Archive for the 'Hardware' Category

Semi-Automatic Paintbrush

Published on December 18, 2011 in Hardware

I bought an InkShield from the Kickstarter a few months ago mostly out of a desire to support an interesting Open Hardware project. It wasn’t until yesterday that I thought of something useful to do with it. Instead of that, I made this project, called the Semi-Automatic Paintbrush. Using an infrared camera, an InkShield, an ink cartridge with an infrared LED stuck to it, and your arm, you can copy great works of art, or just any old picture.

The desktop side software involved is called paintbrush.py. It conveniently uses the homography module I wrote a year ago to map what the IR camera sees to the coordinate system of the canvas. The mapping is calibrated interactively by placing the cartridge/LED at each of the four corners of the canvas and pressing a key when prompted. After that, the motion of the LED is tracked, the corresponding region of the image is found, and the script sends serial commands to an Arduino with the InkShield telling it which nozzles to fire at what duty cycle to achieve the correct level of gray, or in this case, green. The painted regions are tracked to prevent flooding.

As you can see from the image above, the results are not going to end up in the Louvre, but they do have a kind of partially mechanical, partially organic flavor to them. If you have an InkShield, an IR LED, and a pygame supported IR camera (I use a modified PS3 Eye), and you’re interested in making your own lazy artwork, the script is available on github under an ISC License. The Arduino sketch requires the InkShield library and is LGPL. Usage instructions for the script are contained with it.

2 Comments Tags: arduino, art, infrared, pygame.

For Sale: RepRap Parts for Bitcoins

Published on July 9, 2011 in Hardware

Bitcoin is exactly the kind of fantastic real life science fiction kind of project that I enjoy: a peer to peer, anonymous, cryptographically secure currency. I’m not even an armchair economist, but I suspect the hardest part of starting any new economy is the chicken and the egg problem. Sellers won’t join the market unless there are potential buyers, and buyers won’t join unless there are people selling things they want to buy. Unfortunately in the case of Bitcoin, both the chicken and the egg have been eaten by the monster called currency speculation. It is likely that the majority of actual transactions are between speculators and exchanges, taking advantage of volatility to make a profit in BTC or USD. Half a paragraph later, I’m still not an economist, but I also suspect that as a larger fraction of the economy goes to goods and services, the currency will stabilize, encouraging more people to use it. Therefore, I am doing my part in bootstrapping the Bitcoin economy by using a project that loves to bootstrap.

I’m selling a set of SAE Prusa Mendel parts printed on the Mendel used in many of my recent projects. The parts are from the current files in the PrusaMendel git repository, and are printed in PLA. They are quite clean and strong, but may need a little work with a knife or drill bit. The Wade’s Extruder and PLA bushings from the repository are also included. But wait, there’s more! Between getting misaligned on the trip home from Maker Faire and a torn belt, my printer was in fairly rough shape for a few weeks. While repairing it, I printed RepRap parts to test the calibration. I’m including the usable parts printed during that time and some more good spare parts I printed recently; this is the pile on the left in the bottom picture. The full set of good parts from the top picture and the Wade’s Extruder are in separate bags.

I’m selling this set for the hopefully reasonable price of 5 BTC, shipped USPS Priority Mail to anywhere in the US. At the exchange rate at this moment, that is roughly $72.50. It could be $20 or $200 by tomorrow for all I know, but I’m willing to take the risk if you are. Email me, and we can arrange the transaction. Sold! There was less interest than I was hoping for, so I probably won’t be doing it again.

1 Comment Tags: 3d printing, bitcoin, reprap.

Physical Keygen: Now for Disc Detainer Locks

Published on June 20, 2011 in Hardware

The Physical Keygen post got reactions, but there was a common claim among many of them that it was just a gimmick because there are more practical ways of getting past basic Schlage and Kwikset pin tumbler locks. I agree with that, and I’ll also admit that a fair number of my projects are gimmicks, or as a stretch, art. Schuyler Towne of Open Locksport saw past the gimmick (or art) and into the possibility of printing keys for more interesting locks.

