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Fail of the Week: Physical Pixel Display

posted Thu, 12 Dec 2013 11:01:26 -0800", in *www


This physical pixel display reminds us of a couple of different hacks that we’ve seen over the years. It looks impressive, but [Matt] couldn’t quite get it to work. It wasn’t the Kinect sensor and image interpretation that was the problem. It was a failure to get the hardware components seen above to perform reliably.

If you can’t figure out what this is supposed to do, take at look at the inFORM morphing table or the pixel wall installed at the Hyundai expo last year. [Matt's] attempt is much more modest with a grid of just 10×6. The pixels themselves are ballpoint pens (he gets bonus points for cheap and easy materials). The pens move in and out thanks to some Bowden cables connected to hobby servos. The mechanical engineers have probably already figured out the fail… the pixels seem to get hung up and despite several revisions in the materials used , it couldn’t be fixed.

The hobby servos were chosen because they are much less expensive than proper linear actuators. We thought maybe [Matt] should build his own solenoids but that’s not a great idea because you can’t have variable depth that way (can you?).  Perhaps the pens should be vertical and the servos could pull on a string attached to the pen via a pulley with gravity to return them to the starting position? There’s got to be an inexpensive and relatively simple way get this thing working. Let us know how you’d get the project back on track by leaving a comment below.

2013-09-05-Hackaday-Fail-tips-tileFail of the Week is a Hackaday column which runs every sweeeeeeeet Wednesday. Help keep the fun rolling by writing about your past failures and sending us a link to the story – or sending in links to fail write ups you find in your Internet travels.

Filed under: Hackaday Columns

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Enginursday: Homopolar motors and a greater understanding of Magnetism

posted Thu, 12 Dec 2013 09:08:00 -0800", in *www

Recently, I have been trying to gain a better understanding of how motors work. While searching the interwebs, I found a number of tutorials explaining the magnetic interactions found in motors. But many of these sites and videos failed to explain the mechanics of magnetism itself. So I dusted off my E&M book and went for it. One hour later, and my brain was fried. I had forgotten how complex Electricity and Magnetism was. Doing what any self-respecting engineer would do, I watched an unhealthy amount of YouTube. During my binge, I continued to see “Homopolar motor” and “Simplest Motor” show up. Being curious, I decided to build one and see how it worked.

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As you can see, it’s about as simple as it gets: a piece of wire, magnet, and a battery. Well, how does it work? Let’s take a look!

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(Credit: Wikipedia)

Simply put, the Lorentz force is responsible for propelling the motor. To be more exact, it’s how the Lorentz force acts on a current-carrying wire. The resultant force is the cross product of current (along a length “l”) and the magnetic field. For our purposes, we will ignore length to keep things conceptual.

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An easy way to represent the cross product is to think of the Right Hand Rule.

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To re-phrase our use of the Lorentz force definition: Force is the product of current as it is orthogonal to the magnetic field. The resulting force must be orthogonal to both current and the magnetic field. What if current and the magnetic field are not perfectly perpendicular? The cross product helps us make this easy. Let’s take a simple problem:

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The cross product helps us take only the parts of the field as it acts on current. In my example, “B” would represent current, and “A” would represent the magnetic field. To determine the direction of the force, you always start with your thumb along the first vector (Ay), and point your fingers in the direction of the second vector (B). The force will be in the direction your palm is facing. In our case, this is “into the page.” The circle with the “X” is supposed to look like arrow fletchings flying away. A arrow coming towards you, or “out of the page,” would have a single point.

What if I do the same problem only with C = BxA? Well, what are you waiting for? Try it! The only difference is now your thumb goes along B and your fingers along Ay. You get the same force, but reversed. This demonstrates the importance in the order we solve things. The cross product is not what mathematicians would call communiative. Now, take our example motor diagram above and reverse the current. Following the rules of the cross product and reversing the direction of current reverses the motor! Let’s take a look a one running.

(Credit and special thanks to Maurice Woods III!)

The magnetic field is created by the magnet below the battery. This is shown as red field lines traveling from the north to south pole of the magnet. Current is represented by the yellow arrows as it flows through the wire (the magnet is providing the slip ring connection to the bottom of the battery). The green arrows are showing the force created by the interaction.

Well that was cool! What happens when you lay it out flat? You get a linear homopolar motor!!!

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Same rules apply F=IxB.

Building one is simple. You just need some form of rails, magnets, and a non-ferrous conductive rod/tube. I found that model rail track was easy to get. I grabbed a box of magnets from inventory, and the copper tube was something I found at the hardware store. Finally, I laser cut some plastic to help me hold it all together. It’s important to glue all the magnets in the same orientation or the rod will not continue down the track. This can be done by marking them or checking polarity as you assemble. Special thanks to Riley H. for helping me glue all these magnets together!

Powering it with a current limited DC supply is suggested. We used 5 amps in the video

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Assembly view showing magnet orientation

What if we crank up the current? Thanks for asking! Well, for starters, things get hot. So hot that when we add say, 5 million amps, things start to turn to plasma.

