Dual CT running on one motor

[Crissa]

I think Tesla can disengage the motors... Certainly you can cycle a neutral amount of energy through it, though.

That's what you do with a Zero when you want to 'coast'. They're really manual.

-Crissa

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[HaulingAss]

For reasons I don't understand Tesla will not allow its motors to be driven passively i.e. you cannot tug tow a Tesla vehicle and are strongly warned against doing so in their manuals.

If your Model 3 runs out of charge in the middle of nowhere you can charge it back up by towing it with another vehicle and using regen braking to fill the battery. Towing like this (with the car in Drive and a driver in the seat) is really no different than regen braking down a long grade as far as the car is concerned. It charges surprisingly quickly at 15 mph.

 

[HaulingAss]

That's cool ^-^ Tho driving in limp mode is no fun.

-Crissa

Apparently, limp mode on a Tesla is a maximum speed of 75-80 mph. Of course your acceleration is impacted down to the level of your typical gutless gasoline car, lol!

 

[FutureBoy]

Apparently, limp mode on a Tesla is a maximum speed of 75-80 mph. Of course your acceleration is impacted down to the level of your typical gutless gasoline car, lol!

So as long as you don’t take on any challengers at stoplights, no one will know you are in limp mode.

 

[ajdelange]

If your Model 3 runs out of charge in the middle of nowhere you can charge it back up by towing it with another vehicle and using regen braking to fill the battery. Towing like this (with the car in Drive and a driver in the seat) is really no different than regen braking down a long grade as far as the car is concerned. It charges surprisingly quickly at 15 mph.

Apparently, limp mode on a Tesla is a maximum speed of 75-80 mph. Of course your acceleration is impacted down to the level of your typical gutless gasoline car, lol!

I don't know what kind of lockout the car may impose to prevent "limping" furthther than to the side of the road. As for towing to charge the manual makes it quite clear that you must not do that nor in fact tow it at all if its wheels are in contact with the ground.

From the X manual (caps are theirs):

"Warning: NEVER TRANSPORT YOUR VEHICLE WITH THE TIRES IN A POSITION WHERE THEY CAN SPIN. DOING SO CAN LEAD TO SIGNIFICANT DAMAGE AND OVERHEATING. IN RARE CASES EXTREME OVERHEATING MAY CAUSE THE SURROUNDING COMPONENTS TO IGNITE."

Later paragraphs indicate that allowing the wheels to spin while towing voids the waranty.

Now it stands to reason that if you are strongly advised to not passively drag the motors while towing you ought not to drag one of the motors with the other.

I don't know why this is. I can think of lots of questions about it I'd ask a Tesla engineer if I had access to one. Rivian says that you can indeed charge their trucks by towing them. When asked about limping on a failed motor or motors the CS person said she would have to research that and get back to me. Never did.

 

[ajdelange]

I believe you I misspoke here. I think you meant induction (or asynchronous) where you say synchronous. But I do not know the history of the MX to know for sure. PM motors are synchronous motors.

You don't need to know the history of the X to realize that i clearly bobbled that. Thanks for pointing it out. I fixed it,

 

[Diehard]

the electricity generated needs somewhere to go

A brand new dual motor owner living on high elevation in Colorado chargers to 100% and start rolling down the mountain hitting the break. Where does the regen juice go? I accept for some problems, it would not be safe to drive it but Elan used the additional motor as having the piece of mind to be able to go home If one failed in one of his presentations. I have a hard time believing at least for some failures, the system can not make the appropriate determination and adjustments to get you rolling. Frankly that is the main reason I would get a dual motor over single. If that does not work, the towing and range is not enough for me to upgrade from single.

 

[ajdelange]

A brand new dual motor owner living on high elevation in Colorado chargers to 100% and start rolling down the mountain hitting the break. Where does the regen juice go?

It doesn't go anywhere because there isn't any. Regen has been disabled. That's why he has to use the friction brake if he has to slow down.

What I don't understand is why it is OK to let gravity spin the motor going down the hill when regen is disabled but not OK to let a tow truck do that.

