Tesla Semi

[BioSehnsucht]

Pulling from Market Action

If the shield is part of the pack, then you are stuck with top v.s. and possibly fore vs aft bottom version. I'm expecting all 4 packs are the same. The Tractor has higher ground clearance, so road debris is less of an issue. Elon said the bottom was flat, so I expect that to be a welded plate that stiffens up the frame and provides shielding.

Why not a plate that is bolted in place? This way if the packs must be replaced, you don't take the whole cab off, you drop the plate, then (or possibly all together with plate) drop the packs. One might argue welding is stronger, but ... as I understand it SpaceX is switching from welded to bolted octaweb structures for Falcon 9 Block 5 or possibly just for the Falcon Heavy center core variant (I'm not sure exactly...). If SpaceX can make bolted thrust structures work on a rocket, which ideally has the tiniest mass fraction possible, surely Tesla can make it work with a truck for something so pedestrian as battery protection and frame stiffening?

I'm not saying it has to be bolted in a way that makes pack swapping easy - just easier than removing the cab or cutting welds. This would be battery swaps for repair, not range.

 

[mongo]

Why not a plate that is bolted in place? This way if the packs must be replaced, you don't take the whole cab off, you drop the plate, then (or possibly all together with plate) drop the packs. One might argue welding is stronger, but ... as I understand it SpaceX is switching from welded to bolted octaweb structures for Falcon 9 Block 5 or possibly just for the Falcon Heavy center core variant (I'm not sure exactly...). If SpaceX can make bolted thrust structures work on a rocket, which ideally has the tiniest mass fraction possible, surely Tesla can make it work with a truck for something so pedestrian as battery protection and frame stiffening?

I'm not saying it has to be bolted in a way that makes pack swapping easy - just easier than removing the cab or cutting welds. This would be battery swaps for repair, not range.

My post originally had "welded or bolted"

But I pulled it out because then you have a bunch if bolt heads and nuts protruding. SpaceX is using friction stir welding for their tanks/ rockets, so I figured Tesla might for semi (ok really I pictured robot welding arms).
My guess is the batteries are loaded from the sides after the skirt and side protection frame is removed.

 

[mongo]

And none of this changes the fact that a tandem axle is and always will be measured as an axle group

Right, I am operating under the bounds of 20k on one axle, and 34k on the tandem. I am not saying running 6k off balanced is a good idea. I'm not saying the the 5th wheel needs to be over the fore axle (that just makes math easy). What I am saying is that differential load of the rear axles changes steering axle loading.

Doesn't really work that way. Airbags level loads and soften the ride but they do not transfer weight, there is no fulcrum on the axle/air bag to transfer weight, this can be seen at the scales.

If you have a common air system for the fore and aft axles, I agree. The distribution of load front to rear does not change. I am talking about different pressures on all 3 axles (mostly on the fore and aft rear though).

If you air up one bag to 60psi and 'transfer the weight' you'll notice there isn't a rise in the the other bags. If the weight had transferred you should see a rise in the other bag because there is now more weight compressing the other bag and raising the bag pressure.

At the extreme, if you remove or lift one of the rear axles, does the steering weight change?

This is the same thing on a pickup with two axles, I air up the rear bags from 10 to 100psi I raise the rear 6 inches but the front stays the same, if I had transferred weight to the front the front axle/ suspension would have sunk down from added weight, the weight would show up on the scale; it doesn't. Raising a load will will change the load triangle but there is no fulcrum in which to transfer the weight somewhere else.

On a two axle pickup, there is only the truck CG and two supports to work with, so the front/ rear distribution cannot change. There is only one lever to work with.

The tractor situation is different in that it has 3 supports and two loads (tractor and trailer).

The net sum of the three supports and the two loads must be zero.
The net torque produced by the supports and loads must be zero.
Using fake numbers for easy math.
Locations: front axle: 0
Tractor CG: 1
Fore rear: 2
Aft rear: 3

Tractor weight: 12
If the aft axle is removed, there is 12 load at 1 and supports at 0 and 2.
12×((2-1)/(2-0))=6 units of weight (fore as fulcrum)
Fore: 12x((1-0)/(2-0))=6 units (steering as fulcrum)

If instead we remove the fore axle, there is a 12 unit load at 1, and supports at 0 and 3.
Steering: 12×((3-1)/(3-0)) = 8 units
Aft: 12×((1-0)/(3-0)) = 4 units
Thus change in steering load due to change in lever arm.

Trailer weight is another load with the load at the 5th wheel point (it pivots, so that simplifies things, for more complicated calcs, check out the oh man weight distributing hitch threads)

If you were to use axle 2 like a fulcrum something has to change with the angle meaning the nose of the trailer would either sit higher or lower than the rear. You'd also be changing the clearence of the tractor and trailer relationship as you rotate around a fulcrum. So uneven loading, off level, and clearence discrepancy between cab/tractor and trailer.

