Cliff notes on Roadster transmission problems...

[Fr23shjive]

I was just wondering if somebody can explain to me what happened with the problems that Tesla had with the original Roadster 2 speed transmission.

Did they originally try to develop it themselves? They ended up outsourcing the work to other companies but still couldnt get it to work?

Did they end up solving the problem themselves with the one speed transmission?

 

[doug]

The full history should be in these pages but the wikipedia page gives a summary that's mostly accurate:

http://en.wikipedia.org/wiki/Tesla_Roadster#Transmission

 

[PopSmith]

Did they originally try to develop it themselves? They ended up outsourcing the work to other companies but still couldnt get it to work?

Did they end up solving the problem themselves with the one speed transmission?

Check out this Reuter's article (Warning: PDF!) for a pretty good (and detailed) story about the Roadster's early life.

Basically:
Tesla tried to develop a two-speed transmission for the Roadster but it couldn't handle the torque of the motor. This threatened the Roadster's launch and someone from BorgWarner heard this they got in touch with Tesla. After that they worked out a deal and BorgWarner now builds Tesla a single-speed transmission that is currently in the Roadsters.

 

[eledille]

I remember reading that the large difference in gear ratios also had something to do with it. I think more than one company tried and failed to build a reliable two-speed transmission.

BorgWarner developed a single-speed transmission that could handle the torque, and Tesla engineers solved the problem of lowered acceleration due to taller gearing by finding a way to send far more current through the motor than the battery can deliver directly.

This trick is possible because at low rpms, little voltage is needed to max out the current rating of the battery. As rpms rise, the motor generates more internal voltage that opposes the applied voltage, which means that you need to apply more voltage to feed the same current through it. This is called counter emf (electromotive force). The battery has a relatively high voltage (375 V?) and a relatively low max current (600 A?). At low speeds, only a fraction of the full voltage can be applied, so you have "spare" voltage that can't be used directly. By converting the battery power to lower voltage and higher current, they were able to send more current through the motor, 1500 A if I recall correctly.

A detailed explanation of the solution was posted on the Tesla blog.

 

[Fr23shjive]

Thanks guys.

I was actually discussing Tesla motors on another forum with a bunch of Detroit fan boys. They kept mentioning how Tesla completely failed to build a transmission for the roadster and needed to outsource that work to a 3rd party.

The way I see it is that Tesla is a trail blazer when it comes to electric cars and of course they're bound to have issues with the first vehicles they put out. They've had a chance to build a few thousand roadsters and now have a much better understand of what to expect with the model s.

I still think they can successfully release the model S by 2012. Their team is filled with former executives from the big automakers who know exactly what it takes to get a car from the design room to the showroom floor.

 

[TEG]

http://www.wired.com/autopia/2008/05/tesla-v15-has-r/
http://www.teslamotors.com/blog/engineering-update-powertrain-15

 

[eledille]

Ok, TEG, I didn't recall correctly The current step-up was from 640 to 850 A, and they also had to improve the motor substantially to handle the extra current. But the principle was as I described. The solution isn't rocket science, just excellent engineering. The end result was far better than the two speed gearbox would have been.

 

[mt2]

I was actually discussing Tesla motors on another forum with a bunch of Detroit fan boys. They kept mentioning how Tesla completely failed to build a transmission for the roadster and needed to outsource that work to a 3rd party.

I didn't see this explicitly mentioned above or any of the articles quoted, but Tesla outsourced the gearbox from day one. Borg Warner did not get involved at the time because (as I believe Elon mentioned at a town hall) no large supplier wants to build a small quantity of special order parts. It's just not cost effective. But the small suppliers (two were mentioned) just couldn't deliver.

 

[vfx]

That Tesla blog on the transmission shows they are the heros. Pulling it out at the last moment. Solving the problem no one else could.

Though the 0-60 time remained the same, the acceleration curve was different. At least it felt that way. The old first gear had even more blast off than today's version. (!)

 

[Alan]

Thanks guys.

I was actually discussing Tesla motors on another forum with a bunch of Detroit fan boys. They kept mentioning how Tesla completely failed to build a transmission for the roadster and needed to outsource that work to a 3rd party.

Nothing wrong with outsourcing the transmission. Most high end BMWs, Audis and Mercedes use gearboxes made by ZF.

 

[TEG]

Ok, TEG, I didn't recall correctly The current step-up was from 640 to 850 A, ...

Now with even more:
http://www.teslamotors.com/roadster/technology/motor

...The Power Electronics Module supplies as much as 900 amps of current to the stator...

 

[PopSmith]

The old first gear had even move blast off than today's version. (!)

I test drove a Sport 2.0 back in July and was amazed at the acceleration, of course it was the first real sports car (and EV) that I've ever driven. I can't even imagine the feeling of a Tesla with even more gusto!