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Model S Performance vs BMW M5
- Thread starter CapitalistOppressor
- Start date
Right. Exactly. I have only done a couple of times and always on a flat surface. It is possible that the computer holds the brakes as in park assist, but it is in neutral (or clutch-in) and you don't need to have foot on brake (in fact I think this would cancel the sequence). This is not "brake boosting" as would be done in a conventional automatic with turbo (like a 996 TT).
Not sure about the F10, but on the E60 I believe the "non LC" dragstrip technique is to pulse the throttle pre-launch to force it to drop the clutch at RPMs higher than normal idle.
In the Model S video, if they did NOT use LC, I assume they just mashed the throttle. I assume the specific combo of video and sound we see were chosen in the editing bay and not on the track.
There's been a lot of discussion about transmissions in this thread. Some maintain that MS would gain a lot by adding a transmission, and someone said that "with an electric motor, there's many ways to skin the cat". There are purely electrical ways to skin this cat:
The purpose of a transmission is to keep the motor in its sweet spot, allowing it to deliver full power. If you can efficiently deliver full power at any speed, then you don't need a transmission. In an ICE, the transmission has the additional purpose of allowing you to reduce fuel consumption when you don't need power, but that's not needed in an EV anyway.
The ideal motor delivers constant power from 0 to infinite speed. This is obviously impossible, torque will be limited by tire grip, and at some speed the motor will tear itself apart. A more realistic ideal is a motor that delivers as much torque as the tires can handle until max power is reached, and then stays at max power up to the rpm limit. In the constant power region, torque is inversely proportional to speed, so torque must necessarily drop as speed increases.
The battery has a specific voltage, and there is a limit to how much current it can safely deliver.
The motor also has limitations, and it behaves in a certain way. Torque depends only on current - if you pour more current through it, it will pull harder. More amps also mean much more heat (proportional to square of current), so to avoid melting the windings, including those in the difficult-to-access rotor, you have to be able to remove the heat at a sufficient rate.
As the motor spins up, it starts generating its own voltage, opposing the voltage fed to it. This is called "counter electromotive force" or "back emf". This means that the effective voltage across the motor will drop as the rpms increase if the supplied voltage is constant. This causes less current to flow through the motor, or rather, it gets harder and harder to push the current through the motor as its speed increases.
So at low rpm, the system is limited by how many amps can be sent through the motor without either melting it or blowing up the battery. Full battery voltage can't be applied, that would result in too much current, and this means that you can't get full power.
As rpms increase, due to back emf at some point the effective voltage drops below the voltage required to push max amps through the windings even when you apply the full battery voltage. Torque starts to drop. Then you have almost the reverse situation - you have the capacity to deliver more amps, but can't, because the battery voltage is too low.
When Tesla decided to drop the transmission, they made up for it in a very clever way. They realized that they weren't using all the available voltage - significantly less than battery voltage is required to push max amps through the motor at low rpms. So the battery would not deliver max power (i.e. max volts * max amps) in the lower rpm range. They fixed this by adding a voltage converter that traded unneeded voltage for more amps. In other words, the battery would supply something like 600 A at 500 V into the voltage converter, which would output something like 900 A at 333 V into the motor. Those numbers are pure guesswork and just an example.
When back emf from the motor resists the applied voltage so much that max battery amps can no longer be forced through the motor at the battery voltage, one could add another voltage converter to increase voltage to counter the back emf. In principle, nothing prevents you from continuing to push the full battery power through the motor up to the rpm limit - albeit at lower amps and higher voltage. Torque would still drop, but not as much, and the power curve can stay flat, instead of peaking.
For all I know, maybe Tesla already does this, and what we see in the drag strip videos is just the result of lower max power and higher weight of MSP vs M5.
Why add a transmission when the same thing can be achieved with power electronics? I think there are reasons to do that too. If you choose a very long gear ratio and make up for it with more current, you will also increase heat loss, so I think you will lose some range. This could be countered by increasing the system voltage. On the other hand, a transmission also wastes some energy. I'm sure there are many more tradeoffs in motors, power electronics and economics that must be considered. But as the Roadster and Model S have proved, the transmission is already almost as obsolete as the ICE, at least for automotive use, and there might still be room for improvement.
The purpose of a transmission is to keep the motor in its sweet spot, allowing it to deliver full power. If you can efficiently deliver full power at any speed, then you don't need a transmission. In an ICE, the transmission has the additional purpose of allowing you to reduce fuel consumption when you don't need power, but that's not needed in an EV anyway.
The ideal motor delivers constant power from 0 to infinite speed. This is obviously impossible, torque will be limited by tire grip, and at some speed the motor will tear itself apart. A more realistic ideal is a motor that delivers as much torque as the tires can handle until max power is reached, and then stays at max power up to the rpm limit. In the constant power region, torque is inversely proportional to speed, so torque must necessarily drop as speed increases.
The battery has a specific voltage, and there is a limit to how much current it can safely deliver.
The motor also has limitations, and it behaves in a certain way. Torque depends only on current - if you pour more current through it, it will pull harder. More amps also mean much more heat (proportional to square of current), so to avoid melting the windings, including those in the difficult-to-access rotor, you have to be able to remove the heat at a sufficient rate.