He stopped by recently with a collection of said locks, and over the period of a few hours we determined that keys for disc detainer locks were printable and created a nearly working ABUS Plus key. He left me a cutaway lock, and over the next week, I refined the model to the point of working straight off of the printer. Despite being a higher security lock than the SC1 or KW1 pin tumblers I was working with before, the key is much easier to print accurately. The OpenSCAD model is linked below, and like the last files, you simply edit the last line to match the code for your key.

The ABUS Plus and other disc detainer locks are much more common in Europe than the US, but we do have a pretty ubiquitous example around here. After the Bic Pen debacle in 2004, Kryptonite switched their bicycle U-locks from tubular to disc detainer. I designed a model off of the key from the Kryptonite Evolution I have, but as of yet, I have not successfully opened the lock with it. The key is smaller and thinner than the ABUS Plus, causing it to flex too much to effectively turn the last few discs. I’ve posted the file anyway, in case someone has stronger plastic or an idea to strengthen the model.

Edit: The Kryptonite key works. I tightened my X and Y belts and printed it a bit slower. Apparently some of the blobbing on the corners before was catching on disks.

Download:
abus_plus.scad
kryptonite.scad

0 Comments Tags: 3d printing, key, lock, openscad, security.

Physical Keygen: Duplicating House Keys on a 3D Printer

Published on May 30, 2011 in Hardware

It occurred to me recently that I had printed almost nothing actually useful on my RepRap 3D printer, aside from parts to improve on or build more RepRaps. I am rectifying that with this project. The goal here is to generate working house keys by inputing the key code of the lock into a parametric OpenSCAD model. Instead of having to explain to my landlord how I ended up with a wedge of plastic jammed in my front door, I ordered a box of (well) used locks and latches from eBay to experiment on. Luckily, the lot includes both Kwikset KW1 and Schlage SC1 locks, which are the two most commonly found in the US. I created an SC1 model to start with, ~~but I’ll probably make a KW1 soon~~. I’ve uploaded the KW1 model now as well.

Designing the key model was actually pretty straightforward. I measured a key with a ruler and calipers and created an approximate model of it that is reasonably easy to print. I then got pin depth specifications and parametrically differenced them out of the model. To generate new keys, you can just edit the last line of the file and enter in the key code for your key. If the code isn’t written on the key, you can measure the height of each bit and compare to the numbers in the Root Depth column on the aforementioned pin depth site. Perhaps more nefariously, you could implement something like SNEAKEY to generate key codes without physically measuring the key.

You’ll of course need OpenSCAD to edit the .scad file and generate an STL to print out, unless your key just happens to be 33172 like the example STL posted below. If it is, you can unlock the doorknob currently sitting on my desk. As a small, precise object, this is a great test of how accurate your Skeinforge settings are. You may need to adjust some thicknesses or the built in pin depth fudge factor to get it working properly with your printer. The pictures above show the key being used on a disconnected lock cylinder, but I found it was also strong enough to turn a deadbolt. If your lock needs a lot of force to turn, you may need to cut a space into the key to use a torsion wrench with it.

Download:
sc1.scad
sc1.stl
kw1.scad
kw1.stl

16 Comments Tags: 3d printing, key, lock, openscad, security.

FaceCube: Copy Real Life with a Kinect and 3D Printer

Published on March 4, 2011 in Hardware

This project is a tangent off of something cool I’ve been hacking on in small pieces over the last few months. I probably would not have gone down this tangent had it not been for the recent publication of Fabricate Yourself. Nothing irks inspires me more than when someone does something cool and then releases only a description and pictures of it. Thus, I’ve written FaceCube, my own open source take on automatic creation of solid models of real life objects using the libfreenect python wrapper, pygame, NumPy, MeshLab, and OpenSCAD.

