Evolution brings a generative process into contact with a selective process, and before we can do any productive thinking about what might constitute fitness, we have to get the generative process working. Before we can evolve tensegrities we have to be able to grow them, and last time I explained that I felt unprepared to do make the next step, so let's extend this prerequisite: Before we can grow tensegrities we have to be able to build them by hand.

So I took the challenge of putting a new version of Tensegrity online for myself, Hans Moor, and the rest of you to play with so we can all get a real feel for what tensegrity is like. Please take some time to play around with it a bit, and let me know what kind of feeling it gives you and what it makes you think about or what questions come up in your mind.

http://www.darwinathome.org/tensegrity-20080217/

This version is by no means refined to be idiot-proof, so don't expect it to seem finished. I did come up with one really nice interactive feature, and that is the highlighting of triangles where the building will happen. The code for this is quite nice, but of course the way it works is most important: when you see a triangle highlighted, you can click your mouse button and a new tensegrity module will appear! Enjoy experimenting with the program, and let your imagination wander.

Yesterday I once again participated in the very fascinating Biota.org Live radio show podcast and delving into the idea of Intelligent Design with the four other guys and how it applies to ALife developers like us. I talked about how I think it's a perfect description of what we do, and that our artifical life efforts only serve to elucidate the absurdity of the religious notion of Intelligent Design. The challenge that we seem to have taken on is to design intelligently enough that the design becomes intelligent in some way, or in other words to build something that surprises us. I make the point that it's very hard to prove to yourself and to others that you have built something that doesn't need your steering, but it's somehow autonomous instead.

I also mentioned that I'm very reluctant to call something intelligent design or artifical life until it has really surprised me. Currently with this tensegrity project we are not yet even approaching evolution yet. Instead we're still taking steps towards developing the generative growth processes.

One thing that I finally got right this week (actually at 1am saturday morning!) is the physics of the rigid bars when they hit the ground. A while ago I set it up with antigravity below the floor, but that really didn't work well. I kept seeing unwelcome artifacts of the physics appearing, and more recent changes have left me with tensegrities spontaneously scooting across the floor instead of coming down to the surface with a thud. The way I solved the problem was, upon floor collision, to eliminate the component of the other joint's velocity pointing in the direction of the bar. This was exactly the "thud" that was missing. They now act exactly like rigid bars.

Last time I talked about reducing degrees of freedom in the tetra and now the simplicity that this has added to the model is starting to pay off. There's one thing from last time that I got wrong, and that's the name "tension factor". The lower the tension factor the higher the tension so the name just doesn't seem right. A great name for this quantity occurred to me suddenly: "Slack"! The desired length of the four cables in a tetra, added up, divided by the sum of the length of the two bars crossing in the middle is now called slack. I've loved the word slack ever since I came across The Church of the Subgenius. This version has a slider for you to raise or lower the slack, and I recommend you play around with it, probably best with zero-gravity.

Technorati Tags: