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Discussion in 'TSLA Investor Discussions' started by jhm, Sep 20, 2017.
Musk said the Semi will have a "bunch" of motors.
What application are we talking here?
As the first four I concur with others that two on each of two driving axle allow differential to be electronic.
That is seriously next level, Six would just be overkill.
2 per drive axle. 1 per steer axle.
Motors on the Semi tractors. There may be different configurations, so you can select up to 3 choice.
So I think they will have a three and five version.
Three might be doable for regional haul. Five for heavy haul.
3 One motor for each axle. Same dynamics as AWD. Push or pull depending on need.
Pretty sure he already stated it would use 6 Model 3 motors.
I was hoping for a motor on each axle so it could do some crazy cool maneuvering at low speeds. Spent too much time looking for videos or animated gifs of toy cars spinning. You get the idea!
Edit: I guess I mean 2 per axle, one controlling each drive wheel. Optimally 6.
Pardon my ignorance, but do you really need an "axel" if you have a drive motor for each wheel?
Honda has a 2 motors per axle unit in production, Mitsubishi is prepping a 2 motors per unit for production.
For trucks, I expect Tesla to prioritize number of axles driven, over number of wheels driven. Road damage is based on the 4th power of weight per axle, and heavy loads simply require more axles to stay legit.
Exactly what I was thinking when I began reading through this thread. An axle simply adds unnecessary complexity, cost, and maintenance to an EV once you have a project of enough scale to justify putting a drive motor on each wheel. And the final result is no mechanical connection across the vehicle through the axle that would require a differential to allow the drive wheels to turn at different speeds around corners, etc. The motors will simply spin at slightly different speeds as necessary under normal conditions, but could be locked to spin together if needed (similar to windmills locking in phase once they are up to speed). A limited-slip mode could engage 'on the fly'. For someone who has repaired and replaced too many failed Jeep and old Chevy Blazer axles over the years, this is a very refreshing topic and just one more of the many big positives for EV's. No more failed ring and pinion gears, no more U-joint issues, no more leaky seals, no more differential oil............etc, etc. Thanks @TalkingMule
I think we are talking about "axle" in two different ways here. One, there is the physical structure that connects wheels on opposite sides of the vehicle. Two, there is row of wheels from side to side.
So with two drive units per axle (row of wheels ) it may be possible to avoid a physical axle spanning those wheels.
Just trying to be clear. I'm not sure what the technical language is to make this distinction.
Axels do have the benefit of allowing the use of leaf spring or airbags. Without the steel cross tube, it would need a multi-link.
Having half-shafts allows the motors to be hard mounted to the frame, this provides the counter force to the torque vs the linkage needing to handle acceleration as well as braking (and with regen, braking force can be more directly transmitted to the frame). It also eliminates flex in the power leads to the motor assembly and reduces sprung mass.
The Tesla set up doesn't have the usual ring/pinion since the motor shaft is parallel with the axle. The motor output gear drives the differential ring directly.
Using a solid cross beam that is bent to clear the motors and half shafts may be a good blend. Similar to the solid front beam on some heavy duty trucks.
Could also expand what was formerly the differential and package dual motors as one large assembly, no CVs or U joist needed. Since they are centrally located, it would reduce harness flex and provide more protection than if they were more outboard mounted. Two per axle, with one axle having motor to the front, and one toward the rear? Or both sets in the middle given the wheel spacing? Or even mounted above the axle? That would give space for an under beam for load transfer.
It will be interesting.
Half-axles are required at any rate.
Axles are significantly more stable than half-axles, so you have to do a bunch of funny stuff if you don't have axles.
I believe the only realistic options are 3 (one per axle) and 6 (one per half-axle), obviously with none on the trailer.
I eould like 5 or 6. Two motors on each axle in important for braking, more than acceleration. The front axle maybe has one motor, but I think 2 for each axle is best for overall mileage. Maybe the customize though, truck buyers like highly customizable trucks.
Thanks Mongo, and agreed. My post was intended to be focused on the eliminating the differential from the 'axle'. I think @jhm caught that on his follow-up post too when he mentioned that it might simply become a physical connection across the body of the vehicle. Your diagram and discussion are very helpful to clarify the concept. I was once again wrapped up in the excitement of another incredible paradigm shift from Tesla - in this case a concept that eliminates big leaky 'pumpkins' from the drivetrain. After years of playing with 4x4's in Idaho and Alaska I could almost play ring toss and put them back together, but it was the $$$$, the time, and the inconvenience of where they failed and left me stranded that makes me glad to see the potential for them to go away for ever. I am hopeful it is simply a straight physical connection to support suspension and parallel electric motors, as you much more clearly stated.
And while the big boom trucks and flatbeds we drove for work in Alaska rarely had the same differential maintenance issues as the smaller vehicles (although the cold weather cold be brutal on them), this discussion could also include the significant benefit of eliminating the transmission on semi-truck style vehicles as well through the conversion to electric motors. Allison sure brought a great product to market years ago that greatly reduced the corrective maintenance and cost to maintain previously constructed automatic transmissions in big vehicles, but they are not flawless either. Huge automatic transmissions need expensive maintenance, and they are expensive up-front. And the entire driveline - including the transmission and pumpkin - take a considerable amount of space on the vehicle as well. It will be really fun to see what Tesla and their semi-tractor manufacturing design partners did with all the space they created by eliminating all of these driveline components. There has been some great discussion and fun debate on TMC regarding the location of the batteries (tractor vs trailer). And while I think it makes a lot of sense to include a battery on the trailer, the driveline elimination in its current form - to include the motor, transmission, axle(s), and differential(s) will eliminate so much weight and space that the sizing of the batteries for the tractors themselves could allow the tractors to morph into something in shape and purpose that is really unexpected.
So if Tesla does all this engineering and programming to put two drive units on an axle and to optimize torque vectoring, it raise this question:
When will P100Q come out for Models S and X?
Honestly? If they do reveal this for the Semi, perhaps the first other Q model will be the pickup or van. For S and X, maybe early 2019, maybe 2020, maybe 2021? I guess it depends how fast they can engineer it and alter the production line / build a new one, and whether that seems like the best use of their capital.
They're still somewhat capital constrained; I think this will be alleviated sometime in 2018 as Model 3 deliveries ramp up. So I'm thinking we won't see any such change before 2019 -- but it could be later. It may be simultaneous with the switch to permanent magnet motors and around the same time as the change to 21-70 cells. Maybe with a minor interior redesign. I actually think we won't see much of an interior redesign on the S -- maybe the cupholders, seatback pockets, grab handles and so forth that people have been complaining about the lack of -- but remember how little the Model T design changed from year to year.