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Question about Electic Motors
Most motors seem to have the same proportions of length to diameter so
there must be some theoretical principal there. However, I once operated a milling machine that had what was called a Pancake motor that drove the feeds. It was large diameter and only about 2 inches deep. Then there is the direct drive washing machine. Any website I should read to clear this in my mind. |
Question about Electic Motors
On Thu, 15 Feb 2018 12:46:24 GMT, DerbyBorn
wrote: Most motors seem to have the same proportions of length to diameter so there must be some theoretical principal there. However, I once operated a milling machine that had what was called a Pancake motor that drove the feeds. It was large diameter and only about 2 inches deep. Then there is the direct drive washing machine. Any website I should read to clear this in my mind. I designed, built and 'raced' an electric motorbike with the BVS and used a 24V DC motor that I believe was originally used in some aircraft application. At the time I was racing, a young lad called Cedric Lynch designed, build and raced his own two wheeler but also designed and built his own 'pancake' motor, that performed way better than pretty well anything available commercially at the time. Only one person ever beat him ... and that was just though (my) 'luck'. ;-) https://en.wikipedia.org/wiki/Lynch_motor http://lynchmotors.co.uk/ https://www.youtube.com/watch?v=KnqoH0YaCsE Cheers, T i m |
Question about Electic Motors
On 15/02/2018 12:46, DerbyBorn wrote:
Most motors seem to have the same proportions of length to diameter so there must be some theoretical principal there. However, I once operated a milling machine that had what was called a Pancake motor that drove the feeds. It was large diameter and only about 2 inches deep. Then there is the direct drive washing machine. Any website I should read to clear this in my mind. I don't know for sure, but it is easy to see how pancake motors might be a favourable geometry in some applications where space is tight for other reasons. But in a pancake motor, I suspect that both the armature and stator windings might be more difficult to make (and perhaps need more copper) than in a conventional geometry. There is also a bit more scope for "flux leakage". I suspect the conventional geometry will have arisen from manufacturing considerations. It is also now to some extent "locked in" because there are standard frame sizes. If you make a "long, thin" motor then the larger separation of bearings and thinner shaft give you more issues with vibration, especially at higher speeds. |
Question about Electic Motors
On 15/02/18 12:46, DerbyBorn wrote:
Most motors seem to have the same proportions of length to diameter so there must be some theoretical principal there. However, I once operated a milling machine that had what was called a Pancake motor that drove the feeds. It was large diameter and only about 2 inches deep. Then there is the direct drive washing machine. Any website I should read to clear this in my mind. Not really. There is no perfect size or shape for an electric motor - think linear motors!!! On general a given weight of iron will produce a given peak force, before the iron saturates so you can get more *torque|* with a larger *diameter* motor for the same amount of iron, BUT it wont rev so highly so its power won't be any higher Low RPM high torque - or high RPM low torque. If you dont want a gearbox you may well tend towards pancake. long thin motors rev very highly and can be very high power to weight - but you may need a gearbox to get down from 100k plus RPM -- Those who want slavery should have the grace to name it by its proper name. They must face the full meaning of that which they are advocating or condoning; the full, exact, specific meaning of collectivism, of its logical implications, of the principles upon which it is based, and of the ultimate consequences to which these principles will lead. They must face it, then decide whether this is what they want or not. Ayn Rand. |
Question about Electic Motors
Well it all depends on what sort of motor it is. All use magnetism in the
end and how the poles that repel and attract are arranged makes many shapes possible. Some direct drive motors operate via locally generated dc or different frequency ac. Thos generally are used when speed differences are required, unless the device has more than on motor, or has switch windings to make it change speed and torque. Brian -- ----- - This newsgroup posting comes to you directly from... The Sofa of Brian Gaff... Blind user, so no pictures please! "DerbyBorn" wrote in message 2.236... Most motors seem to have the same proportions of length to diameter so there must be some theoretical principal there. However, I once operated a milling machine that had what was called a Pancake motor that drove the feeds. It was large diameter and only about 2 inches deep. Then there is the direct drive washing machine. Any website I should read to clear this in my mind. |
Question about Electic Motors
"Brian Gaff" wrote in
: Well it all depends on what sort of motor it is. All use magnetism in the end and how the poles that repel and attract are arranged makes many shapes possible. Some direct drive motors operate via locally generated dc or different frequency ac. Thos generally are used when speed differences are required, unless the device has more than on motor, or has switch windings to make it change speed and torque. Brian I was thinking of the "leverage" effect of the magnetic field being greater at a bigger radius - or more of it if the armature was longer. --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
Question about Electic Motors
On 15/02/18 21:42, DerbyBorn wrote:
