Karma -vs- Model S

[mattjs33]

... the architecture of the car just looks very massive and clunky in contrast to the Tesla.

Thank Lotus for that. Light weight has always been one of Lotus' design mantras. That's why the Roadster is such a performer (performance specs and range) -- strong motors in the lightest chassis available in the industry.

It's probably not really fair to compare construction of the two.

 

[Tommy]

Thank Lotus for that. Light weight has always been one of Lotus' design mantras. That's why the Roadster is such a performer (performance specs and range) -- strong motors in the lightest chassis available in the industry.

It's probably not really fair to compare construction of the two.

I took siry's comment to mean in contrast to Tesla Model S not the Roadster as the Model S and Karma were both designed around the same time frame and both designed from the ground up by their respective companies.

 

[siry]

Yes, Tommy is right - I am comparing it to the engineering/design of the Model S chassis, and particularly the integration of the motor/PEM/gearbox and rear suspension, which is outrageously cool. So Lotus has nothing to do with that.

 

[TEG]

The Karma is overly complex. Model S is downright elegant in comparison.

 

[doug]

Yeah, this kinda looks like a mess:

Now it might not be a completely fair comparison since we haven't seen the Model S motor plumbed up yet, but it has to look cleaner than this. Hoses all over the place, and very few look custom molded or the proper length in a single piece (lots of hose extensions). Just seems a bit kludgy and not particularly refined.

Consider that each motor and inverter is liquid cooled and has a hose in and a hose out. That's eight hoses connected to this octopus. (I believe these pictures above are from a motor and an inverter that failed due to a kinked hose.) Where the Model S motor-diff-inverter package just has two: one hose in and one hose out.

Then you have six high power lines running from the inverters to the motors, whereas with the Model S they're just contained within the package.

Of course Fisker is claiming much higher torque, though Tesla appears to be doing more with less (which I consider to be a sign of good engineering).

 

[siry]

I don't understand why people go with DC permanent magnet motors and not AC Induction. The whole problem here is DC PM has very high torque but low max RPM. Low max RPM means they have to use a very tall gear to achieve a certain top speed (say 100mph or whatever). As a result even with these two monsters, 400 lb. ft. + and all their associated hoses, the car still has a poor 0-60.

AC Induction can spin to a high enough RPM that it can get the right gearing to enable great 0-60 and still get a good top speed. This is the Tesla approach and it isn't magical.

When discussing Fisker, I also always end up ranting about how inane it is to use a 2 liter turbo engine for a range extender. This is the key difference between Tesla and Fisker - intelligent engineering.

 

[doug]

2012 Fisker Karma | Karma Features and Specifications
Fisker claims 1300 N m of torque (650 N m per motor). Looks like they no longer advertise the horse power, though I believe previously they claimed about 400 hp. That's likely been downgraded along with the revised performance specs.

This graph (which I can no longer find on the Tesla web site) claims 415 N m of torque for the Model S.

Has Tesla released any revised specs?

 

[siry]

I'd be interested in the transmission gear ratios. That would tell the story.

 

[donauker]

I'd be interested in the transmission gear ratios. That would tell the story.

4:1

http://www.fiskerautomotive.com/en-us/karma/specifications

 

[doug]

I don't understand why people go with DC permanent magnet motors and not AC Induction.

Fisker is driving them with inverters, so I'd assume they're AC.

 

[woof]

Kinda Reminds me of this http://www.tgdaily.com/games-and-entertainment-brief/61954-steampunk-aperture-portal-gun-is-epic

 

[doug]

 

[stopcrazypp]

I don't understand why people go with DC permanent magnet motors and not AC Induction. The whole problem here is DC PM has very high torque but low max RPM. Low max RPM means they have to use a very tall gear to achieve a certain top speed (say 100mph or whatever). As a result even with these two monsters, 400 lb. ft. + and all their associated hoses, the car still has a poor 0-60.

AC Induction can spin to a high enough RPM that it can get the right gearing to enable great 0-60 and still get a good top speed. This is the Tesla approach and it isn't magical.

I guess siry was talking about "Brushless DC" AKA "AC synchronous". It seems he is right about the low max rpm. At 6000 rpm, it's about 10k rpm less than the max rpm of the Model S.

 

[doug]

Right. Nomenclature aside, his comments are valid (which is why I posted that image here).

I'd add that the control for AC induction is a bit more complicated, which might be a reason for Fisker to go with DC Brushless since they seem to have had limited drivetrain engineering resources. They've also hinted that they may go with a multi-speed gearbox setup in the future which might mitigate their RPM limitations.

 

[bonnie]

Fisker vs. Model S Video Debate: here.

 

[ckessel]

Fisker vs. Model S Video Debate: here.

The more of these types of things I see the more disappointed I am in the basic research. Had the wrong deposit info, wrong acceleration numbers, just basic stuff that's been on the Tesla website forever.

 

[smoothoperator]

I think Nina vs Model S is probably a better comparison than Karma vs Model S

 

[dsm363]

They seem to continually mix up the Signature series reservation with the production car. Nick Jaynes says he's going to correct everything the other guy is going to say but then gets a few things wrong. The Model S goes 0-60 in 5.3 seconds (not 5.6-6.5 seconds not including the sport) and also wonders how many people will put down the $40,000 deposit down on the Model S thinking that will limit the number of people willing to put down that money.
They also state the base pack is 180 miles.
I'm sure reporting on these things isn't easy but this is all publicly available information
Model S Options and Pricing | Tesla Motors

 

[DrTaras]

The Model S goes 0-60 in 5.3 seconds (not 5.6-6.5 seconds not including the sport)

Here is is from Tesla's Site:

 

[richkae]

More and more, this is a key spec of the Model S for me:

The carge space in the frunk alone is probably bigger than the trunk of the Karma.
I don't see how the Nina can be much better, considering they are going to use the same drivetrain configuration.