200 kWh Roadster Pack: How is Tesla Pulling This Off?

[Peteski]

Another thing that works in EV's favor is electronic feed back loop gives you much faster responses than those done mechanically and hydraulically in ICE cars. You could create much better torque vectoring and traction control in an EV that you would never be able to in an ICE car. The Roadster will have three independently controlled motors. There is a tremendous potential there.

It's true, but you're still fighting against basic physics with excessive mass. As a trained physicist you should be able to relate to that surely? There's a good reason why the Porsche 919 can lap the ring 87 sec faster than the Nio EP9. The Nio is 1735 kg vs 849 kg for the Porsche. Non of the inherent EV advantages can remotely overcome that kind of weight difference. Remember all those dynamic loads generated by that mass are going through 4 little rubber contact patches, however cleverly you apply it.

Perhaps a better comparison would be the Porsche GT2 RS at 1470 kg. Even with just 690 hp, it's still over 5 sec quicker than the Nio with 1300 hp. So that's trading only 265 kg for around 600 hp. I say again from experience, mass is critically important when it comes to achieving lap times!

 

[Peteski]

You have not convinced me.

It's hard to convince someone who thinks that reducing mass moment of inertia to zero would magically provide "infinite handling". It just means you don't understand the physics involved. Even if you did manage to achieve close to zero inertia, the tyres still have to support the static and dynamic tyre loads generated in accelerating the mass. It just means that the car would be able to spin infinitely quickly if you sat it on an ice rink and gave the front end a good shove. In practice, by reducing inertia to zero for the same mass, you would have a car with the same cornering potential (as dictated by Newton's basic laws of physics F=ma etc) but you would have infinite instability on the limit. Once you exceeded the limit of grip it would spin instantly without a hope of catching it. It's the inertia that makes it controllable.

Try balancing a long stick on your hand like a broom handle. It's very easy. Now try it with a very short stick. Not so easy. Less inertia gives a faster response to any input but also requires faster reactions to keep control of it.

Going back to the Roadster, electronic stability control will greatly help with control, so having an inherently low mass moment of inertia will not be a problem in this case. But excess mass will still greatly limit it's handling potential due to basic Newtonian physics. All I'm saying here is that mass (polar) moment of inertia is a huge red herring and will not compensate in handling for hundreds of kgs of excessive mass. Of course having a low CofG and relatively low mass moment of inertia are good things, but having less mass in the first place is still King! That's why race engineers always build cars as light as they can legally get away with.

 

[Cloxxki]

@Petestki
To be fair to the Nio here, it was driving around the ring with maybe 300. It barely broke 300kph when the track was wide open or downforce plentiful.

Also, the era when cornering and braking are all down to the tyres' contact patches is of course coming to an end.

Already for a while we have active rear wings on some cars that function as air brake. And the likes of Lamborghini and Zenvo (whatever one might think of it) are starting to dabble in lateral aerodynamics.
I foresee a concept car that's light and has an oversized shark fin, oversized compared to all we've seen. Even a similar thing in the front. It would both swivel and have the capacity to instantly transform from a very thin fin to an airfoil. It's not that complicated with pliable carbon and hydraulic actuators. Imagine 2m² or more of fin that on demand (for instance tire load input) turns into a wing with lateral lift. Downforce is nice, but you could cancel out a good portion of your centrifugal force here, and corners don't require super slick aero anyways as you are grip limited.
Everyone who's had their hand sticking out of a speeding car or train knows the forces that act upon it, just changing its orientation into the drive wind a tiny bit.
A rear wing for instance could easily have a few upright vanes in it which along with end plates scoop air laterally either just by swiveling and/or changing shape to an airfoil. For all I care, the whole skin and floor of a run of the mill supercar could be lines with such active vanes that not only moderate downforce but also lateral air flow.

Also, Tesla has now announced a comic book style cornering aid in the form of cold air thrusters. To be used in a Space X labeled upgrade package to the upcoming Gen2 Roadster. In certain modes, part of the available energy from regen or battery or maybe even brake heat could be diverted to pressurize a thruster tank. Nozzles around the car could offer likely mostly short bursts of boost in any direction, help balance out turns, accelerate even quicker or brake harder. Even help prevent accidents when programmed properly. I'm still at a loss at to how much thrust and work would be available from a system that fits into an already crowded little car and how much there would be over the course of a lap or stint.

