For Sale: RepRap Parts for Bitcoins

SAE Prusa Mendel RepRap Parts

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.

Wade's Extruder and spare parts

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.

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Maker Ant Farm: Minecraft Skin Generation with a Kinect

Since my seemingly fragile 3D printer had never left my desk before and even in prime condition could only print an object every 10 minutes or so, I decided that I needed a backup project for the Bay Area Maker Faire last month.  I conscripted Will to help me out on a purely software Kinect based project.  After downscoping our ideas several times as the Faire weekend approached, we eventually settled on generating Minecraft player skins of visitors.  The printer ended up working fine (and more reliably than the software only project), but the Minecraft “Maker Ant Farm” was more of a crowd pleaser.

A visitor would stand in front of the Kinect and enter fieldgoal/psi calibration pose.  We used OpenNI and NITE to find their pose and segment them out of the background for a preview display.  Using OpenCV, we mapped body parts to the corresponding sections of the Minecraft skin texture.  Since we could only see the fronts and parts of the sides of a person, we just made up what the back would look like based on the front.  This was of course imprecise and resulted heads that often looked like they had massive bald spots.  Rather than trying to write some kind of intelligent texture fill algorithm on a short schedule, we just gave all of the skins yellow hard hats (not blonde hair, contrary to popular opinion).  After generating the skin, we loaded it back onto ShnitzelKiller’s player rig in Panda3D.  I had planned on writing full skeletal tracking for the rig, but ran out of time and settled on just having it follow the position and rotation of the user and perform an animated walk.  After walking around a bit watching a low res version of him or herself, the user could enter in a Twitter handle or email address to keep the skin.  The blocky doppelgänger was then dropped onto a Minecraft server instance we had running as a bot that did simple things like walk around in circles or drown.

Minecraft Skin

Despite some crashiness in NITE and the extremely short timeframe we wrote the project in, it ended up working reasonably well.  Thanks to the low resolution style and implied insistence on imagination in Minecraft, the players avoid looking like the ghastly zombies in Kinect Me.  You can see examples of some of the generated skins on @MakerAntFarm.  I hate not releasing code, but I almost hate releasing this code more.  It is very likely to be the worst I have ever hacked together, and I can’t help but suspect it will be held against me at some point.  Nonetheless, for the greater good, it’s up on github.  There are vague instructions on how one might use it in the README.  Good luck, and I’m sorry.

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Physical Keygen: Now for Disc Detainer Locks

ABUS Plus Disc Lock

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

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Physical Keygen: Duplicating House Keys on a 3D Printer

3D Printed House Key

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.

Key in Lock

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

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Speeding Up Skeinforge with PyPy

PyPy 1.5 vs CPython 2.6.6 for Skeinforge

Now that I’ve recovered from Maker Faire, I can continue documenting what I did.  In the lead up to the event, I tried to streamline the FaceCube project as much as possible so visitors wouldn’t have to waste precious Faire time waiting for a print to start.  On the hardware side, I kept the extruder and heated bed warmed up to operating temperature and (literally) hot swapped 4″x4″ pieces of glass so that prints could run back to back.  I updated the FaceCube script to do capture, cleaning, meshing, scaling, and running through OpenSCAD with a single button press.  The remaining bottleneck was running Skeinforge on my geriatric in computer years laptop.  Skeinforge is an amazing utility, but written in Python, it is slower than a drunk sloth.

There are ways of speeding up drunk sloths though.  Psyco is commonly recommended, but does not support 64 bit architectures.  My roommate Will came up with a plan to run a Skeinforge server on PyPy on a faster computer and have a client on my laptop send STLs to it for skeining.  We ran out of time on that, but we did get PyPy running normal Skeinforge on my laptop.  As of PyPy 1.5, there is support for Tkinter.  Following those instructions to install PyPy and Tkinter and run Skeinforge on 64 bit Linux:

wget https://bitbucket.org/pypy/pypy/downloads/pypy-1.5-linux64.tar.bz2
tar -xjvf pypy-1.5-linux64.tar.bz2
cd pypy-c-jit-43780-b590cf6de419-linux64
wget http://peak.telecommunity.com/dist/ez_setup.py
./bin/pypy ez_setup.py
./bin/easy_install tkinter-pypy
./bin/pypy ~/path_to_skeinforge/skeinforge.py

The fonts may look slightly different, but the application should behave the same.  Export times should decrease the first couple of times you put a file through as the JIT compiler optimizes and then stay good as long as you keep the process running.  On my laptop with a 2.00 GHz Core 2 Duo, Skeinforge runs 2 to 3 times faster on PyPy than on stock CPython 2.6.6. The tested objects were a Weighted Storage Cube, a Flower, Whistle v2, and the Prusa Mendel vertex.

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Gestural Printing: Jumping the Shark on Kinect Hacks

We’ve seen a seemingly endless array of amazing Kinect hacks over the last few months, from superhero generators to obstacle avoiding quadcopters.  However, it was only a matter of time before someone came up with a hack so inane and irrelevant that it would bring shame to the entire hobby.  That time is now, and that someone is me.  I bring to you, gestural 3D printing!  Using the Kinect to track your hand, you can draw one layer at a time, with the printer following your every move.  Pushing forward extrudes plastic, while pulling your hand back will start a new layer.  Who needs difficult and confusing CAD software when you can just directly draw the object you want to print?

Really though, you can only get through 4 or 5 layers before your arm feels like it’s going to fall off, and the resulting object will look like a stringy blob of plastic vomit.  The source is in the FaceCube GitHub repository.  I don’t recommend actually using it, but if for some reason you want to, the dependencies are mindbogglingly complex.  You’ll need to install OpenNI and NITE to start with; this guide at Keyboardmods is helpful.  You’ll also need my branch of OSCeleton, which improves on hand tracking.  With the Kinect hooked up, you can run ./osceleton -n -f to start hand tracking in an Open Sound Control server.  You can then run the gestureprinter.py script, which requires pyOSC, pygame, and the RepRapArduinoSerialSender script from Skeinforge, which is also in the FaceCube repository.  Of course, you’ll also need both a Kinect and a 3D printer that is compatible with the Gcode that RepRap firmwares use.  The script is set up for my printer specifically, but it should be straightforward to tweak for others if you dare.

Gestural Print

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

Thumbs Up

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.

FaceCubeSegmentedPoint 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.

MeshLabOpenSCADRepsnapper

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");
}

FaceCube Tray

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

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AC Powered Heated Build Platform for RepRap

Heated build platform

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.

Thermistor

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.

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