Conclusive proof gearboxes are awesome.

[Hillhater]

Unless you redesign the drivetrain around a dual motor set up, you need some form of differential.
Maybe put the diff inside the hollow rotor of the bigger dia motor ?
But if that motor is 3 x the dia of the current motor,.....that wont work !

We are completely redesigning the motor, why not the drive train while we are at it? You make the motor what ever diameter you need to give you the torque required. The 3 times the gap diameter would give you roughly the same amount of overkill torque that the gearboxed version does now. Was hoping the simple concept would turn some lights on for some folks. It was just a example of how flawed the argument is against dropping the unneeded components. You need a motor, a connecting shaft (at least for a simply integrated easy to steer wheel), and a wheel. First mouse to it gets the cheese.

That depends greatly on what diameter that "3times" ends up being,.
In the Tesla example, it would be something like 30" , which makes mounting it on centreline for the drive shaft angle a major issue !....but a transfer box solves that.... But then you have not gained anything except more motor weight !
Even if you went with 2 motors, each developing half the required torque,hence only 2.2 times the dia of the original, they would still be well over 20" dia....same driveline problems,...and even more motor weight. ,
So whilst i really would like to eliminate unneccessary components, gear trains, complications, efficiency loss, and unreliability,....... I do not see a practical way to do it currently.

 

[speedmd]

The tesla rotor diameter is very small. Would be nothing like 30"

Video of the motor. http://insideevs.com/video-primer-tesla-model-s-electric-motor/

Most of the stator thickness looks to be aluminum. 20" diameter if you actually needed that would be no issue at all fitting into a car that size and meaningless with regards to drive shaft angle IMO. I don't see any reason at all other than the design R&D it would take to make something new that is bullet proof.

 

[Hillhater]

So you think they just throw uneccessary metal into the stator ?
Im am certainly no expert, but i suspect there is a reason the stator diameter is what it is (look closely, its steel laminations, with a solid aluminium case), and all i have done is asumed the same stator thickness on a diameter to match the increased rotor diameter...( rotor itself would be 8" x 3= 24" OD !)
Im sure there are many ways a motor could be improved, but i thought we were trying to be realistic and use current, established design parameters ?

 

[speedmd]

they just throw uneccessary metal into the stator

Possibly. If the diameter is your issue for saying this will not work, maybe they are doing it for cooling or some other issue that can be solved some other simple way. Why think in simplistic terms of just taking the same motor topography and not start with a blank sheet approach. I don't see any way you will ever accept the trade off that a larger diameter motor could easily replace the high reduction mechanical parts and work well. Do you know the actual rotor diameter? I can find it nowhere.

 

[Hillhater]

Rotor dia ?.there are enough pics and vids around to see that it is about 8" +_.

..... Why think in simplistic terms of just taking the same motor topography and not start with a blank sheet approach. ...

..because its established technology, with known performance characteristics, and i was trying to be realistic
Blank sheet approach ?...sure, may as well make it out of unobtanium, and VTOL whilst we are at it.
Its not that i dont want to see it done..quite the oposite,..but i am just trying to establish why it is not being done on any of the current commercial EV's.
My conclusion so far is that its because all the options for DDrive motor just result in more weight and more complex installation issues due to size.

 

[Hillhater]

Rotors..
Sorry, dumb ipad wont let me resize the pic !

 

[speedmd]

Thanks for posting the photos. Looks like lots of extra metal in this motor. Looks like weight savings was not a major part of the design criteria. Giving its relatively small size, I can understand the desire to make it solid for a host of reasons, but if one were to scale it up in diameter, I can see some possibility to make some improvements in this regard. Regardless, we are talking hypercar acceleration in a large sedan. We don't need all of the torque / acceleration of the current design for 99% of the folks that will drive these. I understand the marketing appeal this snappiness generates, but certainly do not need it. It may be just a matter of the right folks making this happen in the right package and we can see how it plays out. Time will tell.

 

[Hillhater]

If you want to consider a less extreme performance car, you only have to think of the Leaf.
Its a similar drivetrain, 10k rpm motor ( PM) with a 8:1 reduction drive to the diff and drive shafts.
But its only 80kW and 280NM
The motor has similar dimentions to the Tesla,..see pics here..
http://www.marklines.com/en/report/rep1104_201209
So, you can see that practically the same situation applies, ..
You still need approx a 3 times bigger motor again to retain the same torque at the wheels and look how that would fill the motor bay and drag on the floor !
...never mind the weight again !

 

[Arlo1]

If you want to consider a less extreme performance car, you only have to think of the Leaf.
Its a similar drivetrain, 10k rpm motor ( PM) with a 8:1 reduction drive to the diff and drive shafts.
But its only 80kW and 280NM
The motor has similar dimentions to the Tesla,..see pics here..
http://www.marklines.com/en/report/rep1104_201209
So, you can see that practically the same situation applies, ..
You still need approx a 3 times bigger motor again to retain the same torque at the wheels and look how that would fill the motor bay and drag on the floor !
...never mind the weight again !

