One of the most obvious ways to mitigate the effect of the high cost of REEs is to eliminate rare earth magnets and return to conventional materials. With conventional radial designs, however, that means going back to the bad old days of large, heavy motors. This is because conventional materials simply cannot produce the same field strength as rare earth alloys.
Neodymium iron boron (NdFeB), for example, features an energy product -- essentially, a measure of field strength -- of around 55 MGOe, compared to roughly 4.5 MGOe for ferrite. That bump in energy product is what makes it possible for radial rare earth motors to deliver lots of muscle in a tiny package compared to their ferrite counterparts. The solution required taking a different approach to the problem.
Figure 2: The stator assembly consists of six of these laminated-steel field poles, each surrounded by a bobbin-wound coil. (Source: NovaTorque)
The design starts with a stator assembly formed of six laminated field poles of oriented steel, each threaded through a bobbin-wound coil (see figure 2). The rotor consists of two separate conical ferromagnet assemblies designed to match the cavities on the ends of the stator, leaving a conical air gap. Now, instead of the interaction taking place in two dimensions, it takes place in three dimensions.
If we compare the cross-sectional area of the stator at the coils with the surface area of the laminated pole structure, the ratio is roughly 2:1. This leads to a correspondingly large increase in flux density for the same motor diameter. What that means is that even with ferrite magnet material, the axial design can deliver similar torque density compared to a radial designs based on REE magnets.
“By concentrating flux in three dimensions, we can use quite a bit of low-cost ferrite material and concentrate flux to get a flux density in the stator that is comparable to what you would have in a rare earth magnet motor," says Alan Crapo, vice president of engineering at NovaTorque Inc. Essentially, the approach flips the conventional model of moderate Φs and very high ΦR to moderate ΦR and very high Φs. The result is better performance from conventional materials. “We can get the same kind of efficiency as rare earth magnet motors and we can operate the steel at similar flux density levels that rare earth magnets will operate at," says Crapo.
There are tradeoffs, of course. Even with the flux focusing, the axial designs need more of the conventional magnet material to get the desired performance. The NovaTorque team added more magnet material without significantly increasing frame size by narrowing the air gap between rotor and stator. In addition, the team potted the stator to enhance heat transfer. The result is a motor that may maintain a competitive frame size but more of the overall volume is filled with motor materials, giving it more mass and inertia than its rare earth counterparts.
To me, the message here is that innovation isn't just about coming up with the next new technology idea, but also being creative enough to see there can be novel approaches to old problems. The rare earth shortages are likely to continue for some time. This is a great example of deft engineering and being able to shift gears to another way of problem solving when something stands in your way.
I know many folks are poking fun at the idea of a push to asteroid mining, but as our high-tech gadgets require more and more high-tech materials that are becoming more and more scarce, looking off-world for new supplies sounds like a logical next step. It also beats the heck out of our entire technical workforce generating new mobile apps for their entire career...
The interesting thing to me about this work is that NovaTorque initially started out working with rare-Earth magnets and only tried the technology on ferrite magnets after rare-Earth pricing got out of hand. whatthat means is that in a few years, when new sources come online and the price of rare-Earth materials drops, NovaTorque can take what they've learned and begin making rare-Earth versions of their design, which could create uber-high-performance motorseven more compact and conventional rare-Earth versions.
Kristin, That is a great point. In solving a material problem in the near term you set yourself up for even more effeciencies when that material comes down in price.
Interesting idea, William. This is the basis of the Alien movie series, that space travel will essentially be based on mining. That may be the case. Yet, given our gains in creating sophisticated robot technology, the mining missions may not involve humans.
I agree, Beth. This is a great story of innovation in the face of economic necessity -- a great example of the old saying, "It's not what you have, it's what you do with it."
I suspect that transporting tons of raw materials back to earth will be a lot more costly than transporting them from under the ocean -- unforeseen difficulties are sure to play an economic role there. Still, I agree with you that our taste for high-tech will one day make asteroid mining a reality.
Beth, there are enough rare earth metals are available in China. They are possessing about 85% of the total availability. If China is willing to open up their market for international customers/companies, most of the problem may get resolved.
As a user of rare-earth magnets I hear there are large quantities of the resources necessary here in the USA but for the cost of getting it out of the earth. I guess the "rare" part is the permits, etc.
China broke international agreements in withholding this material from the world. I think it is a brilliant maneuver to raise prices. Saudi Arabia, et al, do it with oil. I do it with my vast mental capacity and my stunning good looks. So, the solution is an engineering one. How can we get around China? We got around the buggy whip cartel with the automobile. We can find ways to extract it from our own soil effectively, safely, and cleanly (unless the government has another hidden agenda in agreements with China). Or we can find substitutes. Maybe there is a substance we can use like "I Can't Believe It's Not Neodymium!"
I don't know if I buy the "hoarding" excuse. Speculators tend to stabilize prices. I think dark-side politics are at play, Mr. Watson.
Our missing link to successful space mining is that we have no space drive like all the science fiction crafts and what has been observed in "UFO's". We need something to replace the rocket to break earth's gravity before real economic feasibility is here.
Where are we at on the carbon nanotube ribbon hooked to a geosynchronous satellite?
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