Tag: Fablab

Blending and Bending Prosthetic Leg Fairings

From Kinect scan to laser cutting

Opened the original scan in Blender, selected the portion of the scan we’re concerned with. Separated it from the rest of the mesh and exported as stl.

Used Netfabb to repair the mesh and cut into a top and bottom portion.

Found out netfabb decimates the mesh upon export, from 27000 triangles to 24000 triangles, and manages to make it pretty rough, so it looks like this in 123D Make.

Inspected the files before and after repairing in Netfabb…

Used MeshLab’s Filters → Remeshing → Surface Reconstruction to “Shrinkwrap” the model and fill in gaps and holes without losing the smoothness of the scan.

Used this guide to split the part in two using Blender’s newish “Bisect” function.

Played around with different options in 123D Make…

Drew a circle in Blender against the scanned cLeg and stool, confirmed that the units of the scan are in meters. (The circle is .355 units wide and in real life the stools are too.) But, since many programs interpret these STL units as mm, our objects are 1000 times too small. Let’s scale them up.

Settled on a slicing pattern in 123D Make. Used the Modify Form feature to hollow out the leg and picked out the Radial Slices construction technique. The arrangement has some collisions at the bottom, but I don’t want a closed model anyway, so will do some hand-tuning in Inkscape. Exported the model to Blender to check that the cLeg would sit inside it okay.

Using Inkscape to layout the the pieces onto less than 4 sheets of plywood… (nesting is apparantly a difficult problem for computers, and not one that many softwares implement, certainly not free ones. just have to eyeball it)

123D Make is sadistic and exports the objects as groups of thousands of lines instead of a single vector, so editing the exported PDF is really really slow. (It takes 20 seconds to select a text object and type in a new number. I counted.) Learned things:

On the left: the highlighted list of numbers 4,000 characters long describes a single path. On the right side, two coordinates of a single line segment are surrounded by markup. The file containing 2 objects takes 73 lines of text. The file exported by 123D Make takes up 6151 lines of text for the same object. Inkscape modifies this information in memory every time you move something.

Inkscape operates with SVG, which is plain text, ASCII, one character equals one byte. When a path is exported as 677 individual paths, each one of those line segments has 8 lines of markup surrounding it in the SVG file (between the g tags, with information for position and stroke and fill attributes). So what could be saved (and manipulated in memory) as 20 bytes if it was appended to the list of nodes in a single path instead takes 389 bytes to be kept in memory as a standalone object.

I found this forum post describing how to select all the separate objects, Path → Combine them into a single object, and in node edit mode you can select all nodes and click Join Selected Nodes and it simply merges overlapping nodes. Hallelujah!

So to downsize the files enough that they’re not a pain to work with:

Open the PDF. I learned that if you check the “import via Poppler” option Inkscape can detect the colors of the stroke (otherwise imported PDFs have “undefined” color unless you adjust it yourself). So check that box. CtrlA, CtrlU to ungroup everything. Click a blue line segment. Edit →Select Same →Stroke Color. Path →Combine. F2 (Edit Paths by Node). CtrlA. Wait for a minute. Join Selected Nodes (one of the buttons in the node edit toolbar, 3rd from the left, just after the delete node button. It might take a few minutes for Inkscape to chew on this one. It will probably become unresponsive. Let it do its thing. In my case this trimmed the file size by 97% and I could then translate and rotate and rearrange the objects without any lag.

Two hours later…have my minified cut file, fitting on 1.5 sheets instead of 4. I’ve trimmed the tops and bottoms off the vertical slices so the end result will be open.

20 minutes of lasering + 10 minutes of assembling: Hey I made a thing!

Met up with Shawna and learned the design constraints: how the leg has to move, what areas can’t be covered, etc. We picked out a pattern she wouldn’t mind having wrapped around her leg:

I took a few measurements of the wooden positives and drew the outer shape of the fairing in inkscape by hand (using auto-smooth of course!). A few booleans later I had my cut file, which took about 20 minutes apiece. To get the part ready to shape against the mold, I stuck it in our convection oven to bake at 300F for about 5 minutes (don’t worry, we keep one oven for circuit boards and plastics and a different oven for foods 🙂

So the process was: semi-soften the plastic in the oven, then roughly fold it over the wooden form, then stick the whole wooden form in the oven. If you let it soften all the way when it’s sitting on the metal it’ll stick to the metal. Better to have it roughly on the wood form when it reaches maximum droopiness. When it’s as soft as rubber, we take it out and push the plastic against the form, holding it in place as it cools.

