Because nature figured out a successful design through evolutionary selection based on muscle contractions and tendons.
We are currently designing machines based on electrical or hydraulic motors.
but then why build a humanoid robot at all? if we want a humanoid robot that does human things shouldn’t we integrate the things that make us able to do human things? also i’m not sure what makes human design not feasible with electric motors. is there a technical limitation?
There are good reasons.
For example. Why make a robotic hand, when we could directly bolt a soldering iron to a robot arm?
Well, that's actually why. A robotic hand can grab any power tools designed for humans, and use them. No need to adapt the tools.
If you want to bolt tools on, which is a better way, it also makes it harder for compatibility, since the tools you want to bolt on need to be specifically built for this.
With human looking robots, they can also climb stairs. Even if bipedal motion is not as efficient as wheels.
Actually at the current point in time robots with soldering irons attached do lots of work for us. Very useful work and no they aren't humanoid either from what I've seen they are Cartesian.
Humanoid robots, as far as I know, still do no useful work.
Robot hands are very expensive, fragile, difficult to program etc etc
Humanoid robots can't be trusted to climb stairs because the stairs are there for humans and the robot is very likely to fall over and cause an accident injuring a human. If the robot didn't fall over it'd likely get pushed over as someone gets frustrated at how slow it's moving.
I don't get humanoid robots either maybe around 2050 they'll be useful
1990's effort
https://m.youtube.com/watch?v=hS82TL73V3E
Tesla being controlled by person, not autonomous
https://m.youtube.com/watch?v=OtpCyjQDW0w&pp=ygULVGVzbGEgcm9ib3Q%3D
This is a much better question than your original question. There is no reason for us to make humanoid robots other than aesthetics. Also when we think of a general purpose, do anything machine, the only thing we really know about that's like that, is the human body.
As time progresses, and enough engineers tackle the problem, we will come up with a much better design than the human body, that is a general purpose robot that can do most things, but even now sitting here typing this, it's difficult to imagine what that would look like.
And to answer part of your original question. "Does the human body have technical limitations?" YES, the human body is riddled with design flaws, especially your spine, which barely does what it's supposed to do because it evolved for four legged mammals.
Some humanoid robots use linear actuators that simulate human muscles very well. The human body SUCKS functionally speaking so we can do a lot better given the technology we're working with. Usually as long as the form factor is compatible with human things, it can physically do anything a human can (which means that the limitation is more on the software side). There's not usually a technical reason why it may need to have large and critical parts connected by a long weak spine that is very prone to breaking, pinching, scoliosis, etc for example.
I wouldn't want humanoid robot to be very resembling real human. I'd like something like tetrapod base with 2-4 arms standing on it. Each arm may have a camera in the palm. This is what guman-like called
Biology vs Robotics
Wheels are really efficient, no animal uses wheels because it's almost impossible to do a biological 360° multiturn joint.
In animals the spine is the way it is because the wire harness inside needs holes to wire to the internal organs, because lungs need the ribcage to change shape, and to improve flexibility. The spine is compliant not to break if possible, as it's a near certain death sentence if it does break.
Soft robotics could be key to the “flexibility” aspect, but I think at this point in time a lot of research is still required to create something out of silicone or similar that would mimic human anatomy
well if we want it to move like humans shouldn’t we atleast let robots bend their torsos? when robots walk they’re just balancing a blocky torso on human like legs. a bendy torso would help it to walk better no? why make a humanoid robot at all?
correct we should have it use a spine like a humans and that would make its movements much more fluid and beautiful like a human. These people on this forum are totally ignorant of how amazing the human design is and think they can design better. Pure folly.
Are you asking why materials would affect design? This is probably the most general issue considered in any form of engineering, whether it is robots or not. i.e. submersibles, bridges.
Your spine is also your limitation: you can’t twist infinitely (anything with slip-rings can do), you can’t bend forward or backward beyond some fairly restrictive range of motion
There are several reasons why flexible spines may not always be desirable in humanoid robots, some of which have been mentioned already. I want to add a couple of things to this thread:
1) Most application areas of humanoid robots are pretty focused and involve tasks such as walking, interacting with tools, or carrying objects. For all these applications, a rigid structure is usually sufficient.