 

[AWDtsla]

It's hard to convince someone who thinks that reducing mass moment of inertia to zero would magically provide "infinite handling". It just means you don't understand the physics involved. Even if you did manage to achieve close to zero inertia, the tyres still have to support the static and dynamic tyre loads generated in accelerating the mass. It just means that the car would be able to spin infinitely quickly if you sat it on an ice rink and gave the front end a good shove. In practice, by reducing inertia to zero for the same mass, you would have a car with the same cornering potential (as dictated by Newton's basic laws of physics F=ma etc) but you would have infinite instability on the limit. Once you exceeded the limit of grip it would spin instantly without a hope of catching it. It's the inertia that makes it controllable.

Try balancing a long stick on your hand like a broom handle. It's very easy. Now try it with a very short stick. Not so easy. Less inertia gives a faster response to any input but also requires faster reactions to keep control of it.

Going back to the Roadster, electronic stability control will greatly help with control, so having an inherently low mass moment of inertia will not be a problem in this case. But excess mass will still greatly limit it's handling potential due to basic Newtonian physics. All I'm saying here is that mass (polar) moment of inertia is a huge red herring and will not compensate in handling for hundreds of kgs of excessive mass. Of course having a low CofG and relatively low mass moment of inertia are good things, but having less mass in the first place is still King! That's why race engineers always build cars as light as they can legally get away with.

No I'm pretty sure it's you that doesn't understand the physics. At best you're describing using mass as damper to your control inputs. Which only implies you need to fix your control inputs. That's the most charitable interpretation. Less mass is always increases the acceleration potential for a given amount of tractive force, doesn't matter if that's in a linear direction or rotational.

 

[mongo]

No I'm pretty sure it's you that doesn't understand the physics. At best you're describing using mass as damper to your control inputs. Which only implies you need to fix your control inputs. That's the most charitable interpretation. Less mass is always increases the acceleration potential for a given amount of tractive force, doesn't matter if that's in a linear direction or rotational.

Yes, from a physics POV, a photon has infinite handling, just like a massless car would, (sort of, since there would be no friction to steer with, let's just call it inertia less), but it would not be driveable by humans (only by software).

 

[Peteski]

No I'm pretty sure it's you that doesn't understand the physics. At best you're describing using mass as damper to your control inputs. Which only implies you need to fix your control inputs. That's the most charitable interpretation. Less mass is always increases the acceleration potential for a given amount of tractive force, doesn't matter if that's in a linear direction or rotational.

Oh right, so maybe I was just very lucky with my degree and career in motorsport engineering! I don't even know WTF you are talking about in your last post. Sounds like a load of BS to me. But feel free to educate me, lol.

 

[Peteski]

Yes, from a physics POV, a photon has infinite handling, just like a massless car would, (sort of, since there would be no friction to steer with, let's just call it inertia less), but it would not be driveable by humans (only by software).

Let's not confuse mass itself with its moment of inertia. The former (mass) is a first order vehicle dynamics parameter and the latter (mass moment of inertia) is very much a second order parameter and not even relevant to a basic steady state cornering model. But they are being tossed around here as one and the same thing (or even worse that moment of inertia is even more important than the mass itself). But this is typical of a public discussion of this nature, so I'm not that surprised.

 

[Peteski]

At best you're describing using mass as damper to your control inputs.

You've totally lost me here. When/where did I do that??

 

[mongo]

Let's not confuse mass itself with its moment of inertia. The former (mass) is a first order vehicle dynamics parameter and the latter (mass moment of inertia) is very much a second order parameter and not even relevant to a basic steady state cornering model. But they are being tossed around here as one and the same thing (or even worse that moment of inertia is even more important than the mass itself). But this is typical of a public discussion of this nature, so I'm not that surprised.

While I agree with the physics side of things you are saying, I was writing in terms of @AWDtsla 's original statement

Convince me all inertia going to 0 wouldn't result in infinite handling.

