New Semi Information

This video claims to have more current information on the Semi:

Highlights:

• Change to motor layout: One motor per Axel: Front/Middle/Rear.
• Only one charge port. (MCS only?)
• TACC currently active (The rest of AP not yet.)
• Extra cameras won't be needed on the trailer for AP usage.

 

[Olle]

6WD Semi, how awesome!

• Rarely a need to use the friction brakes -> More regen, even better efficiency.
• Slightly more traction.
• Will be exciting to see if it will have a live axle like in the rear but with steering or individual suspension like a car.

 

[TSemi]

6WD Semi, how awesome!

Awesomeness!!! I posted this back in 2020:

Tesla Semi with AWD and adaptive advanced air suspension settings

Who wouldn't love to have an option for AWD(a single motor to drive front wheels) and adaptive advanced air suspension settings? Although the Semi may come with the AAASS anyway. I haven't seen it mentioned but I also have to believe the Semi will come with same things mentioned by Elon...

teslamotorsclub.com

 

[TSemi]

Only one charge port. (MCS only?)

https://twitter.com/x/status/1633390154512744448

 

[gsmith123]

Warning: at the 6:45 mark in this video the presenter gives some incorrect info. He's talking about motor configurations and says with Model 3 and Y the front motor is more efficient highway cruising. This is not the case. The rear permanent magnet motor is more efficient at all speeds and the car will bias towards using only the rear motor when it can.

Note: on S and X (recent generations) the front motor is the more efficient one.

I mention this because it makes me trust all the other info presented a bit less. It's a minor mistake but a pretty obvious one for people familiar with Tesla drivetrain design.

6 wheel drive Semi doesn't make any sense considering engineering first principles. It adds two more half shafts and two more differentials. Wasted weight for no gain.

 

[EbS-P]

I don’t see any advantage of an AWD over the road and or short haul semi. Unless they want DOD contracts, it’s a waist. Extra parts to wear out.

Loaded traction is **almost**never a problem on dry roads and if road conditions are bad enough to need AWD most carriers would prefer to have their equipment off the road.

**edit

 

[TSemi]

I don’t see any advantage of an AWD over the road and or short haul semi. Unless they want DOD contracts, it’s a waist. Extra parts to wear out.

Loaded traction is **almost**never a problem on dry roads and if road conditions are bad enough to need AWD most carriers would prefer to have their equipment off the road.

**edit

The Tesla Semi started out with 4 Model 3 PMSM motors(one per wheel on the 2 rear axels) then went to the newer carbon-wrapped motors - 2 on one rear axle and one on the other rear axle. Then decided(per the video) that they just moved one of the motors to the front axle and 1 motor each on the 2 rear axles. So you are telling the Tesla engineers they need to use only 2 motors because "extra parts to wear out"?

Maybe you should join the Tesla Engineering Team so you can tell them how wrong they are.

 

[gsmith123]

So you are telling the Tesla engineers they need to use only 2 motors because "extra parts to wear out"?

Hey, "Extra parts to wear out" is a great reason to eliminate parts! As the classic Elon-ism goes "The best part is no part". Note: I don't think the previous poster was specifically saying 2 vs 3 motors, just that the semi doesn't need all 6 wheels to be driven.

I'm just confused what you're seeing as the advantage of shifting one of the two motors from the rear axle to the front axle. That's a net addition of two differentials and two halfshafts, for no benefit. You're still running the same motors and have added weight and inefficiency (from the extra differentials). You even lose the torque vectoring capability!

What's the point?

Architecture at semi delivery event:
Front axle: no motor
Middle axle: 2x independent acceleration optimized motors. Zero differentials. 2x half shafts.
Rear axle: 1x efficiency optimized motor. 1x differential. 2x half shafts.

Proposed new architecture:
Front axle: 1 efficiency optimized motor. 1 differential. 2x half shafts.
Middle axle: 1 acceleration optimized motor. 1 differential. 2x half shafts.
Rear axle: 1 acceleration optimized motor. 1 differential. 2x half shafts.

Help me understand, am I missing something here?

 

[TSemi]

Help me understand, am I missing something here?

Are you an engineer? I'm not. If you happen to be an engineer that is involved with designing electric class 8 trucks then I suggest you march on down to Tesla's engineering dept. and tell them they got it all wrong. It really is pointless to argue back and forth over this issue in this forum.

 

[stopcrazypp]

Are you an engineer? I'm not. If you happen to be an engineer that is involved with designing electric class 8 trucks then I suggest you march on down to Tesla's engineering dept. and tell them they got it all wrong. It really is pointless to argue back and forth over this issue in this forum.

Except there is no confirmation from Tesla that they are using the configuration the presenter said in the video, it still remains a rumor.

 

[stopcrazypp]

Hey, "Extra parts to wear out" is a great reason to eliminate parts! As the classic Elon-ism goes "The best part is no part". Note: I don't think the previous poster was specifically saying 2 vs 3 motors, just that the semi doesn't need all 6 wheels to be driven.

I'm just confused what you're seeing as the advantage of shifting one of the two motors from the rear axle to the front axle. That's a net addition of two differentials and two halfshafts, for no benefit. You're still running the same motors and have added weight and inefficiency (from the extra differentials). You even lose the torque vectoring capability!

