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Comment by para_parolu

5 days ago

When comes to lower part it’s always bipedal (hard to balance) or wheels (low capabilities). Why no one makes 4-6 legs, insect like? That seems like an easier problem to solve while gives much better mobility.

22 comments

para_parolu

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solid_fuel  5 days ago

Going from 2 to 4 legs doubles the amount of actuators required and substantially increases power consumption since you must move more mass, going to 6 compounds the problem further. In a future where we have more dense power storage and better (and cheaper!) motors, you probably will see robots with more legs. But for now, the most efficient solutions are bipedal.

Especially because this thing is already $8k, I imagine they have already done some substantial price optimization.

  • goobatrooba  5 days ago

    I agree on the rest but don't see why it would be heavier. If you have more feet standing at any particular moment the load would be more distributed, i.e. movement should be easier with more legs (depending on leg weight of course).

    • solid_fuel  5 days ago

      You're confusing (pressure on the ground / surface area) with overall weight (the sum of all pressure on the ground). Having more legs is heavier simply because now you have additional struts and motors that you didn't before, those items are linear with the number of legs, and the total weight is weight_of_leg x num_legs.

  • bensyverson  5 days ago

    Real question: what about 3 legs? Is tripedal locomotion a viable compromise?

    • solid_fuel  5 days ago

      It's been done, I don't really know how the efficiency compares but I'm sure there's some research out there on it. The main issue I see though is that the advantage you get with 4+ legs is stability at slow speed - you can be stable on three legs while moving one, which makes precise movement easier.

      With three legs, as soon as you pick one up you will start to fall over, so you either need legs with enough freedom of movement to shift the center of mass of the robot back to offset the lack of support, or some other way to shift the center of mass.

      You have to balance with two legs, as well, but there isn't a transition from "stable" to "balancing" with every step - you're always actively balancing - which makes movement easier to plan.

      Overall I suspect that tripedal locomotion isn't really any more efficient than bipedal movement, and it might even be less stable.

      Just one example: https://spectrum.ieee.org/martian-inspired-tripod-walking-ro...

    • scotty79  5 days ago

      If the robot has two legs with wheels at the ends it could combine speed and flexibility. Adding a third leg for additional stability when the robot needs it might be great. But the third leg would probably need to be between the first two and I don't think humans are mature enough to have that.

    • stubish  5 days ago

      There is likely no benefit over 2 legs if you need to step over things. And if you don't, wheels are just fine. Maybe stairs changes this.

shaewest  5 days ago

I wonder how much of it is training data. We can very easily get training data of 'human tasks' because humans can wear tracking suits, and those suits track bipedal movement. Anything we train off that isn't bipedal (ie dogs) don't do human tasks, don't hold anything, so a different set of requirements.

05  5 days ago

They make robot dogs, e.g. famously Boston Dynamics but many others as well. And 6 is probably overkill for price/performance increase incremental to 4. Wheels are still much more practical and you can use them as feet in hybrid designs to be able to step over obstacles but still more agile than comparable bi/quadrupeds

jonfw  4 days ago

wheels are so much simpler that it seems much easier and more cost efficient to solve the "transporting a wheeled robot up the stairs problem" than it does to go fully bipedal.