from 5 Feb 2014

I recently built a 3D printer from a kit. It was surprisingly easy to build and it more or less worked right away when I did a test print. But even though much about the kit was really impressive, "plug and play" does not describe this thing.

In a word, it's taken a good bit of trouble-shooting to get the thing working dependably right. But that word does not quite capture the wonderful model for pedagogy that is emerging from this experience. Because the thing was basically sound, when things went wrong focus was rewarded. The first few problems were simply assembling backwards things that were close to symmetric. Sometimes it seems there is a Murphy's law governing such pieces and one suspects they are always first put together the wrong way, but it's an attention bias thing: one only notices the ones that go in wrong. But still each time this happens one learns a little bit about the underlying design as one grasps WHY the other way round does not quite work or what it is that makes the right way round right.

And then some things do not work. The most troubling bit with the PrintrBot is the "fishing string" drive system. It's quite clever: a small dremel-tool sanding drum is mounted on the shaft of a motor and the motor is mounted perpendicular to one of the planes of motion of the printer. A bit of string is then stretched from one end of a moving part to its other end with two loops taken around the sandpaper drum along the way.

printrbot-pully.png

The first thing you notice when you rig this thing up is that it's not clear whether the string wraps should sit next to one another or span the width of the drum and if they should be next to one another should they be toward the back or the front. And then you notice it is hard to get the string tight. The first few times you try to move the thing the string gets all loosey and flops off the drum. But you cannot completely avoid this as you notice that as the motor drives it one way or the other the direction opposite the "pull" gets all floppy every time.

You do a little google searching and find discussions about the proper tension in the string and ways to achieve it. Lots of people have lots of ideas. And so you experiment with different ways to get the string tight and you find something that seems to work for you.

And then there is getting the printing bed level with respect to the way the print head moves in the X and Y directions - hint: it may not be the same as level with respect to the earth. And then, as the thing gets ready to print you have to try out different initial Z positions (i.e., how far above the print bed is Z=0.0?).
And none of this includes the settings in the software. The instructions give you some default starting settings but there are dozens of them and at first you have no idea what they are for and what the possible values are.

But over a period of a few days you start to get an handle on all of this stuff. Things go wrong. You mess up print after print as you try to fix things. But with each failure comes a little more familiarity with how things work. Some of this is familiarity with the idiosyncrasies of your own set-up - the actual machine you built - and some are about the machine as designed and some of the combinations you manage to get to work may be ones that no one else has tried yet.

The point of all this is that the process of getting the damn thing to work is one of learning a lot about how the thing works. But the order is important: it's the trouble shooting and experimentation that produce the insight. You simply cannot learn how this thing works except by repeatedly breaking it and fixing it.

And so this started me thinking about whether or not there is any opportunity for building this kind of learning into the kinds of things we teach. The ethos in our classrooms seems to be built around the idea of taking off points for mistakes so that the number of mistakes you make on the way to learning something counts against you in the long run. How can we set up a learning situation in which we expect many of the things that people try to fail and that success will likely only come after lots and lots of wrong turns?