No one is going to have a battery breakthrough
It will be into the 30's by the time we see 1000Wh/kg
Roadster will be about 2000kg and similar to a Veyron driving wise
It wont be taking on Mclaren Senna etc on the tracks, it's not possible
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200 kWh Roadster Pack: How is Tesla Pulling This Off?
- Thread starter jackbowers
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- Batteries Roadster 2020
No one is going to have a battery breakthrough
It will be into the 30's by the time we see 1000Wh/kg
Roadster will be about 2000kg and similar to a Veyron driving wise
It wont be taking on Mclaren Senna etc on the tracks, it's not possible
It will have to take on those cars if Elon wants to make true on his claims that it is going to be the fastest car in every aspect and to give that hardcore smackdown to gasoline cars. It needs to beat everything at everything to make that claim.
Sure, you don't want to take any corners at speeds over 300kph, let alone 400kph. But all that weight from the battery is not going to help with cornering at speed. Inertia is something that's going to be huge with that amount of weight. I'm afraid the Roadster will not be as nimble as we all hope it will be.
Advanced torque vectoring directly counters angular mass. It will feel lighter than it is.
Other lighter BEV supercars already use this. So not much to be gained.
Low downforce also. The thrusters will need to work a charm. And let's assume they develop those as quick as they do a better web browser. Or much desired HUD. ;-)
I'd rather like to see an augmented reality windscreen instead of a simple HUD. If AP can see lines way better than we do in poor visibility circumstances, it should display them on the windscreen, mapped to the road surface. Same for navigation. Like a better version of this: https://gizmodo.com/this-augmented-reality-windshield-tells-you-how-to-take-1603452937
Didn't have time to read through all of the posts. But all the talk is about a 200 kWh battery. My question is, is it really necessary to have that big of a battery? A 5000 lb P100D does 0-60 in what, 2.5 seconds? Wouldn't a 3000 lb P100D do close to 1.9 just from saving 2,000 lbs? Then the car could handle a lot better.
Based on how much more efficient the Model 3 is, because it's a smaller and lighter car, a 2,000 lb lighter P100D would also be a whole lot more efficient in normal driving situations.
I guess probably the biggest issue would be repeatability in the performance. The P100D can't go for long distances maxed out. So, I guess the 200 kWh battery would allow it do what it needs to do more easily. Just seems like a lot of weight to carry in a "super car".
Plus, is 600 miles in range really necessary on a super car? Seems a little backwards to me. The family sedan for road trips could use the range more than a super car being driven on weekends only. 400 miles in range would be more than enough for this segment. Especially with supercharging available. How many people drive 600 miles straight without stopping?
Based on how much more efficient the Model 3 is, because it's a smaller and lighter car, a 2,000 lb lighter P100D would also be a whole lot more efficient in normal driving situations.
I guess probably the biggest issue would be repeatability in the performance. The P100D can't go for long distances maxed out. So, I guess the 200 kWh battery would allow it do what it needs to do more easily. Just seems like a lot of weight to carry in a "super car".
Plus, is 600 miles in range really necessary on a super car? Seems a little backwards to me. The family sedan for road trips could use the range more than a super car being driven on weekends only. 400 miles in range would be more than enough for this segment. Especially with supercharging available. How many people drive 600 miles straight without stopping?
The highway range is a side effect of having enough battery capacity to perform on the track for a good period of time. You can easily use 5 times as much energy on the track. The other reason is that Elon wants to make sure that no production ICE car beats the Roadster in any metric.
NeverFollow
Active Member
Especially considering the speed limit in US, not like in Germany.
Thinking about last summer Pikes Peak EV record,
I can't wait to see an EV finishing, or even winning, the 24 Hours of Le Mans.
The race is about 3,000 miles or 5,000 km.
Typically, race cars stop every 100 miles or 160 km for refill.
Average speed is 140 miles/h or 225 km/h.
Max top speed 210 mils/h or 340 km/h.
May be with swappable batteries, by 2025 I would not be surprise to see an EV winning Le Mans.
