3 ms·

Agree on all counts. IMO the future is large-diameter motors with between 1:1 to 1:10 reduction and very high power/efficiency(roundtrip) batteries. Many diff

Agree on all counts. IMO the future is large-diameter motors with between 1:1 to 1:10 reduction and very high power/efficiency(roundtrip) batteries. Many different labs are converging on it, BD is a stark exception.

modeless 9y ago
So direct drive motors with something akin to regenerative braking to recover energy? Could a direct drive motor hooked to a capacitor bank recapture energy efficiently enough to act like a muscle in a walking gait?
- Animats 9y ago
  Maybe, if you had a place to put a motor that large. Modern motor realities: 1. Electric motors can be enormously overdriven for short periods when you need huge torque. The limits are heat dissipation and demagnetizing the permanent magnets in permanent magnet motors. With modern rare-earth magnets, the second is no longer a problem. Water cooling can deal with the first problem. If you have temperature sensing, you can safely overload temporarily and wait for cool-down. When you see one of those videos of a Tesla car accelerating in "launch mode", you're seeing this in action. 2. Power semiconductors have become really good. Power control is no longer a limiting factor on motors. For most of the 20th century, variable speed motor control for large motors was hard and took bulky, expensive gear. It was a serious problem with electric cars into the 1990s; burning out power controllers was a problem. That's been fixed. Modern electric cars and locomotives use AC synchronous motors with IGBT or MOSFET devices producing 3-phase power at the desired voltage, frequency, and phase to run the motor optimally. Locomotives synchronize all the wheels with electronics and software. This scales down all the way to hobbyist drone size. Robots get to use all this now off-the-shelf technology to run their motors. 3. Some research robots use "series elastic actuators". These are simply a motor driving a screw drive with a stiff spring attached. The trick is how they're used. When the actuator gets a shock load, as when a foot lands, the stiff spring is compressed. As it compresses, the control system detects this, and frantically spins the motor to unload the spring before the spring bottoms out. This works, but it's the opposite of energy recovery; it takes energy to absorb a load. It's possible to write software which makes such devices behave like a spring with an adjustable spring constant, but there's no energy recovery. Good for research, because these can be assembled from off the shelf parts. Not so good for battery life. 4. Gears are terrible at dealing with shock loads. One of the big advantages of direct drive is that "you cannot break the teeth of a magnetic field", as an early GE locomotive designer put it. The downside of direct drive is that torque increases with motor diameter (more leverage), and big flat motors tend to be inconvenient in robots. But there's been recent progress. See this direct-drive robot arm with small motors.[1] Very nice. No gears. No cables. No pulleys. Good force feedback. Nothing to break if somebody forces the arm. Energy recovery possible. Only 10Kg lift capacity, which is OK for industrial arms but not enough for a legged machine. Progress marches on; there may be an all-electric leg solution in time. For decades, motors were a dull, boring, mature field. Motors came in standard sizes and speeds, and were interchangeable across vendors. Nobody worked much on new designs. Now, with much more elaborate control systems, people are innovating again. By the time there's a market for humanoid robots, the motors will probably be ready. [1] http://www.kollmorgen.com/hi-in/service-and-support/knowledge-center/success-stories/direct-drives-in-lightweight-robots/ http://www.kollmorgen.com/hi-in/service-and-support/knowledg...
