ALL CyberTruck discussion

[mongo]

My opinion is that RWD is the affordable option, dual rear motors are a cost increase without advantage to a daily driver.

This transitions the inefficient mechanical differential into more efficient SW where improvements in regen, handling, performance and durability can be realized across all model lines simply by improving SW.

The rear differential is not inefficient. Unless the car is turning, the entire assembly moves as one piece, so the only impacts are inertia and lubricant slosh.
Dynamic torque vectoring is a plus, but not needed at typical driving levels.

Linking FSD NN path prediction into a SW based differential further advances handling and regen.

Not needed for typical driving.

This allows the same dual motor drive unit to be used in the front which brings Tesla into a true 4 motor configuration sooner further advancing improvements in regen, handling, performance and durability while simplifying production options.

Packaging constraints are dominant here, and there is no need for dual front motors (assuming the single motor can output sufficient power).

Thermal management opportunities are improved. (Probably towing performance as well)

Definitely true, but when are the limits of a single motor reached? What pack size is need to feed the dual under those conditions?

 

[ggr]

I doubt there will be any meaningful improvement in regen. The existing limit on regen is the cell level charge acceptance rate.

True, but the higher capacity packs can absorb more current. The limit is on the C rate, not the number of amps. So a 500 mile pack can allow regen 500/300 = 1.666 times more than a 300 mile pack. At some point the physics of friction take over the limit.

 

[JRP3]

I was referring to the claim that eliminating the differential would lead to improved regen.

 

[JRP3]

Cyber has some competition in the off road EV category

 

[JRP3]

Turns out that's not an EV, just a very well muffled 2.7 liter 4 cylinder. I guess the gear whine is so loud I thought I was hearing an electric motor
Under hood shot here at 3:33

 

[bhtooefr]

I was referring to the claim that eliminating the differential would lead to improved regen.

It means that there'll be more situations in which full regen can occur, though, because it's less likely to be traction limited.

With an open differential (which is, AFAIK, what Tesla has always used), regen is always limited by the torque that the tire with the least grip can handle. With dual rear motor, regen can harvest from both tires at their respective maximum grips.

This may not show up in an EPA test, but in traction-limited scenarios it can show up in real-world.

 

[mongo]

It means that there'll be more situations in which full regen can occur, though, because it's less likely to be traction limited.

With an open differential (which is, AFAIK, what Tesla has always used), regen is always limited by the torque that the tire with the least grip can handle. With dual rear motor, regen can harvest from both tires at their respective maximum grips.

This may not show up in an EPA test, but in traction-limited scenarios it can show up in real-world.

Split mu at the limit of traction is not yet the boundary the system is dealing with due to differences in C rate for charge and discharge.

Regardless, you do not want one rear tire providing more braking force than the other, lest you induce a spin.

 

[bhtooefr]

Split mu at the limit of traction is not yet the boundary the system is dealing with due to differences in C rate for charge and discharge.

Regardless, you do not want one rear tire providing more braking force than the other, lest you induce a spin.

That depends on your suspension design, and even if you have that constraint, with dual rear motors, you can still get double the maximum regen braking force in low-traction situations, rather than being limited by one tire's traction limit.

 

[mongo]

That depends on your suspension design, and even if you have that constraint, with dual rear motors, you can still get double the maximum regen braking force in low-traction situations, rather than being limited by one tire's traction limit.

How can suspension design prevent a rotational moment if you have different amounts of force on each wheel?

You're also losing me on how two motors increase the available force available due to friction.
Two wheels with X traction run through a differential is the same force as running each wheel to its own motor. There is no additional doubling.

 

[Artful Dodger]

cybertruck body shell engineering analysis - YouTube

"Conclusion: this is a brilliant design for a very strong yet light vehicle"​

 

[jerry33]

How can suspension design prevent a rotational moment if you have different amounts of force on each wheel?

You're also losing me on how two motors increase the available force available due to friction.
Two wheels with X traction run through a differential is the same force as running each wheel to its own motor. There is no additional doubling.

No idea on the first one, but the second one just means that each wheel can be controlled independently to give the most traction. Current methods either have (during slippery conditions) one wheel driving (open diff), the wheels slip a bit (limited slip diff), or both wheels always turn (locked diff).

