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To ensure that the Tesla Roadster is as safe as possible in extreme conditions, we have just finished putting one of our Engineering Prototypes through an extensive test schedule at the Continental Proving Ground in Arvidsjaur, Sweden. The proving ground is in a beautiful location on and around a frozen lake about 60 miles from the Arctic Circle.
Sunset in Arvidsjaur, Sweden
Initially we were slightly nervous about driving on water, as it were, but the locals convinced us that the minimum 80cm of ice was ample support for the weight of the Tesla Roadster. And besides, there were plenty of other prototype cars around that were considerably more portly than the diminutive Tesla Roadster (to say nothing of its occupants – a 7 pound weight gain is considered normal during a winter test trip).
The testing was focused on the following two safety systems, both of which act to stabilize the car:
- Anti-lock braking system (ABS)
- Traction Control - using the sophisticated electronics from Tesla Motors
Our development partners at Continental are supplying our ABS system, which is calibrated specially for our car and subjected to a vigorous testing program. Winter testing is only one part of the development program; the car had previously been put through its paces at one of Continental’s other proving grounds in Germany. The proving ground at Arvidsjaur, however, offers a range of different surfaces on which to test every worst case eventuality – snow, polished ice, and “split µ” (or split surface) in various configurations, such as hills, circles, and checkerboard layouts.
The Greek letter µ (pronounced moo in Norfolk, or mew in the rest of the world) is the symbol used in physics for the co-efficient of friction. The lower the number, the more slippery the surface. “Split-µ” surfaces, where one side of the car is on a low friction surface (in our tests, ice) and the other side is on a high friction surface (in our tests, asphalt), can cause particular difficulties. The wheels will behave differently depending on the surface they are reacting against. Under braking, the wheels on the ice surface will lock earlier than the wheels on the asphalt, tending to spin the car. ABS will stabilize the car in this situation by controlling the brake pressure to each wheel individually, preventing any wheel from locking. Check out the video below of our tests braking on a split-µ corner. The split-screen video shows the car on the left with ABS on and the right with ABS off. Without stabilization from ABS (right screen), the car spins out when the driver applies the brakes.
ABS testing 
(Free QuickTime player required to view video.)
Whilst in Sweden we also took the time to refine our traction control system. The exact algorithm is another part of our “secret sauce.” Suffice to say, it works by controlling motor torque in response to wheel slip and ensures the car stays stable. Wheel speed sensors form a part of the ABS system and they send individual wheel speeds to one of our processors 100 times per second. These speeds are constantly analyzed in order to determine if any wheel is slipping, and, if so, the motor torque is limited until the slip is brought back under control. This system works not only when the throttle is applied but also under regenerative braking.
Regenerative braking works by reversing the direction of the current to flow into the battery, effectively turning the motor into an electrical generator. This negative motor torque is used to slow the car and feels similar to engine braking on a regular gasoline vehicle. Not only does this minimize brake wear, it also gives some lovely charge back to the battery. One potential downside: If too much negative torque is applied, the car’s wheels could lock and the car could become unstable, so our traction control system is tuned to take this into account and ensure that we can safely maximize the level of regen without upsetting the car’s balance. The regen control is always on, but the traction control can be switched off by a button on the center console, and that’s when some real fun can be had… Time for a disclaimer here: The video below shows driving with winter tires on a closed track and nothing to smack into. Please don’t try this at home.
Testing with traction control turned off (Free QuickTime player required to view video.)
Sliding around is not just done for kicks, though. An important part of the car’s development was tuning the throttle response – i.e. how much torque you get from the motor for a certain pedal position. This has been set up very carefully to allow the best control of the car over the full motor speed range – this sort of drifting just isn’t possible without very good throttle response. (That said, with only five hours of daylight you do need something to lighten the workload!)
Testing the Tesla Roadster
Beyond the dynamic vehicle development, we also gained lots of useful learning on how the car behaves in real-world, extreme-cold conditions. This supports our ongoing climatic chamber development (see the Blowing Hot and Cold blog). This chamber can replicate cold temperatures but cannot simulate snow ingress, for example. Among the (non-automotive) interesting discoveries we made was that -17° C (1.4 ° F) is the temperature below which your nostrils start feeling crunchy, though I guess readers in New York state will already know this!
Other cold weather testing completed includes that of our Tire Pressure Monitoring System (TPMS ). This system constantly monitors tire pressures to warn you if they are outside of spec. As pressure varies with temperature, it is important to calibrate the system for all operating conditions – including extreme temperature changes, such as driving from a hot garage into the cold outside – otherwise the system could throw up spurious warnings.
