Absolutely. The advantages of multiple electric motors over a single ICE drivetrain are already very much in evidence in the Tesla S and X traction and stability control systems. Not having to slip a clutch off the line (either manually or by electronics) is a major advantage too. That was always the achilles heel in F1!
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200 kWh Roadster Pack: How is Tesla Pulling This Off?
- Thread starter jackbowers
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- Batteries Roadster 2020
Absolutely. The advantages of multiple electric motors over a single ICE drivetrain are already very much in evidence in the Tesla S and X traction and stability control systems. Not having to slip a clutch off the line (either manually or by electronics) is a major advantage too. That was always the achilles heel in F1!
@ Peteski
Don't take this as hostility but for the sake of accuracy, it's not ideal to focus on just battery weight (and cost) when comparing ICE and EVs. You need to compare powertrain+fuel . Sure a full tank is maybe 50-70kg for competitors but that's enough to be relevant. Excluding the battery pack, EVs do achieve much higher performance density. EVs tend to offer a stiffer chassis, no fuel moving around. Tesla was working on reducing the wiring harness size.
Anyway, if they use the same cells as with M3, my guess is that the pack is some 1000kg, maybe 10% more. If they use a carbon fiber chassis my hope is that they land around 1700kg.
I do wish they would focus more on the suspension, maybe bring that in house. Active, preemptive, low latency is closer to home for them than for others.
Smaller battery would hurt acceleration and top speed, Musk mentioned:
"The air exiting the thrusters would immediately be replenished whenever vehicle pack power draw allowed operation of the air pump, which is most of the time."
So they expect to push power draw to the limit. In theory, I suppose, a smaller battery with better cooling could get them similar peak power draw at lower weight but this car is commute friendly, they don't push product design towards hyper car track only kind of thing.
I view the 200kWh decision as a positive one as the battery would drain quickly when the car is pushed and a convertible tends to take the scenic route more often so chargers are harder to find. Larger pack tends to create more value than better cooling too. At the end of the day, there re always trade-offs
I think , perf is so abundant with EVs as long as you have a large enough pack, that the focus should be on grip (mostly aero) and suspension going forward.
Don't take this as hostility but for the sake of accuracy, it's not ideal to focus on just battery weight (and cost) when comparing ICE and EVs. You need to compare powertrain+fuel . Sure a full tank is maybe 50-70kg for competitors but that's enough to be relevant. Excluding the battery pack, EVs do achieve much higher performance density. EVs tend to offer a stiffer chassis, no fuel moving around. Tesla was working on reducing the wiring harness size.
Anyway, if they use the same cells as with M3, my guess is that the pack is some 1000kg, maybe 10% more. If they use a carbon fiber chassis my hope is that they land around 1700kg.
I do wish they would focus more on the suspension, maybe bring that in house. Active, preemptive, low latency is closer to home for them than for others.
Smaller battery would hurt acceleration and top speed, Musk mentioned:
"The air exiting the thrusters would immediately be replenished whenever vehicle pack power draw allowed operation of the air pump, which is most of the time."
So they expect to push power draw to the limit. In theory, I suppose, a smaller battery with better cooling could get them similar peak power draw at lower weight but this car is commute friendly, they don't push product design towards hyper car track only kind of thing.
I view the 200kWh decision as a positive one as the battery would drain quickly when the car is pushed and a convertible tends to take the scenic route more often so chargers are harder to find. Larger pack tends to create more value than better cooling too. At the end of the day, there re always trade-offs
I think , perf is so abundant with EVs as long as you have a large enough pack, that the focus should be on grip (mostly aero) and suspension going forward.
Interesting if ugly/cynical thought experiment from a different optimisation idea I have for the 2020(s) Roadster:
The 200 kWh figure is indicative of a notably poorer efficiency than the Model 3, and even the S, particularly given that the vehicle is noticeably smaller in dimensions even than a Model 3, and crucially, is obviously better streamlined - it doesn't have spoilers, for instance.
For 620 miles that's only an official range average of 3.1 mi / kWh versus the Model S P100D at 3.3 mi / kWh.
Another fact which I am surprised people on here have not noticed is the the power to capacity ratio is likely LESS than that for the Model S.
The 2020 Roadster is commonly estimated across many articles to have 1000 to 1300 hp versus the Model S P100D at 760 hp ish. So basically that power can be achieved realistically with only 160 to 170 kWh.
