One just never knows. Tesla changes things on the fly so much, that what they have planned now, could change in a few months. It will be really interesting to see the Model X, and E design unfold.
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Since the primary motor is in the rear, isn't it true in AWD that the front motor will not be used unless slip is detected in the rear?
There are systems that work that way, and others that push power to all four wheels all the time.
I don't think anyone knows what Tesla has in mind on that score - though the history of making high performance cars would suggest they'd lean towards using both motors under hard acceleration since that'd make the car faster.
Model Ss don't become battery/power limited until ~50 mph - below that speed there's always excess battery capacity which could be used to drive the car faster through the front motor.
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There are systems that work that way, and others that push power to all four wheels all the time.
I don't think anyone knows what Tesla has in mind on that score - though the history of making high performance cars would suggest they'd lean towards using both motors under hard acceleration since that'd make the car faster.
Model Ss don't become battery/power limited until ~50 mph - below that speed there's always excess battery capacity which could be used to drive the car faster through the front motor.
JRP3
Hyperactive Member
We were basically both right, D has two small motors, PD has big and small. (Though I'm pretty sure the front motor does have it's own inverter).
I think you are right. The inverter appears to be much smaller than the rear inverter(even when the power difference is accounted for).
Yes, that was a good bit of reasoning in your post of 2013-10-28. I think you're also probably right about using the same smaller motor for the Model 3. Then Tesla would only need to produce two motor designs for
- Model S RWD (big motor)
- Model S AWD (small motor front, small motor rear)
- Model S AWD Performance (small motor front, big motor rear)
- Model X AWD and AWD Performance - same as Model S
- Model 3 (small motor - rear?)
JRP3
Hyperactive Member
I think you'd need a larger battery pack to support higher power levels, or one with a higher C rating. You'd also lose even more of the frunk.
Tesla supposedly had a test car with the dual P drive units. One of the engineers said it was pretty unstable. He didn't say whether the battery was a stock 85kwh pack, but if it was, it would probably be thrashed much quicker with 940hp being sucked out of it. I have to wonder what Tesla does with these Frankenstein test cars? They would make very fun track cars. Anyone remember the Roadster drivetrain Smart car? That thing was bananas.
We know based on JB Straubel's blog posting that "the new generation small front drive unit is actually more efficient at converting battery DC electricity into mechanical shaft power".
Shouldn't we anticipate that Tesla will also replace the larger older/existing units with "the new generation" technology? And based on the assumption all the drive units are newer technology what will that change? And is their any reason to assume the Model X's larger drive units will also be using the newer technology helping to improve range? Why would Tesla delay using better drive units going forward?
http://www.teslamotors.com/blog/driving-range-model-s-family.
Shouldn't we anticipate that Tesla will also replace the larger older/existing units with "the new generation" technology? And based on the assumption all the drive units are newer technology what will that change? And is their any reason to assume the Model X's larger drive units will also be using the newer technology helping to improve range? Why would Tesla delay using better drive units going forward?
http://www.teslamotors.com/blog/driving-range-model-s-family.
JRP3
Hyperactive Member
A larger diameter motor produces greater torque so I don't expect it to be replaced with a smaller one in a high performance application. To put it another way, efficiency isn't everything.
JRP3 I wasn't making the case for replacing the larger motor with a smaller one. My question is if the smaller motor is "a new generation" as quoted from JB why wouldn't they upgrade the larger motors to the new generation? Not necessarily right away but within a reasonable time period to gain some efficiency since every bit helps.
JRP3
Hyperactive Member
My guess is most of the efficiency gains were just the result of the motor being smaller. Any other tweaks they may have already integrated into the larger motor if applicable.
I suspect similarly: less rotating mass and therefore less inertia to overcome likely leads to a good chunk of any greater efficiency.
Something else that has been discussed some time previously is that there was talk of being able to gear the 2nd motor differently than the first motor. Assuming it was geared taller, that would lower the RPM at a given speed, allowing it run run at a more efficient speed.
JRP3
Hyperactive Member
To a point, it's not like an ICE where low RPM's are necessarily more efficient. Depending on how a motor is built it will have an RPM range where it's most efficient. I expect with slightly different gearing each motor will have a slightly different most efficient RPM range in relation to vehicle speed, so being able to favor one motor over another when the RPM range is in the sweet spot for an individual motor provides a benefit.
JRP3
Hyperactive Member
They also draw more current at lower speeds, (and lower voltages). Each motor has an efficiency range, which is usually not at the very low end of it's RPM range.
There has been many changes to the Model S drive units over the 3 years it has been in production.
The rotor has been completely redesigned.
Early rotors
Latest rotor design
D front drive unit(very similar to the latest bigger drive unit design)
JRP3
Hyperactive Member
I don't remember. I saved them from some video that was posted at the unveiling. I tried to find the video again with no luck.
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