"Brian Gaff" wrote in : Well it all depends on what sort of motor it is. All use magnetism in the end and how the poles that repel and attract are arranged makes many shapes possible. Some direct drive motors operate via locally generated dc or different frequency ac. Thos generally are used when speed differences are required, unless the device has more than on motor, or has switch windings to make it change speed and torque. Brian I was thinking of the "leverage" effect of the magnetic field being greater at a bigger radius - or more of it if the armature was longer. yes, but thats just torque. Bigger diameters can't rev as much so teh power generally is no better. It just avoids the need for a gearbox, thats all --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus -- Gun Control: The law that ensures that only criminals have guns. |
Question about Electic Motors
On Thu, 15 Feb 2018 23:25:07 +0000, The Natural Philosopher
wrote: On 15/02/18 21:42, DerbyBorn wrote: "Brian Gaff" wrote in : Well it all depends on what sort of motor it is. All use magnetism in the end and how the poles that repel and attract are arranged makes many shapes possible. Some direct drive motors operate via locally generated dc or different frequency ac. Thos generally are used when speed differences are required, unless the device has more than on motor, or has switch windings to make it change speed and torque. Brian I was thinking of the "leverage" effect of the magnetic field being greater at a bigger radius - or more of it if the armature was longer. yes, but thats just torque. Bigger diameters can't rev as much so teh power generally is no better. I guess that can depend on the design of the motor. For example, if you had a PM DC motor and were able to back off the power of the permanent magnets using a coil (coils), then you could allow the motor to rev higher once you had made best use of the lower rev torque. It certainly seemed to work well from what I saw as it sailed past me .... stuck at max rpm on my conventional PM motor. ;-( Cheers, T i m |
Question about Electic Motors
In article 6,
DerbyBorn writes: Most motors seem to have the same proportions of length to diameter so there must be some theoretical principal there. However, I once operated a milling machine that had what was called a Pancake motor that drove the feeds. It was large diameter and only about 2 inches deep. Then there is the direct drive washing machine. Any website I should read to clear this in my mind. Larger diameter motors have lower max speeds above which the forces on the armature will break it. Larger diameter motors also allow space for more poles giving lower speed higher torque characteristics. To increase torque with a given diameter, the motor body can be made longer. Obviously, there may be physical constraints on fitting a motor into a given space too. Some mains tools/appliances with limited space will use a DC motor with a rectifier, because it enables replacing the field windings on what would have been a universal motor with a permanent magnet which can be made significantly smaller than a set of field windings, and reduce the outer diameter. -- Andrew Gabriel [email address is not usable -- followup in the newsgroup] |
Question about Electic Motors
On Thursday, 15 February 2018 12:46:29 UTC, DerbyBorn wrote:
Most motors seem to have the same proportions of length to diameter so there must be some theoretical principal there. However, I once operated a milling machine that had what was called a Pancake motor that drove the feeds. It was large diameter and only about 2 inches deep. Then there is the direct drive washing machine. Any website I should read to clear this in my mind. Most elecric induction motors run at near synchronous speed or half or one third. The speed they run at is determined by the number of (pairs of) poles. Either 1, 2 or 3, Low speeds are obtained by use of pulleys or gearboxes with these motors. However"pancake" motors have many more poles and hence run much slower. It's become feasible to have slow speed motors with many permanent magnets/poles when neodymium magnets were developed. This can do away with the neccesity for gearboxes. They started off very small but now there are bigger ones. https://en.wikipedia.org/wiki/Electr...al_rotor_motor |
Question about Electic Motors
On Fri, 16 Feb 2018 14:01:39 +0000, Andrew Gabriel wrote:
In article 6, DerbyBorn writes: Most motors seem to have the same proportions of length to diameter so there must be some theoretical principal there. However, I once operated a milling machine that had what was called a Pancake motor that drove the feeds. It was large diameter and only about 2 inches deep. Then there is the direct drive washing machine. Any website I should read to clear this in my mind. Larger diameter motors have lower max speeds above which the forces on the armature will break it. Larger diameter motors also allow space for more poles giving lower speed higher torque characteristics. To increase torque with a given diameter, the motor body can be made longer. Obviously, there may be physical constraints on fitting a motor into a given space too. Some mains tools/appliances with limited space will use a DC motor with a rectifier, because it enables replacing the field windings on what would have been a universal motor with a permanent magnet which can be made significantly smaller than a set of field windings, and reduce the outer diameter. Not only that but the use of the latest rare earth magnets means less copper can be used for a more efficient motor or else the space within the motor taken up by *both* rotor and stator windings can be concentrated to the stator (DC Brushless motor example) allowing even heavier gauge wire again than the reduced turns that the much stronger magnetic field produced by powerful rare earth magnets allows, resulting in a considerably more powerful motor for a given volume or mass. It's the use of rare eath magnets in those tiny motors used in drones that allows them to achieve more useful endurance times out of their LiPo battery packs (much greater power to weigh ratios out of what generally makes up most of their mass). Indeed, I'm surprised that they haven't replaced the complex mechanical transmissions that seem to still curse most electric cars today by being incorporated as part of each wheel where the transmission is entirely heavy duty cable (with a specially flexible section to feed the power past the suspension to the hub motors), reducing the 'gearbox' to nothing more than a sophisticated program controlled heavy duty switch mode converter. This might not suit the handling demands of a more extreme performance road car but it should do nicely for a typical family saloon or small runabout. -- Johnny B Good |
