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Comment by rfv6723 | Hacker News Reader

> Before too long (and we already start to see this) humanoid robots will get wheels for feet, at first two, and later maybe more, with nothing that any longer really resembles human legs in gross form. But they will still be called humanoid robots.

Totally agree. Wheels are cheaper, more durable and more effective than legs.

Human would have wheels if there was an evolution pathway to wheels.

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The world is full of curbs, stairs, lips, rugs, vehicles, etc. If you're a human-scale robot then your wheels need really wide base to not tip over all the time, so you are extremely awkward in any kind of moderately constrained space. I wouldn't exchange my legs for wheels. Wheelchair users have to fight all the time for oversights to be corrected. I can see maybe see a wheel-based humanoid robot, but only as a compromise.

On the other hand there is not much reason to constrain ourselves to the unstable and tricky bipedal platform or insist on having a really top-heavy human-like torso. You could have 3-4 little legs on a dog scale body with several extra long upwards reaching arms for eg.

> if there was an evolution pathway to wheels

It's hard to see one. Even a nice flat world with ample incentive and taking good "bearings" for granted, how can you evolve a wheel-organ that maintains a biological connection as well as being able to rotate an indefinite number of time?

A few difficult and grotesque endpoints:

* The wheel only rotates a fixed number of times before the creature must pivot and "unwind" in the opposite direction. This one seems most plausible, but it's not a real wheel.

* The main body builds replacement wheels internally (like tooth enamel) and periodically ejects a "dead" wheel which can be placed onto a spoke. This option would make it easier to generate very tough rim materials though.

* A biological quick-release/quick-connect system, where the wheel-organ disconnects to move, but then reconnects to flush waste and get more nutrients.

* A communal organism, where wheel-creatures are alive and semi-autonomous, with their own own way to acquire nutrients. Perhaps they would, er... suckle. Eeugh.

In one of Philip Pullmans His Dark Material novels there is a race of creatures that have a symbiosis with a tree whose huge perfectly round nut can be grasped by their fore and hind limbs and they roll around that way.

One of the Animorphs spin offs had them too, it was meant to be specifically genetically engineered or something from distant memory.

There are lizards or beetles that tumble down sand dunes.

Maybe cartwheeling humans could lead to some adaptation where the whole body becomes the wheel.

Wheels are not balls. Balls are common in nature. Wheels are not. The difference is that wheels need roads, which are not common nature and a large scale artificial objects.

That makes sense. Even in the Pullman book there were natural roadways for rolling.

Wheels are great until the robot encounters uneven surfaces, such as a stairway, or a curb. So some kind of stepping functionality would still be necessary.

What would be the evolutionary pressure to grow wheels? They are useless without roads

Roads, i think you answered your own question, would be an evolutionary pressure, hypothetically speaking.

I sometimes imagine wheeled creatures evolving in a location with a big flat hard surface like the Utah salt flats or the Nazca desert, but I guess there's not much reward for being able to roll around since those places are empty as well as flat. Tumbleweed found some success that way though, maybe?

The golden wheel spider lives in the sand dunes of the Namib Desert. When confronted by a spider-hunting wasp, it can perform a "cartwheeling" maneuver to escape. By tucking in its legs and turning onto its side, it can roll down a sand dune.

Humans can also do this, sometimes they use tools like a tractor wheel to conver themselves into downhill wheels, often to hillarious effects.

Is there any biological examples of freely rotating power systems? We have nice rotating joints with muscles to provide power, but I can't think of any joint that would allow the sort of free rotation while also producing torque, a wheeled animal would require.

Some microorganisms have cilia that rotate like a propeller. With complex molecular structures to provide a rotor effect

Something internal to some shellfish, I believe, a kind of mixing rod that rotates. Hold on, I'll check if it's powered. (Also rotifers but they're tiny.)

Hmm, no, it sounds like it's externally powered:

> The style consists of a transparent glycoprotein rod which is continuously formed in a cilia-lined sac and extends into the stomach. The cilia rotate the rod, so that it becomes wrapped in strands of mucus.

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

Or maybe the cilia ( = wiggly hairs) could be seen as a kind of motor. Depends how you count it and exactly what the set-up is, I can't tell from this.

I think I would count internal power created by the rotating component itself. I hadn't though of that possibility, since human made machinery usually has the power producing component located in the main body and transferring that power to a freely rotating component is quite hard. Biological systems wouldn't necessarily look like that, and could feasibly be powered by the wheels themselves deforming as if the wheels were a separate, but connected, biological system.

That's quite interesting.

> Wheels are [...] more effective than legs.

Maybe in your living room. But step into a dense forest (which is what we are made for) and that statement will be far away from reality.

Power to wheel sensors are the paws. Where is the CNS/brain going?

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