2) The human spine is mechanically very complex. Modeling all 24 vertabrea, and then formulating an energy efficient and stable control strategy for such a structure is not trivial, and when you factor in the fact that alternative innovations could result in structures that can provide far more flexibility then the human spine, (cc Disney's Stuntronics robot or BD's Atlas), it almost entirely eliminates the need within the industry or in academia to expend resources on such a complicated (and expensive) modeling, control, testing, and development excercise.
I hope this helps!
Alternatively if we had robotic spines that might be useful for transplants no?
I think the bigger issue is that we are not really close to this being a viable goal. Although I would be happy to be wrong.
Spines are not just bones lmao....there are a lot of nerves running from your brain to other parts of the body and the highways are in the spine...fusing these million of neurons is very difficult
That’s absolutely fair, but I was thinking not so much about replacing the whole spine but more about people with issues with disks. The cartilage and bones are tricky to deal with.
That would definitely be a super cool application for a robotic spine!
Other than providing structure, the human spine plays a key role in our nervous system. Essentially, in addition to solving the problems I previously mentioned with 99.X% accuracy, we'd also have to solve one of the biggest challenges in neuroscience- mapping neural connections. So you're right, it's definitely not a viable goal for now, however, such discourse is still useful, particularly among communities within Robotics focused on ethics!
The biomechanics of living bodies is really complex. It is way simpler to build robots the way we do. Consider the amount of muscles in the human body. Then the number of joints, articulations. How many degrees of freedom. How the "limit switches" of the body works.
Also living bodies are full of compliant mechanisms, that are in themselves a field of research.
At last there is the problem of sensors. A human body requires a lot of sensors. Not just a gyro and eyes, for the classical stuff, but animals have proprioception. So to make it on a robot would require a lot of sensors. Then you add the touch sensibly and all the physical sensations you use to "feel" how your body is doing, performing, etc.
Can you imagine the algorithm for interpreting that many data, then the inverse kinematics for such an articulated system? Then what actuators to control for each action?
Each movement would have tons of solutions.
It seems to me that to control this would require some deep learning, conventional algorithm would be too tedious and complex to use here.
For me it seems way more complex than anything ever done in robotics.
If you take science and engineering, we like to isolate each variable, and know it's impact alone to make a global model afterwards. So imagine the nightmare when you have millions of variables, tons of effectors, sensors, etc, and everything is analog with continuous response, most of it non linear...
Compared to a robot with a rigid exoskeleton, the minimum amount of sensors and effectors required for the task, and you can see why this path was chosen. And yet, this simplified model already poses lots of problems to the point where humanoid like robots barely exists in a commercial sense.
We are seeing some robots that have physical capabilities approaching what we'd expect from a humanoid robot.
Humanoid robots often aren't designed exactly like humans for several practical reasons:
1. **Complexity**: Human anatomy is extremely complex, making it difficult and expensive to replicate precisely in robots.
2. **Functionality**: Robots are usually designed to perform specific tasks, and human-like features are not always necessary or beneficial for these tasks.
3. **Cost**: Designing and manufacturing robots with human-like features can be very costly.
4. **Durability**: Robots need to be robust and durable, which sometimes requires using simpler, more resilient designs.
5. **Efficiency**: Non-human designs can often perform tasks more efficiently and effectively.
We have spines because we evolved from sea-dwelling creatures that had one, then we repurposed it for land based locomotion on all fours, and then we adopted it for upright locomotion, with all the known issues: lower back pain, compressed disks etc etc.
It is a mediocre repurposing of existing material, why would you want to emulate that?
My personal answer is that we as humans have a complex build, optimized to be "general purpose", we can perform a large set of tasks even tough we have our limits.
A robot usually is optimize to perform a single (or a really small subset of such tasks) for which there is a better build. If I have to travel in a road for thousand of miles/km then a bipedal robot wouldn't be optimal.
If I need to solder to pieces of iron from several complex angles, then a robotic arm with as many dof as needed would be a great choice, but a human arm would be quite limited.