  - hwillis 9y ago
    WRT 3: There is energy recovery, but it's very small and it's more like impedance matching. They've been used for outright storage (eg DURUS) but the springs are usually just too stiff. It still saves energy since there's a smaller initial current spike, but it doesn't save energy step-to-step. Unless you take really small steps, I guess.
    - Animats 9y ago
      Soft spring systems are not usually considered series elastic actuators. There's a "soft actuator" branch of robotics, Shadow Robotics having been doing that for years. Disney has done some work in that space, because they want machines which are safe around people. As control techniques improve, that concept works better. There's a useful arrangement where you have two opposed springs powered by separate actuators. If you tighten up both springs, the system stiffens up; if you loosen both, you get better energy recovery but worse position control. This is a reasonable muscle model, and can recovery energy, but is bulky mechanically. Movement without load is cheap; changing the compliance is expensive from an energy standpoint. There's also a pneumatic version of this, where you pressurize an air cylinder from both ends. That works well if the valves are close to the cylinder. There are mechanical approaches to variable compliance, but they're complex mechanically and usually seem to involve string and pulleys.[1] The trend seems to be towards all-electric systems, rather than clever mechanics. [1] http://mime.oregonstate.edu/research/drl/publications/_documents/hurst_2010a.pdf http://mime.oregonstate.edu/research/drl/publications/_docum...
- hwillis 9y ago
  Yes, exactly like regeneration. However it's a highly multifaceted problem to optimize. Batteries, capacitors, drivers, motors and drivetrains all have very picky efficiency regimes. Grease is very inefficient at low torques or high speeds, since it's shear-thinning and viscous. Motors have to have their voltage, current, field strength, size and a few other aspects all optimized. You run the gamut from metallurgy to fluid dynamics to chemistry to EM fields. It requires tons of high performance custom parts. That said a few groups have done it. Heavily optimized drivetrains can be ~96% efficient at the right speed and torque. Extremely precise drivers can regen at 98%+. If you charge gently enough batteries can be 98%. 88.5% total efficiency. That's extremely good, enough to reduce power consumption by 8.7 times. It's better than a human but not quite as good as an insulated spring.
  - Animats 9y ago
    It requires tons of high performance custom parts. Yes. Which is the big problem with robotics. No volume and high tooling cost. With enough money, something like Big Dog or Atlas can be built, with large numbers of custom moving parts. But the price tag is in 8 figures. Other than the industrial robot arm people and the vacuum cleaner people, nobody is making money in robotics. (Well, the individuals who were bought out by Google exited OK, but overall, the Google thing was a lose.)
    - sbierwagen 9y ago
      Other than the industrial robot arm people and the vacuum cleaner people, nobody is making money in robotics. There are modest amounts of money being made in educational mobile robotics. (Lego, VEX, the FIRST consortium) FIRST robots are moderately interesting, but cost something like $5K-$10K each. VEX and Lego robots are cheaper, but are basically toys. (I work with VEX) Think erector sets with microcontrollers bolted on. Press video for the 2016 VEX World Championships. Thousands of people. https://www.youtube.com/watch?v=0Y1YiGZv_F4 https://www.youtube.com/watch?v=0Y1YiGZv_F4