Loading does not correspond to displacement due to adjustability of the air suspension. I could put a 4 inch block under an axle and readjust all axles to the same initial loads and the truck would sit the same. Pressure in airbag vs volume in airbag. Compression increases pressure and reduces volume. Releasing air returns it to original pressure and reduced volume. Same force, different displacement.

 

[jhm]

The Electric Truck Revolution Is About To Accelerate | OilPrice.com

This is a nice article from a thoughtful oil analyst, who happens to drive a Tesla. He tries to find an analog to electric trucks challenging diesel in the history of diesel locomotives displacing steam. This transition took about 30 years. Note that the third comment to the article points out that initially diesel locomotives had just a fraction of the pulling power as steam. It would take 4 or 5 diesel to match one steam. But even so, other advantages of diesel allowed it to win out before much later diesel technology was able to mach power. The author seems unaware of this power difference. And this make the 30 year transition period seem like a fairly slow analog to the electric trucking situation. At least Tesla Semi will not suffer from a lack of horsepower compared to diesel and I don't see any other drawback that could seriously slow adoption. So maybe 30 years is just an upper bound on the time it will take electric trucks to climb the S curve.

(Really, just getting halfway up the S curve is an important marker. Beyond that you're just waiting for old assets to fall out of service.)

 

[LCR1]

No other draw back to slow adoption? How about I can buy diesel at 4 different places every few miles along interstates. I can't supercharge either of my cars from here to my folks house 3 hours away, I'd have to take an hour detour to get to one. Granted the Megachargers won't be congested because there won't be many trucks on the road but its the number of locations that matter. As it stands you are forced to stop at one super charger in 100-200 miles, that's your choice whether your hungry tired or not. Until there are chargers dotting the interstates every 50 miles it will be a big hang up to the common carriers.

 

[TMSE]

No other draw back to slow adoption? How about I can buy diesel at 4 different places every few miles along interstates. I can't supercharge either of my cars from here to my folks house 3 hours away, I'd have to take an hour detour to get to one. Granted the Megachargers won't be congested because there won't be many trucks on the road but its the number of locations that matter. As it stands you are forced to stop at one super charger in 100-200 miles, that's your choice whether your hungry tired or not. Until there are chargers dotting the interstates every 50 miles it will be a big hang up to the common carriers.

For truckers, the #1 concern is cost. They will overlook the perceived inconvenience of not seeing a mega-charger every few miles if it means saving costs. Tesla wins here on cost of operation.

 

[Reciprocity]

No other draw back to slow adoption? How about I can buy diesel at 4 different places every few miles along interstates. I can't supercharge either of my cars from here to my folks house 3 hours away, I'd have to take an hour detour to get to one. Granted the Megachargers won't be congested because there won't be many trucks on the road but its the number of locations that matter. As it stands you are forced to stop at one super charger in 100-200 miles, that's your choice whether your hungry tired or not. Until there are chargers dotting the interstates every 50 miles it will be a big hang up to the common carriers.

Honestly, I think this is how they are going to have to build the Megacharger network. If Tesla really does intend on using Solar, they are gong to need a few football fields for each Megacharger so it would be better to have a lot more locations with few chargers at each one and space them out evenly down the major routes. I am sure they will partner with the big truck stops as well, but I dont see a lot of 20 stall Megachangers in the near future. Each one would require a battery pack like in Australia and solar field like in Kauai. Its very perplexing to me how they are going to pull it all off. The other reason to space them out is that there are high usage fees for larger volumes of peak charge, so each location would have a lower threshold and would of course use Solar and batteries to keep the spikes to the grid to a minimum. Wholesale rates can be under 7c, but these high volume usage fees blow those rates up pretty badly. My guess is that Tesla has done the math and figured something out.

The other solution would be to build out utility grade solar and just offset the costs for the grid tied Megachagers where they cant realistically build solar+battery. For example, Alaska. The could build a ton utility grade solar+battery in places like CA and FL to offset costs. They could also partner with utilities to do a direct swap.

 

[LCR1]

For truckers, the #1 concern is cost. They will overlook the perceived inconvenience of not seeing a mega-charger every few miles if it means saving costs. Tesla wins here on cost of operation.

You can't have chargers 4 hours apart it's that simple.

 

[jhm]

No other draw back to slow adoption? How about I can buy diesel at 4 different places every few miles along interstates. I can't supercharge either of my cars from here to my folks house 3 hours away, I'd have to take an hour detour to get to one. Granted the Megachargers won't be congested because there won't be many trucks on the road but its the number of locations that matter. As it stands you are forced to stop at one super charger in 100-200 miles, that's your choice whether your hungry tired or not. Until there are chargers dotting the interstates every 50 miles it will be a big hang up to the common carriers.

