Model S vs. E63 AMG Mercedes 0-110 mph race

[stopcrazypp]

Actually, here's how max power relates to mph (which is directly proportional to rpm because of the single gear):

But keep in mind that this is MAX power. At any given speed, if all you care about is maintaining that speed then you won't be using the max power, but only a fraction of it (like 20kW/27hp for 60mph and 60kW/80hp for 100mph). And assuming the efficiency of the motor is the same throughout the rpm range (true for electric motors, not true for ICE), gearing is unlikely to effect steady speed efficiency. All a taller gear will allow you to do is reach a higher top speed, assuming you don't hit the power limit first (for the P85, the peak power of the motor at max rpm is about 220hp, which is good for about 150mph top speed).

 

[CapitalistOppressor]

Actually, here's how max power relates to mph (which is directly proportional to rpm because of the single gear):

But keep in mind that this is MAX power. At any given speed, if all you care about is maintaining that speed then you won't be using the max power, but only a fraction of it (like 20kW/27hp for 60mph and 60kW/80hp for 100mph). And assuming the efficiency of the motor is the same throughout the rpm range (true for electric motors, not true for ICE), gearing is unlikely to effect steady speed efficiency. All a taller gear will allow you to do is reach a higher top speed, assuming you don't hit the power limit first (for the P85, the peak power of the motor at max rpm is about 220hp, which is good for about 150mph top speed).

Not true.

And again, if you are physically moving faster for a given period of time you move farther. Why would a motor which is drawing the maximum amount of power available suddenly be able to draw more than that just because of a gear ratio change?

How can maximum output not be maximum output? If a battery can supply maximum power for an hour, it will still supply maximum power for an hour if the gear ratio changes and the car goes faster. An hour of faster will get you further than an hour of slower.

For the car to travel the same (or less) distance while traveling faster, it must be the case that it is drawing MORE power from the battery. Which means you are saying that at 130mph the current version of the Model S Performance is limited by the power of the motor, not the power output of the battery. Is it actually the case that the Model S is only using a fraction of the potential throughput of its power electronics when it is at top speed?

New multi-speed Electric Vehicle transmission improves EV performance and range

“Electric motors have a very wide operating range, but that doesn’t mean that they are equally efficient at every speed,” explains Vocis EV transmissions specialist Andy Turner. “The torque curve of a typical traction motor is well suited to vehicle propulsion, having maximum torque from zero speed and a wide constant power region. However, there is a ‘sweet spot’, typically at medium speed and medium to high loads, where the delivery of power is most efficient. A choice of gear ratios allows the motor to be kept in this operating region during more of the drivecycle.”

Gear ratio - Wikipedia, the free encyclopedia

The torque ratio of the gear train, also known as its mechanical advantage, is determined by the gear ratio.

Mechanical advantage - Wikipedia, the free encyclopedia

Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. Ideally, the device preserves the input power and simply trades off forces against movement to obtain a desired amplification in the output force. The model for this is the law of the lever. Machine components designed to manage forces and movement in this way are called mechanisms.

If a Model S had a transmission, going faster would indeed result in less efficiency because of aero dynamic losses, tire resistance and mechanical losses, all of which rapidly increase with speed. But to the extent that you are able to go faster with the same power output, you will increase your range.

And that's what a transmission does. Allows you to go faster with the same power output, by amplifying that power. The amount of amplification is the gear ratio. When the increased efficiency losses balance with the amplified power output, you will have reached your new top speed. But the initial power input is the same.

Gas powered cars don't suspend the laws of physics to achieve relatively high ranges at high speeds. They just use a transmission. And their narrow power bands in comparison to an EV only matter in that they require more gears to stay at the optimum efficiency levels.

 

[stopcrazypp]

And that's what a transmission does. Allows you to go faster with the same power output, by amplifying that power. The amount of amplification is the gear ratio. When the increased efficiency losses balance with the amplified power output, you will have reached your new top speed. But the initial power input is the same.

I seems you have mixed up force/torque with power. Look at all the sources you quote, it says "mechanical advantage" (AKA torque multiplier) and "force amplification". Power is the dot product of force and velocity or torque and angular velocity. All the transmission does is change the ratio of the force/torque to the velocity/angular velocity.
http://en.wikipedia.org/wiki/Power_(physics)

By the conservation of energy, the power output by the motor, going through the transmission and reaching the wheels is always equal or less (some loss to heat). There is no way of "amplifying power" without having an additional power source in between or violating the conservation of energy.

 

[fiksegts]

heh, no problem going 0-60 in less than 2.7 seconds? not a trivial task, only 2-3 production cars in the world can do it..... It's not Tesla's aim and it's not going to happen.... especially in the RWD roadster.... 2.7 and under 2.99 are worlds apart...