Question about Electic Motors
Johnny B Good wrote:
It's the use of rare eath magnets in those tiny motors used in drones that allows them to achieve more useful endurance times out of their LiPo battery packs (much greater power to weigh ratios out of what generally makes up most of their mass). Indeed, I'm surprised that they haven't replaced the complex mechanical transmissions that seem to still curse most electric cars today by being incorporated as part of each wheel where the transmission is entirely heavy duty cable (with a specially flexible section to feed the power past the suspension to the hub motors), reducing the 'gearbox' to nothing more than a sophisticated program controlled heavy duty switch mode converter. This might not suit the handling demands of a more extreme performance road car but it should do nicely for a typical family saloon or small runabout. Given the huge environmental costs of rare earth element extraction its maybe no bad thing that theyre not being used in the booming electric car market. If Tesla can manage without them I reckon thats good enough for most of us. Additionally, €śmotor in hub€ť adds hugely to unsprung weight (which isnt supposed to be a good thing). I appreciate that this might be mitigated by the use of rare earth magnet motors but that brings us back to the environmental problems again. As Im sure you know, €śrare earth elements€ť arent actually rare, just fecking difficult, dirty and expensive to extract. https://e360.yale.edu/features/boom_..._toxic_ri sks Tim -- Please don't feed the trolls |
Question about Electic Motors
On Friday, 16 February 2018 18:39:21 UTC, Tim+ wrote:
Johnny B Good wrote: It's the use of rare eath magnets in those tiny motors used in drones that allows them to achieve more useful endurance times out of their LiPo battery packs (much greater power to weigh ratios out of what generally makes up most of their mass). Indeed, I'm surprised that they haven't replaced the complex mechanical transmissions that seem to still curse most electric cars today by being incorporated as part of each wheel where the transmission is entirely heavy duty cable (with a specially flexible section to feed the power past the suspension to the hub motors), reducing the 'gearbox' to nothing more than a sophisticated program controlled heavy duty switch mode converter. This might not suit the handling demands of a more extreme performance road car but it should do nicely for a typical family saloon or small runabout. Given the huge environmental costs of rare earth element extraction its maybe no bad thing that theyre not being used in the booming electric car market. If Tesla can manage without them I reckon thats good enough for most of us. Additionally, €śmotor in hub€ť adds hugely to unsprung weight (which isnt supposed to be a good thing). I appreciate that this might be mitigated by the use of rare earth magnet motors but that brings us back to the environmental problems again. As Im sure you know, €śrare earth elements€ť arent actually rare, just fecking difficult, dirty and expensive to extract. https://e360.yale.edu/features/boom_..._toxic_ri sks Tim unsprung mass kills road holding. You could always use 2 inboard motors rather than 4 in wheels. NT |
Question about Electic Motors
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Question about Electic Motors
On Fri, 16 Feb 2018 12:18:25 -0800, tabbypurr wrote:
On Friday, 16 February 2018 18:39:21 UTC, Tim+ wrote: Johnny B Good wrote: It's the use of rare eath magnets in those tiny motors used in drones that allows them to achieve more useful endurance times out of their LiPo battery packs (much greater power to weigh ratios out of what generally makes up most of their mass). Indeed, I'm surprised that they haven't replaced the complex mechanical transmissions that seem to still curse most electric cars today by being incorporated as part of each wheel where the transmission is entirely heavy duty cable (with a specially flexible section to feed the power past the suspension to the hub motors), reducing the 'gearbox' to nothing more than a sophisticated program controlled heavy duty switch mode converter. This might not suit the handling demands of a more extreme performance road car but it should do nicely for a typical family saloon or small runabout. Given the huge environmental costs of rare earth element extraction its maybe no bad thing that theyre not being used in the booming electric car market. If Tesla can manage without them I reckon thats good enough for most of us. Additionally, €śmotor in hub€ť adds hugely to unsprung weight (which isnt supposed to be a good thing). I appreciate that this might be mitigated by the use of rare earth magnet motors but that brings us back to the environmental problems again. As Im sure you know, €śrare earth elements€ť arent actually rare, just fecking difficult, dirty and expensive to extract. https://e360.yale.edu/features/ boom_in_mining_rare_earths_poses_mounting_toxic_ri sks Tim unsprung mass kills road holding. You could always use 2 inboard motors rather than 4 in wheels. I deliberately made the caveat about their unsuitability for high performance road cars on account of the 'unsprung