Charging infrastructure can be built out just as fast as the trucks themselves. So there is no need for this to delay the transition.

You're making the assumption that the transition will be delayed by a lack of demand owning to a lack of charging infrastructure. But Tesla can easily build out Megacharger capacity faster than they can build out trucks, in which case the obstacle to adoption is removed before supply is sufficient to meet the demand. Deploying charging infrastructure does not delay the ramp up of production.

 

[LCR1]

Yea, cause they're building out the super charger network oh so quickly.

 

[TMSE]

You can't have chargers 4 hours apart it's that simple.

4 Hours apart? What world do you live in? Higher range Tesla is rated 500 miles; at average speeds of 60 miles/hour it takes over 8 hours between charges. Are you expecting Semi trucks race like sports cars at 120 miles/hour on freeway?

 

[LCR1]

Not every truck will be fully charged 100% of the time, if some one leaves houston with 40% headed west and they only have 2 hours of drive time There would be no where to charge. They would have to stop for the night, finish the drive into San Antonio and stop to charge for 30 minutes. Then they would have to stop again to take their required 30 minute break later in the day. They've now wasted an hour of time dealing with charging that could have been done overnight during their rest period. This is why you see truck stops all over the place.

 

[mongo]

Not every truck will be fully charged 100% of the time, if some one leaves houston with 40% headed west and they only have 2 hours of drive time There would be no where to charge. They would have to stop for the night, finish the drive into San Antonio and stop to charge for 30 minutes. Then they would have to stop again to take their required 30 minute break later in the day. They've now wasted an hour of time dealing with charging that could have been done overnight during their rest period. This is why you see truck stops all over the place.

This is an example of a failure to plan. Or using the wrong tool for the job. The Tesla Semi does not need to fulfill every conceivable use case to be viable.
Also, if they stopped for the night, a non-Megacharger power connection could add to their range. Heck a normal Supercharge could refill a 1 MWh battery in 8 hours.

 

[Esme Es Mejor]

if some one leaves houston with 40% headed west

... then they’ve failed at their job of being a truck driver. Why would you leave for your destination without enough fuel to get there? If trucks can get 80% charge in 30 minutes, Megachargers can be 400 miles apart.

 

[jerry33]

On a two axle pickup, there is only the truck CG and two supports to work with, so the front/ rear distribution cannot change. There is only one lever to work with.

Tesla, with it's independent suspension appears to be different (e.g. more than one lever), but in a standard configuration the tandems at the rear of the tractor are fixed to a pivot point between them so effectively there are only two supports just like a pickup. Front axle loading is changed by moving the fifth wheel fore or aft. Fifth wheel loading is changed by moving the trailer tandem fore an aft.

 

[jerry33]

Yea, cause they're building out the super charger network oh so quickly.

Given how fast the rest of the industry and government is rolling out any chargers, they are doing it fast. Actually, much faster than I anticipated. (Of course they haven't done the remaining two that I would really like to have.)

 

[LCR1]

This is an example of a failure to plan. Or using the wrong tool for the job. The Tesla Semi does not need to fulfill every conceivable use case to be viable.
Also, if they stopped for the night, a non-Megacharger power connection could add to their range. Heck a normal Supercharge could refill a 1 MWh battery in 8 hours.

Name one supercharger location that can hold a truck. It's not a failure to plan its a failure of a charger network. I live in "houston" but the nearest super charger is 45 minutes away. in traffic that would be 90 minutes. The tesla doesn't need to fill every conceivable role, this is simply the most common on open trucking, hours of service.

... then they’ve failed at their job of being a truck driver. Why would you leave for your destination without enough fuel to get there? If trucks can get 80% charge in 30 minutes, Megachargers can be 400 miles apart.

No it means they ran out of drive time, but because there was no charger at the stopping location they waste time the next day.

 

[Esme Es Mejor]

No it means they ran out of drive time, but because there was no charger at the stopping location they waste time the next day.

If there was no charger at their stopping location, they stopped at the wrong location.

 

[jerry33]

A lot of this MC discussion is moot because no one would purchase if there was not adequate charging along their route(s). So the first sales will be to those that can do day trips, then those who have trips along MC routes, and finally everyone else. This is far different than a car where early adopters could just use slower chargers such as RV parks until the SC network was built out.

 

[mongo]

Tesla, with it's independent suspension appears to be different (e.g. more than one lever), but in a standard configuration the tandems at the rear of the tractor are fixed to a pivot point between them so effectively there are only two supports just like a pickup. Front axle loading is changed by moving the fifth wheel fore or aft. Fifth wheel loading is changed by moving the trailer tandem fore an aft.

Right, the Tesla does not have a middle leaf or equalizer that works to balance the two rear axles. Fifth wheel position can also be used.

Base issue was whether one could get enough weight on front axle to haul a max gross trailer, numbers seem to indicate that it's possible.