So I thought, if Tesla:
At 4 to 5 kg/kWh, 40 to 50 kWh would have a mass of 160 to 250 kilograms, which is much heavier than a set of high-efficiency motors/gears or simply designing the normal power motors to use special high-efficiency "cruise" mode/gearing, which would unlikely to be heavier than in the tens of kilograms.
So I have two questions related to this scenario:
1. Why would Tesla resist that kind of weight saving?
2. If the 200kWh is indeed a fib and and they did the above, how far could they get away with it?
Would the majority of Tesla's customers actually appear to be concerned if Elon Twittered: "We decided to use less battery as we have now found (cough) that we can achieve the required performance using less battery and less weight through our ongoing improvements (cough)" ?
The 200 kWh figure is indicative of a notably poorer efficiency than the Model 3, and even the S, particularly given that the vehicle is noticeably smaller in dimensions even than a Model 3, and crucially, is obviously better streamlined - it doesn't have spoilers, for instance.
For 620 miles that's only an official range average of 3.1 mi / kWh versus the Model S P100D at 3.3 mi / kWh.
Another fact which I am surprised people on here have not noticed is the the power to capacity ratio is likely LESS than that for the Model S.
The 2020 Roadster is commonly estimated across many articles to have 1000 to 1300 hp versus the Model S P100D at 760 hp ish. So basically that power can be achieved realistically with only 160 to 170 kWh.
So I thought, if Tesla:
- Gave up on 40 to 50 kWh of battery (down to 150 to 160 kWh) in favour of an extra set of high-efficiency non-performance motors at 3.8 to 4.2 mi/kWh thereby maintaining the same cruising range.
- Maintained a realistic, roughly 250-200 Wh/kg or 4 to 5 kg / kWh for the whole battery pack (75-80% cell mass at 2170 specific energies), resulting in a far more believable battery pack mass of 600 to 800 kg, which is still a bit much in my opinion.
- Ignored the decrease in "full pelt range" which is never really noticed by anybody, especially given that a university has judged the "full pelt time" to be a whopping 25-30 minutes versus the Veyron/Chiron's 10-15 minutes.
- Took advantage of a higher voltage for the battery cells with a 150 to 160 kWh battery. Assuming it's higher than 1300 hp.
- Simply used a higher power to weight ratio largely restricted to start-offs which are sporadic and unlikely to damage the cells further than a 200 kWh battery.
At 4 to 5 kg/kWh, 40 to 50 kWh would have a mass of 160 to 250 kilograms, which is much heavier than a set of high-efficiency motors/gears or simply designing the normal power motors to use special high-efficiency "cruise" mode/gearing, which would unlikely to be heavier than in the tens of kilograms.
So I have two questions related to this scenario:
1. Why would Tesla resist that kind of weight saving?
2. If the 200kWh is indeed a fib and and they did the above, how far could they get away with it?
Would the majority of Tesla's customers actually appear to be concerned if Elon Twittered: "We decided to use less battery as we have now found (cough) that we can achieve the required performance using less battery and less weight through our ongoing improvements (cough)" ?
I suspect most future Roadster 2 owners couldn’t care less how big the battery pack is. Even range isn’t that big an issue (it’s a sports car, not a long distance traveler). All that matters are the performance specs, handling ability, and design (Model 3 prototype hood looked a lot better than the production version, but I can write that off to cost savings. Roadster 2 has to look as good if not better than prototype).
If future Roadster 2 owners are concerned about handling performance then they certainly should care how big the battery pack is! Battery pack size is a major compromise between handling, range and arguably peak power output. Cost too, but that's mostly irrelevant in a "halo" supercar like this.
Most ICE weights are quoted with a 90% fuel fill (DIN kerb weight). EU kerb weight even adds a further 75 kg for a driver. So you can easily find directly comparable weights without having to take fuel into account (unless comparing against a quoted "Dry Kerb weight")
The bottom line is that at present an EV drivetrain + battery is significantly heavier than an equivalent ICE drivetrain + fuel. Weight has always been the achilles heel of EVs in general and it will be especially critical in a supercar designed to have the ultimate handling capability. So the choice of 200 kWh battery and 600+ mile range seems a bit at odds with what you would want from the ultimate sports car. The Rimac 2 with a carbon chassis is reported to weigh 1,950 kg (still pretty heavy) with a 120 kWh battery.
Maybe some customers will prefer the 600 mile range and live happily with the heavier battery, but any serious driver would give up some of that range for a lighter car. The obvious thing would be to offer different pack sizes as they do with their other cars. Then everybody would be happy!