mass' issue but I feel that a fully integrated hub motor will weigh little more than the steel wheels currently used by most saloon cars today (and may possibly prove to be slightly lighter through the use of suitable materials). They'd be a horrible compromise for a high performance car but most likely a more than acceptable compromise for a 'standard electric road' car, considering the elimination of the weight and expense of a klunky space consuming mechanical transmission system. A fully developed active energy recovery suspension system could ultimately overcome this problem of 'unsprung mass'. It's also worth remembering that the suspension components themselves (spring, damper and drive shaft on each driven wheel) form a part of this 'unsprung mass'. Also, let's not forget the mass of the disk brake assemblies which, with regenerative braking, can be reduced in size thus offering yet a further reduction in 'unsprung mass'. This latter weigh saving would require an emergency electric backup in the event that the normal regenerative braking system suffers a failure that could result in burning out the downsized disk brakes on a long and steep descent. I'm sure such risks can ultimately be addressed if given sufficient thought and development. :-) -- Johnny B Good |
Question about Electic Motors
On Saturday, 17 February 2018 02:27:01 UTC, The Natural Philosopher wrote:
On 16/02/18 20:18, tabbypurr wrote: unsprung mass kills road holding. You could always use 2 inboard motors rather than 4 in wheels. If the motor mostly replaces the shaft and disc brake its a tossup whether its heavier or not a motor of such low weight would have little performance NT |
Question about Electic Motors
On Saturday, 17 February 2018 06:38:06 UTC, Johnny B Good wrote:
On Fri, 16 Feb 2018 12:18:25 -0800, tabbypurr wrote: On Friday, 16 February 2018 18:39:21 UTC, Tim+ wrote: Johnny B Good wrote: Additionally, €śmotor in hub€ť adds hugely to unsprung weight (which isnt supposed to be a good thing). I appreciate that this might be mitigated by the use of rare earth magnet motors but that brings us back to the environmental problems again. As Im sure you know, €śrare earth elements€ť arent actually rare, just fecking difficult, dirty and expensive to extract. https://e360.yale.edu/features/ boom_in_mining_rare_earths_poses_mounting_toxic_ri sks Tim unsprung mass kills road holding. You could always use 2 inboard motors rather than 4 in wheels. I deliberately made the caveat about their unsuitability for high performance road cars on account of the 'unsprung mass' issue but I feel that a fully integrated hub motor will weigh little more than the steel wheels currently used by most saloon cars today (and may possibly prove to be slightly lighter through the use of suitable materials). the wheels are still required. A low speed motor must necessarily be large, and that means a lot more weight than the wheels. The resulting heaviness is unsuitable for ordinary road holding performance. They'd be a horrible compromise for a high performance car but most no, they're not be compatible with high performance at all likely a more than acceptable compromise for a 'standard electric road' car, considering the elimination of the weight and expense of a klunky space consuming mechanical transmission system. they'd increase unsprung weight greatly. Good enough for a low speed bus. A fully developed active energy recovery suspension system could ultimately overcome this problem of 'unsprung mass'. it can't It's also worth remembering that the suspension components themselves (spring, damper and drive shaft on each driven wheel) form a part of this 'unsprung mass'. suspension can't be eliminated Also, let's not forget the mass of the disk brake assemblies which, with regenerative braking, can be reduced in size thus offering yet a further reduction in 'unsprung mass'. not really, the friction brakes still need to stop the car from top speed. This latter weigh saving would require an emergency electric backup in the event that the normal regenerative braking system suffers a failure you can't back up a safe braking system with an inherently unsafe one that could result in burning out the downsized disk brakes on a long and steep descent. that's easy to work around with electronics. Use regenerative braking. Also monitor brake temp, and warn then stop the car if too hot. NT I'm sure such risks can ultimately be addressed if given sufficient thought and development. :-) |
Question about Electic Motors
DerbyBorn wrote in
2.236: "Brian Gaff" wrote in : Well it all depends on what sort of motor it is. All use magnetism in the end and how the poles that repel and attract are arranged makes many shapes possible. Some direct drive motors operate via locally generated dc or different frequency ac. Thos generally are used when speed differences are required, unless the device has more than on motor, or has switch windings to make it change speed and torque. Brian I was thinking of the "leverage" effect of the magnetic field being greater at a bigger radius - or more of it if the armature was longer. --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus Thanks all - very enlightening stuff |
Question about Electic Motors
In article ,
Andrew Gabriel wrote: Larger diameter motors have lower max speeds above which the forces on the armature will break it. Larger diameter motors also allow space for more poles giving lower speed higher torque characteristics. To increase torque with a given diameter, the motor body can be made longer. Yes - remember a pretty advanced design of 1/4" tape recorder. Had twin capstans with direct drive. And they stopped turning when the tape stopped running. They were pancake motors. Had a very fast start up time. That would explain it. -- *Kill one man and you're a murderer, kill a million youand 're a conqueror. Dave Plowman London SW To e-mail, change noise into sound. |