Drop in the drive-train of the Model X Performance in a lighter more aerodynamic body and they have a 465kW (624 hp) car with 33:67 rear biased AWD. That should be able to beat the GT-R no problem in 0-60.
http://www.teslamotors.com/modelx

If you are talking about an upgrade to the old Roadster, the old pack used 2400 mAh cells @ 4.018C (225/56kWh). If they swap in the 4000mAh cells that will likely be used in the Model X (and make the appropriate upgrades elsewhere) they can push 1.6x the power, 1.74x if they are willing to push the cells as hard as they are pushing the 40kWh pack (4.375C = 175kW/40kWh). That will boost available power for the Roadster to 391.5kW (525hp, 225kW*1.74). From the Elise forums, ~500hp should push 0-60 to the 3 second range or under.

The current GTR makes 545 hp and has adjustable rear bias (front can receive 0-50% of the torque) AWD. Judging from the older model, launch control shaves about 0.6 seconds, so without it the car would have 0-60 in 3.3 seconds.

I say Tesla can get better or really close if they really wanted to.

 

[stopcrazypp]

heh, no problem going 0-60 in less than 2.7 seconds? not a trivial task, only 2-3 production cars in the world can do it..... It's not Tesla's aim and it's not going to happen.... especially in the RWD roadster.... 2.7 and under 2.99 are worlds apart...

I agree it will be unlikely to be 2.7 with just RWD Roadster (unless they go the Hennessy Venom route and stretch the body in order to add more batteries and a larger motor to go straight for brute power), but it should be possible using the AWD architecture from the Model X (just like the 911 Turbo uses an AWD system based on the one in the Cayenne).

An upgraded Roadster should still be able to match a GT-R that doesn't use launch control (~3.3 seconds 0-60).

It's not Tesla's aim and it's not going to happen....

The Roadster was always aimed at the 911 Turbo because that was the "family car" Elon owned before the Model S (he used to have his two kids in the rear seats). The GT-R was also created to shoot down the 911 Turbo and today they go head to head. So I'm pretty sure the next Roadster's aim is in that direction.
http://www.automobilemag.com/features/news/1208_q_and_a_elon_musk_ceo_tesla/viewall.html

 

[CapitalistOppressor]

I seems you have mixed up force/torque with power. Look at all the sources you quote, it says "mechanical advantage" (AKA torque multiplier) and "force amplification". Power is the dot product of force and velocity or torque and angular velocity. All the transmission does is change the ratio of the force/torque to the velocity/angular velocity.
http://en.wikipedia.org/wiki/Power_(physics)

By the conservation of energy, the power output by the motor, going through the transmission and reaching the wheels is always equal or less (some loss to heat). There is no way of "amplifying power" without having an additional power source in between or violating the conservation of energy.

I may have gotten sloppy with the semantics of my comment by using the generic word "power" for both the electrical energy input and the mechanical power output, but that has nothing to do with actually addressing my argument.

Here is an example of how gear ratio's affect an EV from an EV design website. The tables address how 2 different gear ratios affect the EV in question.

Electric Vehicle Design

gear ratio = 6         input   output 
Torque current motor   power    power   force speed
lb-ft   amps    RPM      KW      Hp       lb   mph 
  10     100    8000    14.4    15.2      57    100 
  20     150    6500    21.6    24.8     114    81
  30     190    5600    27.4    32.0     171    70 
  50     280    4600    40.3    43.8     286    58 
  70     350    4000    50.4    53.3     400    50 
 100     460    3500    66.2    66.6     571    44 
 140     600    3000    86.4    80.0     800    38  

gear ratio = 8         input   output 
Torque current motor   power    power   force speed 
lb-ft   amps    RPM      KW      Hp       lb   mph  
  10     100    8000    14.4    15.2      76    75 
  20     150    6500    21.6    24.8     152    61
  30     190    5600    27.4    32.0     228    53 
  50     280    4600    40.3    43.8     381    43 
  70     350    4000    50.4    53.3     533    38 
 100     460    3500    66.2    66.6     762    33 
 140     600    3000    86.4    80.0    1066    28

Note that electrical power input (KW) into the motor is a constant at a given RPM in both cases. What changes is speed. If you had read my links you would know that this is because the mechanical advantage of the system changes.

So again. If electrical power input (from the battery) is a constant, but speed increases, that means that range increases as well.

Conservation of Energy has nothing to do with it, except that the total energy in the system is the same on both sides of the equation (barring heat losses, as you said). Mechanical advantage is the same principle by which you can use a lever to shift a multi-ton rock using human muscles. Or drive a 20 speed bicycle at 40mph, vs 15mph for a single speed.

 

[PeterSZ]

Nice technical discussion, however the bottom line remains this:
M5/E63AMG/Viper stand at the end of 100years and zillions of dollars development of the ICE
Tesla Model S stand at the very beginning of the EV with, by comparison, almost no money at all.
Tesla = David in a world of Goliaths.
A miniscule newcomer among giants who have infinitely more resources in every aspect.
And STILL they can deeply impress with their very first car.
Not very difficult to see where the future of automobility lies...

