4 ms·

Having read the article you linked that seems to be a misrepresentative summary of it.

by rndmio 7y ago

murkt 7y ago
Yep, I've also read the linked article and for me the summary is more like "HET motor has some interesting ideas, some difficulties, some claims are incorrect and it's probably a bit difficult to manufacture."
- hwillis 7y ago
  Interesting ideas- kind of, but the interesting ideas are not new. Dimensionality is one of the oldest formulated motor-related problems. Hybrid rotors are certainly an active area. The motor is a pretty novel and clever way to draw all these things together, but it's not the kind of thing to build a product around. Some difficulties- these are fundamental issues. They are fundamentally unsolvable with the suggested architecture. Eg anything that adds cooling back in will conflict with the rotors or coils. On manufacturability: > Flux paths in the teeth seem very much 3-dimensional, which would require sintered materials to be used to limit eddy-current losses. This really belies how much of a fucking nightmare this would be. First, an unrelated area of development: grain-oriented electrical steels have 30% higher permeability (in one direction) than non-oriented steels. People are actively looking to ways to orient steel grains into the arches necessary to make a motor, because even small improvements in permeability can lead to smaller and more efficient motors. A 30% improvement would be incredible, and justify a large cost increase since the cost of motors is effectively determined by the electricity usage. The permeability of sintered soft materials is at best ~1/10th that of the electrical steel used in motors. So... thats a huge issue. Its also much more expensive. Its also mechanically unsuitable for high torque motors, because it's weak and brittle. It also has much higher losses. The shape of the stator would also require entirely new technologies to even make. Die-sintered powders are very precise in two axes- since you're pressing into a mould, you can rely on near-thousandth repeatable tolerances once you have accounted for shrinkage after sintering (which can take multiple tries to get right). That third axis is a real bitch. Powder will never be consistent; you cant apply hundreds of tonnes of pressing force and be precise to thousandths of an inch, and even if you can get the force repeatable the compressability of powders varies too much between batches due to grain shape and size, temperature, additives, humidity... And even if it was consistent, you cant design for that. You can only adjust a ten thousand dollar mould after the fact. And that z dimension is the most critical, since any asymmetry will cause uneven forces on the axle bearings. In a normal motor you can trivially be off by several hundredths of an inch because the axial force is negligible. In this design a thou will cause a large force imbalance, so each motor will need to be a precision part. Even variations inside the rotor will cause large vibrations, so sintering + heat treating will be a nightmare. Not to mention that the magnets will have to be matched individually, both for size/thickness and permeability tolerance. If my boss wanted me to produce this thing, I'd quit.
  - murkt 7y ago
    Thanks for a detailed response, it's quite informative and educational.
hwillis 7y ago
The article is diplomatic, but not ambiguous. For instance: > Cooling issues: can enough cooling air be forced inside the rotors? > Cooling issues, again. The primary cooling path for more traditional motors is usually conduction through the stator yoke, to the frame, to either air or coolant fluid. For the HET, this path seems almost completely missing. > [four lines later] Assuming the cooling performance remains unchanged, the reduced winding losses could then be cashed in by increasing the current density, and thus torque, torque-per-mass, and bringing losses back to the original level. This may read as if there are good ideas here, but make no mistake- the implication is that these problems are nigh-unworkable. The possibilities of minor increases are locked behind immense problems. There is a parallel with combustion engines here. The ideal combustion cylinder is spherical: it ensures more even burning and minimizes the area heat from escape from a given volume. You could make an engine with spherical combustors instead of cylindrical and reap that improvement. That's basically what toroidal motors try to do- use more surface area per unit of rotor volume (although due to the nature of air gaps[not discussed in the article], it's not obvious that this is actually beneficial). In both cases, you're cutting off your nose to spite your face.

Having read the article you linked that seems to be a misrepresentative summary of it.

by rndmio 7y ago

Having read the article you linked that seems to be a misrepresentative summary of it.

Yep, I've also read the linked article and for me the summary is more like "HET motor has some interesting ideas, some difficulties, some claims are incorrect and it's probably a bit difficult to manufacture."

hwillis 7y ago
Interesting ideas- kind of, but the interesting ideas are not new. Dimensionality is one of the oldest formulated motor-related problems. Hybrid rotors are certainly an active area. The motor is a pretty novel and clever way to draw all these things together, but it's not the kind of thing to build a product around. Some difficulties- these are fundamental issues. They are fundamentally unsolvable with the suggested architecture. Eg anything that adds cooling back in will conflict with the rotors or coils. On manufacturability: > Flux paths in the teeth seem very much 3-dimensional, which would require sintered materials to be used to limit eddy-current losses. This really belies how much of a fucking nightmare this would be. First, an unrelated area of development: grain-oriented electrical steels have 30% higher permeability (in one direction) than non-oriented steels. People are actively looking to ways to orient steel grains into the arches necessary to make a motor, because even small improvements in permeability can lead to smaller and more efficient motors. A 30% improvement would be incredible, and justify a large cost increase since the cost of motors is effectively determined by the electricity usage. The permeability of sintered soft materials is at best ~1/10th that of the electrical steel used in motors. So... thats a huge issue. Its also much more expensive. Its also mechanically unsuitable for high torque motors, because it's weak and brittle. It also has much higher losses. The shape of the stator would also require entirely new technologies to even make. Die-sintered powders are very precise in two axes- since you're pressing into a mould, you can rely on near-thousandth repeatable tolerances once you have accounted for shrinkage after sintering (which can take multiple tries to get right). That third axis is a real bitch. Powder will never be consistent; you cant apply hundreds of tonnes of pressing force and be precise to thousandths of an inch, and even if you can get the force repeatable the compressability of powders varies too much between batches due to grain shape and size, temperature, additives, humidity... And even if it was consistent, you cant design for that. You can only adjust a ten thousand dollar mould after the fact. And that z dimension is the most critical, since any asymmetry will cause uneven forces on the axle bearings. In a normal motor you can trivially be off by several hundredths of an inch because the axial force is negligible. In this design a thou will cause a large force imbalance, so each motor will need to be a precision part. Even variations inside the rotor will cause large vibrations, so sintering + heat treating will be a nightmare. Not to mention that the magnets will have to be matched individually, both for size/thickness and permeability tolerance. If my boss wanted me to produce this thing, I'd quit.
- murkt 7y ago
  Thanks for a detailed response, it's quite informative and educational.

hwillis 7y ago

The article is diplomatic, but not ambiguous. For instance: > Cooling issues: can enough cooling air be forced inside the rotors? > Cooling issues, again. The primary cooling path for more traditional motors is usually conduction through the stator yoke, to the frame, to either air or coolant fluid. For the HET, this path seems almost completely missing. > [four lines later] Assuming the cooling performance remains unchanged, the reduced winding losses could then be cashed in by increasing the current density, and thus torque, torque-per-mass, and bringing losses back to the original level. This may read as if there are good ideas here, but make no mistake- the implication is that these problems are nigh-unworkable. The possibilities of minor increases are locked behind immense problems. There is a parallel with combustion engines here. The ideal combustion cylinder is spherical: it ensures more even burning and minimizes the area heat from escape from a given volume. You could make an engine with spherical combustors instead of cylindrical and reap that improvement. That's basically what toroidal motors try to do- use more surface area per unit of rotor volume (although due to the nature of air gaps[not discussed in the article], it's not obvious that this is actually beneficial). In both cases, you're cutting off your nose to spite your face.