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CarlK
Active Member
Couple of observations to make here.
The 200 kWh battery probably is not there for range but for putting out enough power for maximum acceleration and top speed. It could also help the battery longevity at cruising speed too. Each cell will not need to work as hard in order to maintain the speed when you have more of it.
The effect of extra weight could be at least partially offset by center located weight of the skidpad layout. Greater polar moment of inertia of ICE's front and rear weight location ruins handling which is the main reason why they always want to reduce weight. That is less of a concern for Tesla. Elon had a simple explanation of this.
Elon Musk on Twitter
The 200 kWh battery probably is not there for range but for putting out enough power for maximum acceleration and top speed. It could also help the battery longevity at cruising speed too. Each cell will not need to work as hard in order to maintain the speed when you have more of it.
The effect of extra weight could be at least partially offset by center located weight of the skidpad layout. Greater polar moment of inertia of ICE's front and rear weight location ruins handling which is the main reason why they always want to reduce weight. That is less of a concern for Tesla. Elon had a simple explanation of this.
Elon Musk on Twitter
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With all due respect here, I have to say this is simply not true or at the very least a very skewed perspective! Speaking as an ex F1 Race Engineer (Masters degree in vehicle dynamics, 20+ years trackside experience, etc, etc), polar moment of inertia is very much a second order handling parameter and most definitely NOT the reason why "they" always want to reduce mass. Mass and the location of its centre of gravity (both height and fore/aft position) are the primary factors in handling, not polar moments which merely affect the feel and response. In fact if you reduce the polar moment too much, you can make the car twitchy and harder to control. In F1 we even go as far as increasing the polar moment to make the cars more controllable, although they do have a relatively low polar moment moment compared to most road cars. Watch how quickly they spin out of control on the limit. In controlled tests with differing polar moments (same CofG and total mass) we saw no significant change in cornering potential, but the drivers all preferred a higher polar moment due to the increased stability it provides. As far as the tyres are concerned, they see the same loading either way (providing the total mass and CofG are unchanged) and only the transients are affected i.e. speed of response to a steering input slows with increased inertia.
Basically Elon's dumbbell analogy is far too simplified and extreme to be of any real relevance here. It's not like a contemporary ICE hypercar like a Porsche 919 has sluggish reactions to a steering input!
Anyway, we can discuss this to death and keep going around in circles, but this Roadster is not going to set any track records if it ends up significantly heavier than its competition. To put this in perspective, every 10 kg of mass you add to an F1 car slows it down by typically 0.3-0.4 sec per lap (obviously track dependent). So a 100 kg on an F1 car would cost in the order of 3 or 4 seconds per lap. Increasing polar moment of inertia by even a large percentage has little or no effect on laptimes, only the feel of the car, and higher is generally more user friendly!
Yah, rotational inertia mostly matters when you want to rotate (or stop rotating). Does it also apply in the pitch axis, directly impacting suspension and response when handling dips and bumps? More front end weight means more peak force needed to keep the front of the car off the pavement on a rise.
F1 is reaching the limit of engine power, so mass directly impacts acceleration and lap speed. Roadster is not limited to 1.6L, so if the extra 100kg increase peak motor power, mass can improve lap time. Only to a point, since mass does work against total tire traction.
To answer your first question, of course there is inertia around the pitch axis too, but it's even less significant. It's just the total mass and CofG (both height and fore/aft position) that really matters here. BEVs inherently have a very low CofG height, which is obviously great for minimising roll and dynamic lateral load transfer, but unfortunately they are also inherently heavy, which is not good for anything at all however you try to dress it up!
On your second point F1 is mainly a tyre and aero limited formula. Power is important of course, but it's not the main factor even if it often gets discussed. For sure an EV has an inherent advantage in traction/stability control, but simply adding more and more power isn't going to guarantee competitive lap times. I heard they actually turned down the power on the Nio EP9 when it did it's record breaking Nurburgring lap to make it more forgiving. It was probably both overheating and chewing its tyres up at the same time! But considering it had something like 1300 hp it was still nowhere near the Porsche 919 hybrid with around 1100 hp and slightly slower than a McLaren P1 with 980 hp or even a Porsche GT2 RS with "only" 700 hp. Basically the Nio being 1700+ kg was doing it no favours at all against cars weighing hundreds of kg less. So if this Roadster rocks up at even 2000 kg (which I think is highly unlikely with a 200 kWh battery) it's not going to set any lap records regardless of how much power it churns out.