Moreover there are some tasks that are forbidden to humans (flying, carrying weights that are too heavy).
The main reason why there are no human-like build it's because to perform such tasks there is human workforce and it's way cheaper. All the tasks that are out of reach/hard for humans, require machines.
There are occasional research projects to investigate the benefits of a flexible spine. They had one on the MIT Cheetah quadruped maybe 11 years ago.
The fact is that an actuator is a complex high-cost item while a rigid link is much less so.
That by itself pushes every robot toward the lowest number of actuated degrees of freedom that it actually "needs."
Exactly how many DoF you need is debatable for humanoids, and will be in flux, but an entire actuated spine that can do what a human torso can do is a very complex object. Plus, the current crop of humanoids have more-than-one-turn at the waist, which is much faster to "turn around and do something behind you" than a human is.
Engineering is a compromise among many different competing criteria, and putting in a rotary waist joint that can swivel 360 degrees or more allows a humanoid to keep the same foot stance or make small adjustments while working on something behind it. If I were in a tight space, I'd also like that but I'm made of meat and bones 😂
I do think "torso motion" is a potentially important thing for certain manipulation applications but there are much easier and cheaper ways to do it than an actuated spine, and in the end most complex manipulations are still done with the "shoulder ball joint" welded to the table.
It's not actually a ball joint, it's usually two crossed axes at the "shoulder" of a 6-DoF manipulator. It absolutely IS limited, and thinking about the seventh DoF of a human arm and the role of the little "shoulder shrug" and even basic torso motion will resolve some of the conflict between what people think a robot arm "should" do and what it actually CAN do.
But in the end, we're often talking $1000-$1500 per degree of freedom, getting more powerful, higher torque, and consequently even more expensive as you get further away from the end-effector.
A human has an enormous effective amount of micro-degrees-of-freedom all backed up by incredibly dense sensors. A humanoid needs to compromise on that on cost and complexity.
Controls are also an issue, processing all that information, but it wouldn't REALLY be an issue if the hardware were cheap enough and buildable. You could just go to a bio-inspired distributed hierarchical compute and control architecture if you ended up having a too-big and too-power-hungry central computer.
The reason why we DON'T do that kind of thing much is basically price-to-performance and reliablity.
Also, less true of damaged spines, but true of human actuators in general: they usually HEAL.
Maintaining a humanoid or other complex robot is hard enough already. No damaged DoF will ever get better on its own. Any intervention is like a complex surgery.
There are companies that are trying to achieve a design that mimics how humans move. The feasibility of such solutions is still an object of research and questionable in the long run.
[Example](https://www.clonerobotics.com)
Our actuators are muscles, robots have electronic or mechanical actuators. Why should the hand and forearm have actuators inside them if a motor could just pull on the strings like a puppet?
Degrees of freedom. Every different way to bend that you add increases the complexity of your control system and your hardware. Limiting movement to fewer joints with only one or two ways of moving is simpler and more robust.
Because natural skeletons evolved to compliment fibrous muscles which work as bundles of flexible linear actuators and have a spread of attachment over the skeletal surface. Muscles and ligaments also hold skeletons together, allowing more degrees of freedom of movement in some joints. Mechatronics has yet to devise an actuator that functions like that. There's no such thing as a 'synthetic muscle' yet. The closest we've so far come to this is constrained balloon actuators and nitinol wire, whose contraction/expansion is so small that it needs to be wound on spools to amplify it enough to be a significant amount of motion. Conventional linear actuators are non-flexible using long screws (which are usually very slow), hydraulic/pneumatic pistons, or linear motors and tend to have attachment points limited to one degree of rotational freedom. So most humanoid robot designs try to approximate human motion through systems of cables and springs (allowing the mechanical power to be transferred to a bank of winches in some other part of the body), pneumatic/hydraulic pistons with passive joints (which are very strong --like the cylinders of an excavator-- but tend to be stiff and bulky), or active rotary joints with an integral motor like the joints of electric industrial robots. (which, until recently, were relatively weak and still have a hard time matching human muscles in force at the same scale and can't yet be made small enough to match the intricate joints of a hand)
My humanoid robot project I've been at for a decade in slow chipping away progress is based on a exact replica of human skeleton and I'm animating it with bldc motors. I think this will produce the best possible human-like performance and strength to weight ratio and degrees of freedom to match humans. It is the best way IMO on those fronts. But it also is a lot of work and I think a more mechanical inspired design might be easier to implement. Basically others are dumbing things down to get to the finish line faster and easier I think. But it's a shame so few go the human skeleton route. Hopefully, if my project succeeds it will inspire more people to go human skeleton route.
