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New Roadster 4.0 Battery developement with Model S cells

Earl

Member
Jan 22, 2014
801
1,152
USA
somewhat centrally located
I don't profess to be the expert on where what matters (I'm only an EE). I'm only paraphrasing those who designed the car and sharing it with this forum.
Remember, however, that the Roadster has a 60:40 weight distribution, not the ~50:50 of the S and subsequent Tesla cars.
Perhaps 200# (~10% of car mass) is insignificant. Maybe not.
They may have been thinking of something closer to 500# reduction (~50% of battery mass, ~20% of vehicle mass).
What do cheap tires have to do with the topic?
Further indication of the sensitivity of the tuning of the Roadster.

. . . all just food for thought and consideration. This may all be irrelevant, however, one should be sure before candidly throwing around how 200# savings might be all good.
 
Not so.
The Tesla Roadster was completely redesigned from the Lotus Elise. They just started with the Lotus design but nearly everything was redesigned and retuned, especially, the suspension.
You must not be familiar with the Lotus. Tesla used the complete Lotus suspension. The coilovers were calibrated for the extra weight, reinforcements were welded on the control arms, 5 lug hubs (from the Vauxhall VX220), and a rear sway bar added. Tesla considers the part "redesigned" if they had to add a hole for an attachment bracket or a wire. That is how they claim such a low percentage of Lotus parts in the Roadster. Most of the Lotus parts can be easily modified to Tesla specs. They did "tune" the brakes with bigger rotors, and we all know how terrible the brakes are. 1000 lbs of extra weight on the same tires is just nuts. The car was set up to understeer at the limit, and changing the sticky OEM rear tires to something that wears longer gives you oversteer-abrupt oversteer. The actual weight distribution is 35:65, so its easy for things to go bad real quick.

Take what you have previously heard with a grain of salt. I remember several claims made by Tesla about the Roadster that were stretching the truth or downright lies - 100% carbon fiber body (its at least 60% fiberglass by weight and 80% by volume - not including all the plactic parts), battery cells that could disconnect from each brick if they went bad (nearly impossible). I'm sure what was originally discussed and what actually got produced were very different.
 

Earl

Member
Jan 22, 2014
801
1,152
USA
I'm sure what was originally discussed and what actually got produced were very different.
Yep. In true Tesla fashion, there were changes made even between units, not just between 1.5 and 2.0 and 3.0 levels. This is especially true when it came to swapping out Carbon Fiber parts with Fiberglass or even injection moulded.

I've observed pretty much everything else you say as well.
 
Wow...
That's one that I had taken literally for years! :eek:
I guess the bigger body parts are plain fiberglass (side panels, doors) while the smaller ones (hood, top) are CF?
All the body panels except the bumpers (plastic) have two thin layers of carbon fiber with a much thicker center of fiberglass, along with an outer fiberglass surfacing veil for a smooth surface to paint. The inner door structure is fiberglass. The mirrors and rear spoiler are plastic. The only parts that are actually carbon fiber are the roll bar hoop cover, and the optional hardtop and carbon spoilers. They painted the hardtops when the carbon fiber didn't look good when bare. Early cars also had a carbon trunk bucket. Even the optional carbon interior parts are just an overlay over the existing plastic. The center console is the only true carbon part on the interior.
 

TEG

Teslafanatic
Moderator
Aug 20, 2006
22,074
9,429
We are working on a Tesla Roadster 4.0 Battery developement. It will be same design as original with 11 sheets and 99 bricks. We will use Model S cells which have 30-45%* more capacity then 2.x Roadster.
There will be also 4.0 lite option with same capacity as Roadster 2.x and 25% less weight - good for all wanting to accelerate even faster and have better handling and better weight distribution.
We expect that first pack will be ready for sale in Q3 2021. Price is not known yet.
I will post soon some photos of our work.

*tbc after tests

Best Regards,

Kris Rosa
Rosa Motors
Germany


My understanding is that Model S cells have more capacity in part from greater useful voltage range. In particular they can be discharged more to lower voltages safely (?) Are you changing the ESS and/or PEM to be able to handle deeper discharge on the cells (Model S compared to old Roadster?)
I thought there was some hardware issue (Roadster hardware not designed for Model S type cells), not just something you could "fix" with firmware.
 