I accept for some problems, it would not be safe to drive it but Elan used the additional motor as having the piece of mind to be able to go home If one failed in one of his presentations. I have a hard time believing at least for some failures, the system can not make the appropriate determination and adjustments to get you rolling. Frankly that is the main reason I would get a dual motor over single. If that does not work, the towing and range is not enough for me to upgrade from single.

Plainly there are aspects to this that neither you nor I understand. Tesla tells me I shouldn't tow and, presumably therefore, not use one motor to drag another. Rivian says I can't tow but they can't tell me whether I should "limp" or not.

I'm enough of an engineer to understand that a vehicle with two motors is approximately twice as likely to experience an engine failure as a vehicle with one so one of my first question to Tesla sales personnel was "What do I do if a motor fails". The answer was "Drive to a service center". But the manual contradicts that. Should it ever happen, I'll pull off the freeway and call.

 

[Diehard]

What I don't understand is why it is OK to let gravity spin the motor going down the hill when regen is disabled but not OK to let a tow truck do that.

That was my whole point. There was a guy that drove it home at highway speed in limp mode and didn’t set anything on fire. Tesla just need to get better at sharing technical information. It seems like they released their technical manuals in China and then they shut it down again. I wonder if there are any copies floating around. It is ridiculous that we have to speculate on operation of cars that are already on the road. Please share if you come across any new info.

 

[ajdelange]

I promise but don't hold your breath.

I didn't want it to get too geeky here but something of this may relate to the use of PM motors. You have a magnet and coils. if the magnet gets whipped past the coils a voltage is induced. You also have the "reluctance switching" aspect to a PM motor. I'm already in terra incognita here so I'll say no more than that.

 

[Diehard]

I promise but don't hold your breath.

I didn't want it to get too geeky here but something of this may relate to the use of PM motors. You have a magnet and coils. if the magnet gets whipped past the coils a voltage is induced. You also have the "reluctance switching" aspect to a PM motor. I'm already in terra incognita here so I'll say no more than that.

Man, now you are making me google stuff.....

 

[Crissa]

I think, because a tow truck is doing it when the car has something broken, and cannot be certain it is safe to let the motors spin.

It's just, 'this is safe, unless something is wrong.' Well, the corollary is , 'when something is wrong, we can't be sure this is safe'.

-Crissa

 

[Bill906]

There has been a lot of discussion in this thread about what will the car do if a motor fails. I suspect the answer to that would be very much dependent on the mode of failure. First what component failed? The motor itself? The inverter? gearbox maybe? What type of failure? Electical, mechanical, thermal, control, communication? Was the electrical failure a short? An open?... Asking what will happen if a motor failed is a vague and open ended question. I suspect that some modes of failure will allow you to drive home with little issue. Some will allow you to “Limp” home and some will require you to poor gas on the car and light it on fire were it sits.

 

[Diehard]

There has been a lot of discussion in this thread about what will the car do if a motor fails. I suspect the answer to that would be very much dependent on the mode of failure. First what component failed? The motor itself? The inverter? gearbox maybe? What type of failure? Electical, mechanical, thermal, control, communication? Was the electrical failure a short? An open?... Asking what will happen if a motor failed is a vague and open ended question. I suspect that some modes of failure will allow you to drive home with little issue. Some will allow you to “Limp” home and some will require you to poor gas on the car and light it on fire were it sits.

That is the problem. If with gazillion sensors everywhere, Tesla does not tell us which is which we may end up setting the car on fire unnecessarily when just giving it a good kick would be sufficient.

 

[ajdelange]

We can be quite certain that the truck will be engineered to protect itself just as the cars are today. If a failure occurs that requires attention or is likely to require attention in the near future you will get, as you do today, a message on the screen informing you that service is needed, In extreme cases the truck will shut down or reduce power delivery to a level such that it can only be moved a few feet per minute sufficient to get it off the road and on to a trailer truck.

We are not qualified to interpret the multiple sensors whose readings are uses to make the decisions as to what action is appropriate, You want the car and/or the Tesla technician to make that determination so that the entire liability falls on them. If you are smart you don't call your HVAC people and tell them the TXV is hunting. You tell them something is wrong with your air conditioner. It's the same thing here.

You can search "Tesla motor failure" on the web. Fortunately you won't find much but you will find a few anecdotes about motor failure in multi motor Teslas.

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