How can Dual motor get 310 Mile Range

Toadmanor

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#1
I have been thinking a lot about Model 3 and have a test drive scheduled for today in two hours. HOORAY!

I will probably purchase the LRB Dual Motor version. I have been thinking about the claimed 310 mile range which is the same claim as for the single motor version. This may be painfully obvious but not to me.

How can two motors with the same 75KW battery pack achieve the same range as a single motor with the same battery pack? Wouldn't two motors use more energy than one motor does?
 

MelindaV

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#2
I have been thinking a lot about Model 3 and have a test drive scheduled for today in two hours. HOORAY!

I will probably purchase the LRB Dual Motor version. I have been thinking about the claimed 310 mile range which is the same claim as for the single motor version. This may be painfully obvious but not to me.

How can two motors with the same 75KW battery pack achieve the same range as a single motor with the same battery pack? Wouldn't two motors use more energy than one motor does?
On the S , when it was available as either rwd or dual motor, the dual motor configuration had better range.
One motor is tuned to be most efficient at consistent highway speeds, one at stop and go inconsistent speeds.
 

garsh

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#3
How can two motors with the same 75KW battery pack achieve the same range as a single motor with the same battery pack? Wouldn't two motors use more energy than one motor does?
That's not *necessarily* the case.

As MelindaV states, the dual-motor S is actually *more* efficient than the RWD version. In that case, the rear motor is geared for acceleration, while the front motor is geared for highway efficiency. The better highway efficiency of the front motor makes up for the added weight (that also means the Model S is a front-wheel drive car during normal highway cruising ;)).

In the case of the Model 3, it turns out that the AWD version is less efficient than the RWD version. During EPA range testing, the RWD version ended up with a range of 334 miles, while the AWD version received a range of 308 miles. But in both cases, Tesla asked for a "variance" to advertise them both as having a range of 310 miles, which the EPA granted.

https://electrek.co/2018/07/24/tesla-model3-epa-ratings-advertise/
 

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#4
Just wish I knew how it lost the 11% (or more specifically, the non-weight-related ~7-%-ish of it) - wheel selection, drivetrain losses, or broken torque sleep - because it really matters in terms of buying decisions :Þ I'm surprised there's not been a proper attempt by anyone to test this out yet. But I'm sure we'll get one.
 

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#6
My AWD model 3 should be here soon, and I will be doing range tests with it against a friends RWD.
Excellent!!!!

Don't forget:
  • Same route (loop, flat land, at a time and place with little traffic and few stops / starts / sharp turns)
  • Same day, close to the same time (but not so close as to be drafting)
  • Same speed
  • Same tire pressure
  • Same wheels and tires, with tires at least roughly in the same tread condition.
Also, ideally:
  • Multiple test speeds (55, 65, 75, 85 mph?)
  • Rolldown tests (e.g. on flat land, with a camera pointed at the speedo, and at a preferably high speed, shift into neutral and roll to a stop. Then do the same thing in the opposite direction)
We can figure out where the energy is going with this and what the actual efficiency difference is! :)
 
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#9
Just wish I knew how it lost the 11% (or more specifically, the non-weight-related ~7-%-ish of it) - wheel selection, drivetrain losses, or broken torque sleep - because it really matters in terms of buying decisions :Þ I'm surprised there's not been a proper attempt by anyone to test this out yet. But I'm sure we'll get one.
Even torque sleeping the front motor, the gearbox (Tesla's have gearboxes, just with a single reduction gear vs a shifting transmission) and motor itself still have to spin. This adds resistance even while torque sleeping. + about 200lbs of extra weight.
 

KarenRei

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#11
Even torque sleeping the front motor, the gearbox (Tesla's have gearboxes, just with a single reduction gear vs a shifting transmission) and motor itself still have to spin. This adds resistance even while torque sleeping. + about 200lbs of extra weight.
Yes, that - drivetrain losses - is one of the three listed possibilities. But that would be a huge amount of drivetrain losses. And if drivetrain losses are that big, why no locking hubs?

It's certainly a possibility, but also certainly not definite.
 

garsh

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#12
And if drivetrain losses are that big, why no locking hubs?
Theoretically, I'd say simplicity. Locking hubs are another moving part that can break. Plus you'd have to add electronics to control the locking hub. And software to control those.
 

KarenRei

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#13
Theoretically, I'd say simplicity. Locking hubs are another moving part that can break. Plus you'd have to add electronics to control the locking hub. And software to control those.
Do they make electronic locking hubs? I'm only familiar with two types - manual (where you unlock them from the wheels) and automatic (where incoming torque triggers it).
 
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#14
Yes, that - drivetrain losses - is one of the three listed possibilities. But that would be a huge amount of drivetrain losses. And if drivetrain losses are that big, why no locking hubs?

It's certainly a possibility, but also certainly not definite.
You also have to factor in the reduced efficiency of the induction motor itself, which presumably is activated at some points during the test cycle. Drivetrain, weight, and reduced motor efficiency add up to a ~8% loss.This is inline with what most people in the know were expecting.

Not sure where you are getting the 11% number?

 

RoadToLevel5

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#15
On the S , when it was available as either rwd or dual motor, the dual motor configuration had better range.
One motor is tuned to be most efficient at consistent highway speeds, one at stop and go inconsistent speeds.
I wonder how the motor is tuned on the RWD. If it's tuned somewhere in between the two motors of the AWD, I can see the lower range overall. If it's identical to one of the motors on the AWD, I would think RWD would always outperform in range in the scenario where the same motor in AWD is engaged and other is idle, since the RWD would weigh less.

Never thought about AWD providing greater range on any vehicle than its 2WD counterpart. Rather fascinating.
 

Ed Woodrick

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#16
I have been thinking a lot about Model 3 and have a test drive scheduled for today in two hours. HOORAY!

I will probably purchase the LRB Dual Motor version. I have been thinking about the claimed 310 mile range which is the same claim as for the single motor version. This may be painfully obvious but not to me.

How can two motors with the same 75KW battery pack achieve the same range as a single motor with the same battery pack? Wouldn't two motors use more energy than one motor does?
Let's see, how can this be true?

  • All energy sent to rear wheel and the front is left to free wheel?
  • 50% energy to front 50% to the back.
These aren't gas engines. They really don't cost anything if they are just sitting there. They are pretty efficient, so 50% front, 50% rear isn't that bad of an option.
But as others have mentioned, Tesla has optimized the power train, allowing one motor to be more efficient at lower speeds and the other better for the higher speed. By using intelligent controllers, they are able to transition between the two without anyone noticing.

So, in reality, the question is more like "Why would you lose efficiency if you had two motors."
 

oey192

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#18
There is also (theoretically) more Regen gained back with the 2nd motor
You do not gain extra energy by having the second motor assist with regen. The only difference between AWD and RWD in regards to regen is that the AWD (dual motor) car can* capture the energy faster, thus slowing you down more quickly. However, the total amount of energy recaptured should be almost identical (AWD might capture a tiny amount less since there are now two places where energy can be lost as heat, but I would expect the difference to be a few percent or less)

* I say “can” because an AWD doesn’t necessarily slow down faster than an RWD. I don’t know if anyone has tested the regen g-force of an RWD Model 3 vs an AWD Model 3. I have seen subjective reports the AWD has stronger regen (e.g. that the regen feels stronger) but no evidence.
 

KarenRei

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#20
You do not gain extra energy by having the second motor assist with regen.
Yes, you can. It lets you use physical braking less because you have more total regen capability. Furthermore, a front motor is in a better position for regen than a rear one because the center of gravity shifts forward when decelerating.