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Worldbuilding

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  • $\begingroup$ How does this work out? Because motors can be 90%+ efficient. So where is the 7x reduction in power consumption coming from? $\endgroup$
    – DKNguyen
    Commented Jan 25 at 4:04
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    $\begingroup$ Because batteries are dead-weight with bad [specific energy/energy density], and even worse, it is constant regardless if your battery is full or empty (compare to human stomach). E.g. you typical lithium-ion battery might have specific energy of 0.8 MJ/kg, while body fat has 38 MJ/kg. Of course you could make it run on gasoline (46 MJ/kg) or even liquid hydrogen (120 MJ/kg!), but those require bulky, heavy and needy combustion engines (cooling), so don't work well for human-sized robots (but truck-sizes robots are much better match). $\endgroup$
    – Matija Nalis
    Commented Jan 25 at 4:31
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    $\begingroup$ @DKNguyen also, electric motors are heavy, due to being mostly metal. Just because they have relatively good mechanical_motion/heating ratio (i.e. efficiency), does not mean their mechanical_motion/mass ratio fares as good - they are made mostly of metals, and metals are heavy... Also while you can use more of human-alike sugar/fat burning and energy transport mechanisms to avoid bulky and heavy rechargeable Li-ion batteries, but then your robots becomes being more like human replicants with few prosthesis enhancements than "real" robots... $\endgroup$
    – Matija Nalis
    Commented Jan 25 at 4:41
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    $\begingroup$ @DKNguyen MN is correct about the mechanical systems. I coach my daughter's robotics team, and the amount of power loss the kids see for every gear, belt, and axel they add to thier designs is very significant, and engineering something as complex as a hand can not be done with a bunch of direct motor connections because they would not all fit where you need them to fit. I've expanded on my answer to cover this. $\endgroup$
    – Nosajimiki
    Commented Jan 25 at 15:46
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    $\begingroup$ @DKNguyen Muscles are bad at doing motor things, and motors are bad at doing muscle things, you lose efficiency either way when you try to use one to do the other's job. Also, horsepower is a bit of a misnomer. It is the linear power of a walking horse. most horses max out at 10-14 horse power iirc. $\endgroup$
    – Nosajimiki
    Commented Jan 25 at 17:02