
Dexter Walks (first dynamically balancing biped robot) - perler
http://www.paulgraham.com/anybots.html
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Alex3917
It's interesting to look at the differences between the way Dexter's doing it
and the way we do it. Dexter appears to be lifting his foot straight up off
the ground and then falling forward to produce the forward motion.

The way humans walk is exactly the opposite. The toes are at a different angle
from the foot (when walking), so that our feet effectively look something like
___/ , with the underscores being the foot and the / being the toes. We then
transition from the ___ part of the foot to the / part of the foot and push
forward, and land flat footed with the other foot. For whatever speed you are
going, there is a proper ratio between landing on the ___ part of the foot and
pushing off the / part of the foot, and that's where balance comes from. That
is, the faster the acceleration of the fall, the faster you transition from
___ to / .

So in humans, balance comes from the way one step connects to the next step,
whereas Dexter appears to be treating each step as a discrete unit, where it
has to attain balance at the end of one step before going on to the next step.

If you actually have to balance yourself after each individual step instead of
using the next step for balance, the problem seems in some ways to be much
harder.

Also, the balance problem is greatly compounded by the small steps Dexter
takes. Compare this to doing lunges. When you do a lunge, you basically take a
long stride forward and then sink into it, all while keeping your torso
perfectly upright. This gives you a much bigger platform for stability. As
terrain gets steeper, the way humans walk becomes more like a lunge for this
reason.

So my guess is that taking one tiny step and then balancing is the hardest
part of this problem, because you have the least tools at your disposal. For
example, you can't use the next step to balance you. However, once you can do
the last step of the sequence, all the preceding steps working backward from
the last one get progressively easier.

I don't know anything about robotics, but as an athlete and sports physiology
geek I find the problem interesting.

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jadams
> [...] Dexter appears to be treating each step as a discrete unit, where it
> has to attain balance at the end of one step before going on to the next
> step

I doubt that. I don't think that would qualify as dynamic balance. Remember,
it's only been a couple of weeks since Dexter's first step -- he's walking
quite well.

This is one of those situations where the approach bounds the eventual
utility. There are a lot of non-dynamically balanced robots that would just
blow the minds of researchers from 20 years ago, but they are still limited.

By solving the dynamic balance problem, even though to the untrained eye it
may currently look less impressive than some other systems, there's no more
ceiling to what it can do, dynamically (control-wise, not accounting for power
density). All of the behaviours you mentioned can be implemented on top of
this substrate.

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Alex3917
That makes sense. Thanks for the insight.

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BrentCastle
Would anyone care to comment on what the downfalls of the commercial gyros
were? Is it precision or time-lag? I know I can't get specifics, but I'm
curious in general what is different in this application that commercial gyros
were not capable. Any info would scratch my itch! Thanks!

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brezina
Congrats Tevor - I suspect the military has spent 1000X the money with 1/
1000X the progress.

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altay
Incredible!! Congrats, Trevor!

Now, if you'll excuse me, I need to go prepare my bunker for the coming War
with the Machines.

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ecuzzillo
It seems to me that things like this have been done in academia for a while;
because I've only seen a video (rather than, say, some code or a paper), I'm
unsure exactly what Dexter is doing, and whether it's different from the stuff
done with bipeds at CMU, MIT, or in Japan. I wonder if there is any more
information available.

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pg
Really? Do you have a reference?

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jadams
Sony claims that Qrio can respond to outside pushing, as here:

http://www.plyojump.com/movies/qrio/sdr-4x_recoverfromfall.mpg

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wicked
That isn't the same. He carefully applies pressure to one side of the robot,
and the robot starts walking in that direction.

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mynameishere
Reminds me of an old person who had a stroke and has to shamblingly re-learn
how to walk.

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jwecker
Brilliant. Well done. It's very cool seeing him go up onto his tip-toes to
keep balance. I also think it's cool that they built a whole other robot just
to try to pick a fight with Dexter.

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chris
I had the opportunity to see Dexter live in action, it was one of the coolest
things I've ever seen!

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BrentCastle
Sorry. Accidentally refreshed and reposted. A moderator can delete this
comment!

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jamiequint
wow, that's the most insane negative feedback system I've ever seen

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jamiequint
um, why the mod-down... http://en.wikipedia.org/wiki/Negative_feedback

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ecuzzillo
The negative feedback wasn't the problem; it was more the ogmz lozl amazing.

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jamiequint
apologies, but it is amazing

