First Dynamically Balancing Biped Robot

damg writes "Anybots, which is three guys led by Trevor Blackwell, has developed the first robot that walks like we do, by dynamically balancing itself rather than being pre-programmed for walking like Asimo. The video shows the robot walking and being pushed by another 'bully' robot to demonstrate that it can't easily be pushed over."

It's like falling and missing the ground

[chriss]

This is ways more impressive than you'd guess from the video, which doesn't look much different from all the other walking biped robot video (it's less shiny than most). Since this always pops up [slashdot.org] and always has to be explained [slashdot.org]:

not dynamically balanced:

When the robot (e.g Asimo) moves, it's center of gravity is ALWAYS above the foot it is standing on. As a consequence, the robot could freeze at any moment without falling. Humans can walk that way, but it's slow.

dynamically balanced:

The center of gravity is not above the foot, basically it's falling forward, the motion cannot be stopped without falling. Much faster to move, much harder to calculate. Anybots managed this, which makes their bots a great achievement. We move this way.

This is cool... but the claim of "first" is untrue

[jkuff]

This is a cool robot, but the claim of being the first "dynamically balancing robot" is an overstatement. There have been many dynamically balancing robots before, the most famous being Honda's P2 unveiled in 1997. After that, there have been dozens of walking and dynamically balancing humanoids.

What I think the story _should_ point out that is very impressive is:

1) The robot uses pneumatic actuators, which are notoriously difficult to model and control. Almost all of the current dynamically balancing and walking humanoids use electric motors (e.g. ASIMO).

2) Anybots claims to have some "learning" in their controller. Although they don't have any papers about what they are doing, perhaps they are using some clever statistical modeling and feedback to adaptively control and regulate the robot's stability.

BTW, I had a chance to meet Trevor Blackwell a few years ago when he visited my lab. He is definitely a talented engineer with a vision for the future. Several years ago he made Slashdot when he announced his homemade Segway:

http://hardware.slashdot.org/article.pl?sid=03/09/ 28/1756241 [slashdot.org]

From my point of view, any interest by hobbyists and industry in humanoid robotics in North America is great for the field of robotics research.

Re:It's like falling and missing the ground

[jkuff]

This comment is spreading misinformation.

ASIMO _absolutely_ dynamically balances. I have one in my lab at CMU and have worked with walking humanoids [kuffner.org] for years.

First of all, static stability means the center of gravity (CoG) is inside the base of support (the convex hull of the ground contact points).

Dynamic stability is much more difficult to analyze because it involves stability over time. The velocities of any moving parts of an articulated body induce linear and angular momentum that can result in a dynamic stability over time _without_ having any of the intermediate poses being statically stable.

The center of gravity absolutely _does not_ always stay above the support leg for ASIMO. If you try to freeze his pose during the middle of a step it will fall over.

Instead, ASIMO is controlled to keep the Zero Moment Point (ZMP) always inside the convex hull of the contact points. The ZMP (related to the Center of Pressure) is the point on the contact surface where the sum of all torques (moments) is zero. For a given walking trajectory, if the ZMP always stays inside the base if support, then the walk is dynamically stable.

There have been numerous humanoids that use the ZMP formulation to control and maintain dynamic balance while walking (e.g. Honda P2, P3, ASIMO, U. Tokyo H6, H7, AIST HRP2, Waseda Wabian 1, 2, KAIST Hubo, Toyota Partner Robots, Sony QRIO and many more). ALL of these robots are dynamically balancing and are definitely NOT statically stable.

Re:It's like falling and missing the ground

[cheater512]

Its hardly used for support. Most robots use the cord for debugging output and to collect related data while the robot is moving.

Yes, not the first dynamically stable walker.

[Animats]

Kuffner (above) is right, of course. Dynamically stabilized walking has been around for years. It's not easy to do, but it's been done. Raibert first did it in the 1980s. See his book, "Legged Robots that Balance".

Most of the self-balancing walkers, as Kuffner points out, use a ZMP-based approach. This works for walking, although it's not quite enough for effective running.

Many of the dynamically balanced robots can rebalance after a shove. BDI's Big Dog can. [bdi.com] So can some Japanese hobbyist robots.

If you're not up to date on how far along Japanese hobbyist robotics has progressed, see these videos of this month's humanoid robot soccer match [robots-dreams.com]. These robots are mostly manually controlled, but have computers managing some functions. Many have rate gyros to assist with balance. Gradually, the computers and sensors are taking over more of the control. The hobby robotics manufacturers in Japan now have about 70% of the functionality of Asimo at 2% of the price. There are hobbyist robots with WiFi links and cameras on board. A few more improvements and you'll be able to do all the Asimo stuff with a $1500 robot. But it will only be about 60cm high.

Re:Fascinating

[mblase]

arms are one of the key features of human balance, but then again they do make for more variables.

Yes and no. You could probably walk or run perfectly well around your house if your arms were completely limp at your sides, or tied tight behind your back, or bound to your sides somehow.

Arms CAN improve balance by shifting your center of gravity quickly, but they're absolutely not involved in locomotion.

Re:It's like falling and missing the ground

[anagama]

Watch the video again. The cords are hanging loosely and jiggle when it moves. If they were supporting him, they would obviously be taut, like an actor hanging from a wire or a kid on a swing. It makes plenty of sense for the cords to be there to provide power and transmit/receive data. Without the added weight of a battery and computer, they can work on getting the mechanism to work first, then work on getting it to work untethered under heavier weight loads later.

For those who don't know the reference

[LordEd]

There's been several comments related to pusher/shover robots, the terrible secret of space, and "pak chooie unf". For those who don't know what these refer to, see the ICQ prank that started it [somethingawful.com] and the flash animation/song [devilducky.com] inspired by it.

Re:What, no arms?

[Falladir]

I think running and jumping robots are quite far away. The problem is that modern mechanical actuators can't efficiently generate the kind of power (force times speed, equivalent to energy per unit time) needed for a jump or a sprint. You could get a jump with springs coiled by a slower drive-train, but that kind of explosive, uncontrolled release would not be coordinated.

At this point a shuffling jog is a (serious) programming challenge, but for a running or jumping robot you would need physical technology that we don't have.