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Practical Magnetic Levitating Transmission Gear System Loses Its Teeth
Zothecula writes: A new transmission device that uses magnetic levitation to almost completely eliminate friction and wear has been developed as part of the MAGDRIVE research project, a collaboration of seven European nations. The creation of the unit entailed the development of a magnetic gear reducer and corresponding frictionless magnetic axles. Aimed primarily for use in spacecraft due to its extended mechanical life, the system is also adaptable for use in automobiles, railways, and aircraft.
On 5-10 years back about classic cars from some museum in SoCal or something.
The 3 primary vehicles they discussed were:
A 1900s era Battery Powered car with a 25 mile range.
A Steam powered car capable of 'gas-like' performance, given ample 'warmup' time.
And a 1920s or 30s electrocoupled automatic transmission car that I believe used increasing rotational speed to more closely couple the engine to the output shaft (Can't remember if it also had gears or if the coupling mechanism doubled as the 'gears'.)
Point being: So they're finally getting back to R&D on 'non-mechanical' coupling mechisms in modern vehicles. Yay! Only took like 90 years.
Research into the 'most exciting aspect' (room temperature gearbox) part of this has been done before:
http://www.magnomatics.com/technology/magnetic-gears.aspx
But the idea of using the low temperature and vacuum of space to run superconducting systems seems quite innovative.
One of the main limitations with magnetic gears is that material properties (the saturation flux density of iron/cobalt basically) limits the amount of force that can be transmitted across the airgap. If the motion is being generated by an electric motor in the first place, then it doesn't really make sense to attach this to a magnetic gearbox - you might as well just direct drive the system. Whether the airgap sheer stress is being generated by rotating permanent magnets or sequenced electromagnets, the final torque/speed output limits will be limited by the same physics.
I'm sure there are special applications, but don't expect to see this in your day to day life any time soon.
I think that the Voyager probes would have been happier with a working instrument platform rather than with an efficient but broken one.
Ezekiel 23:20
It looks too bulky to provide a lot of gears in an automotive application, but if it could provide just two that you couldn't strip out no matter how much torque you put through them, it could be a really nice match for EVs. They would benefit from a transmission, but it's difficult for any transmission of a reasonable size to handle the output torque.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
Way more efficient than gears for loads it's designed to handle - but it's not meant for heavy lifting; the "magnetic gears" will "slip" if the load is too high, and in this case "too high" is quite low (think force required to move two magnets oriented in "repulsing" way against each other).
It would be great for stuff like stabilizing flywheels - things that once set in motion stay in motion for years, and may take a long time to spin up or stop. It would work well for things that require very little force, like reorienting the solar panels or aiming the antenna.
OTOH, stuff like lander wheel bearings or drills for picking samples are better handled with normal bearings that can take much heavier loads.
It's not a cure-all solution, it's just a good new option for specific applications. You won't use it to build a better crane but gyroscope flywheels could immensely benefit from that!
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Way more efficient than gears for loads it's designed to handle - but it's not meant for heavy lifting; the "magnetic gears" will "slip" if the load is too high, and in this case "too high" is quite low (think force required to move two magnets oriented in "repulsing" way against each other).
If you couldn't move high forces with a transmission like this, then you also couldn't generate them with an electric motor, because you couldn't hope for the magnetic fields to turn the stator against high loads.
OTOH, stuff like lander wheel bearings or drills for picking samples are better handled with normal bearings that can take much heavier loads.
What happens when you put too much torque through a drill? You shatter your bit. What happens when you put too much torque through an axle? All kinds of exciting things can happen, check out some four wheeling videos. There's lots of reasons why some slip designed into the system is not an undesirable thing.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
The question is, how much force can it handle? Large electro-mags can pick up entire cars. Sure, it's huge, but it's lifting up 2700 lbs+. Also the surface area is large because the objects surface area is large. If a really high powered small electro mag was used, it would just rip out that piece of metal.