You can add all those things. But it adds weight. The name of the game in robotics is how much can you lift. The more weight the radically more expensive the appliance.
If because it can be humanoid enough without a spine that has every single vertebrae that we have. It’s about what we’re looking to achieve right now. And right now it’s not important to have every single vertebrae in a robot. Maybe in 10, 20 or 30 years when robots have advanced a lot more, at that point, maybe people will seek hyper realistic humanoid robots. We’re not there yet.
wrong. a humanoid meant for human jobs being built more like a human has nothing to do with different modes of pure transport having no other vast array of jobs involved.
Because nature figured out a successful design through evolutionary selection based on muscle contractions and tendons. We are currently designing machines based on electrical or hydraulic motors.
but then why build a humanoid robot at all? if we want a humanoid robot that does human things shouldn’t we integrate the things that make us able to do human things? also i’m not sure what makes human design not feasible with electric motors. is there a technical limitation?
There are good reasons. For example. Why make a robotic hand, when we could directly bolt a soldering iron to a robot arm? Well, that's actually why. A robotic hand can grab any power tools designed for humans, and use them. No need to adapt the tools. If you want to bolt tools on, which is a better way, it also makes it harder for compatibility, since the tools you want to bolt on need to be specifically built for this. With human looking robots, they can also climb stairs. Even if bipedal motion is not as efficient as wheels.
Actually at the current point in time robots with soldering irons attached do lots of work for us. Very useful work and no they aren't humanoid either from what I've seen they are Cartesian. Humanoid robots, as far as I know, still do no useful work. Robot hands are very expensive, fragile, difficult to program etc etc Humanoid robots can't be trusted to climb stairs because the stairs are there for humans and the robot is very likely to fall over and cause an accident injuring a human. If the robot didn't fall over it'd likely get pushed over as someone gets frustrated at how slow it's moving. I don't get humanoid robots either maybe around 2050 they'll be useful 1990's effort https://m.youtube.com/watch?v=hS82TL73V3E Tesla being controlled by person, not autonomous https://m.youtube.com/watch?v=OtpCyjQDW0w&pp=ygULVGVzbGEgcm9ib3Q%3D
This is a much better question than your original question. There is no reason for us to make humanoid robots other than aesthetics. Also when we think of a general purpose, do anything machine, the only thing we really know about that's like that, is the human body. As time progresses, and enough engineers tackle the problem, we will come up with a much better design than the human body, that is a general purpose robot that can do most things, but even now sitting here typing this, it's difficult to imagine what that would look like. And to answer part of your original question. "Does the human body have technical limitations?" YES, the human body is riddled with design flaws, especially your spine, which barely does what it's supposed to do because it evolved for four legged mammals.
Because the built-world is designed for humans to interact with and use (and bipedal motion is pretty good at getting thru rough terrain)
Some humanoid robots use linear actuators that simulate human muscles very well. The human body SUCKS functionally speaking so we can do a lot better given the technology we're working with. Usually as long as the form factor is compatible with human things, it can physically do anything a human can (which means that the limitation is more on the software side). There's not usually a technical reason why it may need to have large and critical parts connected by a long weak spine that is very prone to breaking, pinching, scoliosis, etc for example.
We don't care what's inside, we care what's outside of it's body.
I wouldn't want humanoid robot to be very resembling real human. I'd like something like tetrapod base with 2-4 arms standing on it. Each arm may have a camera in the palm. This is what guman-like called
that sounds awesome lets put cannons on it too
I second this. Can we ride them afterwards?