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My understanding is that Model S cells have more capacity in part from greater useful voltage range. In particular they can be discharged more to lower voltages safely (?) Are you changing the ESS and/or PEM to be able to handle deeper discharge on the cells (Model S compared to old Roadster?)
I thought there was some hardware issue (Roadster hardware not designed for Model S type cells), not just something you could "fix" with firmware.
This is exactly what hcsharp is pointing out in reply to a statement of JRP3. See #2,445 and # 2,446 in this thread: Roadster 3.0. chrisro, could you please elaborate on how you tackle this issue?
 

slcasner

Active Member
Supporting Member
Feb 20, 2011
1,536
1,078
Sunnyvale, CA
Hello, please respect that I will not explain here our know-how for some reasons. Biggest Tesla's problem to use model S cells was that model S cells have bigger diameter and are higher and are not fitting Roadster sheet.
As I understand it, both the original Roadster cells and the Model S cells are of the 18650 size, that is , 18mm diameter and 65mm length. Are you saying that the Model S cells exceed their nominal measurements?
 

TEG

Teslafanatic
Moderator
Aug 20, 2006
22,074
9,429
As I understand it, both the original Roadster cells and the Model S cells are of the 18650 size, that is , 18mm diameter and 65mm length. Are you saying that the Model S cells exceed their nominal measurements?

FYI, trying different make/models of 18650s in some LED flashlights, I sometimes found some that didn't fit. I think the cells are not all precisely the same size.
Some devices which can have replaceable 18650s have a spring to make connection and hold it in place such that it can accept cells of slightly different sizes.
Perhaps the Roadster ESS sheets are just so tightly packed that there isn't room for much variance in cell size.
 
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X.l.r.8

Active Member
Supporting Member
Feb 18, 2018
1,656
1,111
Toronto/Tampa
The original cells are on the small side of 18650 for sure and the model S cells, like the ncrb’s are fractionally larger making them a squeeze into cell holders. I don’t think anyone is doubting the ability to put an equivalent or more kW into the space, and that will certainly be a propriety move. I think a lot of us are wondering if you have addressed the firmware issues, which so far you have avoided to comment on. You cannot just assume the original parameters will work, and for reasons clearly stated it will not.
 
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hcsharp

Active Member
Jun 7, 2011
3,490
1,616
Vermont
As I understand it, both the original Roadster cells and the Model S cells are of the 18650 size, that is , 18mm diameter and 65mm length. Are you saying that the Model S cells exceed their nominal measurements?
Yes, that's what he's saying. @chrisro described it accurately as well as @X.l.r.8. The difference is big enough that the plastic sheet frames and cooling tubes require difficult modifications. Once you conquer that problem then you have to overcome the hardware and software limitations of the Roadster charging system. Those are the main reasons why Tesla never made a replacement pack using Model S/X cells of which they had an abundant supply. If @chrisro can accomplish his goal it will be a much bigger accomplishment than most people realize.
 
We are working on a Tesla Roadster 4.0 Battery developement. It will be same design as original with 11 sheets and 99 bricks. We will use Model S cells which have 30-45%* more capacity then 2.x Roadster.
There will be also 4.0 lite option with same capacity as Roadster 2.x and 25% less weight - good for all wanting to accelerate even faster and have better handling and better weight distribution.
We expect that first pack will be ready for sale in Q3 2021. Price is not known yet.
I will post soon some photos of our work.

*tbc after tests

Best Regards,

Kris Rosa
Rosa Motors
Germany

Q3 will end in about 2 weeks. Any news to report @chrisro?
 
Whilst I love the steering of the roadster and its acceleration, on track its not as much fun as an Elise (both on same track - Castle Combe in UK). The 3 full-chat lap limit from hot motor, I can live with, but after the lithe elise - eg easy 4 wheel drifts, licking the apex etc. the Roadster has grip but feels a bit lumpen. This is mainly due to the extra weight.

With similar weight and weight distribution, to an elise a 2006-2012 roadster would probably be THE best electric sports car ! Forget big fat heavy Taycans, most over large and heavy ICE and, dare I say, Model S /3 and other 4 door saloons, although some will get faster laps times - a lighter, smaller roadster would be the nearest thing to an electric open wheeled racer, with enough civility (and quietness), for road use.
 

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