 

[GWord]

No I'm pretty sure it's you that doesn't understand the physics. At best you're describing using mass as damper to your control inputs. Which only implies you need to fix your control inputs. That's the most charitable interpretation. Less mass is always increases the acceleration potential for a given amount of tractive force, doesn't matter if that's in a linear direction or rotational.

Just a friendly suggestion: It would probably be helpful in terms of you more effectively making your point, if you actually did the math in your posts. I think the hang up may be in your descriptive language. For example, "Less mass is always increases [SIC] the acceleration potential for a given amount of tractive force" is tricky to read but limit(F/M=A, M->0) might be more understood by those with the aptitude to follow along.

I seem to infer from the debate that the original beef appears to be with your use of the term "infinite handling" which can be interpreted any number of ways from static friction to moment of inertia to a drivers ability to maintain control. It might be helpful to be more quantitative there.

 

[AWDtsla]

Just a friendly suggestion: It would probably be helpful in terms of you more effectively making your point, if you actually did the math in your posts. I think the hang up may be in your descriptive language. For example, "Less mass is always increases [SIC] the acceleration potential for a given amount of tractive force" is tricky to read but limit(F/M=A, M->0) might be more understood by those with the aptitude to follow along.

I seem to infer from the debate that the original beef appears to be with your use of the term "infinite handling" which can be interpreted any number of ways from static friction to moment of inertia to a drivers ability to maintain control. It might be helpful to be more quantitative there.

Right well obviously it won't go infinite, that was a facetious on my part, but yes the limit() is a better description. Point still stands though.

Oh right, so maybe I was just very lucky with my degree and career in motorsport engineering! I don't even know WTF you are talking about in your last post. Sounds like a load of BS to me. But feel free to educate me, lol.

Usually the problem with engineers is they come to a solution that seems to work in excess of their understanding or the ability to generate a model accurate enough from first principles, either through lack of time, computation, or skill. Which also happens to be the benefit of engineering.

You've totally lost me here. When/where did I do that??

I think that's what you missing here. Uncontrollable implies control input generates wild oscillations because the system is underdamped. Well of course it's underdamped, we have hypothetical 0 mass. However even this statement isn't true, as the system no longer needs to be damped by mass, but is damped by traction. You used the example of the car on ice to remove that damping as well, but even the example doesn't work, as ice on rubber STILL has a coefficient of friction, and our hypothetical car has 0 mass, so handling will still be infinite (sorry approach infinity as mass approaches 0), along with controllability.

 

[Peteski]

Usually the problem with engineers is they come to a solution that seems to work in excess of their understanding or the ability to generate a model accurate enough from first principles, either through lack of time, computation, or skill. Which also happens to be the benefit of engineering.



I think that's what you missing here. Uncontrollable implies control input generates wild oscillations because the system is underdamped. Well of course it's underdamped, we have hypothetical 0 mass. However even this statement isn't true, as the system no longer needs to be damped by mass, but is damped by traction. You used the example of the car on ice to remove that damping as well, but even the example doesn't work, as ice on rubber STILL has a coefficient of friction, and our hypothetical car has 0 mass, so handling will still be infinite (sorry approach infinity as mass approaches 0), along with controllability.

So you actually think professional engineers with a University education don't understand basic physics? Yeah sure, whatever.

Nobody was talking about zero mass, quite the contrary. Just to remind you again, the discussion was on the relative effect of reducing mass moment of inertia (i.e. concentration of mass around it's CofG) as a compensation for excess mass. But you seem to have got sidetracked by my apparent lack of theoretical knowledge of a subject I've lived and breathed for a few decades.

Zero mass would indeed approach infinite handling ability and by definition it would also have zero mass moment of inertia. But a point mass of say 2000 kg with zero mass moment of inertia would very much NOT have infinite handling. It would have the same cornering and longitudinal acceleration potential as a 2000 kg mass with a finite moment of inertia, but would be inherently unstable on the handling limit.

 

[AWDtsla]

So you actually think professional engineers with a University education don't understand basic physics? Yeah sure, whatever.

