The Digi-Comp 1 rides again?

As computer people go, I'm rather an old fart, and my favorite childhood toy was this plastic computer, the Digi-Comp 1. See the three horizontal red things that run almost the full width? Those are flipflops, and the window on the left shows whether they are in the zero or one position. The six vertical metal bars in front are AND gates, and the little white tubes stuck onto the pegs on the fronts of the flipflops tell whether that bit is factored into the AND term. The six red plastic things on the top, together with similar stuff on the back, form three OR gates, which drive the values of the flipflops on the next clock edge. The two white sliders on the bottom worked in opposition, providing a hand-powered two-phase clock to drive all this stuff.

Over the past couple of days I placed an order with danger!awesome, a laser cutter shop in Cambridge MA. They have a nifty collection of laser cutters and were happy to hear that design files are available on the Thingiverse website. So I ordered some stuff and picked it up this evening, and that was fun. I had hoped they could make me this marble binary adder, but the designer didn't supply design files they could use. So no marble adding machine for me. Darn.

Thinking about that, my mind inevitably went back to the Digi-Comp 1. I started wondering whether I could build a Digi-Comp 1 using laser cut plywood, like the other trinkets I picked up this evening (a Companion Cube, a desktop trebuchet, a Shrimpbot, and a few little animals). Could that be feasible? The Digi-Comp 1 was basically a programmable logic array, which consists of two rectangular regions, one for AND gates and one for OR gates. On the Digi-Comp 1 these are respectively the front surface and the back surface of the device.

I thought about this for a while and came up with some very incomplete rough sketches to solve the problems of how the gates would work and how the binary values should be latched for one clock cycle. As with the Digi-Comp 1, this would be a rectangular thing with the AND plane on the front and the OR plane on the back. The flipflops would be horizontal bars along the front with two positions (left=0, right=1) and possibly the same window display that appears on the original Digi-Comp 1. The AND gates are vertical bars also on the front, connecting to vertical bars on the back. The OR bars on the back can move left and right if permitted. At a certain point in the clock cycle, the horizontal position of each OR bar is inverted with a little lever and latched as the new position for the corresponding flipflop. There is still a lot of mechanical engineering to think about. Should the bars be retracted with springs or rubber bands? There needs to be a lot of machinery to get everything to move when and where it's supposed to, and there needs to be a crank on the side to drive it. So there will be cams and gears and all sorts of fun stuff.

UPDATE: I found a place called Minds-On Toys that is selling a Digi-Comp kit which reproduces the exact mechanical design of the original. Looks very nice, except for the labor-intensive-looking bit at the bottom about fabricating your own plastic tubes.

Cool new 3D printers

I don't want to fall into the habit of only blogging once per year about MakerFaire. So this post is actually about a crop of cool new 3D printers, and I'll probably see a few of them there, but it's not about MakerFaire proper. These all fall in the $1500 to $2500 price range.

First up is Makerbot's Replicator 2. There is some controversy around this one, because it's a mix of open source technology under the GPL, and some new technology that's very likely not open source, which allows for a much higher print quality. The open source 3D printer advocates are concerned that it violates the GNU General Public License. The open source technology is primarily the work of Adrian Bowyer who started the RepRap project, and he's given (unenthusiastic) permission to Makerbot to use it.

One of the RepRap enthusiasts is my friend Jeff, who will have a table at MakerFaire this year to show off the printer that has occupied two or three years of his nights and weekends. I like Jeff and I think he'll probably not be too happy with Makerbot's decision to include closed-source technology. But the step up in quality for the price is pretty appealing for a non-GPL-purist like myself. I don't worry about running GPL software on closed-source laptops, after all.

Second is the FORM1 from some Media Lab folks. I don't know much about these folks or their history, but the Media Lab has been at the cutting edge of high-end 3D printing for a couple of decades now, so they've probably got something pretty interesting. I think their raw material is a liquid rather than the long plastic spaghetti sticks used by most other affordable machines (based on one photo on their Kickstarter page). This is the most expensive of the lot, price currently listing as $2500.

Third is the UP!Plus from 3D Printing Systems. Their output doesn't look as nice as the Replicator 2 or the FORM1, but they are at the more affordable end.

What's cool about all these printers and some other new ones is that the user friendliness and quality of output are improving rapidly in recent years. Before long, these things will be popping up in homes, dorm rooms, high schools, and the local mall.

Makerfaire NYC 2012 is this weekend, and I'll be there to checkout 3D printers, microcontroller boards, art installations, and whatever else is around, and I'll blog about what I see.