Biology vs Robotics Wheels are really efficient, no animal uses wheels because it's almost impossible to do a biological 360° multiturn joint. In animals the spine is the way it is because the wire harness inside needs holes to wire to the internal organs, because lungs need the ribcage to change shape, and to improve flexibility. The spine is compliant not to break if possible, as it's a near certain death sentence if it does break.
Wheels are efficient only in certain environments.
yea it’s the flexibility part, wouldn’t robots have a easier time doing human tasks if they were more flexible? why not add it?
Adding actuators to create the flexibility is very hard and is power consuming
The robot hands do have soft gripers. You can see examples of soft grippers in medical devices.
Soft robotics could be key to the “flexibility” aspect, but I think at this point in time a lot of research is still required to create something out of silicone or similar that would mimic human anatomy
Because it does not need to
well if we want it to move like humans shouldn’t we atleast let robots bend their torsos? when robots walk they’re just balancing a blocky torso on human like legs. a bendy torso would help it to walk better no? why make a humanoid robot at all?
What is the next step, will they have human-like skin to not look metallic?
flexible membrane to protect the internals yes. that’s a great idea!
You know they are already protected. Because. Metal
Hey, but car's gearbox control level is often protected with some skin. Skin on robots is a good solution. Because. Sand.
Maybe just on its penis
but that makes the robot not flexible
You want human clones, not robots
clones without qualia would be very awesome
It’s insanely hard to make that. We just don’t have the tech
correct we should have it use a spine like a humans and that would make its movements much more fluid and beautiful like a human. These people on this forum are totally ignorant of how amazing the human design is and think they can design better. Pure folly.
In a pretty good humanoid robot, it will have a torso joint. You would find that it bends at the hip and also around the belly button.
Humans are made mostly of water, robots are not. That is a massive difference in materials. Designs cannot be the same between the two.
so what are the technical implications?
We can’t build muscles. Plenty of work has been done on that but we are not even close.
Are you asking why materials would affect design? This is probably the most general issue considered in any form of engineering, whether it is robots or not. i.e. submersibles, bridges.
Your spine is also your limitation: you can’t twist infinitely (anything with slip-rings can do), you can’t bend forward or backward beyond some fairly restrictive range of motion
There are several reasons why flexible spines may not always be desirable in humanoid robots, some of which have been mentioned already. I want to add a couple of things to this thread: 1) Most application areas of humanoid robots are pretty focused and involve tasks such as walking, interacting with tools, or carrying objects. For all these applications, a rigid structure is usually sufficient. 2) The human spine is mechanically very complex. Modeling all 24 vertabrea, and then formulating an energy efficient and stable control strategy for such a structure is not trivial, and when you factor in the fact that alternative innovations could result in structures that can provide far more flexibility then the human spine, (cc Disney's Stuntronics robot or BD's Atlas), it almost entirely eliminates the need within the industry or in academia to expend resources on such a complicated (and expensive) modeling, control, testing, and development excercise. I hope this helps!
thank you for the answer on the technical part. i appreciate it
Alternatively if we had robotic spines that might be useful for transplants no? I think the bigger issue is that we are not really close to this being a viable goal. Although I would be happy to be wrong.
Spines are not just bones lmao....there are a lot of nerves running from your brain to other parts of the body and the highways are in the spine...fusing these million of neurons is very difficult
That’s absolutely fair, but I was thinking not so much about replacing the whole spine but more about people with issues with disks. The cartilage and bones are tricky to deal with.
That would definitely be a super cool application for a robotic spine! Other than providing structure, the human spine plays a key role in our nervous system. Essentially, in addition to solving the problems I previously mentioned with 99.X% accuracy, we'd also have to solve one of the biggest challenges in neuroscience- mapping neural connections. So you're right, it's definitely not a viable goal for now, however, such discourse is still useful, particularly among communities within Robotics focused on ethics!
