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3rd transmission supplier?!

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Kardax: The interesting question is of course if the Roadster can de 0-60 in 3.something seconds in reverse.... In that case they can claim to be "The car with the fastest acceleration in the world (in reverse)" :)

Cobos
 
Maybe the PEM and batteries just aren't capable of absorbing all that energy so fast - not powerful enough

Well, I dig out my old physics formulae and entertained myself with a few calculations. We know eMotor weighs around 90 pounds and is the size of watermellon. This data is somewhat vague so I took different numbers for rotor weight and diameter to see what required power I get. The attached table holds those numbers in kW. On the X-axis there are different possible rotor weights in pounds and kg, and on the Y-axis there are possible rotor dimensions. All scenarios give required power for slowing eMotor from 12.000 rpm down to 6.000 rpm in 1 second - shifting from 1. to 2. under maximum acceleration. I assumed the rotor is homogenous cylinder which certainly it is not but probably has more mass on the outside - yielding even higher momentum and higher required power.

We see the eMotor could be very close to the limit of PEM max power (185kW) when it is required to slow down form 12k rpm to 6k in just one second. All red numbers give dimensions that are over its max power and are so impossible to attain. If we would like to shift even faster, lets say in half a second, those numbers will DOUBLE.

I only looked at the time to slow down the motor, shifting process needs additional time to also reengage the gears. I can now see why the shifting would be unacceptably slow with a clutchless transmission and why clutch and transmission are under such high load.
Normal ICEs do not have such massive angular momentum and slow down much faster and easier.

You know, Lamborgini Galardo has a launch control button. You engage it, rev up the engine, shift into 1. and release the breakes. The car accelerates like mad but the clutch is dead after 7 such launches, it wears off. I guess Tesla is fighting similar problems.
 

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I can now see why the shifting would be unacceptably slow with a clutchless transmission and why clutch and transmission is under such high load.

You know, Lamborgini Galardo has a lounch control button...The car accelerates like mad but the clutch is dead after 7 such lounches, it wears off. I guess Tesla is fighting similar problems.

Because of the different torque profile and the presence of a flywheel, conventional clutch and gearbox manufacturers have an easier task to engineer for lower stresses/greater reliability. And even then, supercars can still wreck them.

So we're into Formula One engineering territory. Except they can afford to replace components after every few hundred miles or so.

Looks like there's a market for someone to develop a clutch/gearbox system specifically for the e-motor.

Martin? You busy? :)
 
Martin probably cannot comment on this (any more) because of his agreement.

It looks to me the roots of these problems stems into original design. It is understood the first plan was to go singlespeed. This is also when motor design was started and main parameters decided on - size, power, rough dimensions.

Sometime after that came Elon with twospeed gearbox demand and they had to figure out how to do it. Motor developement had probably went to far already to restart its design to give it a more managable (lower) momentum so it was transmission which had to adopt. Transmission guys do not have much experience with electric motors or high momentum engines. They know much more about ICE specifics, so they probably just used their knowledge about highrev ICE engines and maybe strengthen a few places where they knew higher momentum could be a problem. Having few experiences gives high chance of suprises and transmission turned out not be up to the task of handling all that momentum and high revs.

I guess it is possible that future will show that there are two right ways:
1. single speed

No transmission, no problem with momentum

2. fluid coupling or wet clutch

Those do not engage suddenly but slowly increase the grip on new gear ratio. The oil is used to transfer torque and absorb surplus rotational energy as it heats up. A racing version would add oil cooler :)

Edit:

BUT: Why not just add a middle gear with some in-betweeen ratio? If revs need to drop from 200/s to only 150/s that drastically lowers the forces involved. Any idea why TM didn't go this way?
 
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Martin probably cannot comment on this (any more) because of his agreement.

BUT: Why not just add a middle gear with some in-betweeen ratio? If revs need to drop from 200/s to only 150/s that drastically lowers the forces involved. Any idea why TM didn't go this way?

Wasn't after a comment. Was wondering if Martin wanted to try transmission design and manufacture for his next venture. :) Unrealistic, I know. He's probably happy to move away from automobiles for a while (maybe forever).

My guess about third gear is the whole ESS mindset. In the early days Tesla was very focussed on the battery systems. Quite naturally, it took priority in decision making. A third gear, offering 160 mph top speed would discharge the battery swiftly - maybe it was never considered as a way to reduce gearbox/motor stresses.