 

[vfx]

...
The Roadster was always aimed at the 911 Turbo because that was the "family car" Elon owned before the Model S (he used to have his two kids in the rear seats). The GT-R was also created to shoot down the 911 Turbo and today they go head to head. So I'm pretty sure the next Roadster's aim is in that direction.
http://www.automobilemag.com/features/news/1208_q_and_a_elon_musk_ceo_tesla/viewall.html

All this is true abouth 911. Elon will want his next supercar to beat his Mcclaren. I predict mid to low two's 0-60.

 

[fiksegts]

there isn't a production car in the world at ANY price that can come close to that.... the $2.5M Veyron Super Sport can get 0-60 MPH in ~2.5 seconds on a good day with traction....

All this is true abouth 911. Elon will want his next supercar to beat his Mcclaren. I predict mid to low two's 0-60.

 

[stopcrazypp]

Electric Vehicle Design

gear ratio = 6         input   output 
Torque current motor   power    power   force speed
lb-ft   amps    RPM      KW      Hp       lb   mph 
  10     100    8000    14.4    15.2      57    100 
  20     150    6500    21.6    24.8     114    81
  30     190    5600    27.4    32.0     171    70 
  50     280    4600    40.3    43.8     286    58 
  70     350    4000    50.4    53.3     400    50 
 100     460    3500    66.2    66.6     571    44 
 140     600    3000    86.4    80.0     800    38  

gear ratio = 8         input   output 
Torque current motor   power    power   force speed 
lb-ft   amps    RPM      KW      Hp       lb   mph  
  10     100    8000    14.4    15.2      76    75 
  20     150    6500    21.6    24.8     152    61
  30     190    5600    27.4    32.0     228    53 
  50     280    4600    40.3    43.8     381    43 
  70     350    4000    50.4    53.3     533    38 
 100     460    3500    66.2    66.6     762    33 
 140     600    3000    86.4    80.0    1066    28

Read the page more carefully, table 2 refers to the situation when there is no real load and represents the peak power that the motor can output at various rpms/speed. It does not mean the motor needs to use that much power at that speed (in come cases the peak power is lower than what is necessary to go that speed). Note this part:

But none of these configurations really give enough power to meet the minimum vehicle specification over the entire operating range as shown in Table 1.

Table 1:

speed   max   grade   accel.  tire    wind     total  horse   equiv.  mph   grade  force   force   force   force    force  power   power  
   5    25%   750 lb  150 lb. 30 lb.   1 lb.  931 lb.  12.4   9.3 kW  
  25    18%   540 lb  150 lb. 30 lb.  16 lb.  736 lb.  49.1  36.6 kW 
  40    12%   350 lb  150 lb. 30 lb.  42 lb.  582 lb.  62.0  46.3 kW  
  55     6%   180 lb  150 lb. 30 lb.  79 lb.  439 lb.  64.3  48.0 kW  
  70     0%   200 lb  150 lb. 30 lb. 127 lb.  307 lb.  57.4  42.8 kW

From table 1, it takes ~222 lbs of force to go 38mph (author has numbers for 40mph@12% grade, I subtracted 350lb "grade force" from 582 lb total force to get 222 lbs@0% grade). This is equivalent to about 17.8kW/23.9hp. The 38mph lines in table 2 are:
50.4kW = 144V*350A peak, 070 lb-ft @ 4000 rpm for gear ratio 8
86.4kW = 144V*600A peak, 140 lb-ft @ 3000 rpm for gear ratio 6

But in both cases you need only 17.8kW or 23.9hp, so for 38mph the actual motor load looks like this:
17.8kW = 144V*124A, 31.4 lb-ft @ 4000 rpm for gear ratio 8
17.8kW = 144V*124A, 41.8 lb-ft @ 3000 rpm for gear ratio 6

The motor will be spinning at different rpms and outputting different amounts of torque (Torque = HP*5252/RPM), but it will be using the same power in both cases (assuming motor efficiency doesn't vary with rpm).

 

[brianman]

there isn't a production car in the world at ANY price that can come close to that.... the $2.5M Veyron Super Sport can get 0-60 MPH in ~2.5 seconds on a good day with traction....

It's good to have goals. "We want to build the best car in the world" was said about the Model S. Did they achieve it? Some say yes, many say no. Does it matter whether they actually achieved it? No. Does it matter that they had that as the goal/target? Definitely. If you don't aim high, you definitely won't achieve it; if you do and fall a little short, that can still be pretty damn remarkable.

 

[Johan]

there isn't a production car in the world at ANY price that can come close to that.... the $2.5M Veyron Super Sport can get 0-60 MPH in ~2.5 seconds on a good day with traction....

Let's see when test results from the Rimac Concept_One start apperaring... I know they have delivered one car, but they did it in "secrecy" per request of the buyer... though I don't think you buy that kind of car to not show it off. So I guess we'll be hearing more soon. Now, if the Rimac is a "production car" or not we can argue, I think it's priced in the range of the Veyron though. Is the Veyron a production car? I know it is road legal at least.

Rimac Automobili delivers first electric supercar, cant let us see it
Best of 2012: The First $1M Electric Supercar: Video - Bloomberg