As with all our development activity, the learning we get at this stage is funnelled into the next level of prototypes and ultimately the finished car. Although we are now thoroughly satisfied with the low-µ performance of car, we are continuing refinement of the traction control and regen systems at the Lotus test track here in the U.K. to ensure that it performs equally well on grippier surfaces. (See map of our facility in Hethel, Norfolk)
However, due to the famous unpredictability of the British weather, we don’t always have a dry, grippy track. In fact, conditions so far this year have occasionally been better suited to testing boats! The solution to this is to go somewhere nice and sunny like IDIADA near Barcelona, Spain. Final ABS / Traction Control testing is scheduled to take place there in early May.
Posted in the categories: Performance, First Post, On the road, Safety, Vehicle Engineering
Iain, thanks for another informative post. One comment that has surfaced in several other blogs is the desire for an all wheel drive version of the Whitestar for those of us in the snow belt states. Would you please explain if the traction control system would alleviate the need for all wheel drive? Rear wheel drive vehicles don’t do as well going up an icy hill as their all wheel drive counterparts. Also, how much data will be available to the owners from the PEM on the performance of the systems in their Roadsters?
The left half of the ABS Testing video is [url=http://www.teslamotors.com/engineering/safety.php]posted elsewhere[/url] where it created speculation about the distinctly internal combustion sounds at the end of the video as the Roadster accelerated away. Were those ICE sounds from the Roadster or did they come from one of the chase vehicles (any details on the engine causing the sound)?
I’m also curious to know whether the Roadster’s traction control handles split-mu acceleration as well as it handles deceleration. How does it compare with a Torsion differential for acceleration?
—-
Editor’s Answer: Direct from Iain Morrison - I’ve just had a listen and can’t hear anything that sounds like an ICE engine. Maybe I’ve been to too many gigs and my ears are getting dodgy! Or maybe the sound on my laptop is just not up to much. The video was taken by Conti staff up in Arvidsjaur. The track was open to other vehicles so the sound must belong to another car on the track. It’s very calm there, so sound carries, and there are lots of other vehicles around.
Jean, I certainly also desire all-wheel-drive. It’s great. Doesn’t seem like there’s any big technical problems in the way, at least no more than any other vehicle. From Lain’s description, the traction control would not require modification. Obviously there would be added complexity/cost/weight in the drivetrain, presumably resulting in reduced efficiency and range. I don’t know how bad these drawbacks would be, and/or whether the resultant car would appeal to me more or less. But it would be interesting to know Tesla’s thoughts on it…I’m betting they’ve already explored the possibility thoroughly.
One other thing; you seem to believe whitestar will be rear wheel drive? I sort of assumed it would be front-engine, front-wheel-drive like most sedans, but I haven’t read anything that says…I would definitely prefer the front-front. As for the roadster, its mid-rear configuration should be wonderful in the snow; AWD may be the best, but MR is certainly next best.
Hi Iain,
I have a question about the accelerator pedal position. Does it correspond to a certain level of power delivery, or is it more like a speed control? In other words, if you’re driving along the flat at a constant speed and then you start climbing a hill, do you need to push the accelerator in to keep up the same speed?
Also, I have a suggestion for the dashboard display: How about including a large bright bidirectional bar that shows the power delivery either out of, or into the battery. Something a little like the IMA display on the Civic hybrid. It would be neat to see how much energy is saved through regenerative braking.
Hello,
thanks for this blog.
As an italian actually residing in Barcelona, i’d love the opportunity to see the Roadster with my eyes.
CAN YOU TELL WHEN YOU’LL BE IN IDIADA?
MAY I GO HAVE A LOOK AT THE CAR ?(I’M NOT PRETENDING TO TEST IT, HEHE, ALTHOUGH THAT WOULD BE JUST FANTASTIC)
Congratulations, i hope one day you’ll sell Tesla cars in continental Europe also…
Bye,
Francesco
Steve, from the posts I’ve read here, it seems the throttle is artificial. That is, the pedal is simply a sensor; software reads the pressure and provides appropriate engine output.
The trick here is what is “appropriate.”
There are lots of possibilities there. The most obvious is emulating the throttle response of an ICE. I really hope they didn’t do that, as it seems to me it would nullify (for normal, untrained drivers) some of the benefits of the electric motor’s torque/power delivery. That said, I wouldn’t expect a “speed control.” The problem is, if you want absolute “speed” control then not touching the pedal is zero mph and the floor is 130. Which would require incredibly fine muscle control for those of us who want to stay within 5 mph of the limit, or want to accelerate/decelerate smoothly. If you want “acceleration” control instead, it’s only slightly less awkward…then you have to keep your foot halfway down to maintain speed, more or less exactly. Either way, no fun, and probably feels worse than a normal ICE car.
The good new is that instead of these options, Tesla has chosen to fine-tune an algorithm that feels great to good drivers, through testing in actual driving conditions. Nothing like empirical validation…
Thanks Iain,
Instead of a heavy driveshaft you could place hub motors in the front wheels. Which would be a lighter method of achieving 4WD, but would be a halibut to control. Hub motors wouldn’t be able to match the max power of the main motor anyway and so this unwieldy system could only be used at low speeds. And before anyone asks, no you wouldn’t be able to use regen on the front motors during non-winter months as this would just increase rolling resistance and require more output from the motor in the back (and therefore increased current drain on the batteries) to maintain steady speed.
