterns. It's the robot equivalent of an Olympic floor routine.

ArtBots 2008 Call for Works
Ribbon Dancer Robots

March 12, 2008

CNC hologram

I posted earlier this week about abrasion holography, a hologram technique that uses a network of simple arc shaped scratches to encode a visible, 3D hologram into a chunk of plastic. Carl was the first to comment on exactly what was on a number of peoples minds:

This is just crying out for someone to generate complex pictures using CNC.

Like many great ideas, someone has already worked this one out! William Beaty was kind enough to write back with a link:

The scratches need to be be almost perfectly smooth with no jaggies at all. Normal CNC doesn't work, but a couple months ago Evan at homeshopmachinist.net found that "drag engraving" does reduce the jaggies enough.

The photo above is Evan's cube, engraved on blackened copper. The top image is what you see in normal diffuse lighting. The bottom is one perspective of the hologram when viewed head-on under a point-source light. Evan writes:

The way this type of hologram is generated is to start with a 2d representation of the subject (the cube in this case). Then an arc is drawn using a point on the visible vertices and edges of the shape. A set of closely spaced points along all visible edges is then used to provide the anchor points for the radii of the arcs. The reason the image isn't perfect appearing is because of slight inaccuracies in the placement of the arcs (my fault) and some waviness in the copper plate which is only 26 gauge material.

There are a lot of creative possibilities with this one. First person to engrave a HACKS hologram on a copper business card wins a standing ovation.

Synthetic Holograms With a CNC Mill - Link
DIY Hand-Drawn Holograms - Link

March 8, 2008

DIY hand-drawn holograms

Typically the creation of a hologram involves lasers and various other expensive equipment and materials. William J. Beaty figured out a low-tech way to create your own holograms using a simple abrasion technique that requires only a compass and a chunk of plastic. He came across the idea while walking through a parking lot, noticing strange hand prints that seemed to float above or deep inside the surface of polished car hoods.

The images were naturally-occurring holograms. The owner of the car had obviously polished the hood with a dirty mit, and the millions of particles of grit in the mit traced out millions of nearly-parallel scratches in the black paint. The particular hand motion had created a geometry of abrasion patterns which turn out to be nearly identical to the interference patterns which make up those embossed-foil Benton whitelight [holograms].

So how do you make one? All you need is a spanner (compass with 2 needles) and a chunk of hard plastic such as Lexan. For simple flat shapes, you just draw the reference shape below where you want the hologram to appear. Set the diameter of the spanner to an inch or two, put one of the points on the shape and score a small arc across the plastic. You then repeat this process for a bunch of other points on the shape, leaving a number of small arc shaped scratches. When you observe the scratches in the light, you'll see a hologram of the shape that appears to float beneath the surface of the plastic.

The image above, from William's site, is actually a stereo photo of one of his holograms. You can cross your eyes to see the effect. The cube that reflects from the scratches appears different based on the angle you view it.

The depth of the hologram is related to the width of the spanner, so you can actually create three dimensional holograms using the same technique. William's FAQs have more details on doing this, as well as hints for creating opaque shapes that have other objects hidden behind them which are only viewable from certain angles.

Abrasion Holography - Link

February 13, 2008

What's your poison?

Robert Bruce Thompson, author of books on everything from PC Hardware to Astronomy, is working on a new book for Make: the Illustrated Guide to Home Chemistry Experiments. So, we've got chemistry on our mind here, which led Dale Dougherty, the Publisher of Make, to ask Robert:

I read a story last week about the alarmingly high levels of mercury found in fish in the top sushi places in Manhattan. Ever since, I've been wondering is it possible/feasible/reasonable to test for mercury in fish -- a DIY mercury test kit. I doubt you could do this in restaurant so let's presume that this is a test kit for store-bought fish.

The answer for mercury is a bit complex:

The problems are that mercury is toxic at unbelievably low levels and that it is a cumulative poison, which is to say it isn't excreted. Accordingly, the allowable levels are set so low that there's no chance they could be detected by any wet chemistry test with a sample of any reasonable size.

I was pretty sure of my facts, but just to be certain I ran them past organic chemist Dr. Paul Jones. His response was, "Maybe you could use a wet chemistry test if you had an entire 500-pound tuna for your sample, but otherwise you'd have to use instrumental tests."

Organic chemist Dr. Mary Chervenak points out the Reinsch Test for mercury (which also produces a positive for several other heavy metals). You dissolve the sample in dilute HCl and put a copper strip in the solution. Any mercury present plates out on the copper as a silvery mirror. The trouble is, if enough mercury is present to produce a visible mirror with the Reinsch test, that sample has enough mercury in it to poison everyone in a radius of several blocks.

