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Comment by vlasev | Hacker News Reader

No one seems to be discussing how this can be improved! Here are a few points:

1. Real cheetahs don't run like that. The action of both pairs of legs is staggered for smoother motion and control. Check this out - https://www.youtube.com/watch?v=131wvVGjZUc

2. Looking at this jumping-over-obstacles video, it seems like the robot is lacking flexibility. The real life cheetah's hind legs go quite a bit underneath in preparation for push off. Contrast this with how the robot's hind legs are a little too behind and the robot stutters a bit after every jump. If the robot could put its hind legs further it would make for a smoother landing.

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1.The goal is not to build a cheetah, buy to learn from them. One thing to consider is that this team is constrained by materials. What works for an animal will likel not transfer directly due to the difference in materials. Harmonics are well absorbed by tissue but the robot may have issues with them.

2. How did you come to this conclusion? Have you built a robot that mimics an animal? If so, may you provide some insight into your discoveries?

Robotics programmer/builder here. Always interested in learning about the work of others.

To your first point, wouldn't a robot like that benefit from staggering the action of the legs? Instead of X impact at one point in time, have X/2 impact at two points in time? Would that create too much strain?

For my conclusion in point two, my insight comes from experience of copying animal movement. When I trained parkour my friends and I would copy animal movement from across the whole animal kingdom[1]. Here's an example of quadrupedal movement[2]. A big problem for us bipeds in trying to run like quadrupeds is that our legs tend to be big, long and inflexible, while our arms tend to be much weaker than our legs. The effect of this combination is to make running properly like a an animal which evolved to run on all fours quite difficult. From my own experience, putting my legs more and more forward past my arms (i.e. copying the cheetah), made for a much easier time.

If you were to try to run like the robot, with symmetrical action, it would be extremely uncomfortable, because the impact is large at every step. Staggering the action allows for a much smoother run. Make any human run like that and they'll eventually automatically switch to the less impactful staggered run.

[1]: https://www.youtube.com/watch?v=Ymg1-Fhl69w

[2]: https://www.youtube.com/watch?v=W8oh5Xuy7NA

Having the back and front legs work as a pair makes the side to side balancing easier. I having them hit separately would require more control and degrees of freedom in the leg to keep the robot from oscillating side to side while running.

I also forgot to point out that their robot is capable of running in a staggered manner [1] and the results are much cleaner than non-staggered action [2]. You can practically feel the second robot nearly tear itself apart even at lower speeds.

[1]: https://www.youtube.com/watch?v=1TXOHAVuS5Q&t=65

[2]: https://www.youtube.com/watch?v=chPanW0QWhA

It seems obvious that the engineers at Boston Dynamics have spent an awful lot of time carefully studying and analysing the movement of real 4-legged animals.

There's a big difference though between learning valuable lessons & taking cues from natural bio-mechanics, and trying to emulate them.

Perhaps the engineers who designed cheetah did learn about how real Cheetahs run, but there are other constraints that are not obvious.

That's very likely considering what they are building.

I think it's safe to assume that the researchers have watched hours and hours of footage of cheetahs running - I'm sure they're aware the ways in which their work is not like the real thing.

Watching some of the cheetah videos, I wonder how much of their staggering is compensation. That is, the "ideal" cheetah gait may actually be non-staggered. But as the cheetah is changing direction, dealing with slightly uneven ground and reaching out for prey, it may need to stagger its legs in order to compensate.

We can't possibly know what the researchers have actually done in their study but I think it's safe to say that symmetrical action is a lot easier to wrap your head around (it essentially becomes a 2D problem). That's why a staggered action should be seen as an improvement to the already existing design.

When it comes to cheetahs, I bet a million bucks that it has everything to do with impact and smoothness rather than a compensation for changing direction and such. My confidence in this comes from my own experience imitating animal movement in parkour. For an example of one person running in a staggered way - https://www.youtube.com/watch?v=W8oh5Xuy7NA. Running like that is MUCH easier on the joints than running with a symmetrical action. If you make a human gallop in a symmetrical way they'd quickly give it up for staggered action, regardless of surface or directions.

You may be correct, but I wouldn't extrapolate from humans. We evolved to walk upright, so running on all fours is not something our structure will be good at.

Muscle, bone, and sinew are about a hojillion times better in building active structures than motors, pneumatics, etc. It'll be a while before robots are as flexible and dexterous as animals.

That's not Boston Dynamics' Cheetah. This is.[1] This new video is MIT's cheetah. It's good to see MIT doing serious legged locomotion work again. Things stalled out there after Raibert left and Gil Pratt took over. Looks like DARPA is funding MIT, now that Google bought Boston Dynamics and stopped taking DoD contracts.

Not sure why they chose a pronk gait, except that they're doing all straight line work. A gallop has more turn options, but roll control is easier for the pronk. Hopping over an obstacle has been done before, by some of the early MIT planar bipeds.[2]

It took about $125 million in DoD funding to get a usable Big Dog and Atlas. It's quite possible to do a lot more in legged robotics, but it is not yet cheap. It's still not clear if Google will achieve commercial legged robots, or decide to "put more wood behind fewer arrows" again and focus on their core business, advertising. The commercial payoff is a long way ahead.

Academic projects rarely have the funding and staff to get beyond the demo level. You need some big assets, like machine shops and skilled machinists. Note that they're borrowing MIT's gym. To get real work done, you need full time access to your own test area. It's hard to get that on a college campus. The typical academic robotics project is one professor and three grad students.

[1] https://www.youtube.com/watch?v=chPanW0QWhA [2] https://www.youtube.com/watch?v=XFXj81mvInc

They are working with relatively inelastic materials and as such they will work very differently from animal muscles, tendons and ligaments.

The biggest difference is that the spine on this robot is not articulated. Most of a cheetah's power for running comes from the strength and flexibility of the muscles along its spine.

It's just hard to beat the density and flexibility of a living mammal with a bunch of servos, chips, and batteries. We probably never will.

I'm not talking about power here. I'm talking about flexibility though. I think it won't be a stretch to think the hind legs range of motion could be extended by 10-15 degrees so the hind legs could hit a point further along the way.

Yeah! And whilst we're at it, wings on aeroplanes don't flap either. RUBBISH.

/sarcasm

Hey man, he took those MIT engineers to school. Despite decades of focused dedication to the study of robots, control theory, gait and dynamical systems, they probably never considered just making their robot work more better.

Hahah, you are so clever! Do you have anything beyond sarcastic remarks though?

Is that not enough?

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