There’s been a lot of discussion on the cold weather performance of Li-ion batteries. Cold temporarily reduces energy density and therefore maximum range - but what about power? (Not that any sane person would want to do 0 to 60 mph in 4 seconds straight off their front drive on an icy morning - I’m just curious)
Please can you confirm how the ESS thermal management system deals with this? Is the cold weather start-up behaviour of the Roadster better than / worse than / same as cold weather start-up on an ICE?
I’m glad to read that you’re keeping us New Yorkers in mind! I can’t wait to drive my own Tesla around Syracuse one day! It’s certainly a comfort to know that the cars will survive in a place that gets a real winter (unlike silicon valley! -no offense -)
Hunter, you make a good point. My assumption was that the Roadster DNA would be propagated to the Whitestar hence the rear-wheel-drive. Maybe that wasn’t such a good assumption. Given the results of the testing I wasn’t real concerned about general driving and handling of the Roadster in the snow. It looks like they have that part figure out just fine. I was just worried about it’s ability to climb those long icy hills that all the semi’s and two-wheel-drive vehicles seem to get stuck on here in Colorado. Short of having AWD I would also prefer the FF configuration.
Hey TM, can you release any information about the configuration of the Whitestar????
While watching this PC Magazine vid (www.autobloggreen.com/2007/04/05/pc-magazine-tests-the-tesla-roadster-check-out-the-video/), I noticed a quick shot of someone using the Vehicle Display System (VDS). It occurred to me that it would be cool to eventually have a web based simulation of the VDS so we can have an idea what the interface is like.
here’s an interresting article about an electric drag motorcycle using A123 batteries.
www.greencarcongress.com/2007/04/electric_motorc.html#more
My suggestion for the display is simply have a sizable LCD display and make everything that goes on it programable. It sounds like you have more than enough computing power to do that. Just put in enough sensors to satisfy everyone. You shouldn’t need to go to a mechanic to diagnose error messages either. If the rumor that you are using Linux is true, it should be possible for several people to develop aplications for the display, perhaps even influencing some of those “trick behaviors” that we heard about in a previous blog entry.
As someone who has recently seen firsthand how important safety is, I am pleased to see how careful and thorough these tests are. I would like to ask, however, if the Tesla is going to undergo any rollover crash tests. You come close to that idea with split-friction tests, but I assume that the side on asphalt was not facing in the direction the car was originally going, and that the car was also not going faster than 65. Having recently been in a rollover in a Mercedes at 85 mph (spun on ice trying to make a turn, then hit asphalt going sideways), I would feel a lot better knowing that at least one Tesla prototype went to examining exactly how bad a high-speed rollover collision would be.
> If the rumor that you are using Linux is true, it should be possible for several people to develop aplications for the display, perhaps even influencing some of those “trick behaviors” that we heard about in a previous blog entry.
Since allowing the system to be hacked could make the car unsafe and potentially involve liability, I wouldn’t be surprised if they were using an embedded OS. With firmware they can secure a chip such that the warranty and liability are null and void if the chip is tampered with. It is very rare that they are sharing so much information with the public, and I think that will pay off, but I wouldn’t expect them to allow open programing of their car unless they had a completely separate section that was for user defined functionality.
Still having a user customizable section would only have limited long term functionality unless it were completely replacable.
There would be a market for a standard upgradable section ( read standard DIN chassis ) PLEASE.. PLEASE..
Over the years I have seen the standard DIN chassis for tape decks, CD’s, now DVD’s and how about
1. XM radio
2. HD digital radio
3. iPod connectivity
4. Navigation systems (from CD’s to DVD’s to live content downloaded by satellite.)
5. who knows what is next yet there is always a standard DIN replacement with minimal cost.
I think NOTHING dooms an old luxury car like a useless entertainment section. For example I looked at a used 740i with front loading multi CD loader and trunk mounted CD Navigation system, no XM or iPod plug in, an ugly ancient phone adapter etc… This is a beautiful car, but the dash is hopelessly dated. Ironically my ancient F150 has a more modern looking dash because it doesn’t have any of the obsolete systems on it.
Based on some interviews with Martin Eberhard that I’ve read recently, the Whitestar is supposed to be rear wheel drive with the ESS up front. I would also expect to see the electric motor between the rear wheels to minimze weight and complexity. Rear wheel drive provides the best driving dynamics, and no other vehicles in the Whitestars class are front wheel drive, though some are all wheel drive.
One possibility for AWD on future Tesla’s would be to use one motor up front and one in the rear. This would not add much weight since each motor is close to 70 pounds, but it would likely cause a significant decrease in range.
Dan, Now that’s a thought. Only engage the second motor for power when required similar to today’s on demand 4WD. It could be used for extra regen braking when in the 2WD mode.