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(Credit: Wikipedia)

The need for an external magnetic field is also removed. Passing current through a wire creates its own magnetic field. This is governed by Ampère’s circuital law. We’ll save that topic for a later date. Now, how is this useful? There are plans to use systems like this to put satellites into orbit without burning rocket fuel. Time will tell if it works out!

This was a great tangent I took while writing the new Motor Tutorial. I learned a lot about magnetism, and it really solidified my understanding of the subject. Check it out and see how some of these concepts are put into the context of a motor you might actually use.

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Robot Battle for the Big Leagues: Valkyrie and the DARPA Challenge

posted Thu, 12 Dec 2013 09:00:09 -0800", in *www


Even though NASA’s Johnson Space Center’s impressive build for the upcoming DARPA Robotics Challenge is one of many entries, it has to be one of the coolest. The gang at IEEE Spectrum got a sneak peak of the robot dubbed “Valkyrie”, which at 1.9m and 125kg boasts 44 degrees of freedom while managing to look like a finished product ready to roll off the shelf. We can expect to see other custom robots at the challenge, but a number of teams will compete with a Boston Dynamics Atlas Robot, which we’ve covered a couple times this year.

A few readers are probably polishing their pitchforks in anticipation of shouting “Not a hack!” but before you do, take a look at the tasks for the robots in this challenge and consider how new this territory is. To that end, the NASA JSC crew seem to have prepared for resolving catastrophes, even if it means throwing together a solution. They’ve designed the limbs for quick removal and even reversibility: the arms are identical and only slight adjustments are required to turn a left arm into a right. Unlike the Atlas, which requires a tether, Valkyrie is battery-operated, and it can run for around an hour before someone needs to crack open the torso and swap in a new one, Iron Man film-style.

The team was also determined to make Valkyrie seem more human, so they added a soft fabric layer to serve as a kind of clothing. According to IEEE Spectrum, it’s even getting custom made footwear from DC Shoes.There are some utilitarian compromises, though: Valkyrie has adopted a shortcut taken by time-constrained animators in many a cartoon, choosing three fingers per hand instead of four. Make sure you watch the video after the break for a closer look.

Filed under: robots hacks

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Frozen Pi: bullet-time photography with the Raspberry Pi

posted Thu, 12 Dec 2013 07:54:50 -0800", in *www

If you were one of the people following us on Twitter a couple of Saturdays ago, when we all hoofed it up to Manchester for the Manchester Raspberry Jam, you’ll have had a sneak preview of this: Dr Andrew “Pi Face” Robinson’s latest Pi escapade. I’ll let Andrew explain what’s going on. (Notice the mildly humiliating guest appearances from me and Clive.)

We think this is one of the most interesting photographic applications we’ve seen in the flesh so far. (Although I will admit to a moment’s disappointment when, on seeing it, getting excited and asking what it did, I was told that it was not a working Stargate after all.) You’ll have read many posts here about bringing down the price of professional photography equipment: we’ve seen focus-stacking on a budget, gigapixel photography, setting up moving time-lapse rigs, and shooting water droplets along with many, many other applications. (The photography tag here is one of my favourites – if you’ve got a few minutes, go and have a read.)

Andrew’s Frozen Pi setup shows us yet another example of bringing photographic technology with an astronomical off-the-shelf price down to achievable levels: of course, with 48 Raspberry Pis this still works out pretty pricey, but it means that any school with a classroom set of Pis suddenly finds it has bullet-time effects photography well within its grasp.

Which is just brilliant, isn’t it? Thanks Andrew!

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Open your Hackerspace Door with a Phone Call

posted Thu, 12 Dec 2013 07:01:16 -0800", in *www


[Mário] sent us a tip detailing the access control system he and his friends built for the eLab Hackerspace in Faro, Portugal. The space is located in the University of Algarve’s Institute of Engineering, which meant the group couldn’t exactly bore some holes through campus property and needed a clever solution to provide 24/7 access to members.

[Mário] quickly ruled out more advanced Bluetooth or NFC options, because he didn’t want to leave out members who did not have a smartphone. Instead, after rummaging around in some junk boxes, the gang settled on hacking an old Siemens C55 phone to serve as a GSM modem and to receive calls from members. The incoming numbers are then compared against a list on the EEPROM of an attached PIC16F88 microcontroller, which directs a motor salvaged from a tobacco vending machine to open the push bar on the front door. They had to set up the motor to move an arm in a motion similar to that of a piston, thus providing the right leverage to both unlock and reset the bar’s position.

Check out [Mário's] blog for more details and information on how they upload a log of callers to Google spreadsheets, and stick around for a quick video demonstration below. If you’d prefer a more step by step guide to the build, head over to the accompanying Instructables page. Just be careful if you try to reproduce this hack with the Arduino GSM shield.

Filed under: Cellphone Hacks, Hackerspaces, Microcontrollers

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