Nobody was talking about zero mass, quite the contrary. Just to remind you again, the discussion was on the relative effect of reducing mass moment of inertia (i.e. concentration of mass around it's CofG) as a compensation for excess mass. But you seem to have got sidetracked by my apparent lack of theoretical knowledge of a subject I've lived and breathed for a few decades.

Zero mass would indeed approach infinite handling ability and by definition it would also have zero mass moment of inertia. But a point mass of say 2000 kg with zero mass moment of inertia would very much NOT have infinite handling. It would have the same cornering and longitudinal acceleration potential as a 2000 kg mass with a finite moment of inertia, but would be inherently unstable on the handling limit.

Let's try this another way, define unstable.

 

[Peteski]

Let's try this another way, define unstable.

I don't see any point. I'm quite happy with my comments in relation to this discussion and don't see any need to labour them any further for your benefit. You've been tossing in all sorts of random terminology with little or no definition, so I think you should be the one to clarify what you mean. You could start by defining what you mean by "infinite handling", which means nothing to me. Not even a Google search throws up any clues! So I guess you just made that up.

 

[CarlK]

Here are more evidences if anyone still not convinced of the potential of Tesla EV. The almost 4,000 lb sedan can match the track time of a Cayman GT4.

https://www.motortrend.com/cars/tes...erformance-track-mode-release-version-review/

 

[AWDtsla]

I don't see any point. I'm quite happy with my comments in relation to this discussion and don't see any need to labour them any further for your benefit. You've been tossing in all sorts of random terminology with little or no definition, so I think you should be the one to clarify what you mean. You could start by defining what you mean by "infinite handling", which means nothing to me. Not even a Google search throws up any clues! So I guess you just made that up.

Wow did I make up a novel thought? Well thank you for the compliment. Ok it really isn't, but still...

Newton's second law still applies for rotation, but the math gets much complex. So lets keep it simple F=ma is still the guiding principle. What happens to a as acceleration, in this case rotational, when F, the available force from traction stays the same while m approaches 0? If we model the mass of the car as two point masses of size infinity, then when they are in the center of the car acceleration (as rotation) approaches infinity, and when they are at the ends of the car, acceleration approaches 0. Unless you can come up with infinite traction, and infinite steering force.

Of course for you, somehow we approach infinite instability, which is a term you cannot define, but insist that exists due to your years of engineering experience. OK. You're making extraordinary claims that somehow less mass is bad for handling, so you need to come up with extraordinary evidence.

 

[Peteski]

Here are more evidences if anyone still not convinced of the potential of Tesla EV. The almost 4,000 lb sedan can match the track time of a Cayman GT4.

https://www.motortrend.com/cars/tes...erformance-track-mode-release-version-review/

Yeah it's all very impressive, but the Cayman is seriously power limited. I would expect tyre degradation to be much higher on the Tesla too because of the higher loads.

 

[Peteski]

You're making extraordinary claims that somehow less mass is bad for handling

I said quite the opposite actually. I clearly stated at least a dozen times that less mass is King for handling.

What I did say was that mass moment of inertia (not mass itself) is not so critical. No need to twist it all around trying to make yourself look smarter. I've contributed to cars that have won world championships so I don't really need your critique. Not that I don't listen to reasoned argument, but you don't even seem to know what we're discussing here.

 

[CarlK]

Yeah it's all very impressive, but the Cayman is seriously power limited. I would expect tyre degradation to be much higher on the Tesla too because of the higher loads.

Cayman is definitely seriously under-powered but the GT4 version not so much. It's on pretty much everyone's best track day car list. Anyway glad to hear you say power can be a factor and help the Roadster to score another point.

 

[Peteski]

Cayman is definitely seriously under-powered but the GT4 version not so much. It's on pretty much everyone's best track day car list. Anyway glad to hear you say power can be a factor and help the Roadster to score another point.

Power is certainly a factor, at least up to a point. As we've seen with various super cars, once you start approaching 1000 hp it becomes less important compared to other variables like aero, mass, tyres etc.

The Cayman GT 4 with 380 hp is certainly power limited. The M3P a bit less so with around 450 hp. Interesting that they can achieve similar laptimes, but I'd put good money on the lighter Cayman having considerably less tyre degradation over a 10 or 20 lap stint.