Is Elon being very conservative with TRI-motor 0-60 times? Is 2.5 possible?

[mrbulk]

Saw this just today on the news and I hope and pray we really will have this kind of game-changing battery tech in our CTs by the time they begin production.

*EDIT: because it means they can fit a 100kwh battery in 3/4 the size compartment of the Model 3.

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[Regenshire]

Saw this just today on the news and I hope and pray we really will have this kind of game-changing battery tech in our CTs by the time they begin production.

*EDIT: because it means they can fit a 100kwh battery in 3/4 the size compartment of the Model 3.

Elon tweeted that there is no 100kwh Model 3 in development as a reply to one of the articles claiming there is an incoming 100kwh Model 3.

 

[drcarric2650]

Why do you say "at best" the 3 motor will be around 2.9 seconds? The MX is 2.6 seconds with only 2 motors...

Need to make the Plaid mode more desirable, how else would you get an extra 5 or 10 grand.

 

[ajdelange]

The acceleration depends on the power delivered to the drive train and the torque. It should be obvious that 3 motors will produce 50% more torque and 50% more power if each of the three motors is the same and each is driven the same. There is no reason why this is necessarily the case and that's the basis for torque vectoring. As I said in No. 2 if the CT weighs 2700 kg it reuires and thrust (torque timew wheel radius) of f = m*a = 24972 N to accelerate uniformly to 60 mpH in 2.9 sec. If we decide to split that between two rear motors that's 12486 N each. And if we designed the motor's gearboxes to handle that much torque each we would be fine. But we would not be fine if we tried to accelerate 3.3 times as much mass (the weight of truck and trailer in anything less than 9.57 seconds as to do so would exceed the torque rating of those motors. Obvious solution: add another motor.

I'm not a physicist but don't those massive wheels somewhat limit the acceleration.

Accelleration is mostly limited by the rate at which one can load m*v*v/2 energy into the mass (m) of the vehicle but some, I*omega*omega/2 has to go into the rotational kinnetic energy of the wheels. The higher I (the moment of inertia which depends on the mass of the wheel and how it is distrubuted wrt radius) the more energy that is robbed from the linear acceleration.

 

[Cybr on]

The acceleration depends on the power delivered to the drive train and the torque. It should be obvious that 3 motors will produce 50% more torque and 50% more power if each of the three motors is the same and each is driven the same. There is no reason why this is necessarily the case and that's the basis for torque vectoring. As I said in No. 2 if the CT weighs 2700 kg it reuires and thrust (torque timew wheel radius) of f = m*a = 24972 N to accelerate uniformly to 60 mpH in 2.9 sec. If we decide to split that between two rear motors that's 12486 N each. And if we designed the motor's gearboxes to handle that much torque each we would be fine. But we would not be fine if we tried to accelerate 3 times
Accelleration is mostly limited by the rate at which one can load m*v*v/2 energy into the mass (m) of the vehicle but some, I*omega*omega/2 has to go into the rotational kinnetic energy of the wheels. The higher I (the moment of inertia which depends on the mass of the wheel and how it is distrubuted wrt radius) the more energy that is robbed from the linear acceleration.

Yea. Like he said?

when I see your name, I prepare myself for the long, but educational read. I may have to read it a couple or several times, but sometimes I get it, and sometimes I don’t. THIS TIME, I GET IT!!! ? I don’t hold any credentials like you most likely have or crunch numbers like you can, but I do enjoy my attempts to understand even though most times I feel like Rocky in the 6th round. ?.

 

[mrbulk]

Elon tweeted that there is no 100kwh Model 3 in development as a reply to one of the articles claiming there is an incoming 100kwh Model 3.

He tweeted "No larger" - see what he did there? If they can shoehorn 100kwh into a 75kwh space then it is still "no larger". But he can't say that now since he doesn't want to Osborne his current sales. Just my personal theory.

