A look at the new Tesla cells

11931 Views 124 Replies 14 Participants Last post by Kevin Sharpe, Dec 1, 2017

PhantomPholly

Discussion Starter · May 28, 2017

2170 cells replaces 18650 standard at the Gigafactory.

Doubtful they will be available to DIY community, though. The big boys will probably contract full production.

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yah something might be up with that chart. I cant find any permutation of mph and torque and units that adds up to anything like 500kw at the wheels at the knee or the end. Assuming 27" diameter tires.

not related to gearing per-se, that is a compromise, not a bad one either, you aren't *really* concerned about efficiency if you are driving 95+ mph, the motor is maintaining power pretty well and trading torque for rpm, like a gear change would, only a hell of a lot more smoothly and reliably.

this might shed some light, same torque-ish shape but they started at 30mph so maybe that is what is off. 920ft lbs and 588 hp, p100d, the peak torque is at about 50mph

https://youtu.be/q5HgthPgzgQ?t=326

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dcb

· #32 · Jul 31, 2017

multiple gears would only slow it down, and make it less reliable. A low power vehicle could make use of it, i.e. be able to climb a hill and have reasonable top speed, but this thing already can break traction with ease on startup and go 150+mph. I wouldn't mess with it, it does 10 second 1/4 miles! a lower gear doesn't buy you anything off the line and a higher gear doesn't buy you much.

also see my previous post.

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dcb

· #42 · Jul 31, 2017

Solarsail said:
Dual (or even triple) 'parallel' reduction is the way to go. Should make the gearheads happy.

take a look at the graph I posted in #30
http://www.diyelectriccar.com/forums/showthread.php?p=885953#post885953

it stays within 15% of 588 hp from ~45mph to 110mph!

parallel clutch paths need multiple gear reductions and efficiency hits, and you are adding a high wear item in a very demanding application, so a driveline that would have lasted a million miles now needs service every 20k miles.

a lower gearing won't help anything (unless tire smoke is a thing), and it doesn't have any problems that need fixing at 150+mph on the high end, and a 10 second 1/4 mile! holds peak torque from 0 to near 60mph in 2.27 seconds, what more do you want?!? dual clutch whatsit is not gonna last or help (noise, lol).

It could use a diet @ 5,000 lbs, and an appropriately lower ratio at the same time, that's about it.

they tried the dual speed transmission, it didn't hold up, and didn't really buy them much except headache and expense. They are hitting all the high profile performance metrics without it. And you have like 2 moving parts...

http://www.autoblog.com/2008/01/23/breaking-tesla-has-a-solution-for-their-transmission-woes-get/

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dcb

· #48 · Jul 31, 2017

brian_ said:
The two-speed seems easy, but manufacturers are not consistently finding it worthwhile.

sure, just take a bulletproof existing design and throw in a couple clutches and gears that can handle the 1000 odd foot pounds and 16,000 rpm, for an imperceptible change in performance and efficiency, what could go wrong?

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dcb

· #54 · Jul 31, 2017 (Edited)

fwiw I do think that a clutchless 2 speed shifting is gonna be a thing at some point. With hi resolution control over motor speed or even gear tooth position (yes, possibly the return of sliding mesh, it is simpler mechanically and more efficient) it will be able to snick it up or down no problem. but it will be for lower powered commuters, or Bonneville.

I really don't see where it helps looking in the graph in post #30, you drop the ratio by 10% the rpm drops to a point with %10 more motor torque (no change in wheel torque), and the power is basically flat anyway., and the performance is more than adequate as is for a road car.

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dcb

· #56 · Jul 31, 2017

yep, flat top means you are at the limit of the controller.

i.e. the flat part of the torque curve is the controller limiting motor current, and a flat top on the power curve is probably the controller limiting battery current.

i.e: http://media3.ev-tv.me/Azure300VDC-400Acurve.pdf a serious flat top.

when at the power limit, the motor behaves like a CVT, which is nice.

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dcb

· #59 · Jul 31, 2017 (Edited)

the neat thing about that graph is how much the peaks resemble a series motor torque curve.

but yah, you can't overload it on the low end like a series, cuz you are just saturating a shorted transformer at some point.

edit, it could be a controller limit (switch rating) or pre-determined motor limit enforced by the controller.

edit2, I don't even understand armature reaction fully, so take it w/a grain of salt.

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