What's the point?

Architecture at semi delivery event:
Front axle: no motor
Middle axle: 2x independent acceleration optimized motors. Zero differentials. 2x half shafts.
Rear axle: 1x efficiency optimized motor. 1x differential. 2x half shafts.

Proposed new architecture:
Front axle: 1 efficiency optimized motor. 1 differential. 2x half shafts.
Middle axle: 1 acceleration optimized motor. 1 differential. 2x half shafts.
Rear axle: 1 acceleration optimized motor. 1 differential. 2x half shafts.

Help me understand, am I missing something here?

It doesn't save parts, but a front motor probably improves regen. This had been an issue with Teslas previously with only rear motors, given the front wheels tend to be the ones that are loaded the most when braking. That's the advantage I can see. It might also have some traction advantages (if in some cases where the rear wheels are on a slippery patch, but fronts are not).

 

[gsmith123]

It really is pointless to argue back and forth over this issue in this forum.

Sorry, that's literally why I'm on an internet forum brainstorming electric semi truck design

No, I'm not an automotive or mechanical engineer by profession. I know enough about mechanical systems and EV design to think through the pros and cons of different designs at a high level though.

I'm just here because I find all this stuff interesting, btw, and discussing the rumors is fun. You don't have to if it's not fun! If you're not interested in having a discussion about the merits of different designs, why even post things like this:

So you are telling the Tesla engineers they need to use only 2 motors because "extra parts to wear out"?

Maybe you should join the Tesla Engineering Team so you can tell them how wrong they are.

I'd love to have a discussion with Tesla engineering about motors layouts, that would be awesome. Probably not interested in moving to CA tho

 

[gsmith123]

@stopcrazypp that's an interesting point about regen. Semis do have more load on the rear two axles tho (apparently something like 70-75% based on a quick Google search, while cars are about 50-50%). Maybe they can still get sufficient regen without exceeding grip limits of the rear wheels?

 

[TSemi]

Except there is no confirmation from Tesla that they are using the configuration the presenter said in the video, it still remains a rumor.

The presenter, Matthew Donegan-Ryan, says in the video @04:33 that Tesla told him there were now 1 motor per axle.
Also watch from @01:18-01:40.

 

[TSemi]

Sorry, that's literally why I'm on an internet forum brainstorming electric semi truck design

Fair enough LOL

Note: on S and X (recent generations) the front motor is the more efficient one.

How do you know this? The front and rear motors are both PMSM.

 

[EbS-P]

I could buy the regen argument if regen was traction limited. I don’t think it is on a semi with loaded trailer. Wear in half shafts at turning angles when accelerating would be substantial. I don’t have faith in Tesla and half shaft design. I own a Model X. 24k miles out of a set of axles. Sure it could all be software engineered so there is very little torque applied if the wheels aren’t straight. It just seems like adding lots of complexity to a front end suspension. It’s not just the part could. You move from a solid from axel assembly to an independent heavy duty front suspension.

 

[TSemi]

Architecture at semi delivery event:
Front axle: no motor
Middle axle: 2x independent acceleration optimized motors. Zero differentials. 2x half shafts.
Rear axle: 1x efficiency optimized motor. 1x differential. 2x half shafts.

Ummm, Middle axle has Zero differentials? HAHAHAHA!!!! You have no clue what you are talking about.

All Tesla drive units have differentials.

 

[MP3Mike]

Ummm, Middle axle has Zero differentials? HAHAHAHA!!!! You have no clue what you are talking about.

All Tesla drive units have differentials.

There is no differential on the rear of the Plaid drivetrain. They have an independent motor on each of the rear wheels. (The Plaid Model S&X only have a single differential on the front drive unit.)

And as Tesla presented the Semi drivetrain they did the same thing with one of the rear axels. The Semi had three axels, three motors, and only a single differential. (That might have changed, but I really doubt it. I suspect that the person mis-interpreted what they were told.)

 

[TSemi]

There is no differential on the rear of the Plaid drivetrain. They have an independent motor on each of the rear wheels. (The Plaid Model S&X only have a single differential on the front drive unit.)

Ok, it has been awhile since I viewed the Munro teardown of the Tesla Model S Plaid

They do explain that there is no differential since they use torque vectoring. But there is still differential *gearing* in the drive unit with split axles.

At the presentation for the Tesla Semi Delivery Event there was no mention of torque vectoring. This wasn't the same set-up as the Model S Plaid. You have to assume since there are 2 motors on one of the axles that it is the same as the Model S Plaid drive unit but this is a mistake. Look at how they presented it

They still have differential *gearing* just split axles.

(That might have changed, but I really doubt it. I suspect that the person mis-interpreted what they were told.)

I agree that Matthew Donegan-Ryan mis-interpreted some of what he was told. Namely when he was talking about wound and hairpin motors.

But it would be hard to mis-interpret IF some executive at Tesla says one motor on each axle.

 

[MP3Mike]

But there is still differential *gearing* in the drive unit with split axles.

They still have differential *gearing* just split axles.

No. There is no differential gearing. There is however, reduction gearing, that is a part of every Tesla drive unit. But that has nothing to do with a differential.