A look at the new Tesla cells

11902 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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So if we eliminate the possibility of two 2-speed gearboxes, then in order to have two rear motors, the following architectures remain:

a) Different reduction ratios + rear (and front) differential. The Model 3 reduction ratio is close to 10. So for the R2, it would be 14 on one motor and 7 on the other motor. A further twist here is that if the 14 motor could be disengaged by a clutch, then the ratios could be wider such as 16 and 6. The front ratio would remain at 10.

b) Another possibility is just one 2-speed gearbox in the rear for one of the motors. One motor runs at ratio 14 the other at 7 but also has the benefit of the 2-speed gearbox and then can also run at 14, for low-speed high acceleration. I don't think this would be a good design.

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brian_

· #122 · Dec 1, 2017

Solarsail said:
a) Different reduction ratios + rear (and front) differential. The Model 3 reduction ratio is close to 10. So for the R2, it would be 14 on one motor and 7 on the other motor. A further twist here is that if the 14 motor could be disengaged by a clutch, then the ratios could be wider such as 16 and 6. The front ratio would remain at 10.

I get that, but with two motors, two sets of gearing, and now a clutch, you're nearly all of the way to the mechanical complication simply having one motor and a two-speed transmission (and you have extra electronic complication). So, this seems very unlikely to me.

On the other hand, having somewhat different motors - and perhaps different reduction ratios - between the front and the rear is quite viable. While this is not done with the Model S and X (even when front and rear motors are different sizes they are comparable characteristics and the same reduction ratio), a moderate version can make sense. The front motor would be optimized for higher speed and used in a greater proportion to the rear at high speeds, leaving the power distribution more rearward at low speed (when acceleration is greater so load transfer to the rear is significant). Logically, in this scenario the two motors in the rear are identical to each other and simply each driving a wheel.

Solarsail said:
b) Another possibility is just one 2-speed gearbox in the rear for one of the motors. One motor runs at ratio 14 the other at 7 but also has the benefit of the 2-speed gearbox and then can also run at 14, for low-speed high acceleration. I don't think this would be a good design.

I agree that this could be built. I also agree that it wouldn't be good.

If using a transmission like this, then there would be no point in having two motors - just one large motor driving through the transmission would make more sense.

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electro wrks

· #123 · Dec 1, 2017 (Edited)

Solarsail said:
So if we eliminate the possibility of two 2-speed gearboxes, then in order to have two rear motors, the following architectures remain:

a) Different reduction ratios + rear (and front) differential. The Model 3 reduction ratio is close to 10. So for the R2, it would be 14 on one motor and 7 on the other motor. A further twist here is that if the 14 motor could be disengaged by a clutch, then the ratios could be wider such as 16 and 6. The front ratio would remain at 10.

b) Another possibility is just one 2-speed gearbox in the rear for one of the motors. One motor runs at ratio 14 the other at 7 but also has the benefit of the 2-speed gearbox and then can also run at 14, for low-speed high acceleration. I don't think this would be a good design.

If I'm not mistaken, the R2 has motor based torque vectoring. This implies symmetry, side to side, for the two motors and gear reduction boxes in the back. Another thing: somebody said that when the Semi was accelerating at the event in Hawthorne, they thought they heard a shift(electronic shift?). Maybe something like a shift from a Delta to a Wye stator configuration? Is this a possibility? Or, something else electronic?

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Solarsail

· #124 · Dec 1, 2017 (Edited)

brian_ said:
The front motor would be optimized for higher speed and used in a greater proportion to the rear at high speeds, leaving the power distribution more rearward at low speed (when acceleration is greater so load transfer to the rear is significant). Logically, in this scenario the two motors in the rear are identical to each other and simply each driving a wheel.

I think this would be something like two identical rear ratios at let's say 14 and a front at 7 - for a 2:1 ratio. The problem is that this will not take you up to 250 mph. The rear motors cannot deliver the power at those speeds, and the front is underpowered and too high RPM for 250 mph is required - the spread of the ratios is not wide enough. But I like the idea that at high speeds, power is mostly delivered by the front, and I think that will make for better high speed driving. So the ratios I propose are 18 for RM1 (rear motor 1), 10 for RM2, 6 for FM, for a 3:1 ratio of the reduction gears.

0 - 60 mph, 100% power on all three motors, torque ratio (RM1, RM2, FM): 60%, 35%, 5%
60 - 150 mph, power is cut to RM1, 100% to RM2 and FM. Torque ratio: 25%, 55%, 20%
150 - 250 mph, power is cut to RM1, RM2, and 100% to FM. Torque ratio: 0%, 30%, 70%

Electrowrks, what is the effect of switching from delta to wye in the stator configuration of a PM motor?

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Kevin Sharpe

· #125 · Dec 1, 2017

electro wrks said:
If I'm not mistaken, the R2 has motor based torque vectoring. This implies symmetry, side to side, for the two motors and gear reduction boxes in the back.

Multiple articles have stated that the Roadster has torque vectoring... I'm not sure what the original source of this is but suspect it will be required to get such a heavy car around corners.

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