SPECIAL EDITION QUAD-MOTOR Cybertruck rumor

[cybercamper]

Imagine if all four motors are inside each wheel hub. Now you can make the truck bed much lower if there is no axle or differential. (does CT have a differential?)
Tesla is capable of developing hub motors that would be powerful enough for this configuration.

Advertisement

 

[ldjessee]

Imagine if all four motors are inside each wheel hub. Now you can make the truck bed much lower if there is no axle or differential. (does CT have a differential?)
Tesla is capable of developing hub motors that would be powerful enough for this configuration.

HUB motors have their own issues. They are subjected to impacts, certain loading forces, and vibration that once at highway speeds, I am to understand these become substantial and results in a short lifespan for hub motors.
Also, they are lower down, more likely to be exposed to elements, and if you live where I do, that means salted roads every winter.

I used to think HUB motors would be so much more efficient, and might be great things for city transit and school buses that do not have to get above 45 MPH.

 

[cybercamper]

Tesla may have already considered and eliminated them. But for a lighter duty vehicle than a CT they might be appropriate. Lots of potential:

 

[rr6013]

75-90% is 10-25% shy of anywhere. 4 wheel drive clearly has advantages in many applications and, as noted in the first paragroph, it comes as a side benefit of the higher efficiencies that stem from the use of multiple motors.

Exactly. Baja 1000 pre-runner 2 wheel drives have caught my attention. As you allude, electrons weigh less than tranfer cases, transmissions, driveline, carriers, housings and running gear.

BEV are torque monsters. Pre-runners thrive on torque. The bigger the electric motor the bigger the torque. Four smaller motors will deliver 4 small torques to the drive wheels. One massive high output motor would divert torque to the wheel that needs it most.

My thinking has gotten wrapped around the gains from losing motors, losing unsprung weight and increasing torque to-the-ground. As an ex-racer, diesel owner and 4x4 off-roader this torque gain/weight loss begins to counter the 4x4 narrative.

The point remains, that 4x4 does reach places and digs through where 4x2 can’t. The answers that I have staring at me, throws into question the % of places I would be shit out of luck with the single motor high torque Cybertruck.

Someone from inside Tesla would have to enlighten the discussion with values to separate the argument for and against. It could very well be that the Sgl-motor CT is puny. No argument can bear up against a Prius CT if that is the case.

 

[FutureBoy]

Tesla may have already considered and eliminated them. But for a lighter duty vehicle than a CT they might be appropriate. Lots of potential:

Looks like a fun ride. Might even fit in the bed of my CT. Seems a little expensive though. But for a 4 hour and 100km charge it would be fun. 1 thing though is that the open cabin would make mountain stream fording a bit of a chill.

 

[Luke42]

Einstein thought it logically perfect to simplify a system until no longer possible to remove a single item.

Einstein was a physicist, not an engineer.

Einstein was trying to unlock the secrets of the universe, not build reliable electromachinery at an affordable price. The world needs both, of course, but let's not conflate the two.

Redundancy has an important place in engineering.

 

[Crissa]

Fewer parts is fewer points of failure. But fewer parts means more points that the failure is blocking.

Important balance.

-Crissa

 

[firsttruck]

Einstein was a physicist, not an engineer.

Einstein was trying to unlock the secrets of the universe, not build reliable electromachinery at an affordable price. The world needs both, of course, but let's not conflate the two.

Redundancy has an important place in engineering.

Elon does not have a Phd in Physics but he does have bachelor's degrees in physics which is very rare among large company CEOs. Also that as impressive because I do not think the U.S. has that many students in that field vs business & computer science.

University of Pennsylvania dual bachelor's degrees in economics and physics.

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

 

[rr6013]

Fewer parts is fewer points of failure. But fewer parts means more points that the failure is blocking.

Important balance.

-Crissa

@Crissa you make a distinction that I am not aware. It must be important. “Blocking“ is not a design failure mode I’m familiar.

Perhaps its rocket science. Can you share how this failure-blocking happens by example? Are you alluding to software by example Boeing incremental testing blocking a failure rather than end-to-end testing?

Whre are you coming from with blocking?

 

[Luke42]

Fewer parts is fewer points of failure. But fewer parts means more points that the failure is blocking.