 

[TyPope]

The acceleration depends on the power delivered to the drive train and the torque. It should be obvious that 3 motors will produce 50% more torque and 50% more power if each of the three motors is the same and each is driven the same. There is no reason why this is necessarily the case and that's the basis for torque vectoring. As I said in No. 2 if the CT weighs 2700 kg it reuires and thrust (torque timew wheel radius) of f = m*a = 24972 N to accelerate uniformly to 60 mpH in 2.9 sec. If we decide to split that between two rear motors that's 12486 N each. And if we designed the motor's gearboxes to handle that much torque each we would be fine. But we would not be fine if we tried to accelerate 3.3 times as much mass (the weight of truck and trailer in anything less than 9.57 seconds as to do so would exceed the torque rating of those motors. Obvious solution: add another motor.

Accelleration is mostly limited by the rate at which one can load m*v*v/2 energy into the mass (m) of the vehicle but some, I*omega*omega/2 has to go into the rotational kinnetic energy of the wheels. The higher I (the moment of inertia which depends on the mass of the wheel and how it is distrubuted wrt radius) the more energy that is robbed from the linear acceleration.

There is another limiting factor I hadn't considered. You could have 8 motors in the CT but if you can't get enough electricity to them fast enough, it doesn't matter. There is a certain number of motors that would pull as much electricity as the batteries can supply and any more motors than that will not help the cause. Is it possible that Tesla's motors are powerful enough that any more than three motors would be more of a hinderance than a help?

 

[azjohn]

Elon tweeted that there is no 100kwh Model 3 in development as a reply to one of the articles claiming there is an incoming 100kwh Model 3.

It wouldnt be the 1st time Elon has said something is not happening but later on it does but worded differently.

IMO there is a 50/50 chance it will happen

 

[azjohn]

I*omega*omega/2 has to go into the rotational kinnetic energy of the wheels

When I saw the "Omega" comment the 1st thing I thought of was an episode of Star Trek Voyager about the Omega Particle

The Star Trek nerds know what I am talking about

 

[ajdelange]

Here it means the rotation rate of the wheel in radians per second. Not familiar with the Star Trek but omega is fraught with connotations in western civilization through its association with the death of Christ - often used to symbolize the END. Alpha and Omega.

 

[ajdelange]

There is another limiting factor I hadn't considered. You could have 8 motors in the CT but if you can't get enough electricity to them fast enough, it doesn't matter. There is a certain number of motors that would pull as much electricity as the batteries can supply and any more motors than that will not help the cause. Is it possible that Tesla's motors are powerful enough that any more than three motors would be more of a hinderance than a help?

Remember that design is an art - one based on science for sure but an art nevertheless. What a design team decides to do ultimately is based on a combination of the science, their experience, cost, manufacturability and a host of other considerations (what marketing tells them....). You can drive a vehicle with 4 wheels in a variety of ways. Yes, the battery can supply power at some maximum rate so that's a constraint. You cannot add a 4th motor and send it more power than the battery can supply less what you are sending to the other motors but you could add another motor and reduce the distribution of power to the other motors so that the total is within the limits of what the battery can deliver. You don't have to send the maximum a motor can handle to it though you don't want to install 1000 HP motors if you never intend to send them more than 500 HP because they will be less efficient than a motor designed for the load its intended to handle.

Why would we want a 4th motor in the CT? The answer would be that we want more flexible torque vectoring at the front. The benefits of this (ability to do tank turns) would have to be deemed worth the extra cost, weight, system complexity etc.

 

[azjohn]

Here it means the rotation rate of the wheel in radians per second. Not familiar with the Star Trek but omega is fraught with connotations in western civilization through its association with the death of Christ - often used to symbolize the END. Alpha and Omega.

The Omega Particle was unstable and thought of could destroy space. In some cases it seems like real science follows science fiction. My favorite author is Michio Kaku who has some books on the subject of comparing science to fiction

https://en.wikipedia.org/wiki/The_Omega_Directive

 

[VolklKatana]

Two other things to consider, the rigidity if the suspension (though the air suspension should take care of that) and the big knobby tires. The question will be, what setup is required to hit 2.9 to begin with? Then the what ifs can start to be answered...

 

[TyPope]

The Omega Particle was unstable and thought of could destroy space. In some cases it seems like real science follows science fiction. My favorite author is Michio Kaku who has some books on the subject of comparing science to fiction

https://en.wikipedia.org/wiki/The_Omega_Directive

Unless you are talking about the Omega Device from Galaxy Quest, one of the best satirical Sci-fi movies out.