“If you run through an optimization routine, you’re going to have certain limits,” said Jim Calico, senior design engineer at the Moog Components Group. “One would be the ratio of the stator outer diameter to the rotor outer diameter. For a given application, there’s going to be an optimal performance ratio for that, but there’s going to be a range within that optimal size. I'm saying push the design to a minimum rotor outer diameter.”
As always, there are tradeoffs. Going with a copper-centric design might preserve the power density but will add to the size, not to mention inertia. How far to push the tradeoff, if at all, will depend on the application.
Another approach is to adjust the air gap between the rotor and the stator. According to Hanselman, the magnetic performance of a brushless permanent-magnet motor is directly related to the ratio of the radial magnet length to the radial air gap length. “If manufacturing allows one to decrease the air gap length by a factor of α, then the magnet length can also be decreased by the same factor of α, and the motor performance will remain unchanged."
Of course, leveraging the technique depends on the supplier’s ability to maintain tight manufacturing tolerances, which can add cost and complicate assembly. It’s also important to keep in mind that the effect is subtle. “It's not substantial,” said Joseph Profeta, director of product management for control systems at Aerotech Inc. “It's more like a 5 percent, 10 percent change.” Depending on magnet pricing and budget, it may still be in effect worth pursuing.
Increasing the number of magnet poles on the rotor can also yield a magnet-sparing design. “If done carefully, this will increase the torque creation ability of the motor while keeping the amount of magnet material constant,” Hanselman said. “Therefore, one might be able to shrink the motor size and still meet the required performance specs.”
For a greenfield design, the sky's the limit. In the case of users searching for a more economical solution for a product, it's important to keep in mind the form factor of the original. Depending on the manufacturing tolerances, a diameter change of a few millimeters may make the difference between a motor that fits into a machine and one that does not. A lower-price motor might be appealing, but not if a redesign ultimately raises the costs for the project as a whole. Once again, there is no right answer -- just a set of tradeoffs.
That's a good question, Cvandewater. In my brief searching on the question, I couldn't find any actual examples of recycling in this area. So it remains a good questions. And it makes sense that you put "rare" in quotes. These materials are listed as "rare earths" on the periodic table, but they are anything but rare.
Always fun to see an old discussion being moved back to the front of the stage... The only issue was that very little hard data was presented during that discussion, so my question is still if this recycling is indeed happening or not and whether it would be a meaningful contribution to the short-term scarcity of "rare" earth material (until the previously abandoned mines/non-China suppliers come back online).
Yes, that's pretty much what I learned in my reporting. It's an expensive ramp-up, so the only mine in North America, Molycorp, went public and raised $394 million to get going. By now they may be delivering materials. Not sure.
Here's a February article from the Atlantic that spells out the history and brings you up to date:
A) the rare earth material availability shortage is a short term (roughly 2 years) issue.
B) Because of the shortage there will be a spike in market price due to demand, but the price will start to come down as these other mining supplies come on stream.
C) the price will come back down and level off at a level somewhat higher than the previous "depressed price", when China was flooding the market with cheaper rare earth materials.
Another question: Does this include Beryllium mining in the USA too?
Good question, David12345. I covered rare earths last year for EDN and was surprised to find that North America has plenty of rare earth materials. The problem is that over that past two decades, these materials have been so cheap in China that is hasn't been cost effective to dig baby dig. Now with China rationing rare earths, it has become profitable to dig. But there is a time-consuming ramp-up. So it will be a couple years before all of these materials are flowing again.
Don't let the term "rare" fool you. Neodymium for instance is quite prevalent in nature but not necessarily in an economically extratable form.
Yes we have them and Canada has them. Extraction of REO is typically from tailings resulting from Uranium, Thorium or Iron mining.There simply isn't as much as in China but it is substantial and US mines are being reactivated. Some of these mines were shut down as a result of Chinese undercutting the market.
World Mine Production and Reserves: Reserves data for Australia, China, and India were updated based on data from the respective countries.
Mine production Reserves 2009 2010 United States — — 13,000,000 Australia — — 1,600,000 Brazil 550 550 48,000 China 129,000 130,000 55,000,000 Commonwealth of Independent States NA NA 19,000,000 India 2,700 2,700 3,100,000 Malaysia 350 350 30,000 Other countries NA NA 22,000,000 World total (rounded) 133,000 130,000 110,000,000
Do we even have appreciable quantities of these raw materials available to consider mining in the United States? I thought that some of these "rare earth" materials had only been found in a very few places on earth.
One obvious conclusion is to start digging on US soil for these materials. As I understand it China eventually will consume the entire supply of REO it is producing for it's wind power industry. We are just funding the construction of these mining operations and developing the technology to use these materials. Once they are in full swing they will have no motivation to sell these materials outside their country.
We looked at a number of sources to determine this year's greenest cars, from KBB to automotive trade magazines to environmental organizations. These 14 cars emerged as being great at either stretching fuel or reducing carbon footprint.
Researchers at MIT and Sandia National Labs have observed a reaction in lithium-air batteries that could help improve the design of these cells for electric vehicles and other applications.
Healthcare might seem to be an unlikely target application for the Internet of Things technology, but recent developments show small ways that big-data is going to make an impact on patient care moving into the future.
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A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
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