Valid points.
For the 'serious driver' case, where are they doing this driving that potentially exceeds R20's handing ability? Are you thinking track, or real world driving? If R20 has best acceleration, braking, range, and nearly best cornering (exceeding that to typical roads), that seems like a good balance for a car one could use in everyday life. On the nimble side of the spectrum, lighter and shorter would likely trade off range and power.
Cool idea regarding the light weight pack option, I'm just not sure what that does to power/ longevity/ cooling.
When you drive a performance car well below its grip limit, you are still fully aware of its weight whenever changing direction. It can also show up in the ride/handling balance as you have to have the spring rates to support that weight. Drive a Model S along a winding and undulating road and you feel the dampers working hard to control all that mass heaving around. It's still very good, but it's not close to a 911 or even as sharp as a Panamera. Those are simply better handling cars on a driving road, regardless of their ultimate grip levels. Drive something truly lightweight like an Atom or Elise and those cars feel super agile like a kart, again regardless of the limit.
I live very close to Silverstone circuit and the roads around here are great driving roads. But a lot of the bigger, heavier supercars are not particularly fun to drive on these roads. It's actually cars like the Porsche Cayman that really excel. On wider more open roads, the bigger cars are fine, but then speed limits and other traffic get in the way of any fun. As a track day car, I prefer lighter cars too. A Porsche GT3 is a good compromise between power and weight and they are just over 1,400 kg DIN. I wouldn't want to be adding 600+ kg on top of that for power that I probably couldn't handle anyway!
I just hope they don't make the Roadster into too much of a beast just to win the top trumps. It's got to be an engaging drive on ordinary roads to get my money. My benchmark for that is a Porsche 911 or Cayman. It has to be more fun to drive than those for the money, not just frighteningly quick in a straight line.
Was thinking yesterday that folks focus too much on weight. yeah in racing you push every lever you got to get the most but this is a different context, different constraints.
In consumer, everything is a product design decision and weight is bad if you don't do anything about it. If heavy, you invest more in suspension, add more downforce. The closer you are to the limits, the fewer options you have but are these cars really the ultimate performer within the legal limits? Not really , usability is still a concern.
On the battery side, don''t know if you've seen this M3 battery teardown (it's very long)
Pack weight 478.1kg
25S long module is 73x11 1/2 x 3 1/2 and weighs 207 lbs
23S module is 67 1/2 x 11 1/2 x 3 1/2 and weighs 191 lbs
(the module info is from a comment to that video)
Stumbled upon this article https://jalopnik.com/the-bugatti-chirons-engine-alone-weighs-almost-1-000-po-1826728629
Bugatti Chiron
Engine: 961 pounds (436 kg)
Transmission: 273 pounds (124 kg)
So would take a very hefty cut in battery size to match a super heavy ICE powertrain and that would come with lower peak power, much quicker perf degradation as max available power declines , fewer miles added per unit of time when charging, shorter range.
To me , the large pack is a simple and brilliant way of solving a bunch of problems and is also a sales and marketing upside The downside being weight and efficiency but efficiency doesn't matter much in this case and weight, maybe can be dealt with.
If you can beat all competitors and keep the car very usable , why not, they are a business after all.
I was hoping for a more aggressive design but i do get their choices.
Edit:
"Drive a Model S along a winding and undulating road and you feel the dampers working hard to control all that mass heaving around"
They could mask it with very low latency active suspension, and if they have sensors watching the road, it can become preemptive for an ideal ride. They could also offer an ample range of driving modes with such a solution.
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Gotcha, handling/ ride in general, not just cornering. Good point on required spring (air pressure) needed to set ride height.
I had an non-Shelby/GLH Omni for a while... It was fun, but I had to take out the interior door handle to clutch...
I imagine there will be signifiant weight saving outside of the drivetrain compared to the P100DL. Plus, they can shape the battery to assist where extra "downforce" is most needed (as Rimac do), saving weight on aero. Torque vectoring (3 motors!) will assist with handling in the curvy bits.
That's an option so not factoring it in.
And about handling, wondering about wheelbase as it might be similar to M3 and that's at 2.875m so pretty large. Maybe the low latency traction control and toque vectoring can compensate for it.
I'm not suggesting they need to exactly match an ICE in weight, but you do have to think carefully about how much weight you can add without ruining it as a driver's car. Aerodynamics, active suspension, torque vectoring etc are all valid things to help mitigate extra weight, but think about those poor tyres on the ground! They see ALL that extra loading and will degrade rapidly as a result. However you want to ignore it, mass is a very fundamental parameter in any vehicle dynamics model.