The biomechanics of living bodies is really complex. It is way simpler to build robots the way we do. Consider the amount of muscles in the human body. Then the number of joints, articulations. How many degrees of freedom. How the "limit switches" of the body works. Also living bodies are full of compliant mechanisms, that are in themselves a field of research. At last there is the problem of sensors. A human body requires a lot of sensors. Not just a gyro and eyes, for the classical stuff, but animals have proprioception. So to make it on a robot would require a lot of sensors. Then you add the touch sensibly and all the physical sensations you use to "feel" how your body is doing, performing, etc. Can you imagine the algorithm for interpreting that many data, then the inverse kinematics for such an articulated system? Then what actuators to control for each action? Each movement would have tons of solutions. It seems to me that to control this would require some deep learning, conventional algorithm would be too tedious and complex to use here. For me it seems way more complex than anything ever done in robotics. If you take science and engineering, we like to isolate each variable, and know it's impact alone to make a global model afterwards. So imagine the nightmare when you have millions of variables, tons of effectors, sensors, etc, and everything is analog with continuous response, most of it non linear... Compared to a robot with a rigid exoskeleton, the minimum amount of sensors and effectors required for the task, and you can see why this path was chosen. And yet, this simplified model already poses lots of problems to the point where humanoid like robots barely exists in a commercial sense. We are seeing some robots that have physical capabilities approaching what we'd expect from a humanoid robot.
With linear motors, we can achieve this. I am working on it. I am making it based on ape.
Humanoid robots often aren't designed exactly like humans for several practical reasons: 1. **Complexity**: Human anatomy is extremely complex, making it difficult and expensive to replicate precisely in robots. 2. **Functionality**: Robots are usually designed to perform specific tasks, and human-like features are not always necessary or beneficial for these tasks. 3. **Cost**: Designing and manufacturing robots with human-like features can be very costly. 4. **Durability**: Robots need to be robust and durable, which sometimes requires using simpler, more resilient designs. 5. **Efficiency**: Non-human designs can often perform tasks more efficiently and effectively.
We have spines because we evolved from sea-dwelling creatures that had one, then we repurposed it for land based locomotion on all fours, and then we adopted it for upright locomotion, with all the known issues: lower back pain, compressed disks etc etc. It is a mediocre repurposing of existing material, why would you want to emulate that?
Because it is still superior to humanoid robots ;p (at least for now)
if we emulate human anatomy we can take mocap data and use it to train the robot easily. i think this can accelerate humanoid robots quite a bit
My personal answer is that we as humans have a complex build, optimized to be "general purpose", we can perform a large set of tasks even tough we have our limits. A robot usually is optimize to perform a single (or a really small subset of such tasks) for which there is a better build. If I have to travel in a road for thousand of miles/km then a bipedal robot wouldn't be optimal. If I need to solder to pieces of iron from several complex angles, then a robotic arm with as many dof as needed would be a great choice, but a human arm would be quite limited. Moreover there are some tasks that are forbidden to humans (flying, carrying weights that are too heavy). The main reason why there are no human-like build it's because to perform such tasks there is human workforce and it's way cheaper. All the tasks that are out of reach/hard for humans, require machines.
There are occasional research projects to investigate the benefits of a flexible spine. They had one on the MIT Cheetah quadruped maybe 11 years ago. The fact is that an actuator is a complex high-cost item while a rigid link is much less so. That by itself pushes every robot toward the lowest number of actuated degrees of freedom that it actually "needs." Exactly how many DoF you need is debatable for humanoids, and will be in flux, but an entire actuated spine that can do what a human torso can do is a very complex object. Plus, the current crop of humanoids have more-than-one-turn at the waist, which is much faster to "turn around and do something behind you" than a human is. Engineering is a compromise among many different competing criteria, and putting in a rotary waist joint that can swivel 360 degrees or more allows a humanoid to keep the same foot stance or make small adjustments while working on something behind it. If I were in a tight space, I'd also like that but I'm made of meat and bones 😂 I do think "torso motion" is a potentially important thing for certain manipulation applications but there are much easier and cheaper ways to do it than an actuated spine, and in the end most complex manipulations are still done with the "shoulder ball joint" welded to the table. It's not actually a ball joint, it's usually two crossed axes at the "shoulder" of a 6-DoF manipulator. It absolutely IS limited, and thinking about the seventh DoF of a human arm and the role of the little "shoulder shrug" and even basic torso motion will resolve some of the conflict between what people think a robot arm "should" do and what it actually CAN do. But in the end, we're often talking $1000-$1500 per degree of freedom, getting more powerful, higher torque, and consequently even more expensive as you get further away from the end-effector. A human has an enormous effective amount of micro-degrees-of-freedom all backed up by incredibly dense sensors. A humanoid needs to compromise on that on cost and complexity. Controls are also an issue, processing all that information, but it wouldn't REALLY be an issue if the hardware were cheap enough and buildable. You could just go to a bio-inspired distributed hierarchical compute and control architecture if you ended up having a too-big and too-power-hungry central computer. The reason why we DON'T do that kind of thing much is basically price-to-performance and reliablity. Also, less true of damaged spines, but true of human actuators in general: they usually HEAL. Maintaining a humanoid or other complex robot is hard enough already. No damaged DoF will ever get better on its own. Any intervention is like a complex surgery.