Robert's got more details over at his daynotes journal, and a couple of other tests have come to our attention since Dale's original question. Dale sent a link to a Heavy Metals Test (Robert posted his thoughts on this test in his journal as well), and Popular Science just posted a link to a portable blood test for heavy metals. Have any of you come across some interesting tests for poisons in your body, food, or environment? What results have you had?

From The Maker Store:

Illustrated Guide to Home Chemistry Experiments by Robert Bruce Thompson
Price: $34.99
Pre-order/Buy: Maker store - Link.
For students, DIY hobbyists, and science buffs, who can no longer get real chemistry sets, this one-of-a-kind guide explains how to set up and use a home chemistry lab, with step-by-step instructions for conducting experiments in basic chemistry. Learn how to smelt copper, purify alcohol, synthesize rayon, test for drugs and poisons, and much more. The book includes lessons on how to equip your home chemistry lab, master laboratory skills, and work safely in your lab, along with 17 hands-on chapters that include multiple laboratory sessions.

January 31, 2008

R: open source statistical computing

I was digging around for an open source statistics package today and came across R, a GPLed statistics and and data analysis suite. Sweet!

R provides a wide variety of statistical (linear and nonlinear modelling, classical statistical tests, time-series analysis, classification, clustering, ...) and graphical techniques, and is highly extensible. The S language is often the vehicle of choice for research in statistical methodology, and R provides an Open Source route to participation in that activity.
One of R's strengths is the ease with which well-designed publication-quality plots can be produced, including mathematical symbols and formulae where needed. Great care has been taken over the defaults for the minor design choices in graphics, but the user retains full control.

So I've been messing around with this for the last half hour and it's really an exciting package, especially if you're a coder or unix geek. You interface with R through a command line programming interface, executing simple statements, setting variables, and defining functions. It feels similar to issuing commands at a unix prompt, except you're working with data sets instead of file descriptors.

What's cool is the robust capability of the standard function set. Want to read in a data set from a tab delimited table you found on the internet? Check this out:

# Read a table in from a URL (tab delimited table with row headers) Mydata <- read.table(http://someserver.com/table.txt', header=TRUE) # Display summary (mean, median, min, max, etc.) for each column summary(Mydata)
# Get the standard deviation for the values in column "foo" attach(Mydata) sd(foo)

Learning the command set is a little daunting at first, but the console even does tab completion. If you don't know what a function does, just put a question mark before it. For instance, "?sd" will quickly pull up help for the standard deviation function.

I've only scratched the surface, but there are links below to some R beginner guides which should help you get started. Anyone out there more familiar with the package? Please share any useful links and tips in the comments.

The R Project for Statistical Computing - Link
An Introduction to Statistical Computing in R - Link
Producing Simple Graphs with R - Link

September 6, 2007

Electrolytic rust removal

ToolNut put together a nice guide for using electrolysis to clean up rusty tools:

This is a relatively simple, safe and cheap way to remove light or heavy rust from any ferrous object. I used this process to restore an old wood plane that I bought for $1 (it looked totally un-usable because of the rust). As opposed to grinding, heavy wire brushing and acid bath processes, this method removes none of the original steel and is not noisy or caustic.

I'm going to clean up a few tools in the basement that haven't been taken care of as well as they should have... too bad none of them are as sweet as that plane ToolNut came across for a buck.

Electrolytic Rust Removal aka Magic - Link

September 5, 2007

Moldable plastic from styrofoam

Common packaging styrofoam is actually puffed polystyrene, the same polymer that's used to make things like CD cases and plastic model parts. When acetone is used as a solvent, the expanded polystyrene will easily dissolve and you'll be left with a liquid acetone/polystyrene solution. As the acetone evaporates, the polystyrene becomes increasingly viscous: first pourable, then moldable, and finally solid polystyrene plastic.

Solid polystyrene will dissolve in acetone as well, but with the vastly larger surface area (due to all the little gas bubbles) styrofoam dissolves much faster. That, and it's readily available if you have a basement full of old packaging materials.

There must be an easy method for pouring or spin-casting custom plastic parts or action figures using dissolved polystyrene. Have any of you ever tried this or have any ideas on the subject? Please let us know in the comments!

Instructable: How to "make" plastic - Link
Wikipedia: Polystyrene - Link

March 2, 2007

SeisMac: Turn Your MacBook Into a Seismograph

"SeisMac is a Mac OS X application that turns your MacBook or MacBook Pro into a seismograph. It access your laptop's Sudden Motion Sensor in order to display real-time, three-axis acceleration graphs. Version 2.0's enhancements make SeisMac an even more valuable tool for classroom demonstrations of seismic concepts and techniques." -Link.