Coming soon: a complete RepRap kit

BitsFromBytes.com is an on-line store based in the UK which will be offering a complete set of parts for the RepRap for UK£299, or somewhere around US$600 given current exchange rates. They will offer both hardware and software.

I wish I could claim to be so ambitious that I would take a more active approach than simply ordering all the parts in a kit. But I'm as lazy and tired as the next guy, so a kit is really the only practical way I'm likely to do this. And the price is just about right. Months ago, Adrian Bowyer was talking about $400 as a target price for the long term, after lots of self-replicating machines had brought the price of parts down to a minimum. To get so close to the long-term price so quickly is fantastic.

With this kind of head start, the scenario where RepRaps bootstrap themselves to microeconomic ubiquity looks very plausible.

RepRap is now half-way to replication

Vik Olliver has made good progress (1, 2, 3) on the goal of self-replication for the RepRap, having now been able to use a RepRap to fabricate half the RepRap's parts.

It's interesting that you can see the size of the volume pixels Vik is working with. These pieces were printed with polylactic acid, I believe.

Unrelated but cool: Kovio is a non-hobbyist company working on a process to inexpensively print working transistors. Early applications will include smart cards, later you'll see wall-sized displays.


Also unrelated but also cool: Fernando Muñiz has been working with UV-cured resins. This will work a bit like the CandyFab, except the uncured resin is still a liquid so under-support structures are still required. Interesting, I'm not sure if it's better or worse than the FDM approach used by RepRap, Fab@Home, and Tommelise. Also, I don't have any idea how environmentally benign these resins are; it's hard to imagine they're as green as polylactic acid.

Tommelise project

Tommelise is Forrest Higg's attempt to build his own RepRap-like gadget before RepRap itself is ready for wide distribution. He has spoken at an O'Reilly conference about the RepRap project and he has some fascinating ideas about architecture and how fabbers might relate to it. The recent (early Feb 2008) postings in his Tommelise blog describe his success in connecting stepper motor axles to threaded rods, something I had been wondering about myself.

In the Tommelise FAQ, Higgs mentions Linux and Java (which have been adopted by the RepRap project) as presenting a steep learning curve to people without a software background, citing Microsoft Windows and Visual Basic as more user-friendly alternatives. My own early experiences with Linux required enormous patience. Higgs writes Tommelise has been created for people who aren't particularly clever and may be living in modest circumstances. Any open-source "fabber revolution" (1, 2, 3) will be an empty exercise if it fails to serve such people. Then again, if a genuinely open-source revolution is to occur, we'll eventually need to wean ourselves from Microsoft and make our own tools equally user-friendly.

Brilliant RepRap video (thanks to Emeka Okafor)

I am deeply indebted to Emeka Okafor, author of the Timbuktu Chronicles blog and director for the TEDGlobal 2007 conference in Tanzania, for stumbling across this brilliant Poptech video of Professor Adrian Bowyer, the inventor of the RepRap fabber. I would also like to thank Mr. Okafor for giving attribution to my nanotechnology blog, and call attention to his postings on technologies that can help Africa and other developing regions. There is an Emeka Okafor who plays basketball, I'm not sure if it's the same guy.



Bowyer talks about the economics behind the project, particularly its ability to empower communities that are now economically depressed. There is some yummy game-theory stuff in the paper linked here that does not get mentioned in the video, check it out. He also talks about using polylactic acid (wikipedia) as a printing material for the RepRap. This is significant because you can make PLA from starchy vegetables like potatoes and corn, and when you're finished using your PLA object, you can compost it to help grow next year's crop of starchy vegetables. You can have a closed-loop local manufacturing economy that doesn't require trucks or trains or ships to move products around. In fact there are several materials under consideration, and thought has been given to printing a single product from multiple materials. The Fab@Home folks also have an impressive list of materials that can be fabbed, including chocolate.

I got curious about PLA and did a little googling. In a RepRap forum there is a discussion of just how easy it is to turn starchy vegetables into PLA. From the sound of it, it is non-trivial and demands that the person attempting it be quite knowledgeable. One person compares "home PLA production today to home biodesiel production 20 years ago, when it was arcane, a little dangerous, and rare, but theoretically possible" and notes that for many people it will simply not be economical compared to mail-ordering some PLA. I found a place that sells utensils, plates, and cups made from PLA. NatureWorks appears to be a source for PLA in ready-to-work form.