Hacker News Reader

Comment by timonoko | Hacker News Reader

Why are these walking machines always so slow? I think Neal Stephenson described a skateboard with hundreds of tiny feet, moving faster than wheels on any surface. I want to see that.

View on HN

Progress takes time, and ambulatory motion is a finicky, delicate nightmare that only seems simple in humans and animals thanks to millions of years of evolution. CAM was created in the 1960s[0], but BigDog[1] and other recent Boston Dynamics quadrupeds that aren't designed for human passengers are much faster[2], but still awkward.

Also remember these are expensive prototypes designed to test things other than speed. Making them faster only guarantees that they break themselves harder when they run into a wall or trip over a cliff or something.

[0]https://www.youtube.com/watch?v=ZMGCFLEYakM

[1]https://www.youtube.com/watch?v=W1czBcnX1Ww

[2]https://www.youtube.com/watch?v=3OKZ_n8QW4w

>I think Neal Stephenson described a skateboard with hundreds of tiny feet, moving faster than wheels on any surface. I want to see that.

I am neither Neal Stephenson nor a physicist but I'm pretty sure the friction caused by the increased surface contact of "hundreds of tiny feet" versus wheels would still make the wheels faster and more efficient. Geckos and things can stick to vertical surfaces and move quickly because they're lightweight. Anything capable of sticking to an arbitrary surface and supporting human weight is going to be slow. And if moving downhill, wheels don't really need to do work - gravity does the work. Something with "hundreds of tiny feet" either has to slide or "walk."

I disagree. Centipedes and other many-legged critters can move very fast. Every leg is just a tiny lightweight thing with its own balanced dynamics, just a part of a wheel basically. First thing that came to my mind is a plastic brush with flexible back. If you move a rollers along the back the bristles extend downwards and move backwards in a walking motion, just like a sea urchin does. Scale that and you have a walking machine moving amazingly fast. Tiny bristles yield and conform to any surface.

You're not taking inertia and friction into account.

Centipedes appear to move very fast because they're small relative to us and lightweight - at scale, they don't move very fast. But if you take a centipede and scale it up to the size of a train (square cube law notwithstanding), it would just be a very slow train-sized centipede. To make it faster, you would have to make its legs longer, because legs are levers.

I found such a brush with flexible back (from a broken sauna brush). Amazing discovery: If you move the said roller forward along the back the bristles make the walking movement backwards. Need to make room for the Nobel prize now.

CWU's "whegs" are much in this vein: http://biorobots.case.edu/projects/whegs/

I could also see Brook's Genghis platform being extended to "centipede" multiples of legs and probably working well.

https://en.wikipedia.org/wiki/Genghis_Robot

EDIT: fixed mistake - put "Dante" but meant Genghis...

>Centipedes and other many-legged critters can move very fast.

Can they?

Humans have legs too, but they aren't very fast at all. I can easily outrun any human on my bicycle.

The main advantage for legs is dealing with rough terrain. I can hike over/through extremely rough terrain that I would never dream of taking a bike on. But for speed, nothing beats wheels on a smooth surface. You can't have both.

> Something with "hundreds of tiny feet" either has to slide or "walk."

IIRC the Neal Stephenson version was tiny feet mounted on wheels - not walking or sliding but rolling. But better than rubber pneumatics at evening out curbs or other obstacles.

Sounds more like legs than feet...

For the record, Stephenson's skateboard smartwheels used a bunch of little pads mounted on telescoping spokes instead of a solid wheel. The board had a terrain-scanning laser mounted in the nose, and pulled the spokes in and out so that the wheel was perfectly shaped for the contours of whatever it was about to roll over; you can ride a smartwheel board down stairs as smoothly as you would a ramp. But they were still very much wheels. There was no walking motion involved.

To me, I envisioned them as being a wheel made with a bunch of shock-absorber leg-like "spokes" with feet.

They seemed similar to old-tech Pedrail wheels:

https://en.wikipedia.org/wiki/Pedrail_wheel

I think something like them has been made - but instead of the spokes ending in "feet" - they instead were encircled by a rubber deformable tread; Tweels are another interesting style of this technology, and simpler mechanically:

https://en.wikipedia.org/wiki/Tweel

Stephenson's skateboard smartwheels were still wheels. They moved by rolling, not running. They just used their extendable pads to roll smoothly over rough terrain.

Reply on news.ycombinator.com