The process is currently multi-step, but I hope to have it down to one button press in the future. First, run facecube.py, which brings up a psychedelic preview image showing the closest 10 cm of stuff to the Kinect. Use the up and down arrow keys to adjust that distance threshold. Pressing spacebar toggles pausing capture to make it easier to pick objects. Click on an object in the preview to segment it out. Everything else will disappear; clicking elsewhere will clear the choice. You can still use the arrow keys while it is paused and segmented to adjust the depth of what you want to capture. You can also use the H and G keys to adjust hole filling to smooth out noise and fill small holes in the object. If the object is intended to have holes in it, press D to enable donut mode, which leaves the holes open. Once you are satisfied, you can press P to take a screenshot or S to save the object as a PLY format point cloud.

You can then open the PLY file in MeshLab to turn it into a solid STL. I followed a guide to figure out how to do that and created a filter script attached below. To use it, click Filters -> Show current filter script, click Open Script, choose meshing.mlx, and click Apply Script. You may have to click in the preview, but after a few seconds, it will say that it Successfully created a mesh. You can click Render -> Render Mode -> Flat Lines to see what it looks like. You can then click File -> Save As, and save it as an STL. You can probably get better results if you manually pick the right filters for your object, but this script will be enough most of the time.

You can then open the STL in OpenSCAD or Blender and scale it and modify to your heart’s (or printer’s) content. Of course, the real magic comes from when you take advantage of all that OpenSCAD has to offer. Make a copy of yourself frozen in carbonite, put your face on a gear, or make paper weights shaped like your foot. This is also where the name FaceCube comes from. My original goal going into this, I think at my roommate’s suggestion, was to create ice cube trays in the shapes of people’s faces. This can be done very easily in OpenSCAD, involving just subtracting the face object from a cube.

difference() {
	cube([33,47,17]);
	scale([0.15,0.15,0.15]) translate([85,140,120]) rotate([180,0,0]) import_stl("face.stl");
}

Since all of the cool kids are apparently doing it, I’ve put this stuff into a GitHub repository. Go ahead and check it out, err… git clone it out. The facecube.py script requires the libfreenect from the unstable branch and any recent version of pygame, numpy, and scipy. You’ll need any recent version of MeshLab or Blender after that to do the meshing. I’ve been using this on Ubuntu 10.10, but it should work without much trouble on Windows or OS X. The latest code will be on git, but if you are averse to it for whatever reason, I’ve attached the script and the meshlab filter script below. Since Thingiverse is the place for this sort of thing, I’ve also posted it along with some sample objects as thing:6839.

Download:
git clone git@github.com:nrpatel/FaceCube.git
facecube.py
meshing.mlx

6 Comments Tags: 3d printing, kinect, meshlab, openscad, pygame, reprap.

AC Powered Heated Build Platform for RepRap

Published on February 14, 2011 in Hardware

One of the unpleasant surprises you come across when first learning how to operate a RepRap is that any object longer than an inch or so in any dimension printed in ABS will warp quite a lot as the lower layers cool. The workaround, other than switching to another plastic, is to print onto a heated build platform. There a few varieties available to buy, but I decided to build one out of parts I could get at Halted. I found a ~2mm thick sheet of aluminum in roughly the correct dimensions with holes predrilled for $2, and a few 50 watt resistors for about $2 each.

My primary design goal was to avoid putting more load on my (fused) RAMPS board and mini-ATX power supply by directly powering the bed off of AC. As a purely resistive load, this is also by far the most efficient way of doing it. I connected the resistors in series with 16 gauge high temperature teflon insulated wire and JB-Welded them to the sheet. I also used JB-Weld to mount a thermistor near the middle resistor to get temperature readings. I then mounted the board on springs above the normal build platform and covered the surface with Kapton tape. The relay is being switched by one of the MOSFETs on the RAMPS board. A red LED indicates that the relay is powered, and there is a flyback diode across the relay coil. The Arduino Mega was resetting randomly partway through prints until I added a decoupling capacitor in parallel to the coil as well.
Schematic

Overall, it works well. With roughly 80 watts of power, it heats up to 110C in around 5 minutes, which is sufficient for ABS. I managed to print a 150mm long object with no warping. I’ve also been using it with PLA at 60C. Right now it poses a mild electrocution hazard sitting on my desk, but I plan on printing out an enclosure for it as soon as I figure out how to use OpenSCAD.

