Stepper motors simply provide accurate and fast occasional rotational positioning. This requires high torque at a wide rpm range, including 0 rpm, for obvious reasons. stepper motors are a very bad application for induction motors, since everything other than steady state operation requires advanced control systems and switching power supply circuitry. For the basic induction motor without an advanced control system, the starting torque must be provided by inefficient means, and is still very limited.
Synchronous motors are motors where the rotation of the magnetic field is synchronous with the rotation of the motor. For all induction motors, the induced field is a result of a varying magnetic field across the element in question. This implies that the speed of the rotor must be different than the speed of the magnetic field. Thus, no induction motor is a synchronous motor, almost by definition.
I actually wasn't aware that induction motors don't use permanent magnets. RC model aircraft is a hobby of mine, and all I knew is that the commonly-used brushless AC motors certainly use permanent magnets.
As a first order simplification, motors are all about pairs of magnetic fields attracting / repelling each other. Often, one side of the pair is a permanent magnet. If instead the magnetism is induced (implying no magnet involved, as the other side must be switchable / controllable / varying, thus not a permanent magnet), you have an induction motor.
At low power levels, permanent magnet motors (specifically brushless motors) tend to have higher efficiency than induction motors, additionally, they don't require complicated control systems to operate efficiently at varying speeds. Thus you are unlikely to see an induction motor in an RC model anytime soon.
Yep, Permanent Magnet AC (PMAC) motors are common types of synchronous motors. They are generally more compact than induction motors for the same power output. Induction motors are generally less expensive.
DC Brushless and PMAC are interchangeable. Oh, and nowadays, you don't need sensors (hall, encoder etc). 'Sensorless' motor control is possible by sensing the back emf of the motor or reconstructing the motor current via (super inexpensive) shunt resistors on the legs of the inverter.
While the motors may be REE-free, I wouldn't be so sure about the rest of the vehicle.
Many models of LED's, lasers, displays, headlights, and power circuits use trace but nonetheless essential amounts of rare earths. The motors and actuators (power windows and locks, charge port and frunk poppers) and seat heater relay might also contain them.
Tesla does not use rare earth metals in our battery or motor.
The HN Title [1] should be changed, as it is in effect editorializing beyond the information provided, IMHO. As others have noted, there is no information to suggest the statement is generally true, beyond these two sub-system components.
[1] Currently: "No rare earth metals in the Model S"
there are almost certainly rare earth metals in the speakers, for example, although the mass would be relatively cheap compared to what you would need for a motor.
Does the tesla have regenerative braking system, and I wonder if there are rare earth metals there?
Which is a completely different thing than a rare earth metal. (Which incidentally are not rare or precious.)
To be fair, the group is badly named, but rare earth metals has a very precise meaning -- if something is not one of the lanthanides, Scandium, or Yttrium, it's not REE.
> Does the tesla have regenerative braking system, and I wonder if there are rare earth metals there?
As far as I understand it, they use the motors for regenerative breaking, and the motors don't contain permanent magnets. Where permanent magnets would be used, they use more coils, and thus can vary the strength of the magnetic fields, much like your car's alternator. This is also how they forgo the need for a gear box.
I wasn't sure what the implications of rare earth metals were, so I looked it up. In sort,
Rare metal extraction involves substantial pollution in the mining, onsite processing, and refining phase. Mines create environmental degradation through topsoil loss, poorly controlled tailings ponds that leach into groundwater as well as lakes and rivers, roads slicing through habitat, and the use of large amounts of energy to extract and process the materials they uncover. Some rare earth metals require substantial processing, and that provides a number of opportunities for pollution at every step of the way.
More here: http://www.theguardian.com/commentisfree/2011/sep/26/rare-ea...
I think it's more to do with the fact that China has a monopoly on most rare earth metals, and the supply can get constrained, like they did last year against Japan.
Actually, there are a number of places with large Lanthanoid deposits, but since China was supplying them so cheap, the mines were not economical. Now that China is tightening supplies, they have reopened the California mine in Mountain Pass that used to be a major supplier.
Nitpick: China doesn't have a monopoly on rare earth metals, they just have the least restrictive policies on mining them, and they won't export the raw materials which forces companies to bring their processing operations into china.
The US has plenty of rare earths, they just always come up with thorium, which regulators regard as a nuclear waste that must be disposed of at exorbitant cost to the mine operators.
As others have stated, China does not have a monopoly, but they do supply 95% of rare-earth metals, and have been buying mines in other countries, which is leading to a monopoly type situation.
The linked page describes this as something that "absolutely belongs up on the Model S Facts page". Is there anything particularly negative about rare earth metals aside from their potential scarcity?
Edit: fersho311 answers my question in the same minute I ask it. Thanks :)
Why is this notable, beyond possibly price associated with them? The only issue with rare earth metals is that at various times the supply of them has been politically shaky, though I think that is currently not the case? I'm not really sure...
currently not the case, as the US has spun up rare earth metal mines (molycorp, e.g.) also the environmental concerns are less (not to say they are nonexistent) when the US does it because we tend to care about the environment more than china does, especially in california.
Also don't be decieved by the term, rare earth metals aren't really all that rare. If anything their expense comes from the difficulty in extracting them selectively from their ores - because rare earths are chemically similar (has to do with the f electron shell being physically "buried" under the d and s shells) they tend to ore together, and then become tricky to separate.
It would be possible to build a more compact motor using NFeB
magnets, but the cost outweighs the slight weight/performance gain. It is also my understanding that induction motor that Tesla uses is more efficient at regenerative braking.
Because they want to have DC motors, while Tesla uses an AC motor. There are various advantages disadvantages to both. DC motors require permanent magnets. The AC motor on the other hand has the problem that the power coming out of the battery is DC. So it has to be converted back to AC in order to be used in an AC motor.
The Tesla has a large inverter that converts the DC to AC. Most other makers choose to have a DC motor in order to remove the need for an inverter.
Some people joke that Tesla chose an AC motor, because that was the motor invented by Nicola Tesla. But the AC motor has other advantages such as its excellent torque curve. The latter ensures that the model s has no gearbox while it features amazing acceleration at all speeds.
Well, I know for a fact that the Leaf also uses an AC motor with an inverter. It's documented all over the place. But, they have permanent magnets in theirs, while Tesla apparently does not.
I think the point the poster is trying to get across is that there are no more rare earth metals in a Tesla model S than any other car of its class. Of course there may be some small amount of rare earth metals in the speakers or the electronics, but this is not an increase from any other car.
The issue of rare earth metals was used by some nay-sayers to incorrectly argue that the Tesla model S is more environmentally damaging than equivalent gasoline powered cars.
The typical hipster that would complain about "rare earth" metals in a car they'll never afford doesn't care about the rare earth in their iPhone or iPad (which is one of the reasons they are made in China).
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