 

[mongo]

No idea on the first one, but the second one just means that each wheel can be controlled independently to give the most traction. Current methods either have (during slippery conditions) one wheel driving (open diff), the wheels slip a bit (limited slip diff), or both wheels always turn (locked diff).

Yah, but if you keep both wheels at the same load to avoid spin, then differential vs dual yeilds the same available force.

 

[jerry33]

Yah, but if you keep both wheels at the same load to avoid spin, then differential vs dual yeilds the same available force.

True, but often not possible.

 

[mongo]

True, but often not possible.

Yah, if you are operating at the limits of traction. My confusion is regarding this statement

That depends on your suspension design, and even if you have that constraint, with dual rear motors, you can still get double the maximum regen braking force in low-traction situations, rather than being limited by one tire's traction limit.

 

[jerry33]

Yah, if you are operating at the limits of traction. My confusion is regarding this statement

To me, that statement [double the traction] assumes an open differential and slippery surface so one tire will get all the power. In that situation, the other tire won't move at all so it has zero traction (or maybe 100% traction depending upon how you look at it). With a different motor supplying each wheel, both tires will get the maximum traction, which may actually be way more than double the original traction (the tire that gets all the power may be just spinning).

 

[mongo]

To me, that statement [double the traction] assumes an open differential and slippery surface so one tire will get all the power. In that situation, the other tire won't move at all so it has zero traction (or maybe 100% traction depending upon how you look at it). With a different motor supplying each wheel, both tires will get the maximum traction, which may actually be way more than double the original traction (the tire that gets all the power may be just spinning).

Still does not compute: you don't get double the power of the sticky tire and you don't get double the power of the spinny tire. Plus, the lead in is that both tires have the same grip "the constraint".
If the original motor was undersized and the dual was twice the capacity, that could get you double, but adds on other conditions.

OT and not significant, just wondering if I'm missing something.

 

[JRP3]

It means that there'll be more situations in which full regen can occur, though, because it's less likely to be traction limited.

With an open differential (which is, AFAIK, what Tesla has always used), regen is always limited by the torque that the tire with the least grip can handle. With dual rear motor, regen can harvest from both tires at their respective maximum grips.

This may not show up in an EPA test, but in traction-limited scenarios it can show up in real-world.

Almost never, and not enough to produce any significant regen. How often are you regening at the limits of traction?

 

[bhtooefr]

Often enough that my Prius inhibits regen due to losing traction, and it can only do ~27.5 kW of regen.

 

[lascavarian]

I doubt there will be any meaningful improvement in regen. The existing limit on regen is the cell level charge acceptance rate.

I see what you are saying. I am going at a different issue. Regen during a turn is subject to the differential freeing up one wheel.

IMO, with a dual motor drive unit, both wheels are independently controlled which adds the possibility of regen from both wheels. Presently this is just lost energy in many cases. This may offer some serious advantages when towing.

As I understand it, stability control is often working with mechanical breaking and in some cases I suspect a dual motor unit would be able to substitute regen for stability breaking. I think the performance we have seen on the "ring" suggests the benefits of dual motor drive units beyond just power. Any application of breaking is a lost opportunity for regen in effect. And developing battery technologies may expand cell charge acceptance but that is speculative.

This is a non-trivial SW task but it seems likely to deliver some regen and increase stability control options.

IMO, differentials are a necessary solution but a solution with a cost such as mechanical complexity and wear as well as inefficiencies. Dual motor drive units have the potential to free up some costs.

Differentials also force the application of acceleration power to one motor on a turn with all the thermal issues that go along with power. Dual motor drive units would be able to balance the thermal cost of power between two motors.

There ARE some costs to a standardization on a dual motor drive unit but I think it is likely to be a very close positive for Tesla.

 

[lascavarian]

I still want my “ mobile 5 powerwalls with almost free truck” as a base for a nascent VPP here in SW Florida, where hurricane Irma took out the grid for a number of days in a city of 250,000 based upon no electric for that time.

VPP as in Virtual Power Plant? I like the mega packs on trailers idea. Could be used at holiday travel high points to temporarily expand super charging and for disasters. And while on standby just smooth out the grid.