Robotology, the beginning of the end of the beginning of the story thus far.

10 Jul / by: M&R / 8 comments /

This will hopefully be the final “retrospective” Robotology post, with future posts concerning what we’re currently working on rather than what we have worked on. EDIT: this post was too damn long, so it looks like it will have to be a two-parter.. hence the absolutely hilarious title.

Previously we mentioned the first of our physics tests; we also mentioned that it had shortcomings which pretty much ruled it out as a basis for physics-driven robots — it didn’t support friction, angular constraints, or motors.

By this time we had hit the end of summer 2006, which wasn’t the most productive period of time around here in terms of Robotology: aside from the usual distractions (the standard swelteringly gross Toronto summer and video game addictions — this time it was Tetris DS, which was finally satiated when Raigan attained a paltry worldwide score of 7000) we were also busy trying to secure Telefilm funding for N on XBLA, as well as talking with Microsoft. Tedious, but nevertheless needs to be done.

After the summer we found ourselves desperately broke, and still in contract limbo with Telefilm/Microsoft, so we resigned ourselves to reluctantly doing some webgame development for “quick” cash — this is actually not as bad as it sounds; we’ve worked with one particular company several times, and the producer (or whatever you call the guy you talk with who tells you what needs to get done) is really great about letting us try different stuff. We end up learning a lot.

We also did a quick job for a Toronto studio who desperately needed help with a pinball game: the collision detection was a big mess. This seems to happen a lot with Flash/Actionscript: you have very skilled application developers assuming that their skills will transfer easily to making games overlooking the fact that there are a few quasi-game-specific areas which you don’t generally learn while writing server/e-commerce/web apps. Unfortunately pinball is probably the worst possible choice of game to make if you’ve never dealt with physics/collision before. That was a hellish week, but also quite a fun challenge.

Anyway, our narrative has now made its way to the current year, good old 2007. In January we sat down and got back to work on Robotology, starting by figuring out exactly what the hell was going on with the simulator. Raigan was getting pretty stressed out by this point — in the spring of 2006 he game down with stress-induced shingles, and while the extended schedule helped to relieve the pressure that summer, the clock had started to tick yet again.

Thankfully, Mare came up with a fantastic plan: rather than scrambling about randomly, we would make a list of technologies which were known to solve the problems we were facing, and then systematically try to implement each one until we found something that worked. If nothing worked, we would revise our design to fit with whatever our technology could handle. The genius of this plan, amazingly, was that it was a plan: a nice, simple recipe for accomplishing a goal.

So, plan in hand, we made our list of the known technologies for simulating articulated bodies:

  1. mass+spring systems:
  2. impulse-based rigid bodies:
  3. esoteric/alternative particle-based methods:

Actually, this is a list of known technologies which not only do what we need, but which (more importantly) we could realistically implement! There are a wide variety of other methods which we rejected due to the fact that they were beyond our ability to comprehend well enough to use:

  • The entire family of reduced-coordinate methods, which are pretty much custom-made for simulating articulated bodies as we needed, but which sadly require an understanding of “generalized coordinates”. These are things so terrifyingly difficult to understand/visualize/intuit that someone actually invented a completely different simulation methodology, just to avoid having to learn them! If you are interested, Kokkevis’ GDC2004 presentation is a good start.
  • David Wu’s amazingly awesome implicit-Euler-based solver, whose presentations we read diligently every few months and yet still have only a 10-15% understanding of. This is really unfortunate since he actually presents a fully working method for doing exactly what we want to do: physically-driven skeletal animation. Sadly we just can’t quite wrap our heads around the advanced numerical/optimization math required.
  • Weinstein/Guendelman-type iterative impulse-based methods; while these have definitely been used with success (jiglib), we felt that they didn’t really do anything that the previously-listed Catto/Bender methods didn’t, while being more involved/complex. So, why bother?

Hmm.. this post is definitely getting long. The results of our systematic experimentation will have to wait until next time.

comments ( 8 )

  • i don’t mind long posts, just finish the tale!

  • do you find sometimes when you read a paper on this kind of stuff you just fail to understand, you lose concentration and just sit there absentmindedly looking at the thing and thinking about how complicated it is?

    I have that very problem, but obviously with less complex physics. lol.

  • Man! Nice work finding… stuff. I have a tendency to hit the graph paper, then jump right in long before I care to even look if anyone that speaks mathenese has encoded madness to whitepaper. Good for figuring stuff out, but not so good for the whole “reinventing the wheel”/saving time thang.

  • Even though I don’t understand a great deal of the details, this is the kind of post I like to read. I’m interested in what goes on in making the game, and you are quite good at describing the process and challenges in a way that’s interesting even to someone with no programming background.

    Keep these progress reports coming!

  • I want to do a post about this in the future, but reading research papers is definitely an acquired skill. I think the problem is that most people read things once and then give up if it doesn’t make sense; sadly the papers are written so that even experts are meant to read them several times.

    Even with something as straightforward and simple as the Jakobsen paper, over the course of a couple years I reread it maybe a dozen times, and each time I learnt something new.

  • Indeed. I can’t even remember how many times I’ve read the Jakobsen paper myself, especially after I “got” verlet. I think though, the content of many papers could be described much better, simpler. Be it initially, or by a 3rd party “translator”. Even an alternative perspective on a topic can be beneficial for understanding or filling in the holes of an idea. We should be rereading for wisdom, not to actually understand it in the first place.

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