The leaf motor will do something ~ 180-200kw continuous. They run it at 80kw at 2500rpm and 80kw at 6000rpm Nissan had to reduce the phase current as rpm increases past ~2400 rpm because the battery could not handle any more amperage. By reducing the phase amps as rpm increases you can keep the battery amps the same.

 

[Hillhater]

Sounds good.
Does the Leafs IPM motor have more potential than a similar (size , weight) induction motor ?
What levels of torque could the Leaf produce with the right battery and inverter.?

 

[Arlo1]

Sounds good.
Does the Leafs IPM motor have more potential than a similar (size , weight) induction motor ?
What levels of torque could the Leaf produce with the right battery and inverter.?

I think the comparison for peak power and possibly continuous power between an induction motor and a IPM motor the IPM motor wins by a small margin.
But a comparison efficiency at lower power (power below its continuous rating) the induction can win.

So although the tesla motor might not make quite as much power as it possibly could if it was a IPM motor it is chosen because Tesla needed the most range possible during cruising.

 

[parabellum]

I see, Hillhater is stuck and can not get the word "weight" out of his system, even there where multiple attempts to explain how motors work. Will try it again but really with no particular hope, must get it out of my system. :lol:

The MOTOR PART of the motor is made of ACTIVE MATERIALS and you can make virtually ANY TORQUE configuration with SAME POWER output and same ACTIVE MATERIALS WEIGHT just reconfiguring geometry of the motor (there are several ways and diameter is only one of them).

Then, the "weight" of supporting and cooling structure is up to your imagination and engineering skills, but must not necessary increase with diameter.

Sorry, just got finally tired of Hillhaters scratched, repeating disk.

 

[InterestedinEVs]

I think the issue more is more accurately described as "packaging."

 

[Hillhater]

I see, Hillhater is stuck and can not get the word "weight" out of his system, even there where multiple attempts to explain how motors work. Will try it again but really with no particular hope, must get it out of my system. :lol:

The MOTOR PART of the motor is made of ACTIVE MATERIALS and you can make virtually ANY TORQUE configuration with SAME POWER output and same ACTIVE MATERIALS WEIGHT just reconfiguring geometry of the motor (there are several ways and diameter is only one of them).

Then, the "weight" of supporting and cooling structure is up to your imagination and engineering skills, but must not necessary increase with diameter.

Sorry, just got finally tired of Hillhaters scratched, repeating disk.

Sorry if it irritates you P, but there seems to be a huge shortage of motor experts willing to explain how exactly you construct a motor 3 times the diameter ( stick with that proposal for now) , one third as long, to generate 9 times the torque, and yet not significantly increase the weight ?(oops, sorry , there is that word again)
And , yes i notice you have slipped in the ACTIVE materials word, which doesnt cover the total motor weight.!
Care to have a crack at that issue ?

 

[Arlo1]

I see, Hillhater is stuck and can not get the word "weight" out of his system, even there where multiple attempts to explain how motors work. Will try it again but really with no particular hope, must get it out of my system. :lol:

The MOTOR PART of the motor is made of ACTIVE MATERIALS and you can make virtually ANY TORQUE configuration with SAME POWER output and same ACTIVE MATERIALS WEIGHT just reconfiguring geometry of the motor (there are several ways and diameter is only one of them).

Then, the "weight" of supporting and cooling structure is up to your imagination and engineering skills, but must not necessary increase with diameter.

Sorry, just got finally tired of Hillhaters scratched, repeating disk.

Sorry if it irritates you P, but there seems to be a huge shortage of motor experts willing to explain how exactly you construct a motor 3 times the diameter ( stick with that proposal for now) , one third as long, to generate 9 times the torque, and yet not significantly increase the weight ?(oops, sorry , there is that word again)
And , yes i notice you have slipped in the ACTIVE materials word, which doesnt cover the total motor weight.!
Care to have a crack at that issue ?

Brake it down to this the weight of the motor is what determines the continuous power it can run the motor can then be configured to make power at high rpm with low torque or power at low rpm with high torque but both would have the same continuous power rating.

Example a motor with peak power at 1000 rpm and 100 kw continuous rating would be making 704 ft-lbs but if you used the same materials for the same continuous power rating of 100kw but make the peak power at 5000 rpm your toque would be 140 ft-lbs.
The parts of the motor that determine the power rating are the copper and laminations saying you can use the same amount of materials for cooling there is no reason the same weight of copper and lamination steal can't produce the same continuous rating in different sizes.

A real world example of this is a Zero VS a Alta motors MX bike the Zero is a bigger motor but hollow and not to heavy the Alta is similar in power density but runs higher rpm needing more stages of reduction.