How many pounds of force can the small one withstand? It's possible using two small unpowered magnets to easily make one that could crush a hand if a hand was implace and restraints were let go on the mags.
I imagine it could potentially with a little voltage withstand a lot of torque, and limited slip to prevent spin outs, it might be fantastic for rovers.
They're often in lower gravity environments to begin with.
The other point being that it could be designed only to replace the kinetic friction parts of a transmission, the parts that synchronize the system. The gearing itself can probably still be mechanical. Not having to replace clutch plates, for example, might be a nice and relatively easily doable thing.
Even when the experts all agree, they may well be mistaken. --- Bertrand Russell.
3 N-m on the output of the reducer.
For the confused: A milk float is a small flatbed vehicle for delivering milk, and not an alternative name for a milkshake.
When our name is on the back of your car, we're behind you all the way!
The rest of the universe always acts upon. One of the laws of thermodynamics.
When our name is on the back of your car, we're behind you all the way!
A magnetic clutch.
Life is not for the lazy.
We already have extremely low friction fluid-drive connections, they're called torque converters.
Do not look into laser with remaining eye.
It would work well for things that require very little force, like reorienting the solar panels or aiming the antenna
Maybe you should look into this natural phenomena called "wind". It's there in many parts of the world. It's something that can put massive forces on things like solar panels, and to a lesser extent antennas.
I'm confused. Doesn't "loses its teeth" mean that it has failed and/or become less powerful? I was expecting to hear how the research had failed.
When our name is on the back of your car, we're behind you all the way!
Deep-space power systems to run big space probes like Galileo and Cassini are nuclear powered, but use incredibly inefficient RTG... which are only 1-2% efficient.
Somebody (US Department of Energy) was looking to boost this by using a plutonium heat source to drive a Sterling engine coupled to a generator. The problem with this arrangement is that moving parts wear out.
It just so happens that deep space is very cold...
Just like IC motors, electric motors do not provide constant power/torque across their whole speed range. There's a reason why cordless drills often have two or three speed transmissions.
A typical universal motor generates max torque just before it stalls, and relatively little torque at high speed. This is great for fast acceleration from a standstill, not so much for trying to hit maximum speed with just a single-speed gearbox.
This should really be looked at by those producing Diesel engines for Airplanes.
The biggest problem tinker's face when trying to put a Diesel engine on an airplane is that the Diesel has very massive "power surges" each time a cylinder fires, and a nasty power "stall" when it's compressing a cylinder. This isn't a huge deal with the other applications of Diesel engines, they just add mass to the fly-wheel and transmission and that takes care of it. In Airplanes however, the mass costs too much (in terms of airplane weight) so they try to reduce it as much as possible, however if you reduce it too much the propeller is literally torn apart by the surges and stalls. Early tests had the propeller lasting only hours when running on a 4 or 6 cylinder diesel. If there is a reduction drive on it to bring the RPMs further down they too like to self destruct with a Diesel.
If they could use a low-weight magnetic coupler to absorb the surges and stalls and provide smooth power that would solve the biggest problem putting a diesel on an airplane and would really boost that market!
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AARON: Villain, I have done thy mother.
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If you couldn't move high forces with a transmission like this, then you also couldn't generate them with an electric motor, because you couldn't hope for the magnetic fields to turn the stator against high loads.
Electric motors can stall, and when they do so they draw a terrifyingly huge amount of power compared to when they're operating properly. Providing that static torque is very expensive and often dangerous unless the motor and controls were designed for it.
It's not that magnetic fields can't be strong enough, it's getting fields that are strong enough without additional energy input.
=Smidge=
We already have extremely low friction fluid-drive connections, they're called torque converters.
Yes, but you have to be already making use of fluid pressure for that to be worth using, and they have lots of drawbacks. Some hybrids replace the TC with an electric motor already, starting with the Honda Insight and including Subaru's hybrids. This is already a form of magnetic coupling, and the only friction comes from the bearings themselves. It is capable of doing the TC's job, plus giving full-drivetrain power — and regenerative braking.