I’m pretty happy with the second prototype. I think the next step is 3D printing some bracket system, and maybe taking more time to plan out how the plastic will fold against the form — this was pretty heavily eyeballed.

Continued with a rough prototype of a bracket here: Designing brackets for cLeg cosmetic fairings 

Parametrically Designed

CNC Plasmascreen Coffeetable

Being a university affiliated FabLab has some perks: we get to pull useful items from University Surplus (one department upgrades their computer lab, other departments call dibs on the old hardware, sometimes really new stuff, sometimes really old stuff).

Nearly all of the computer equipment at CUCFabLab was pulled second-hand this way, then topped off with RAM and upgraded to SSDs. A funny assortment of other supplies end up getting collected: decades old oscilliscopes, a 1980s bandsaw, and this big old 60″ plasma screen display.

It weighs about 100 pounds and is fairly low resolution (not quite 720p if I remember right) and it took up an awful lot of table space, so it quickly got basemented. That was until my Fab Academy assignment was to ‘make something big’ and I remembered that I always wanted a coffee table that was a giant computer screen.




The neat thing about plasma screens is that a lot of the electronics are bonded to the glass (tho I can’t recall where I heard that…) and as a result, they often have a pretty thick slab of glass to start with, so it’s sturdy enough that I don’t feel nervous about setting my laptop and maybe a cup of coffee on the screen (tho a spill of the latter might be fairly disastrous if you don’t contain it before it drips into the edges…).

Putting a big slab of acrylic or glass on top of a large display is often the most expensive part of this kind of object, so avoiding that part altogether meant I just needed a cheap MDF base for the TV to sit on. Like most TVs, there’s the front body of the screen that tries to be thinner while the power supply and mainboard sits in a sort of hump on the backside. So the design of a base that goes up to this edge but leaves room for the hump turns out looking like a pool table.



It was designed using the Rhino plugin Grasshopper, which proved to be a very intuitive interface for parametric design. It is a matter of dictating the size and position of 3 rectangles (the top of the table, the base of the table, and one that can be scaled and moved as a midpoint) and then creating “lofted curves” through each set of corners. This is an automatic function that creates the whole smooth shape pictured without any work on my part. I get to just change the position of the midpoint of the curve until I like the look of the resulting curve. Then I just subtracted a box with the inner dimensions I needed from the larger shape.

After that, I have a program to do the work of planning my assembly as well. The free 123D Make by Autodesk has a great workflow to open your 3D file, type in your material parameters (“I’m using 4′ by 8′ sheets of material 1/2 inch thick”)




I got the pieces cut at the architecture lab with lots of help. I learned that with this slotted construction technique it’s necessary to drill holes at every interior corner (so in the CAD file you select each of these corners and create ‘points’ on a separate layer to export as a drill file). This was about $40 worth of MDF and took less than an hour to cut out on Architecture’s giant fancy CNC machine.

Assembling it took a lot longer. Lots of rubber malleting.



I started playing with processing sketches (like the rainbow above), but it takes up a lot of space and there’s not a good spot for it at the lab, but the TV is unvierstity property so it can’t be taken off campus, so it is hidden in a corner — the interactive processing sketches will wait for now.

Hacker Trip To China

Hong Kong

That’s Innovation Tower! Looks like a cruise ship from the year 2070, right? Possibly interplanetary space-worthy? It houses the school of design at Hong Kong Polytechnic University and was the first stop of Noisebridge’s Hacker Trip To China 2015.

We toured three separate spaces just today: the workshops at PolyTech, DimSubLabs, and LAB by Dimension+.


Sewing Studio & Ceramic Studio at PolyTech

We met with William of Dim Sum Labs outside our hotel who took us on a tour of the PolyTechnic University, pointing our the tight grouping of the Business School, Design School, and Textiles School. We interrupted a couple of classes, where students were happy to explain what they were working on. I met one guy doing a papercraft mech (you know, those giant flying fighting robots) which he designed in CAD and broke out all kinds of engineering drawings of how to fold this complex origami. A girl was working on a chair made of bamboo and cord, taking advantage of its tension. Always something being cut in two (I think I saw some chiseling going on) and folded into shape.