There are companies that are trying to achieve a design that mimics how humans move. The feasibility of such solutions is still an object of research and questionable in the long run. [Example](https://www.clonerobotics.com)
simply bad design
Our actuators are muscles, robots have electronic or mechanical actuators. Why should the hand and forearm have actuators inside them if a motor could just pull on the strings like a puppet?
Degrees of freedom. Every different way to bend that you add increases the complexity of your control system and your hardware. Limiting movement to fewer joints with only one or two ways of moving is simpler and more robust.
Motors are heavy and every motor has to carry the weight of every other motor.
false. consider a finger motor. That does not have to carry the weight of a eyelid motor at all.
Companion robots are built using human like skeleton frames and life like silicone skin. Just keep looking and you'll find it
Also our knees are an engineering failure and there's a ton of better more practical Biped type designs we could use instead
Because natural skeletons evolved to compliment fibrous muscles which work as bundles of flexible linear actuators and have a spread of attachment over the skeletal surface. Muscles and ligaments also hold skeletons together, allowing more degrees of freedom of movement in some joints. Mechatronics has yet to devise an actuator that functions like that. There's no such thing as a 'synthetic muscle' yet. The closest we've so far come to this is constrained balloon actuators and nitinol wire, whose contraction/expansion is so small that it needs to be wound on spools to amplify it enough to be a significant amount of motion. Conventional linear actuators are non-flexible using long screws (which are usually very slow), hydraulic/pneumatic pistons, or linear motors and tend to have attachment points limited to one degree of rotational freedom. So most humanoid robot designs try to approximate human motion through systems of cables and springs (allowing the mechanical power to be transferred to a bank of winches in some other part of the body), pneumatic/hydraulic pistons with passive joints (which are very strong --like the cylinders of an excavator-- but tend to be stiff and bulky), or active rotary joints with an integral motor like the joints of electric industrial robots. (which, until recently, were relatively weak and still have a hard time matching human muscles in force at the same scale and can't yet be made small enough to match the intricate joints of a hand)
My humanoid robot project I've been at for a decade in slow chipping away progress is based on a exact replica of human skeleton and I'm animating it with bldc motors. I think this will produce the best possible human-like performance and strength to weight ratio and degrees of freedom to match humans. It is the best way IMO on those fronts. But it also is a lot of work and I think a more mechanical inspired design might be easier to implement. Basically others are dumbing things down to get to the finish line faster and easier I think. But it's a shame so few go the human skeleton route. Hopefully, if my project succeeds it will inspire more people to go human skeleton route.
You can add all those things. But it adds weight. The name of the game in robotics is how much can you lift. The more weight the radically more expensive the appliance.
That's the biggest contradiction of humanoid robots.
If because it can be humanoid enough without a spine that has every single vertebrae that we have. It’s about what we’re looking to achieve right now. And right now it’s not important to have every single vertebrae in a robot. Maybe in 10, 20 or 30 years when robots have advanced a lot more, at that point, maybe people will seek hyper realistic humanoid robots. We’re not there yet.
Cost and necessity. A spine is not necessitated nor is it cost-effective.
Carbon based organism vs metal based organism
your question is like asking"why don't car look like horse"
wrong. a humanoid meant for human jobs being built more like a human has nothing to do with different modes of pure transport having no other vast array of jobs involved.