So is this going to be a top trumps posing wagon or a proper sportscar able to top production car lap times around a track? I'm not sure at this point, but alarm bells were ringing when I saw the pack size.
Let's not forget that we have no info on weight actually. I expect it at 1700kg, most expect it at 2000kg so quite a lot but plenty are as heavy.
And at same weigh Evs have some advantages so they should beat those competitors as long as they have sufficient downforce - do they?
My concern is aero as we got no details. They can use technology to keep the car balanced and do it better than others, the tires are likely not exclusive so can't make a difference but would not be great if they lack downforce. And yeah ofc ,higher the weight , higher the downforce needed.
The info we do have is 200kWh and 250 mph top speed. That sounds heavy and low downforce to me.
I would be surprised if they can get it down to 2000 kg with that battery. If they hit 1700 kg then great. But then I'd still take a 100 kWh version at 1200 kg and give up some top speed. Acceleration might even be better and handling certainly would! It's not like a Model S P100D is slow off the line and this would be 1000 kg lighter if your prediction is true!
thegruf
Active Member
@Peteski - I think the opposite is the case.
The P100D essentially maxes out the current that can safely be drawn per cell.
The only way to get more power is
a) some as yet unannounced development resulting in drop in cell IR, or more likely
b) more cells required to make more power available. The side beneift is huge range (and Spacex goodies), the compromise is weight.
Remember also that inevitably the next roadstar will be expected to perform for extended periods on a track, so this will be less of a burst rating, more an intermittent/average cell draw rating for which thermals have to be managed.
One thing I don't expect Tesla to compromise on is pack longeivity through excessive current draw as this quite likely will yet turn out to be one of Tesla prime USPs as other manufacturers scramble to compete with higher cost battery tech from 3rd parties and over-stress packs in the process leading to early degradation.
I'm with you that lighter is better but unfortunately BEV technology can't deliver this (yet), and BEVs also have to have huge strength to mitigate accident damage to batteries, so again difficult to do without weight penalty.
1900Kg (and just under 2000Kg with the Spacex option) is my bet.
The P100D essentially maxes out the current that can safely be drawn per cell.
The only way to get more power is
a) some as yet unannounced development resulting in drop in cell IR, or more likely
b) more cells required to make more power available. The side beneift is huge range (and Spacex goodies), the compromise is weight.
Remember also that inevitably the next roadstar will be expected to perform for extended periods on a track, so this will be less of a burst rating, more an intermittent/average cell draw rating for which thermals have to be managed.
One thing I don't expect Tesla to compromise on is pack longeivity through excessive current draw as this quite likely will yet turn out to be one of Tesla prime USPs as other manufacturers scramble to compete with higher cost battery tech from 3rd parties and over-stress packs in the process leading to early degradation.
I'm with you that lighter is better but unfortunately BEV technology can't deliver this (yet), and BEVs also have to have huge strength to mitigate accident damage to batteries, so again difficult to do without weight penalty.
1900Kg (and just under 2000Kg with the Spacex option) is my bet.
Based on the weight of the M3 modules from that teardown and assuming M3 has 80.5kWh, the modules for 200kWh would end up just under 900kg.So depending on how much they invest in the frame of the pack, it ends up at 1000-1100kg. For chassis i hope for carbon fiber.
Some years ago there was a mention that the 362 horsepower motor used in Model S at the time only weighs 70 pounds - just the motor.- but remains to be seen if they optimize motor+inverter for weight or they reuse existing parts.
And best case, Musk mentioned a couple of things on batteries at the shareholders meeting.
Probably 2-3 years for 30% gains in volumetric density.
And a second relevant bit, with further work on chemistry and manufacturing, along with more integration at the cell level and then improved design at the module/pack they can get bellow 100$ per kWh at pack level long term - long term meaning definitely less than 2 years.
Assuming this second bit implies a significant improvement in weight too, even if they don't hit 30% volumetric gains.
Granted my 1700kg is optimistic and would require a serious focus on weight.
Yep. I am no track driver- but i am still a serious driver. They are not the same thing!
I want a smaller Model S with better suspension (NOT the stupid, backwards air suspension) and 600 mile range. Then, range is NEVER going to be an issue for me. Hurry up and build it, Elon, so I can buy it. Otherwise, I might be tempted by a Porsche or a Jag or something else.....
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