Iain,
As an Upstate New Yorker, I’d like to ask a question near and dear to those of us in snow country. How well does the heater work? I’ve read the blog “Blowing Hot and Cold” but there were no comments made from a driver’s perspective.
Since a large part of the weight of the car is in the battery I would expect placing the battery a little in front of the traction wheels would be the best solution for maximizing acceleration and for driving uphill.
All wheel drive would not help much under these circumstances unless you need to maximize traction for specific conditions like going uphill on snow or ice.
Also a heavy battery placed very low may help make the car more stable. As the Tesla is now, I believe it’s close to ideal, and it would be a pity to change it in future projects.
mark wrote on April 5th, 2007 at 12:47 pm
>Since allowing the system to be hacked could make the car unsafe and potentially >involve liability, I wouldn’t be surprised if they were using an embedded OS.
I was talking about the user display only. Some people want to know things that others don’t care about. A programable display could also give out warnings if a sensor reading was outside a pre selected range. Battery too cold or too hot for instance or you were using power too quickly. If someone needed to maximize range (for a trip perhaps) they would have different requirements than someone going out on the track for the afternoon. Depending on circumstances, that might even be the same person.
Some people may even want information displayed in a diferent order than others. With all the computing power in the car, it should be posible to acomadate many diferent needs and desires. One could also select between diferent preprogramed “trick behaviors” and perhaps join 2 or more together. I understand that some of them are tied to a user access code, one of which is a valet mode that would keep someone from joy riding when all they are supposed to do is park the car. So long as the sensors are there, information could be displayed in a variety of ways.
> I was talking about the user display only.
If you are asking for Tesla to provide different skins and some flexibility that is reasonable.
My comments were based on the fact that unless the UI is on a completely separate computer system from the rest of the computer that there is reason to be extremely leery of unleashing a the world of hackers on the car. Keep in mind that many of the people getting this car are technically savvy people.
After watching a guy program his roomba to be controlled by his Wii wireless bluetooth controller, I can only imagine what would happen if the Tesla had a bluetooth interface, but I could see having firmware upgrades available for download like there are for digital cameras and many other devices. Still if they could lock it down it would be really interesting to see what people come up with an SDK that could talk to the car.
Doug @ Stanford wrote on April 5th, 2007 at 8:49 am
> It occurred to me that it would be cool to eventually have a web based
> simulation of the VDS so we can have an idea what the interface is like.
I suggested this to Tom Colson at Tesla during a “Ride Saturday” event in February. He liked the idea a lot, and said he would pass it along. I imagine that there are more good ideas than available resources, though.
“I can only imagine what would happen if the Tesla had a bluetooth interface”
Yours for $100
Options & Accessories:
Two-tone premium interior, $1,800
Touch-screen navigation system with voice guidance, $1,200
Matching body-colored carbon fiber hardtop with full headliner, $3,200
Bluetooth cellular phone integration, $100
Not sure how far the intergration….er….integrates.
Dan: You wouldn’t happen to have a link handy to some of those Eberhard interviews, would you? I’ve been reading all I can find for a few months now, and he’s always been 100% tight-lipped about whitestar from what I’ve seen. Also, what “class” do you perceive whitestar to be in? I can’t think of a class of sedans that has no front-engine, front-wheel-drive cars in it. And finally, what do you mean by “the best driving dynamics”? Don’t want to sound too over-skeptical about this information….but it does seem to me that putting the weight (ESS) in one end of the car and the drive wheels in the other sounds rather backwards…
Jean: With respect to “propogating the roadster DNA to whitestar” I would agree that it’s a good idea. But that doesn’t really lead to a rear-wheel-drive roadster. Most mid-rear drivetrains are actually very similar to front-front drivetrains, certainly more so than they are similar to front-rear ones.
Malcolm: In addition to the problems you note, the big issue that Tesla has cited for not using hub-motors is unsprung weight. Basically, the car would handle terribly with motors in the wheels, because too much of the car’s weight would be below the suspension. This is discussed in one of the blog posts from a month or two ago.
Mark-
First off, from the pics it looks like the stereo is a standard DIN unit, which I’m happy about just as I’m sure you are.
Secondly, as to the “liability” issues with using Linux or similar in the electronics, I think you are way off base here. If someone willfully and materially alters the functional nature of the car in such a way as to make it unsafe, the company that made the original, safe car is not liable for what he does to himself. Consider the guy with the jet engine coming out the back of his new beetle crashing it and suing VW. Or a closer, more realistic scenario…I go buy a programmable engine control chip for my ICE car, screw up the settings, and blow up my engine; I can’t go sue the manufacturer because they made the chip upgradeable. I agree with you that going out of their way to make the system “hackable” is a poor decision (simply from an image/quality perspective…you don’t want people’s 100k cars out there with dashboards looking like some 14 year-old’s KDE setup) and not worth their time. But I see no problems with them using Linux…on the contrary, it seems like a natural fit and I’d actually be a bit surprised if they weren’t using it somewhere.