0 Comments Tags: 3d printing, mendel, reprap.

It lives!

Published on January 30, 2011 in Hardware

0 Comments Tags: 3d printing, mendel, reprap.

This is why you haven’t heard from me in months

Published on December 21, 2010 in Hardware

3 Comments Tags: mendel, quagmire, reprap.

Not even geeks have these problems

Published on September 5, 2010 in Hardware

U19, a power management IC, arrived halfway unconnected on my new BeagleBoard xM.

3 Comments Tags: beagleboard, problems.

Normal people don’t have these problems

Published on August 9, 2010 in Hardware

I drive the least interesting car in the world, a gray 2004 Toyota Camry. To stave off death from boredom while driving, I use a tape adapter connected to an A2DP receiver to wirelessly listen to music from my iPhone. A few weeks ago, the tape deck developed an extremely irritating clicking noise. The easy options, the ones that most Camry owners would choose, would be to turn on the radio, get an FM transmitter for the iPhone, listen to CDs, or just let the tape deck click. Being an engineer, I refuse pick the easy option, but rather the one that seems best, which inevitably devolves into a weekend of hacking, cursing, and setting things on fire, with a best case of eventually restoring the object of interest to something resembling a functioning state.

The plan was to enable direct auxiliary input, which the Internet claimed was possible on this model. The backup plan was to resolve the clicking noise by just unplugging the tape motor, which we assumed was unnecessary to operate the adapter. My roommate Will and I popped the head unit out of the car with much effort and two trips to the hardware store. Apparently stealing a radio isn’t easy, even from your own car.

Attempting to power the unit off of the 12v rail of a 350w ATX power supply resulted in it shutting off immediately. With a 450w PSU connected to the battery and accessory voltage lines, a tiny laptop speaker from my spare parts bin connected to the massive amp, and another speaker being used as an antenna, we managed to pull in the beautiful sound of late 70′s hits on FM radio.

I’m not entirely sure what happened, but Will managed to break the tape deck in about a dozen different ways over the course of the next couple of hours. It wouldn’t play at all without the drive gears spinning, it refused to eject tapes because it believed it was empty, and still, the clicking gear clicked.

It was then up to me to get aux in working. Apparently, Toyotas from around my model year use AVC-Lan, a communications bus based on IEBus for the head unit to connect to things like a CD changer. There is some pretty solid research across the web on how to emulate a device on the bus to message the head unit to use its aux input. I used the circuit and software from SigmaObjects, as it required only parts I already had or could get from Halted. The code there is designed for an ATmega8, but with some trial and error, I managed to port it to the current ATmega48/88/168 series. Unfortunately, the code doesn’t mention being under any permissive license, so I can’t share my modifications.

While hooking it up to the head unit, the wire connecting the device to ground actually burst into flames, burning part of a connector and melting copper. On later inspection, we found that the wires were extremely high gauge internally, and it is likely that only a single thin strand was carrying the current in the area that caught fire. Miraculously, neither the radio nor the ATmega168 was damaged by the incident. I switched to lower gauge higher quality wire, checked my car insurance terms relating to explosion due to user error, and continued.

After a few more hours of debugging, I realized that I had the two data lines backwards, and after switching them it worked instantly. We repurposed the TAPE button to switch to aux in. I taped the board down, put the head unit back together, and we stuck it back into the car. There was an unnerving startup delay the first few times, but I am now the proud owner of a gray 2004 Toyota Camry with auxiliary audio input… and no tape deck.

6 Comments Tags: audio, avr, camry.