As the motor spins up, it starts generating its own voltage, opposing the voltage fed to it. This is called "counter electromotive force" or "back emf". This means that the effective voltage across the motor will drop as the rpms increase if the supplied voltage is constant. This causes less current to flow through the motor, or rather, it gets harder and harder to push the current through the motor as its speed increases.
So at low rpm, the system is limited by how many amps can be sent through the motor without either melting it or blowing up the battery. Full battery voltage can't be applied, that would result in too much current, and this means that you can't get full power.
As rpms increase, due to back emf at some point the effective voltage drops below the voltage required to push max amps through the windings even when you apply the full battery voltage. Torque starts to drop. Then you have almost the reverse situation - you have the capacity to deliver more amps, but can't, because the battery voltage is too low.
When Tesla decided to drop the transmission, they made up for it in a very clever way. They realized that they weren't using all the available voltage - significantly less than battery voltage is required to push max amps through the motor at low rpms. So the battery would not deliver max power (i.e. max volts * max amps) in the lower rpm range. They fixed this by adding a voltage converter that traded unneeded voltage for more amps. In other words, the battery would supply something like 600 A at 500 V into the voltage converter, which would output something like 900 A at 333 V into the motor. Those numbers are pure guesswork and just an example.
When back emf from the motor resists the applied voltage so much that max battery amps can no longer be forced through the motor at the battery voltage, one could add another voltage converter to increase voltage to counter the back emf. In principle, nothing prevents you from continuing to push the full battery power through the motor up to the rpm limit - albeit at lower amps and higher voltage. Torque would still drop, but not as much, and the power curve can stay flat, instead of peaking.
For all I know, maybe Tesla already does this, and what we see in the drag strip videos is just the result of lower max power and higher weight of MSP vs M5.
Why add a transmission when the same thing can be achieved with power electronics? I think there are reasons to do that too. If you choose a very long gear ratio and make up for it with more current, you will also increase heat loss, so I think you will lose some range. This could be countered by increasing the system voltage. On the other hand, a transmission also wastes some energy. I'm sure there are many more tradeoffs in motors, power electronics and economics that must be considered. But as the Roadster and Model S have proved, the transmission is already almost as obsolete as the ICE, at least for automotive use, and there might still be room for improvement.
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This is an indicator of success in the MSP product. It doesn't take anything from the M5. "Car folks" (generally and on each side) should be excited about what this means for the automotive future.
hans
P631
contaygious
Active Member
1. See several old threads re: Roadster design and 1.0 having a two speed transmission.
2. Pretty sure VFX was referring to new electronic components (IGBTs) for the PEM, so they could better balance torque and top speed with a single gear.
Back on-topic - now that we have more Perf Ss in customer hands, are there any recreations of this test yet? I know an M5 invite was offered...
tdelta1000
Active Member
The mere fact that the Model S can line up on a track with an M5 is more than the automotive world was expecting from Tesla Motors. Great job TM.
My car arrived at port yesterday. Should be ready for pickup in a week or so. I broke it in on the Nurburging in Germany (photo below), so by the time I get it, it will have had it's break-in service. I'm in SF Bay Area. I am also going to an airfield event in NorCal on November 10 in case any MSPs want to play.
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Agreed. Impressive.
gg_got_a_tesla
Model S: VIN 65513, Model 3: VIN 1913
Beautiful! Now, that's the Blue that Tesla should have gone with; not this black-masquerading-as-blue shade.
gg_got_a_tesla
Model S: VIN 65513, Model 3: VIN 1913
artsci
Sponsor
No offense intended, but this is the pinnacle of a soon-to-be dinosaur technology. You've got the very best of antiquity, what will be regarded as an ICE classic.
I agree with the takeaway: the M5 has gotten so fat and soft that it is no longer credible to say that it is fully "two cars in one" (sports car and luxury sedan). The M3 has taken on that challenge. I think it is more fair to now call the M5 the ultimate "Sporty Luxury Sedan." Realistically, no one would buy one as a track toy (although it is fun on track). Which is why it should be considered in the same class as the MSP.
In the end, car companies need to sell cars, and making an M5 that was "more raw" than the screaming V10 E60 variant would have made a few people happy, but probably lost money overall....
I hope Tesla builds an M3 killer.
Hmm, I do not agree. Of course they could offer it as an additional color, but if this were the only blue available I'd get another color. This blue is much too light for my tastes.
I have a Leaf and most of them here are blue too. I got a white one...
Chrisn - I hope you find someone in the area to play with.... Anyone... here... hello?
Norcal, where? (Note: Norcal is anything above Yuba / Clearlake or so IMO. SF, Napa - not Norcal. Sac is debatable)
If they'd give me mine during the first week of November I'd be there for sure!
but 99.9+% unlikely (anything is possible:wink
Norcal, where? (Note: Norcal is anything above Yuba / Clearlake or so IMO. SF, Napa - not Norcal. Sac is debatable)
If they'd give me mine during the first week of November I'd be there for sure!
but 99.9+% unlikely (anything is possible:wink
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