Important balance.

@Crissa you make a distinction that I am not aware. It must be important. “Blocking“ is not a design failure mode I’m familiar.

Blocking is a verb in this context. Reread the comment.

She's talking about the granularity of the failure in failure mode analysis.

She's pointing out that simpler machines are assumed to fail less often than complex machines, but that the failure could affect the whole machine.

In the context of a quad-motor electric car, the single motor variant will have fewer motor failures (fewer parts to break), but it can't limp home (no redundancy).

Balancing simplicity and redundancy can be tricky, especially in the absence of clear requirements. Also, in my experience, some attempts at removing a single point of failure can create multiple points of failure. This stuff is harder than it looks, and it is a careful balance.

I understand this, and Crissa understands this -- but we had to fill you in on the shared knowledge we were referring to.

 

[ajdelange]

In the context of a quad-motor electric car, the single motor variant will have fewer motor failures (fewer parts to break), but it can't limp home (no redundancy).

In the current dual motor Teslas one cannot limp home after a single motor failure. Thus, from the reliability point of view, the second motor does nothing but double (approximately) the probability of ending up on the side of the road from motor failure. The second motor isn't there for redundancy. It's there for improved efficiency and performance.

We wonder how Rivian (quad motor), for example, will handle a single motor failure.

[Edit]I sent them an e-mail in which I asked that question but won't hear back until next week.

 

[Luke42]

In the current dual motor Teslas one cannot limp home after a single motor failure. Thus, from the reliability point of view, the second motor does nothing but double (approximately) the probability of ending up on the side of the road from motor failure. The second motor isn't there for redundancy. It's there for improved efficiency and performance.

I've turned a single point of failure into multiple points of failure enough times that I'm not going to get judgy about that.

Been there, done that, had a good reason at the time, xor caught it in testing...!

 

[Tinker71]

There are sound rumors from Tesla workers about a possible Quad-Motor Super Performance Cybertruck model capable of insane maneuvers. Anyone have any thoughts?

If they do it, I would bet they eliminate the tri motor version or even the current dual motor version. Actually now that I think about it the single motor version would now be dual direct drive to the rear. This should get rid of the expense of the transfer cases and differentials and would standardize all the drive axles across their line up. The current dual motor could have 4 smaller motors and batteries if they wanted to keep the 3 main tiers. If Lucid Motors made a smaller more efficient motor, Tesla wouldn't be far behind. The more I think about it I think this is highly likely.

 

[ajdelange]

If Lucid Motors made a smaller more efficient motor, Tesla wouldn't be far behind.

That's a pretty big if. Many of Lucid's claims, as are those of all the OEMs are marketing claims and have to be taken with a grain of salt. The current state of the art in motors is efficiencies well into the 90's. There isn't much room for improvement left. That does not mean that they will not vigorously pursue those few percent.

Tesla currently has a design for two motors, two inverters, two "differentials" and two half shafts in a single assembly. It's what will go in the back of the Trimotor CT. If they can come up with that for the rear with the current technology they can certainly do it in the front as well. If they decide to do a quadmotor I'd guess that that's how they'd do it.

 

[Tinker71]

That's a pretty big if. Many of Lucid's claims, as are those of all the OEMs are marketing claims and have to be taken with a grain of salt. The current state of the art in motors is efficiencies well into the 90's. There isn't much room for improvement left. That does not mean that they will not vigorously pursue those few percent.

Tesla currently has a design for two motors, two inverters, two "differentials" and two half shafts in a single assembly. It's what will go in the back of the Trimotor CT. If then can come up with that for the rear with the current technology they can certainly do it in the front as well. If they decide to do a quadmotor I'd guess that that's how they'd do it.

I saw the rumor post on the dual motor RWD after my post. Maybe they just standardize the rear drive with 2 motors across all 3 models and the front drive stays pretty much the same. So the dual motor AWD would now be a trimotor and the current tri motor just has larger rear motors and batteries. While they may have spent a ton of money designing a single assembly for the rear it is still more mechanically complex than a direct drive with half axle. The front wheel drive is an entirely different animal. You don't need to transfer near the power and it gets complex with the steering and suspension.