Jean: woops….I typed “doesn’t really lead to a rear-wheel-drive roadster” and meant “doesn’t really lead to a rear-wheel-drive WHITESTAR.”
Hunter: Thanks for the update. Unfortunately, I have never really been interested in high performance cars until I met the Roadster (i always felt they were a wast of gas and money). I am therefore unversed in the drive characteristics of such vehicles. The only dynamic I was ever concerned with was do I take my front-wheel-drive or four-wheel-drive out in the snow (I haven’t purchased a pure RWD in years). Usually the question is, is the snow too deep for the Accord?
From a pure engineering perspective the weight distribution of a mid-rear configuration is closer to a FF configuration but it still lacks the traction of 4 wheels. Maybe you can provide a short “Drivetrians for Dummies” or point me to some sources for some research.
Jean-
Hehe…looks like they’re reading our comments; check out the next blog post for a really good description of the various configurations as it relates to normal handling. The only difference with the snow is that the various drawbacks (over/understeer, traction loss) are much more pronounced.
As for what I was saying with the mechanical similarities between FF and MR/RR is basically just how the engine and transmission and such are laid out. In a FR (say, a pickup in 2WD) the transmission is behind the motor sending the power back. In any of the other three, it’s usually directly under the motor and directly between the wheels. So, as you see, the system would be pretty much the same whether it’s between the front wheels or the rear.
On the other hand, since the weight in this case is the batteries (which can be anywhere) rather than the motor (which requires big heavy shafts/differentials to move power around), Tesla has way more flexibility here. I was looking at it a bit wrong, in that a rear-wheel-drive whitestar would certainly still have its motor between the wheels. It’s just a question of where the batteries are going to go. Which is nice…given the fact that they can put them anywhere they want, I’m sure they’ll make sure that it has a good weight distribution.
Hunter: Never mind David Vespremi next door in the “Feel” blog just posted a great description of this.
> But I see no problems with them using Linux…
Neither do I, although at least historically, QNX was a much better embedded OS with MUCH finer resolution(100-200X better) task switching. Heck QNX’s kernal was designed to fit into the cache of a 486 back in their first POSIX compliant release in 1991. QNX is the antithesis of MS Windows. Linux is about half way in between.
www.openqnx.com/index.php?name=FAQ&id_cat=1
That said, I’m not suggesting that Linux is a bad choice especially when I don’t know what all of their criteria are for their selections of OS’s etc..
Huntrer: I think the information about the Whitestar being rear wheel drive came from the Martin Eberhard interview on autobloggreen.com, but I don’t remember where I read that the battery pack would be in the front. I definately read it somewhere but it could have been a rumor. I would expect the battery pack to be behind the rear wheels and in front of the passenger compartment. This location would allow the weight distribution to be near 50/50 and would decrease the polar moment of inertia of the car, which both positively affect the handling of the car.
As far as rear wheel drive having superior driving dynamics, I say this because during acceleration weight is transferred backward, meaning the drive wheels have more traction. Also, the front wheels have to steer so forcing them to also accelerate causes torque steer and wheelspin coming out of corners. Ofcourse, this applies only to sporty driving, in snow FF does have advantages.
As far as the class of car, I would qualify it as mid-size sport luxury car because it has been described as a competitor to the BMW 5-series. I would expect it to compete with (besides the 5-series) RWD cars: Mercedes E-class, Lexus GS, Infiniti M45, Cadillac CTS/STS and AWD: Audi A6 and Acura RL. The A6 is offered in FWD but I dont think the FWD A6 can compete with the other cars listed.
I guess Tesla beat me too the driving dynamics explanation.
Hunter - I wouldn’t speak so fast in regard to liability in a “hackable” system. In strict liability states (california included) Tesla would certainly be liable if they did left the car open to being easily hacked. It would be comprable to leaving the keys in your car with the brakes disconected - if someone steals the car and ends up a cripple you can’t say “what the hell were you doing in my car?!”. You would be liable because “a reasonable person could expect such a situation to occur”. However if you attach your JATO rocket to the back of your Chevy Impala (see en.wikipedia.org/wiki/JATO_Rocket_Car) it would be difficult to claim that is was forseeable that some schmuck would do something like that…
Correction: I accidentally said that putting the battery pack near the center of the car reduces the polar moment of inertia, I should have said it reduces the moment of inertia. It therefore creates less resistance to angular acceleration, instead of torsion.