modeless 9y ago

So direct drive motors with something akin to regenerative braking to recover energy? Could a direct drive motor hooked to a capacitor bank recapture energy efficiently enough to act like a muscle in a walking gait?

Animats 9y ago
Maybe, if you had a place to put a motor that large. Modern motor realities: 1. Electric motors can be enormously overdriven for short periods when you need huge torque. The limits are heat dissipation and demagnetizing the permanent magnets in permanent magnet motors. With modern rare-earth magnets, the second is no longer a problem. Water cooling can deal with the first problem. If you have temperature sensing, you can safely overload temporarily and wait for cool-down. When you see one of those videos of a Tesla car accelerating in "launch mode", you're seeing this in action. 2. Power semiconductors have become really good. Power control is no longer a limiting factor on motors. For most of the 20th century, variable speed motor control for large motors was hard and took bulky, expensive gear. It was a serious problem with electric cars into the 1990s; burning out power controllers was a problem. That's been fixed. Modern electric cars and locomotives use AC synchronous motors with IGBT or MOSFET devices producing 3-phase power at the desired voltage, frequency, and phase to run the motor optimally. Locomotives synchronize all the wheels with electronics and software. This scales down all the way to hobbyist drone size. Robots get to use all this now off-the-shelf technology to run their motors. 3. Some research robots use "series elastic actuators". These are simply a motor driving a screw drive with a stiff spring attached. The trick is how they're used. When the actuator gets a shock load, as when a foot lands, the stiff spring is compressed. As it compresses, the control system detects this, and frantically spins the motor to unload the spring before the spring bottoms out. This works, but it's the opposite of energy recovery; it takes energy to absorb a load. It's possible to write software which makes such devices behave like a spring with an adjustable spring constant, but there's no energy recovery. Good for research, because these can be assembled from off the shelf parts. Not so good for battery life. 4. Gears are terrible at dealing with shock loads. One of the big advantages of direct drive is that "you cannot break the teeth of a magnetic field", as an early GE locomotive designer put it. The downside of direct drive is that torque increases with motor diameter (more leverage), and big flat motors tend to be inconvenient in robots. But there's been recent progress. See this direct-drive robot arm with small motors.[1] Very nice. No gears. No cables. No pulleys. Good force feedback. Nothing to break if somebody forces the arm. Energy recovery possible. Only 10Kg lift capacity, which is OK for industrial arms but not enough for a legged machine. Progress marches on; there may be an all-electric leg solution in time. For decades, motors were a dull, boring, mature field. Motors came in standard sizes and speeds, and were interchangeable across vendors. Nobody worked much on new designs. Now, with much more elaborate control systems, people are innovating again. By the time there's a market for humanoid robots, the motors will probably be ready. [1] http://www.kollmorgen.com/hi-in/service-and-support/knowledge-center/success-stories/direct-drives-in-lightweight-robots/ http://www.kollmorgen.com/hi-in/service-and-support/knowledg...
- hwillis 9y ago
  WRT 3: There is energy recovery, but it's very small and it's more like impedance matching. They've been used for outright storage (eg DURUS) but the springs are usually just too stiff. It still saves energy since there's a smaller initial current spike, but it doesn't save energy step-to-step. Unless you take really small steps, I guess.
  - Animats 9y ago
    Soft spring systems are not usually considered series elastic actuators. There's a "soft actuator" branch of robotics, Shadow Robotics having been doing that for years. Disney has done some work in that space, because they want machines which are safe around people. As control techniques improve, that concept works better. There's a useful arrangement where you have two opposed springs powered by separate actuators. If you tighten up both springs, the system stiffens up; if you loosen both, you get better energy recovery but worse position control. This is a reasonable muscle model, and can recovery energy, but is bulky mechanically. Movement without load is cheap; changing the compliance is expensive from an energy standpoint. There's also a pneumatic version of this, where you pressurize an air cylinder from both ends. That works well if the valves are close to the cylinder. There are mechanical approaches to variable compliance, but they're complex mechanically and usually seem to involve string and pulleys.[1] The trend seems to be towards all-electric systems, rather than clever mechanics. [1] http://mime.oregonstate.edu/research/drl/publications/_documents/hurst_2010a.pdf http://mime.oregonstate.edu/research/drl/publications/_docum...
hwillis 9y ago
Yes, exactly like regeneration. However it's a highly multifaceted problem to optimize. Batteries, capacitors, drivers, motors and drivetrains all have very picky efficiency regimes. Grease is very inefficient at low torques or high speeds, since it's shear-thinning and viscous. Motors have to have their voltage, current, field strength, size and a few other aspects all optimized. You run the gamut from metallurgy to fluid dynamics to chemistry to EM fields. It requires tons of high performance custom parts. That said a few groups have done it. Heavily optimized drivetrains can be ~96% efficient at the right speed and torque. Extremely precise drivers can regen at 98%+. If you charge gently enough batteries can be 98%. 88.5% total efficiency. That's extremely good, enough to reduce power consumption by 8.7 times. It's better than a human but not quite as good as an insulated spring.
- Animats 9y ago
  It requires tons of high performance custom parts. Yes. Which is the big problem with robotics. No volume and high tooling cost. With enough money, something like Big Dog or Atlas can be built, with large numbers of custom moving parts. But the price tag is in 8 figures. Other than the industrial robot arm people and the vacuum cleaner people, nobody is making money in robotics. (Well, the individuals who were bought out by Google exited OK, but overall, the Google thing was a lose.)
  - sbierwagen 9y ago
    Other than the industrial robot arm people and the vacuum cleaner people, nobody is making money in robotics. There are modest amounts of money being made in educational mobile robotics. (Lego, VEX, the FIRST consortium) FIRST robots are moderately interesting, but cost something like $5K-$10K each. VEX and Lego robots are cheaper, but are basically toys. (I work with VEX) Think erector sets with microcontrollers bolted on. Press video for the 2016 VEX World Championships. Thousands of people. https://www.youtube.com/watch?v=0Y1YiGZv_F4 https://www.youtube.com/watch?v=0Y1YiGZv_F4