we currently have no actuators that are capable of matching biological muscle in terms of combined speed, force, and precision, let alone in such a small package.
And as durable. People don’t really know how much force you are working with as a body in motion. Ground reaction force for a small jump can be 7x someone’s body weight. So a person weighing 200lb can have 1400lbs of mechanical load being distributed by the feet and ankles.
I build and fit prosthetics, it would surprise most people how general use can trash materials like reinforced carbon fiber and titanium. You do the same to your body, but your body repairs itself.
make a robotic limb capable of the force of a human hand it will be incredibly stiff and slow, or require actuators that are too large and heavy to be feasibly carried by a person, to say nothing of the energy storage.
Yep, the actuators in prosthetic limbs are typically located in the wrist, or in the actual terminal device, which makes them pretty clunky. People have tried making ones that are housed further up the limb, but then you are working against the length of the lever arm. Your biceps brachii insertion can exert about 10x more force than what you can curl, it just seems weaker because you have a leverage disadvantage.
They used to have a operation where they attached a terminal device to a trans radial prosthetic directly to the bicep, but those guys could close the terminal devices(claw) with anywhere from 350-500lbs of pressure.
the actuator problem is pretty much the single biggest barrier to creating prosthetics that rival the functionality of human hands.
It’s one of the problems, though I don’t think it’s the main one. The main problem is mimicking anything close to the propeceptive abilities that humans have. The mind body connection that you have to your hands is just eons away from anything we currently have. The current tech most advanced limbs utilize is myoelectrics, which have been around since the late 70s and are for the most part unchanged. There have been some pretty cool improvements in nerve reintegration, but it’s not really a feasible technology atm as it takes dozens of hours for a team of surgeons and a special candidate for a patient.
I would say the second biggest hurdle, especially for lower limb prosthetics is energy storage, it’s not fun to lug around a heavy ass lithium battery that you have to recharge every few hours. Upper limb uses less energy, but only because there’s only so much they can do atm.
I know to a lot of you I’m killing your cyberpunk dreams, but you will never have a limb that even comes close to the quality and utility as your current healthy limb. The technology just isn’t anywhere close to where a lot of people believe it is.
the neural interface to prosthetics is particularly fascinating to me. i read a couple papers a while ago that showed that human muscle control is essentially highly orchestrated bangbang control. it was always confusing to me why we have such over actuated limbs, with thousands of muscle fibers per individual muscle that our brains actuate individually. what they showed was that each cluster connected to a particular nerve is either on or off, with our brains sending complex sequences of on and off to each fiber to perform motion, and our tendons essentially acting like filters to hold the tension and smooth out the motion so we arent super jerky.
the big takeaway to me though is that if we want to make the kinds of prosthetics that come close to replicating the utility of human limbs the actuators should be highly redundant bangbang systems the way our muscles are. my understanding is current mechatronic prosthetics use electric motors with continuous control of monolithic motors for each joint, which is very much not even close to how our brains control our bodies. i think the translation from what our brains do to that causes a lot of issues that would be solved by providing our brains with something closer to bangbang actuators.
one of the papers also showed that while we do use feedback from sensor neurons in our limbs, its actually pretty slow compared to some of the activities people perform, to the point where the action starts and ends before the feedback even reaches the brain. so basically our brains just perform those rapid actions open loop, and only use the feedback for learning after the event. isnt that fucking cool! that suggests that if we can just make actuators that respond similarly to muscles and connect them with existing nerves we could leverage this system to get pretty far along the way to people having fine motor control over prosthetics, even without all the feedback, and potentially completely analog with no microcontrollers required. people just might need to look at their limb while theyre doing stuff, especially during the early neural training when theyre figuring out how to move it.
And as durable. People don’t really know how much force you are working with as a body in motion. Ground reaction force for a small jump can be 7x someone’s body weight. So a person weighing 200lb can have 1400lbs of mechanical load being distributed by the feet and ankles. I build and fit prosthetics, it would surprise most people how general use can trash materials like reinforced carbon fiber and titanium. You do the same to your body, but your body repairs itself.
Yep, the actuators in prosthetic limbs are typically located in the wrist, or in the actual terminal device, which makes them pretty clunky. People have tried making ones that are housed further up the limb, but then you are working against the length of the lever arm. Your biceps brachii insertion can exert about 10x more force than what you can curl, it just seems weaker because you have a leverage disadvantage.
They used to have a operation where they attached a terminal device to a trans radial prosthetic directly to the bicep, but those guys could close the terminal devices(claw) with anywhere from 350-500lbs of pressure.
It’s one of the problems, though I don’t think it’s the main one. The main problem is mimicking anything close to the propeceptive abilities that humans have. The mind body connection that you have to your hands is just eons away from anything we currently have. The current tech most advanced limbs utilize is myoelectrics, which have been around since the late 70s and are for the most part unchanged. There have been some pretty cool improvements in nerve reintegration, but it’s not really a feasible technology atm as it takes dozens of hours for a team of surgeons and a special candidate for a patient.
I would say the second biggest hurdle, especially for lower limb prosthetics is energy storage, it’s not fun to lug around a heavy ass lithium battery that you have to recharge every few hours. Upper limb uses less energy, but only because there’s only so much they can do atm.
I know to a lot of you I’m killing your cyberpunk dreams, but you will never have a limb that even comes close to the quality and utility as your current healthy limb. The technology just isn’t anywhere close to where a lot of people believe it is.
the neural interface to prosthetics is particularly fascinating to me. i read a couple papers a while ago that showed that human muscle control is essentially highly orchestrated bangbang control. it was always confusing to me why we have such over actuated limbs, with thousands of muscle fibers per individual muscle that our brains actuate individually. what they showed was that each cluster connected to a particular nerve is either on or off, with our brains sending complex sequences of on and off to each fiber to perform motion, and our tendons essentially acting like filters to hold the tension and smooth out the motion so we arent super jerky.
the big takeaway to me though is that if we want to make the kinds of prosthetics that come close to replicating the utility of human limbs the actuators should be highly redundant bangbang systems the way our muscles are. my understanding is current mechatronic prosthetics use electric motors with continuous control of monolithic motors for each joint, which is very much not even close to how our brains control our bodies. i think the translation from what our brains do to that causes a lot of issues that would be solved by providing our brains with something closer to bangbang actuators.
one of the papers also showed that while we do use feedback from sensor neurons in our limbs, its actually pretty slow compared to some of the activities people perform, to the point where the action starts and ends before the feedback even reaches the brain. so basically our brains just perform those rapid actions open loop, and only use the feedback for learning after the event. isnt that fucking cool! that suggests that if we can just make actuators that respond similarly to muscles and connect them with existing nerves we could leverage this system to get pretty far along the way to people having fine motor control over prosthetics, even without all the feedback, and potentially completely analog with no microcontrollers required. people just might need to look at their limb while theyre doing stuff, especially during the early neural training when theyre figuring out how to move it.