David, I don’t know what you’re on, but having the system built with open components such that a very technically oriented person could recompile the system and/or add their own custom modules is not the same as leaving your car waiting to be driven with the brakes disconnected. You are talking about someone walking up to the vehicle and attempting to operate it in a normal fashion. We are talking about someone purposefully modifying the vehicle. Which is to say, the JATO analogy is much more apt (although I was talking about the real-life new-beetle mod: jalopnik.com/cars/custom-carshot-rods/jetpowered-new-beetle-152902.php )
Dan wrote on April 6th, 2007 at 3:48 pm
Huntrer: I think the information about the Whitestar being rear wheel drive came from the Martin Eberhard interview on autobloggreen.com, but I don’t remember where I read that the battery pack would be in the front.
# Dan wrote on April 6th, 2007 at 3:48 pm
## Huntrer: I think the information about the Whitestar being rear wheel drive came from the Martin Eberhard
## interview on autobloggreen.com, but I don’t remember where I read that the battery pack would be in the front.
There was some discussion of this on the blog back last November.
This article:
www.autoblog.com/2006/11/24/tesla-electric-sedan-to-join-updated-roadster/
says:
“The Tesla sedan will have the electric MOTOR AND BATTERIES UP FRONT, sending power down the rear wheels. Two powertrain options are expected to be on offer, the smaller featuring a range of 200 miles, and a more powerful version with a 300-mile range. Unlike the Roadster, with a Lotus-built aluminum structure, the sedan is expected to be made of steel. Tesla figures on building 10,000-20,000 sedans each year and will be sold globally.”
Back in the old blog ( www.teslamotors.com/blog4/?p=38 ) I had responded with:
“That surprises me if they do what it says to have the motor up front with rear wheel drive. Drive shafts hurt efficiency, cut into cabin space, and are a maintenance item. I would have thought the PEM could go up front but still have the electric motor in the back between the rear wheels.”
“The Tesla sedan will have the electric MOTOR AND BATTERIES UP FRONT, sending power down the rear wheels.”
This makes no sense. I’m sure he got it wrong. Also Tesla said they will use the same drivetrain.
This blog and others describe the roadster’s traction control as limiting motor torque to control wheel slippage, but how does the roadster deal with splitting the torque between the rear wheels? Most performance cars have a limited slip differential but I’ve never seen a mention of one here. Is it just controlled with the brakes? That can work but just wastes more energy (on top of what you’d already be “wasting” by spirited driving in the first place!).
TEG: I wholeheartedly agree with you about the disadvantages of having the motor up front. I think that the writer of the article might have misinterpretted something from his source.
At www.autobloggreen.com/2007/03/12/autobloggreen-qanda-tesla-motors-ceo-martin-eberhard-pt-2/ Eberhard said:
“Right, it makes a lot more sense if you have a gasoline engine. But remember the size of our motor. I mean, the size of our motor it’s about 10 or 12 inches in diameter and 12 to 14 inches in length and that’s it. So you know, we can package it anywhere in the car front or back without it being a packaging issue. It’s a different problem. The neat thing about WhiteStar not being based on somebody else’s chassis is we can architect the vehicle to optimize it as an electric car instead of trying to cram batteries into an architectural designed for gasoline-powered car.”
Which leads me to believe that the motor will be placed in back as you suggested.
“That surprises me if they do what it says to have the motor up front with rear wheel drive. Drive shafts hurt efficiency, cut into cabin space, and are a maintenance item. I would have thought the PEM could go up front but still have the electric motor in the back between the rear wheels.”
I agree that it makes little sense. A drive shaft is also additional rotational mass that needs to accellerate and decellerate.
My first thoughts were that they may want the motor and the batteries in close proximity because of the need for large power cables between them, additional cooling for the motor from the batteries, and long power cable related crash safety. It could also be an economy of scale issue if they want to use the same setup they have now, but just moved forward. If that is the case I think it is really silly to have the mass produced sedan pay for the design of a low production roadster.
Then again it is possible that just putting the engine in back and making it a mid engine or rear engine(motor) car could automatically make it a higher insurance risk. Remember that this is a whole new product and all of the rules are going to take a while to adapt. That includes safety, insurance, and other preconceived notions we may have.
I don’t think that we know enough to understand why they would make that design decision.
Teg: thanks for breaking that down! I agree totally that as described there it doesn’t make sense. I’m sure they’ll put the engine between the drivewheels. As to where the ESS goes, that’s anyone’s guess, but I’m not one to second guess them…
By the way, my Ford Ranger EV has the AC drive motor between the rear wheels (where a differential would normally go).
Batteries and inverter are in front of it (under the center of the vehicle). The front hood is filled with control electronics and DC motors to power accessories (like power steering, power brakes, A/C, etc.) I hope Whitestar uses a layout somewhat like this.
My “fear” is that they may be thinking of trying to use a conventional F/R car design and so are tempted to put the PEM *and* MOTOR up front so they can use off the shelf parts (like drive shaft and differential) to keep costs and re-design considerations down.
I wonder if Tesla plans to make new tooling for all the chassis and body components of the Whitestar, or if they plan to buy a pre-made chassis to which they affix custom body panels. If they go with the chassis of an existing car, they may be more restricted in component layout choices. Maybe they could put an electric motor where the gas tank or evaporative emissions would go in the ICE chassis!