 

[toolman2]

quote
But heres the critical bit Luke and we need the answer to contain a yes or no:
Is it correct to say that if it was to be highly loaded at relatively low speed, like say a race that is a decent grade uphill, OR say a much higher speed race with lower load, like down a long straight downhill. -That there is likely to be a benefit to either speed or efficiency by changing the drive ratio that it currently has.

As to yes or no for your question, if you add the right artificial constraints it's "Yes". A situation can certainly exist for the transmission to help something work better in some given context with some given design limitations (like my friends Zero motor powered Insight that can only get around because of the tranny). So, it's definitely possible for the answer to be Yes, but it's equally possible to be "No" the vehicle to use a topology which doesn't eat core loss while coasting down a hill powered off, like induction, or ironless PM motors, or switched reluctance etc.

Thanks for the answer on that Luke.
So the Tesla motor falls into the no category because it IS induction, however in this (say down Pikes peak) race with the taller gearing for the job we would be more likely want to apply full motor output, rather than just coast. :wink:
And on the yes side, said artificial constraints are no more artificial than a hill or regular hillclimb event etc, so yea the unavoidable fact here is that gearing always has to be a compromise and adjusting it hear and there is bound to give a benefit for certain conditions.

Im not going to press on from there talking up a 2 speed, although there is an actual advantage to efficiency or power a under some fairly rare conditions, basically, with motors as good as this and the Leaf then i agree a gearbox is completely unnecessary.

Once that is accepted then the larger diameter motor that puts the same amount of copper and iron out further and thinner to produce the torque multiplication at the same weight and power is worth a closer look and i totally agree that its capable of equal power etc from an electromagnetic perspective.

So what would that really mean for the 9 times Tesla torque egsample? cos 3 times the diameter motor would do 9 times the torque sure, at full length,
and be 9 times more powerful. We are not at the same weight or power though so obviously you cut it down by 2/3 and it now cannot give you 9 times the torque, now more like 3. ?
So is it 9 times the diameter?, for 81 times the torque and then 8/9th's cut off the length giving us the right 9 times the torque final result? -sounds a bit wild, I know its totally doable from the same amount of electrical/magnetic material, not sure myself though but would like to know Luke, Miles, and isn't that Biff guy pretty good with motors ? :wink:

 

[Miles]

If we accept the premise that, for a given weight of active material, we can alter the torque:velocity ratio yet maintain the same power output, by manipulating the form factor. What are the obstacles to practical implementations? What are the present limits?

Is this a good place to start?

Maybe we should start a new thread at this point?

 

[Miles]

OK. I've started a new thread: https://endless-sphere.com/forums/viewtopic.php?f=30&t=78923

 

[speedmd]

Is volume or dimensional constraints worth discussing at the same time.

 

[Hillhater]

If we accept the premise that, for a given weight of active material, we can alter the torque:velocity ratio yet maintain the same power output, by manipulating the form factor. What are the obstacles to practical implementations? What are the present limits?

Is this a good place to start?

Maybe we should start a new thread at this point?

Thanks Miles, that is basicly the same question i have been trying to ask but including in the reality of actual operational motor weight.

if Motors can be made with sufficient torque for DD drive ( not necessarrily "in wheel" motors,) what are the reasons no one has yet produced a car using that configuration ?
I would not expect Tesla etc to reengineer thier drivetrains now, but why didnt they, or GM, etc, go DD originally ?
Is it just cost or is there some other technical barrier yet to be overcome ?

 

[Miles]

Thanks Miles, that is basicly the same question i have been trying to ask but including in the reality of actual operational motor weight.

What Cole called the "packaging"... I deliberately left that out for now. The active materials themselves need to also make maximum structural contribution........

 

[Hillhater]

..ok but if you want to answer your question...

...What are the obstacles to practical implementations ?.....

..you have to consider the practicalities of a real motor,..not just theory of "Active Materials" !
IE, If efficiency is poor at low rpm, it will likely need serious cooling systems added.?

 

[danielrlee]

I'm not sure if this question has already been asked in this huge thread, but does the same logic apply to geared hub motors? Is a DD hub motor more efficient than a geared hub motor of the same mass? Even in stop-and-go situations?

 

[liveforphysics]

I'm not sure if this question has already been asked in this huge thread, but does the same logic apply to geared hub motors? Is a DD hub motor more efficient than a geared hub motor of the same mass? Even in stop-and-go situations?

It's complex.

Essentially whatever motor was designed better will be better regardless of the topology.

However for equally well designed motors the direct drive options efficiency will be best.

 

[motomoto]

So I guess the Tesla is a 'geared hub motor' with it's 9.73:1 ratio. Not very direct drive. So the Tesla motor designers
are 'out to lunch' regarding true efficiency. So if you took the Tesla motor and made it larger in diameter to the point
that it was a 1:1 ratio with the motor directly connected to the wheels, LFP would be happy and the motor diameter
would be 9.73 divided by Pi which would result in a motor that is 3 times the diameter and have somewhere in the
neighborhood of 10 times the segments. I guess it's just a matter of cost and size vs. using gears.