Question about Electic Motors
Tim+ wrote:
Given the huge environmental costs of rare earth element extraction its maybe no bad thing that theyre not being used in the booming electric car market. If Tesla can manage without them I reckon thats good enough for most of us. Tesla are using rare-earth magnet motors in (some of?) their Model 3. |
Question about Electic Motors
On 17/02/18 13:12, Andy Burns wrote:
Tim+ wrote: Given the huge environmental costs of rare earth element extraction its maybe no bad thing that theyre not being used in the booming electric car market. If Tesla can manage without them I reckon thats good enough for most of us. Tesla are using rare-earth magnet motors in (some of?) their Model 3. High strength magnets merely reduce the weight of the motor, You can get as high flux densities and efficiences using electromagnets -- The biggest threat to humanity comes from socialism, which has utterly diverted our attention away from what really matters to our existential survival, to indulging in navel gazing and faux moral investigations into what the world ought to be, whilst we fail utterly to deal with what it actually is. |
Question about Electic Motors
On 17/02/2018 13:25, The Natural Philosopher wrote:
On 17/02/18 13:12, Andy Burns wrote: Tim+ wrote: Given the huge environmental costs of rare earth element extraction its maybe no bad thing that theyre not being used in the booming electric car market. If Tesla can manage without them I reckon thats good enough for most of us. Tesla are using rare-earth magnet motors in (some of?) their Model 3. High strength magnets merely reduce the weight of the motor, You can get as high flux densities and efficiences using electromagnets Probably higher, but these take power, unless you're talking superconductors? In terms of energy, a magnet is 100% efficient at providing a magnetic field. |
Question about Electic Motors
The Natural Philosopher wrote:
Andy Burns wrote: Tim+ wrote: If Tesla can manage without them I reckon thats good enough for most of us. Tesla are using rare-earth magnet motors in (some of?) their Model 3. High strength magnets merely reduce the weight of the motor, You can get as high flux densities and efficiences using electromagnets I guess that's why they waited until the change of Model S and Model X, to Model 3 (lighter, lower capacity battery, cheaper) to change motor. AFAIK "rare" earths aren't especially rare, just that nowadays only China seems to bother mining them, still they'll probably dig out lots of Thorium while they're at it ... |
Question about Electic Motors
On 17/02/18 14:43, Andy Burns wrote:
AFAIK "rare" earths aren't especially rare, just that nowadays only China seems to bother mining them, still they'll probably dig out lots of Thorium while they're at it ... China dumped them on the market well below cost, driving out the other mines, then only exported refined materials and finished goods once the competition had gone. Cunning really. -- "Anyone who believes that the laws of physics are mere social conventions is invited to try transgressing those conventions from the windows of my apartment. (I live on the twenty-first floor.) " Alan Sokal |
Question about Electic Motors
Andy Burns wrote:
AFAIK "rare" earths aren't especially rare, just that nowadays only China seems to bother mining them, I think its more a case of €śChina being one of the very few countries prepared to accept the horrendous environmental cost of refining€ť. Tim -- Please don't feed the trolls |
Question about Electic Motors
On 17/02/2018 06:38, Johnny B Good wrote:
A fully developed active energy recovery suspension system could ultimately overcome this problem of 'unsprung mass'. It's also worth remembering that the suspension components themselves (spring, damper and drive shaft on each driven wheel) form a part of this 'unsprung mass'. Also, let's not forget the mass of the disk brake assemblies which, with regenerative braking, can be reduced in size thus offering yet a further reduction in 'unsprung mass'. If you're going to put a drive shaft for each wheel connected to an electric motor why not put the disc inboard next to it? That would really cut the unsprung weight (to just half the shaft) Andy |
Question about Electic Motors
Vir Campestris wrote:
On 17/02/2018 06:38, Johnny B Good wrote: A fully developed active energy recovery suspension system could ultimately overcome this problem of 'unsprung mass'. It's also worth remembering that the suspension components themselves (spring, damper and drive shaft on each driven wheel) form a part of this 'unsprung mass'. Also, let's not forget the mass of the disk brake assemblies which, with regenerative braking, can be reduced in size thus offering yet a further reduction in 'unsprung mass'. If you're going to put a drive shaft for each wheel connected to an electric motor why not put the disc inboard next to it? That would really cut the unsprung weight (to just half the shaft) Andy One problem with that is that it moves the disc (and pads) out of reach of easy inspection/service. Tim -- Please don't feed the trolls |
Question about Electic Motors
On Sat, 17 Feb 2018 18:07:34 +0000, Tim+ wrote:
Vir Campestris wrote: On 17/02/2018 06:38, Johnny B Good wrote: A fully developed active energy recovery suspension system could ultimately overcome this problem of 'unsprung mass'. It's also worth remembering that the suspension components themselves (spring, damper and drive shaft on each driven wheel) form a part of this 'unsprung mass'. Also, let's not forget the mass of the disk brake assemblies which, with regenerative braking, can be reduced in size thus offering yet a further reduction in 'unsprung mass'. If you're going to put a drive shaft for each wheel connected to an electric motor why not put the disc inboard next to it? That would really cut the unsprung weight (to just half the shaft) Andy One problem with that is that it moves the disc (and pads) out of reach of easy inspection/service. The real problem with that is the possibility of a high speed wheel lockup under emergency braking snapping the drive shaft as a result of the rotational energy stored in the wheel. You want to decouple the mass of the brake assembly from the unsprung mass but not at the risk of completely disconnecting it from the wheel in an emergency braking situation. -- Johnny B Good |