In an EV, obviously, we can eliminate the ICE and otherwise use basically the same system, with a larger electric motor. But as Tesla has demonstrated, it actually makes more sense to use a motor per axle, if you don't have an ICE involved.
Torque converters are going away in favor of other solutions, because they are crappy.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
Electric motors can stall, and when they do so they draw a terrifyingly huge amount of power compared to when they're operating properly.
Part of the motor controller's job is to prevent that, but it's irrelevant here, because they're using permanent magnets. The maglev bearings have to be cooled, but the part of the transmission that provides the gearing doesn't require any power at all. You design the system for the torques you're expecting to see and you get limited slip out of it for free. This part of the system could be used even without the maglev bearings, to eliminate gear friction and to prevent damage in the case of a lockup. If I were designing the system for an off-road vehicle, I'd want to have a physical clutch available as a backup in my lowest gear, but for on-road use it shouldn't be a problem at all. As long as just one axle can provide enough motive force to move the car up the steepest hills it's meant to manage, and the brakes are present to lock up any wheels which are spinning (Bosch calls this EDL, and Porsche and VW have been using it since the nineties, often with a torsen diff but sometimes just an open one) then then the rest is just tuning.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
The question is, how much force can it handle?
The video says it has a max input speed of 3000 rpm and a max output torque of 3Nm (~4 ft/lbs) with a gear reduction of 1:20.
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o0t!
Your argument basically boils down to "since electric motors can produce high torque, then permanent magnet couplings can also provide high torque"
My contention is you make it sound way, way simpler than it is. Also, you'll find that the really big motors are not the permanent magnet type exactly because producing a high-torque motor with permanent magnets is more difficult and expensive. It's an issue of flux density.
I'm sure you COULD design a permanent magnet coupling for any particular purpose, but that doesn't mean it makes sense to do so.
=Smidge=
Your argument basically boils down to "since electric motors can produce high torque, then permanent magnet couplings can also provide high torque"
Yeah, pretty much.
Also, you'll find that the really big motors are not the permanent magnet type exactly because producing a high-torque motor with permanent magnets is more difficult and expensive.
Mostly expensive.
I'm sure you COULD design a permanent magnet coupling for any particular purpose, but that doesn't mean it makes sense to do so.
Well, TFA says they did it already, and I suspect they're smarter than you are (or me, to be fair) so I suspect you're on about nothing.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
Look, this great shiny technology. Oops, it's uneconomical...
Costs are an important question as this story happens quite often (mag trains anyone?).
For space projects the cost may not matter, since it's paid for by taxpayers. But for applications for the rest of us making this affordable is as important, if not more.
These comments are mine; I do not speak for my employer.
As the AC said, for a very limited torque; 15 Newton-Meters. For a sense of scale, the recommended torque on a lug nut for a car tire is typically around 8-10 times that.
It's also under cryogenic conditions, intended for space applications, which is a rather special case (ultra-reliable under extreme environments) where it makes makes more sense to use something exotic.
And having said that, the more I learn about it the less I'm impressed with it. Magnetic bearings are pretty old hat technologically speaking, and the harmonic drive aspect is only novel in that it uses magnetic repulsion to flex the spline cup rather than physical contact. Meh. Even their "through-wall transmission" thing is a glorified magnetic stirrer.
=Smidge=
As the AC said, for a very limited torque; 15 Newton-Meters. For a sense of scale, the recommended torque on a lug nut for a car tire is typically around 8-10 times that.
Please forgive my ignorance Smidge but I find that number quite astounding although I have no reason to doubt your comment.
Isn't 150NM about what a small car is putting out in terms of torque? Admittedly one (rightly or wrongly) is supposed to stand on lug nuts to tighten them properly, is this what is meant here?
Just seems quite a lot to me with my limited understanding of the topic.