According to the Roadster specs sheet on the website….The ESS is right behind the seats, the motor has the driveshaft/axle built in (in other words, the motor IS the differential), and the PEM is right above the motor, just aft of the ESS. My biggest concern with the design of the car is where do I put my weekly groceries? Theres no “trunk” space!
—-
Editor’s Answer: Ah, but there is! You can fit a full set of golf clubs or wheeled luggage in the trunk. Check out the FAQ for a picture.
# deafgun wrote on April 9th, 2007 at 3:45 pm
## According to the Roadster specs sheet on the website…
## The ESS is right behind the seats, the motor has the driveshaft/axle built in (in other words, the motor IS the differential)
My interpretation of the specs are that there is a differential integrated into the 2 speed transmission. The A/C motor doesn’t act as a differential.
It only has one side (shaft) feeding the transmission/differential unit. I don’t even think it is a limited slip differential, but they could have electronic limited slip via traction control working the ABS.
See motor attached to transaxle (transmission + differential) here:
i.n.com.com/i/ne/p/2006/720Tesla-071_550×267.jpg
Hi Lain,
I read a very exciting article a few months back in the Rochester Post that your company is coming to my area, Rochester Hills, MI. Can you tell me when they will be opening the new location here? I am very interested in any further information you could give me. I signed up to receive your company’s newsletter by email, but I’m not sure if they will be putting the new development information in it or not. I really appreciate any help you could be. The Roadster looks awesome!
It would be nice to see more information about the cooling system, and what testing has been done on that. It was great to see the videos of the Roadster blasting around that frozen lake — but I live in Texas, not Sweden. My concern is more about what happens when I get out on the highway in August and it’s 100 degrees out there, I don’t want the batteries or motor to melt down.
Hi.
I would be very interested in a 4WD vehicle. I own a sports car and a 4WD truck and feel more in control in the truck in all but the cleanest, flattest, driest roads. On irregular roads, dirt roads, ice or just plain wet roads the best traction control can’t match what 4WD does for you.
I wouldn’t advocate hub motors as they are too heavy and underpowered (and probably fragile) to be practical, but I see nothing wrong with installing four smaller motors equalling the current engine total output. Yes, the net effect would be slightly heavier (partly offset by the loss of a differential) and you would need four gearboxes and voltage controllers (and other stuff) but the level of fine control four independent motors could give a driver would offset all the cost. Just imagine applying to each wheel the exact amout of power you need at any given time (either for acceleration or regenerative braking) under any circumstance. Violentrly start a turn and get the inner wheels braking for an instant, the outer wheels accelerating and then getting just the right power to keep you centered on the curve. Hit the gas in the middle of the curve and get the exact maximum power on each wheel without spinning. Hit ice, water or mud with one tire and apply to it exactly the power needed to maintain control.
Most of these advantages are more significant for a sedan than for a roadster, but safety is paramount in all vehicles. At least I hope you are considering this design for the sedan. I think the extra pounts would be well invested.
Hi!
Im “most put out”
that I didn´t hear beforehand that you were testing the Roadster on Hornavan. I would have gone to spy on you guys in an instant (it´s only 170 miles from where I live, would definitely have been worth the trip! Let me just say that I´m eagerly awaiting the day that I will be able to buy a Whitestar here in Sweden. Preferably a hatchback variety, but if you only make a 4-door sedan, I guess I´ll have to settle. Anyway, I have vowed to NEVER buy another ICE car, so please hurry. Waiting is HARD 
.
Also I would like to put my vote down for the merchandise idea. I know I would buy lots of stuff.
Bjorn> I share your concerns but Tesla is US market only for the mid term future..
As shown in my web pages electric vehicles will play a major role in
future global transportation. Not until all countries agree on
standardizing the battery size and voltage for quick ( one minute)
swap battery recharging stations owned by GE or Exide, Hybrid
Technologies and the like will the public make the big switch
and even then as time moves on they to will then again require
modifications to adapt to an even more advanced dual mode maglev
riding elevated high speed pipeline guideways. In my website above
add — /electriCar.html — for typical swap stations
(I can design them) also my Maglev system — /dualmodemaglev.html —
presented to US DOT in the 1960s which many are now trying to claim
the ideas. I hope I can be of help to all and good wishes to your
company. Jack Marchand
Do you have any data on how the variations in outside air temperature affect the available travel distance between charges? I live in a climate of extremes….110 degrees in summer and 0 degrees in winter.
To Teslamotors pioneers –All the best ! Your right on target
P.S.–In my ‘blog’ above-(-jack marchand wrote on May 10th, 2007) ,my web site was mentioned — trillions.topcities.com — referring to battery exchange stations for EVs. Also in it your vehicles could in a high speed maglev guideways travel the world via tunnel connections to all corners of the globe in a few hours within a few years. if we don’t take those initiatives others wont wait such as China , Russia, India, and others
Meanwhile interference to my web site is occurring and i’m quite suspicious that it may be deliberate by those who have other interests. To access my web site for now follow the suggestion below.