Question about Electic Motors
On Fri, 16 Feb 2018 23:44:48 -0800, tabbypurr wrote:
On Saturday, 17 February 2018 02:27:01 UTC, The Natural Philosopher wrote: On 16/02/18 20:18, tabbypurr wrote: unsprung mass kills road holding. You could always use 2 inboard motors rather than 4 in wheels. If the motor mostly replaces the shaft and disc brake its a tossup whether its heavier or not a motor of such low weight would have little performance You only need to observe the small size of the motors used on the TT lapping E- race bikes to see the absurdity of that statement. -- Johnny B Good |
Question about Electic Motors
On Sat, 17 Feb 2018 14:43:20 +0000, Andy Burns wrote:
The Natural Philosopher wrote: Andy Burns wrote: Tim+ wrote: If Tesla can manage without them I reckon thats good enough for most of us. Tesla are using rare-earth magnet motors in (some of?) their Model 3. High strength magnets merely reduce the weight of the motor, You can get as high flux densities and efficiences using electromagnets I guess that's why they waited until the change of Model S and Model X, to Model 3 (lighter, lower capacity battery, cheaper) to change motor. AFAIK "rare" earths aren't especially rare, just that nowadays only China seems to bother mining them, still they'll probably dig out lots of Thorium while they're at it ... .... which, if the urgently required development of MSR technology becomes realised, can only be "A Good Thing". :-) -- Johnny B Good |
Question about Electic Motors
Johnny B Good wrote:
On Sat, 17 Feb 2018 18:07:34 +0000, Tim+ wrote: One problem with that is that it moves the disc (and pads) out of reach of easy inspection/service. The real problem with that is the possibility of a high speed wheel lockup under emergency braking snapping the drive shaft as a result of the rotational energy stored in the wheel. Compared to the kinetic energy of a car I would have thought that the rotational energy of the wheel is relatively trivial.. I would agree that it introduces a new €śweak point€ť in the braking system though. Off the top of my head, Jaguar E-type, Rover 2000/3,500 and Citroen ZX all had inboard discs,. Did they have a reputation for snapping drive shafts? Tim -- Please don't feed the trolls |
Question about Electic Motors
On Sat, 17 Feb 2018 17:42:21 +0000, Tim+ wrote:
Andy Burns wrote: AFAIK "rare" earths aren't especially rare, just that nowadays only China seems to bother mining them, I think its more a case of €śChina being one of the very few countries prepared to accept the horrendous environmental cost of refining€ť. Which could, assuming Molten Salt Reactor (MSR) technology becomes the de-facto standard for nuclear power station design to tide us over the next half century or longer that it'll take for the dream of "Cheap Pollution Free Nuclear Fusion Power" to finally be realised, end the current fossil fuelled environmental problems resulting from the use of coal fired power stations. Whatever we do to power our high energy western lifestyle, there's always going to be a 'Pollution Problem'. Putting aside the issue of 'Nuclear Accidents', nuclear power by necessity, pollutes the environment far less than conventional coal fired plants do in regard of radioactive isotope emissions. The issue of 'Nuclear Waste' remains addressable even if it means simply locking it up and throwing away the key. Inherently safer LFTR based MSR technology can even help burn up the most lethally radioactive nuclear waste products to mitigate the problem of nuclear waste storage/disposal. On balance, China's interest in mining for rare earth elements (and the Thorium tailings) could well prove to be the lesser of two evils regarding the issue of planetwide pollution. -- Johnny B Good |
Question about Electic Motors
On Sat, 17 Feb 2018 10:28:42 +0000, Dave Plowman (News) wrote:
In article , Andrew Gabriel wrote: Larger diameter motors have lower max speeds above which the forces on the armature will break it. Larger diameter motors also allow space for more poles giving lower speed higher torque characteristics. To increase torque with a given diameter, the motor body can be made longer. Yes - remember a pretty advanced design of 1/4" tape recorder. Had twin capstans with direct drive. And they stopped turning when the tape stopped running. They were pancake motors. Had a very fast start up time. That would explain it. The fast startup times were more probably the result of employing solenoid operated pinch wheels. I'm sure the capstan motors were more likely kept spinning all the time the machine was powered up and ready to go. -- Johnny B Good |
Question about Electic Motors
On Sat, 17 Feb 2018 19:15:42 +0000, Tim+ wrote:
Johnny B Good wrote: On Sat, 17 Feb 2018 18:07:34 +0000, Tim+ wrote: One problem with that is that it moves the disc (and pads) out of reach of easy inspection/service. The real problem with that is the possibility of a high speed wheel lockup under emergency braking snapping the drive shaft as a result of the rotational energy stored in the wheel. Compared to the kinetic energy of a car I would have thought that the rotational energy of the wheel is relatively trivial.. It's the peak shock loading going via a couple of UJs that's the problem. I would agree that it introduces a new €śweak point€ť in the braking system though. Off the top of my head, Jaguar E-type, Rover 2000/3,500 and Citroen ZX all had inboard discs,. That may be but I doubt they were attached to the wheel via a UJ. Even though they might have been described as "inboard" brakes, the section of drive shaft involved would not only have been quite short but also beefed up to take the strain. Did they have a reputation for snapping drive shafts? No Idea, gov. The torque loading from translating the kinetic energy of the vehicle into heat energy in the brake disks at maximum braking force just shy of locking up the wheels is limited by the tyre grip to the road surface, circa 1.5 G. Locking a wheel through overenthusiastic application of the brakes can generate a very high shock loading on the UJs in a system that places the brake assembly at the sprung end of the suspension system rather than more directly at the unsprung wheel side of the UJs. Even assuming the UJs can cope with a limited number of such shock loads, the further away the brake assembly is mounted along a relatively spindly shaft from the wheel, the greater the risk of damage from the sudden torsional forces being applied. A conventional brake is still required on an all electric vehicle that uses regenerative braking just to cover the final 15MPH or so to 0MPH end of the braking phase where the regenerative braking effect fades to nothing. In a direct drive design using wheel hub motors where unsprung mass is an issue, the temptation is there to reduce the mass of the conventional disk brake assembly to a minimum which will reduce the maximum speed rating to just above the tail end of the effective minimum speed range of the regenerative braking system. However, in practice, rather than qualify them for say 20MPH, they're more likely to be qualified for 50MPH to give some margin for emergency braking on a long downhill gradient (provided the speed is held to no higher than 50MPH in this case). Whilst this will add a little more unsprung mass than strictly necessary when assuming the regenerative braking system is never ever going to fail, being mindful that even the best designed systems can suffer catastrophic failure, they'll no doubt hedge their bets on this and add an independant secondary emergency dissipative braking circuit[1] to the hub motor circuit which can, along with the transmission power management control and monitoring logic, log any problems to reduce the likelihood of two seperate, but extremely unlikely (it is hoped) faults occurring in both electrodynamic braking systems simultaneously by alerting the user and the service engineer to any symptoms of impending problems in either system (regenerative or dissipative) which need to be immediately addressed. The 'weedy' lightweight disk brakes can act as a last chance saloon backup in the event of such a double failure (hence the likelihood of them being rated for 50 rather 20MPH). The point I was trying to make was that, given sufficient development, the all electric transmission direct drive system offers far more benefit than deficit in a 'normal' electric road car. I think the issue of 'unsprung mass' is perhaps being a little over stated in this case thanks to rare earth permanent magnet DC brushless motor technology. [1] Such a 'secondary' dissipative electrodynamic braking system will be needed anyway just to cover the worst case scenario of a vehicle setting off with a fully charged battery from the top end of a long downhill stretch of road. Apart from the initial burst of acceleration to reach a sane cruising speed, the battery will be in no condition to accept a prolonged recharge from the regenerative braking system which will then have to call on the dissipative electrodynamic system to keep the kinetic energy build up in check by converting it into waste heat as the vehicle converts its potential energy into kinetic energy during its prolonged descent. This waste heat would simply be dissipated to the environment in mild to warm weather conditions but could be put to good use as cabin heating on early frosty winter morning runs. In any case, an element of electrodynamic dissipative braking will probably still be required to limit the peak charging rate of even a discharged battery under extreme high speed braking conditions to avoid exceeding the battery's maximum charging limit. The control logic to manage the power flows will not only need to be very sophisticated but also very robust. I'm sure the car manufacturers will be able to come up with a safe and reliable solution, after all we've been putting our lives into the care of such 'Fly by Wire' systems for well over a decade now with commercial aviation. -- Johnny B Good |
Question about Electic Motors
On 17/02/18 19:15, Tim+ wrote:
Johnny B Good wrote: On Sat, 17 Feb 2018 18:07:34 +0000, Tim+ wrote: One problem with that is that it moves the disc (and pads) out of reach of easy inspection/service. The real problem with that is the possibility of a high speed wheel lockup under emergency braking snapping the drive shaft as a result of the rotational energy stored in the wheel. Compared to the kinetic energy of a car I would have thought that the rotational energy of the wheel is relatively trivial.. I would agree that it introduces a new €śweak point€ť in the braking system though. Off the top of my head, Jaguar E-type, Rover 2000/3,500 and Citroen ZX all had inboard discs,. Jagura XJS too Did they have a reputation for snapping drive shafts? Mostly when a drive shaft goes iys where the splines enter the diff GF did that years agop - MG Midget, Revved it and dropped the clutch with a bang.. Tim -- Of what good are dead warriors? €¦ Warriors are those who desire battle more than peace. Those who seek battle despite peace. Those who thump their spears on the ground and talk of honor. Those who leap high the battle dance and dream of glory €¦ The good of dead warriors, Mother, is that they are dead. Sheri S Tepper: The Awakeners. |
Question about Electic Motors
On Saturday, 17 February 2018 07:53:06 UTC, wrote:
On Saturday, 17 February 2018 06:38:06 UTC, Johnny B Good wrote: On Fri, 16 Feb 2018 12:18:25 -0800, tabbypurr wrote: On Friday, 16 February 2018 18:39:21 UTC, Tim+ wrote: Johnny B Good wrote: Additionally, €śmotor in hub€ť adds hugely to unsprung weight (which isnt supposed to be a good thing). I appreciate that this might be mitigated by the use of rare earth magnet motors but that brings us back to the environmental problems again. As Im sure you know, €śrare earth elements€ť arent actually rare, just fecking difficult, dirty and expensive to extract. https://e360.yale.edu/features/ boom_in_mining_rare_earths_poses_mounting_toxic_ri sks Tim unsprung mass kills road holding. You could always use 2 inboard motors rather than 4 in wheels. I deliberately made the caveat about their unsuitability for high performance road cars on account of the 'unsprung mass' issue but I feel that a fully integrated hub motor will weigh little more than the steel wheels currently used by most saloon cars today (and may possibly prove to be slightly lighter through the use of suitable materials). the wheels are still required. A low speed motor must necessarily be large, and that means a lot more weight than the wheels. The resulting heaviness is unsuitable for ordinary road holding performance. They'd be a horrible compromise for a high performance car but most no, they're not be compatible with high performance at all likely a more than acceptable compromise for a 'standard electric road' car, considering the elimination of the weight and expense of a klunky space consuming mechanical transmission system. they'd increase unsprung weight greatly. Good enough for a low speed bus. A fully developed active energy recovery suspension system could ultimately overcome this problem of 'unsprung mass'. it can't It's also worth remembering that the suspension components themselves (spring, damper and drive shaft on each driven wheel) form a part of this 'unsprung mass'. suspension can't be eliminated Also, let's not forget the mass of the disk brake assemblies which, with regenerative braking, can be reduced in size thus offering yet a further reduction in 'unsprung mass'. not really, the friction brakes still need to stop the car from top speed.. This latter weigh saving would require an emergency electric backup in the event that the normal regenerative braking system suffers a failure The "Tweel" offers good possibilities for low unsprung weight. https://en.wikipedia.org/wiki/Tweel |
Question about Electic Motors
On Saturday, 17 February 2018 18:07:37 UTC, Tim+ wrote:
Vir Campestris wrote: On 17/02/2018 06:38, Johnny B Good wrote: A fully developed active energy recovery suspension system could ultimately overcome this problem of 'unsprung mass'. It's also worth remembering that the suspension components themselves (spring, damper and drive shaft on each driven wheel) form a part of this 'unsprung mass'. Also, let's not forget the mass of the disk brake assemblies which, with regenerative braking, can be reduced in size thus offering yet a further reduction in 'unsprung mass'. If you're going to put a drive shaft for each wheel connected to an electric motor why not put the disc inboard next to it? That would really cut the unsprung weight (to just half the shaft) Andy One problem with that is that it moves the disc (and pads) out of reach of easy inspection/service. Tim -- Please don't feed the trolls Not at all. The old Citroen had this arrangement. The brake pads were changed very easily under the bonnet. Not even neccessary to jack the car up. A ten minute job. |
Question about Electic Motors
On Saturday, 17 February 2018 13:25:23 UTC, The Natural Philosopher wrote:
On 17/02/18 13:12, Andy Burns wrote: Tim+ wrote: Given the huge environmental costs of rare earth element extraction its maybe no bad thing that theyre not being used in the booming electric car market. If Tesla can manage without them I reckon thats good enough for most of us. Tesla are using rare-earth magnet motors in (some of?) their Model 3. High strength magnets merely reduce the weight of the motor, You can get as high flux densities and efficiences using electromagnets But nowhere near as compact. |
Question about Electic Motors
On 17/02/2018 19:15, Tim+ wrote:
Johnny B Good wrote: On Sat, 17 Feb 2018 18:07:34 +0000, Tim+ wrote: One problem with that is that it moves the disc (and pads) out of reach of easy inspection/service. The real problem with that is the possibility of a high speed wheel lockup under emergency braking snapping the drive shaft as a result of the rotational energy stored in the wheel. Compared to the kinetic energy of a car I would have thought that the rotational energy of the wheel is relatively trivial.. I would agree that it introduces a new €śweak point€ť in the braking system though. Off the top of my head, Jaguar E-type, Rover 2000/3,500 and Citroen ZX all had inboard discs,. Did they have a reputation for snapping drive shafts? The limiting torque on the shaft will be the braking effort available, which is unlikely to be much beyond the traction limit. It's not beyond the wit of man to overspec the thing enough so it doesn't happen. fx googles https://en.wikipedia.org/wiki/Inboard_brake Quite a few manufacturers. Andy |
Question about Electic Motors
In article ,
Johnny B Good wrote: Yes - remember a pretty advanced design of 1/4" tape recorder. Had twin capstans with direct drive. And they stopped turning when the tape stopped running. They were pancake motors. Had a very fast start up time. That would explain it. The fast startup times were more probably the result of employing solenoid operated pinch wheels. I'm sure the capstan motors were more likely kept spinning all the time the machine was powered up and ready to go. No. As I said, the motors stopped. Constant run capstan was the far more common method. -- *If you remember the '60s, you weren't really there Dave Plowman London SW To e-mail, change noise into sound. |
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