CarlK
Active Member
Well if you bothered to read the link Elon had in one of the tweets in the twit stream you should know your perception of it is very wrong.
In there it has a very simple but clear explanation of what polar moment of inertia means for handling.
***Meaning: In the car world, this term refers to any car's resistance to turning. To figure out an individual car's polar moment, you need to know the individual weight of all components of the car separately -- as well as each component's distance from the car's center of gravity. Then you multiply the weight of each component by the square of its distance from the car's center of gravity.Therefore, larger polar moments of inertia occur when individual components of the car with heavier weight are further away from the car's center of gravity. If you're a racecar engineer, you already know this. If you're a car enthusiast who just wants to drive better on the street, you may not have the patience to do all that math. To explain it very simply: keep heavier car components as close to your car's center of gravity as possible in order to lower your car's polar moment issues. A mid-engined car will have a fairly low polar moment, assuming it isn't towing an elephant.***
25 Car Terms You Need To KnowPolar Moment of Inertia
To simply put it polar moment of inertia is "car's resistance to turning". Who wouldn't want less of that? No one would have bothered to go mid-engine design if reducing polar moment of inertia is not better for handling. On the other hand even the ultimate ICE mid-engine layout still can not reach what the skidpad layout could do in terms of both CoG and PMoI.
The example you gave may be because some drivers don't like the lighter steering effort and reduced road feel came with lower polar moment (less resistance of turning) of the possible too simple experiment. Those can certainly be adjusted with suspension and steering tuning to take advantage of it. When you got the physics right to begin with engineering work is much easier to follow. A lot of people have reported the Model 3 has probably the best steering response among all with similar weight without sacrificing too much on ride quality as other performance cars have to. That's even that the Model 3 was designed as a family sporty sedan with range and comfort in mind and not an all out performance car. I have no doubt we will be surprised by how capable the Roadster will be in handling, with or without the SpaceX package.
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I think you both may agree, but wording is getting in the way.
Were you saying polar moment is the main reason to reduce weight, or that handling was the main reason to reduce weight?
Reduction of mass has a bigger impact on handling overall (including turning) and acceleration than it does on turning due to polar moment. Location of mass can have a big impact on polar. However, too little inertia/ moment, and any outside force can make the car turn, which is not a pleasant driving experience. Pothole, cross wind, semi turbulence ...
I've done the detailed polar moment maths on many race cars for a living, including BTCC (much closer to sports road cars) and F1. If you don't want to believe what I say from experience then fine. But others might find it interesting. I'm not saying that designers totally ignore polar moment of inertia, but it's far from being a first order handling parameter like mass and CofG position. I'm also suggesting that you can go too far in minimising polar moments as experienced in F1. These are not exactly average drivers either!
I'll say it again one last time and then leave it to be judged in future. If the Roadster ends up being hundreds of kg heavier than a contemporary ICE supercar, then I don't think it has any chance of putting up competitive lap times around a typical circuit. My reasoning being that the extra mass will totally eclipse any inherent advantage in having a lower polar moment of inertia. Not even the power will be enough to make up for the cornering losses. The only place it will be competitive is on a drag strip.
Even with SpaceX package?
I agree the polar moment will not be the deciding factor, since that only impacts how easily the car rotates, actually getting the velocity vector to change is the job of the tires fighting the mass.
Do you think the dual rear motor thrust vectoring will provide a compensating boost to cornering ability? The outside tire will be more heavily loaded on the turns, and that is the one you want to add more force to to turn the vehicle. Or do current super cars have sufficient additional HP to allow ESC to vector the power via differential and brakes?
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