So it’s a very well equipped university lab, open only to design students. Reminded me that I wish I had access to ceramics wheels again. The thing that attracted my attention the most was the excellent signage! Maybe a boring thing but it’s a topic of constant discussion at CUCFabLab — how to make the signs better, how to make sigs that express rules and expectations and capabilities. So when I saw the wall-sized page-turning displays of materials, I said to myself “Duh!” and when I saw a big poster listing all the tools available at the lab with a key connecting it to its picture, I said to myself, “duh!” There was even a big poster by the laser cutters describing what line weight and file format to use.







So I got organizationally inspired. After concluding our tour, we had a big lunch (I’ve been impressed so far with Hong Kong restaurant’s capacity to cater to a group of 18 people without warning) and headed to Dim Sum Labs, but not before topping off our ‘Octupus Cards’ — which is the tap to pay card for all the public transit systems as well as convenience stores. I forget who it was, but somebody had an app on their phone that could read any NFC chip and dump all of its information on the screen, so with one tap we found out the model # of the microchip and the software version running on these featureless plastic cards. Neat stuff — we joked about editing the information (chiefly, the current balance), but there’s some pretty tight encryption running on those little plastic cards, too.

“Do you think I can edit the balance of this without putting cash on it?”

“Put money on it without paying money? Yeah I’d like to know, too.”



Workshop at Polytech, Dim Sum Labs, and Architecture Model Lab at Polytech

Dim Sum Labs is a one room affair (I think I heard 400 sq ft), which they pay about $1,500 USD/month for. They’ve got some great self-screen-printed tshirts (William is wearing one in the pics) and a great RGB LED lighting system — kind of looks like christmas lights in the picture. One of the members was working on an upgrade: to make the color of the whole room programmable (switching a few amps on and off is a little tougher than blinking one LED).

I was reminded of my dream-classroom for teaching intro to programming: individually addressable LEDs covering the ceiling such that each student in a classroom could start by controlling just the one LED, getting to know how to blink it and effect its color. Then each student could work their way up to controlling larger arrangements: perhaps a row of 5 LEDs, then a grid of 5 x 5 LEDs, until the students’ combined work is creating undulating colors across the whole ceiling.

The benefit of this is twofold:

  1. basic programming is a lot more interesting if you get to control something not on your computer screen (I learned by manipulating strings in a command line, but I see people blinking LEDs are a lot more enthusiastic about a few lines of code.)
  2. As a teacher / mentor, you don’t have to squint and bend down to someone’s screen to see how they’re doing. You can see the progress of the whole class at once. Better yet, the students can see the results of each others work, too, leading to un-plannable “how did you do that?!” learning moments.

So I was going on about how I wanted to build a room like that, and the guy I was talking to (I’ll learn everyone’s names soon enough…) said “Oh, we got a ceiling you could do that with at our hackerspace in Chico (California)”

!!!!

Then a guy across the table says “What? You live in Chico? I grew up in Chico!” The bigger the city, the smaller the world.


The rooftop at Dim Sum Labs.

After hanging out a Dim Sum Labs for an hour or two, and we connected to an acquaintance that was told “We’d like to visit Dim Subs Labs and other places of Geek Interest” by Mitch so we ended up at a very cool espresso bar / third wave coffee shop (that’s the kind where they roast the beans behind the counter and let you pick out which farm you want to try the flavor of) that had local art for sale, the majority of which was laser cut upstairs.




Laser Cut Stuff + Quick-and-Dirty Ceramic 3D Printer at “Labs by Dimension+”

Again, I was inspired and surprised by dioramas that communicated the capabilities of the space. Just a general feeling of “why didn’t I think of that?” all day. So they’ve got these products they sell, both as little assemble-it-yourself kits like the bud vase and as assembled products which you can inspect all of the parts. I’d love to build some of these at my home FabLab as well, just to get people’s minds going on what you can do with these tools.

Afterwards we wandered an electronics market, tho it was late enough that most booths were closed. A few people were figuring out SIM cards and international power adapters. Mitch was testing the charge rate of different USB cables which is a shocking discovery that merits further investigation: some USB cables charged his phone at a piddling 80mAH and others charged at 10 times that rate. Like, what? It’s four wires, there’s nothing in there, how can one cable charge so much faster than another? Hmm…

Anyway, I need to buy an umbrella. It’s going to be a rainy week.