NOTE: If a POP-UP like “vBuddy” shows up in ‘address bar’ and covers the screen hit the “X’ square in top right hand corner to cancel it. To knock out “vBuddy” pop-up should it appear bigger than your screen lower the blue bar at the top and move it to the far left. Then to erase the pop up click on its “X” at top right corner. Some asses may be trying to intercept your access to the web page first mentioned. Depending on your computer’s protection it may repeat when entering other pages. Some may be trying to keep you and others from access to these pages because of their own selfish interests.
All the best and good luck. Sincerely, Jack Marchand — june 26, 2007
NOTE: here is another of my web sites to visit. — globalsys.topcities.com –
Would you please comment on a Palo Alto Online discussion? Many of us (pedestrians & bicyclists) have had experiences of almost being hit by hybrids when they’re in their quiet mode. I’m wondering if Telsa will add an unobnoxious sound to their cars (such as a clip-clop) to protect the people around them.
www.paloaltoonline.com/square/index.php?i=3&d=&t=2003
considering the fact the majority of the worlds population live in wet and or mildly damp climates not deserts being critical of the climate i the uk concidering the number of sunny dry spots of the world are on fire greece for instance and the canary islands. give me rain any day.wouldnt it be great a city full of silent transport. the noise is unnessesary in the cars.how many people do you hear of being knocked down say i did not hear the car.i beleive les people would be hit by cars if they were silent because their is noithing to listen for so walkers cyclist would be more alert look around themselves more if your crossing the road in traffic and a truck and a bus is their you could have a few cars around with engines switch off you would be none the wiser as to weither they were running their engines or not. background noise horns lorries and buses.lorries and buses big and noisey still people end up under them
Regarding the ICE sounds on the split mew video. It is clearly a different vehicle making the sounds (and what sexy sounds!!) since the tesla acceerates and then decelerates while the other source makes a constantly accelereating sound.
Hello
Great Idea for a car. I was wondering how long before the Tesla Vehicles will for sale to the public in Canada? Great job on this car.
This is one way we can get back at the Petroleum Companys of our world. GO GREEN POWER!
SAVE THE WORLD GO ELECTRIC! A++
Hey Thanks for the update. Unfortunately, I have never really been interested in high performance cars until I met the Roadster (i always felt they were a wast of gas and money). I am therefore unversed in the drive characteristics of such vehicles. The only dynamic I was ever concerned with was do I take my front-wheel-drive or four-wheel-drive out in the snow (I havent purchased a pure RWD in years). Usually the question is, is the snow too deep for the Accord?
From a pure engineering perspective the weight distribution of a mid-rear configuration is closer to a FF configuration but it still lacks the traction of 4 wheels. Maybe you can provide a short Drivetrians for Dummies or point me to some sources for some research.
well peace out my man
…:P
Thankyou all for the efforts with tesla motors. But i’m a regular guy…..Where is your model t, your vw, a car for the people. I just need to go 50 miles a day max. Why can’t or why don’t you care for the Average American. Sell a rig for 35k,45k. I can make one for that much …really. Actully i can build a E-car that can fit my basic needs if i’m real frugal for less than 15k. But like most Americans we barley have time to go to a dealer. Come on people, we want your cars now. Look at what folks are paying for SUVS…. I know it’s possible. You guys picked up this ball, but your running the wrong way. Nobody cares about roadsters for the large part. We want a little car that we can plug in now….. In America….now. The bare bones tech. has been around a hundred years, thats 99years to long. Please in name of all that you consider good, help the people now. Just do it, do it now. Go to a garage and build one and sell it. then build 2, then 4 and so on. Remember grass roots. We can’t buy the fancy car till we can save $ with the basic model. We are gonna be dependant on oil till the average guy can drive a basic E-car. Please
My first visit here, found the blog accidentally really, and I just wanted to say I’ve enjoyed my visit and had some good reads while here
Juan
Since the ABS can be turned off with a button and since so much computer control is a part of the ABS it would be a good idea if password subroutine was added at the front end for deactivation. When the button was pressed a voice allert or audio allert would sound and the driver had to enter a userid and password to deactivate the ABS. This would be in addition to any entry security the car has. This should be relatively easy, a simple password subroutine.
When the car is shut off the ABS would reset to ABS ‘on’. This is just a suggestion.
Good to see you proceed on safety issues. I am wondering about the effects of extreme temperatures on operating range.
I live in the Sacramento CA area. I met a Tesla owner who says the A/C system is only effective up to 95 F. In summer it can easily reach 117F on the road surface. How will you address this issue for our corner of the market. I am very interest in the S sedan, but I am very used to my BMW 528i