Sunday, July 13, 2008

Woodworking capability

One concept I have spent a lot of time thinking about is 'capability'. By capability I mean the tools, materials and knowledge necessary to make something. As an example, at home I have soldering capability. I have a soldering iron, some helping hands, a mat to protect the table plus I know how to decently use all of the above. I've set things up a few time, there are boxes where everything goes when it's not needed and I have enough experience to solder passive through hole components. I even have a bit of 'soldering tools maintenance' capability, I've soldered enough for the iron to loose it's initial sheen and I've had to polish and re-tin it a few times.

While a lot of the things we surround ourselves with can be easily manufactured en-masse, we are often faced with the situation where we need some particular item and only want one or two of it. If we have the capability to make those items, the world looks very different. It's a kind of industrial revolution, except in the reverse.

One of the capabilities I've been lacking is basic woodworking. Our apartment does not easily yield itself to work involving large amounts of sawdust, so my repstrap plans have been seriously limited by what can be worked on without generating dust. In the long run this was clearly not tennable. So this weekend we visited two nearby sites that let you use their tools: TechShop and SawdustShop. TechShop is a robotics, metalworking and tinkering heaven, they have an epilog laser cutter, a good metalshop and a ton of handtools and stuff. They also used to have a 3D printer, but it has recently broken down, which was a tiny letdown. Sawdust on the other hand is a pure woodworking shop. They have a large collection of powertools and staff on site to help out in case you have questions.

In the end I did a 2 hour session at Sawdust and managed to produce a few of these:


Not parts of a RepStrap, mind you, but stretcher bars used by artists. I've been promising my wife for ages to start making them for her. The situation is now markedly improved, there are two great shops less than 15 minutes away where a RepStrap can hatch.

Wednesday, July 9, 2008

RepRap protoseedling: toy 2D plotter

So eventually I ran out of funds. My wife and I have for several years been keeping a simple but working budget, we have half a dozen categories and a rolling balance for each of them. Every month each category gets some fresh funds, once they are spent you need to wait for the next month. One of those categories is my RepRap and robotics fund.

Saying I ran out of funds isn't really fair. My wife, being the kind and loving person she is, let me run my robotics account well into the red before she rightly objected. But that meant I was stuck. My specific problem is that I over provision. I bought 5 Stepper Motor Controller v1.1 PCBs and corresponding parts. I have 9 Vextra stepper motors bought cheaply on Ebay. I have a few handfuls of atmega8 microcontrollers, max232's serial chips and a host of support components. Programmers, USB to serial converter, ATX PSU etc. etc. Plenty of parts to build out the electronics for two or three RepRaps or RepStraps. But almost no mechanical parts because I hadn't got to that point yet.

While running the steppers on a table is initially quite fun, my ambition grew quickly. Given that I'd written the AVR firmware myself I was interested in tackling problems like backlash, missed steps and in general seeing how well the controller would perform with several steppers attached. The situation seemed hopeless until I remembered a device built by my good friend Neil Fraser: a simple children's toy converted into a 2D plotter. Some crude woodworking and a bit of assembly later I had a RepRap protoseedling, a simple 2 axis robot:


2d plotter


The microcontroller runs custom firmware geared at reprap control. Interestingly, my humble ATmega8 has 512 MB of storage, accessible using simple SPI commands. And that's only because this was the smallest and cheapest SD card I could buy at the local electronics shop. More about that later.