..Mullah or Pope, Preacher or Poet, who was it wrote: "Give any one species too much rope and they'll fuck it up"?
Not having to replace clutch plates, for example, might be a nice and relatively easily doable thing.
Probably not worth it. A properly functioning clutch should have minimal parasitic loss from friction when engaged, so the only thing you're saving is the cost of replacing the clutch. Since clutches are usually easy to replace and relatively cheap, especially compared to the cost of something like this, it's probably throwing money away.
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Yeah, so could you give me an estimate on the massive force of solar wind pressure against solar panels of a space probe?
Oh, wait, the linked article has it. At 1AU, typically in the range of 1–6 nanonewtons per square meter.
Yeah, massive indeed. The bearings stand no chance.
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150Nm is about what a typical small car engine might be capable of at peak, but torque at the wheels would typically be greater due to gear reductions. Not really relevant, though - the torque of the engine applied to the wheels is not applied to the lug nuts on the wheels as a torque, but applied to the lugs themselves as a shear.
Maybe imperial units will help?
15 Newton-meters is roughly 11 foot-pounds. Most people can comfortably apply that kind of torque with a normal wrench, and that's about twice what a strong person could do with a screwdriver.
Torque specifications for lug nuts are typically in the 80 to 120 foot-pound range, though practically nobody outside of a reputable auto shop will bother with that (and even most reputable shops will gloss over it...). Most people, including myself, either use an impact gun or step on the lug wrench, which results in slight over-tightening. Figure a 150-lb person standing on a 12" long wrench and that's 150 ft-lbs... slightly over but not too bad.
For gasoline car engines, torque (ft-lbs) seems to always be fairly close to horsepower... so 120 ft-lbs is about right for a 120hp engine, plus or minus. It boils down to the fact that most gasoline engines are designed to run at a certain RPM, which makes the math turn out that these two metrics are often within maybe 10% of each other.
=Smidge=
Great explanation, thank you very much. :)
..Mullah or Pope, Preacher or Poet, who was it wrote: "Give any one species too much rope and they'll fuck it up"?
(Hydraulic) torque converters are at very best 95% efficient, which sucks. Why do you think heavy vehicles with automatic transmissions require a separate radiator for the transmission?
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the torque of the engine applied to the wheels is not applied to the lug nuts on the wheels as a torque, but applied to the lugs themselves as a shear.
And that is why lug nut torque is entirely irrelevant. Guess what? Small car, flat surface, don't set the brake, you'll move the car while tightening the lug nuts. But it's still irrelevant.
Torque specifications for lug nuts are typically in the 80 to 120 foot-pound range, though practically nobody outside of a reputable auto shop will bother with that (and even most reputable shops will gloss over it...)
There is no such thing as a reputable shop which won't torque your lug nuts to specification, only idiots who can't identify a reputable shop. My tire shop always torques my lug nuts with a torque wrench, to spec, and so do I. Not doing so risks a wheel falling off.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
You're probably right. Although I've had a standard transmission car go through 100% of its clutch plate and they are not cheap to replace. But what is? And how many cars have standard transmissions any more? And of those, how many go through a whole clutch plate before they die from some other cause. Toyota's magnetic regenerative braking system suggests that one "can" mass produce the requisite magnetic coupling, but there probably isn't a compelling reason to do it in this case.
Even when the experts all agree, they may well be mistaken. --- Bertrand Russell.
You actually expect me to look up videos Myself ?
The new right fascists are bilingual. They speak English and Bullshit.
The point of transmission is not only "displacement" of rotary movement but also exchange of rotation speed for momentum. So, if (as the article says) the gear ratio is 1:20, it means the load on an axis two such transmissions away will be 400 times that of a motor.
And while, yes, the design makes the system safe against damage due to too high load, the load it can provide is still far away from load which could damage the mechanics; if the slippage was to occur at loads ten times as high, it would still be outside the self-damage zone.
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