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Tesla Class 8 Semi Truck Thoughts

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The problem is range doesn't scale directly. Drag and weight have a huge impact on energy consumption. The Model X is only a little less aerodynamic than the Model S, but it has a clear range reduction. And look at what people have said about energy consumption when towing a trailer with an X, the energy per mile skyrockets. To get 300 miles of range out of the semi, they will need considerably more than just a 300 KWh battery. They might be able to haul light loads for 300 miles with 1000 KWh, but they will need 1500 or maybe even 2000 KWh to pull a trailer loaded to the limit 300 miles.

Because of the inefficiencies of ICE, adding weight and increasing drag affect gas mileage, but the effect is far more dramatic with an EV. Added drag or added weight might reduce gas mileage in an ICE by 20-25%, but in an EV the same change could easily halve the range or worse. This is because EVs are so much more efficient to begin with. Every factor that impacts efficiency is more noticeable.

Drag is an issue at higher speeds like freeways for sure, but not an issue at slow speeds. Weight is the opposite, no issues at high speeds but a huge issue when you are starting and stopping a lot. I can assure you that the Tesla semi will not have a 1000KWh battery. There is enough information out from JB and Elon to glean that it will be more like 400KWh max.

I get what you are saying, but a 1000KWh battery is a none starter as it would be a MINIMUM of $125,000 cost just for the battery pack, so if you assume 25% margins on top of that, you would be looking at $156,250 ($312,500 for 2MWh Pack) for just the battery pack and no Truck at all. Semis today cost about $115,000 for a basic class 8 semi. So in your scenario, the Tesla Semi would be $250,000 minimum. Now Tesla could make up the difference by providing free Supercharging for the first Million miles, similar to what Nicola One is doing. The value of that would be 1,000,000/7mpg x $2/gal = $285,714 in fuel savings.

If indeed they need that big of a battery pack, i dont see why they would be doing it, the energy densities would need to go way up. The 2MWh pack would also way more then most fully loaded Semis without any load..
 
Inside EVs is estimating the truck will have a 1200 KWh battery, but a 600 mile range:
The Tesla Electric Semi Truck Will Use A Colossal Battery

I think the initial cost of the truck will be much more than a diesel today, but Tesla might be allowing some kind of free supercharging deal and they said their initial buyers are some fleet buyers. There are some massive distribution warehouses in Nevada. I know Safeway has one and I think a number of other large retailers have them too. Some of those warehouses are built in caves. I don't know if the loading docks are in the caves or not, but if they are, they need to run some heavy duty exhaust fans to vent the diesel fumes.

A lot of those places probably already have solar at the surface and they're probably putting in more. Nevada is fairly sunny most of the year. If a distribution warehouse can fuel their trucks with the sun while the trucks are loading, then get free energy on the road, or at least some kind of subsidy from Tesla for supercharging (like x number of free KWH a year), then the extra expense will pay for itself in a year or two.

Tesla is also talking about doing a pilot program in 2018. They might be partially electrifying one or two distributors and they will probably be electrifying their own truck fleet. Full production might be a few years away and Tesla is waiting for solid state batteries to be ready. Solid state lithium batteries, or some other possible chemistry show promise for higher energy density and a much lower cost per cell.

In the meantime they might just make a low volume truck to experiment with the technology and make sure they get it all right before going into mass production.
 
Has overhead electricity supply come up in this thread? My first reaction was one of considerable mirth, but the longer I reflect upon it, the more I see the advantages. Construction can't be all that expensive, and alongside highly frequented transport corridors, amortization should be easy to calculate. Making use of cheap solar and wind - especially during times of off-peak demand - while simultaneously recharging the batteries, would be an enormous boon to electric trucking.

See
eHighway - Electromobility - Siemens

Edit Addendum - on more sparsely traveled routes, say in a desert, construction of 30 miles of overhead lines for "in-flight' recharging should be cheap and relatively easy.
 
Has overhead electricity supply come up in this thread? My first reaction was one of considerable mirth, but the longer I reflect upon it, the more I see the advantages. Construction can't be all that expensive, and alongside highly frequented transport corridors, amortization should be easy to calculate. Making use of cheap solar and wind - especially during times of off-peak demand - while simultaneously recharging the batteries, would be an enormous boon to electric trucking.

See
eHighway - Electromobility - Siemens

Edit Addendum - on more sparsely traveled routes, say in a desert, construction of 30 miles of overhead lines for "in-flight' recharging should be cheap and relatively easy.

Much of the US has a much lower population density than Europe and things are more spread out. Switzerland has a population density of 204 people/sKm. Only 5 US states are more dense than that, New Jersey, Rhode Island, Massachusetts, Connecticut, and Maryland. California has around 10% of the US population, but is only 97 people/sKm and it's the most densely populated state in the western half of the US. 8 states (all west of the Mississippi) have population densities below 10 people/sKm. Canada has even lower population density.

This is a picture of a stretch of interstate near the Utah/Wyoming border, but there is lots of highway just like this all over the western US. A really long stretch of I-5 through California looks like this. You find yourself looking forward to driving past the cattle feedlot and the stink because it's something a little different, even if it's unpleasant.
http://www.aaroads.com/west/utah080/ut-172_at_i-080.jpg

Overhead lines on rural highways would be expensive to build. It took from the 1950s to the 1990s to just build the interstates that are there today. They have been a massive boon to the US economy, but governments don't want to spend any money on infrastructure. There are bridges literally falling apart and the people charged with maintaining them can't get any money to do more than patch up the bridges and hope money comes through before it falls down. A few years ago a bridge did fall down in Minneapolis during rush hour. The Obama administration tried to break loose funds to get all bridges in similar condition fixed, but only a small amount was allocated.

The current administration wants to have a fire sale to sell off all the assets the government does own.

Private companies don't have the money to sink into these sorts of projects. Just to build charging on the fly would require running power to the highway, then building pylons around the highway to support those lines. The pylons would either have to be built pretty stoutly (at high cost) to resist accidents, or accept that they will be taken out from time to time in accidents.

They would also be a major headache to maintain in the inland West's winters. Especially in the north. Cars and trucks sliding on the ice would be taking out supporting poles weekly and then there would be live lines down on the highway which would close the highway for a day or more. Now the cars and trucks mostly just skid off the road into the rough by the side of the road and people crawl for a bit and is quickly forgotten.

Occasionally there are bad pileups, but nobody is concerned about live power lines down in the middle of an accident with zer visibility. This is the kind of accidents this region can see in the winter:
https://img.ksl.com/slc/2557/255717/25571755.jpg?filter=ksl/img614

Seattle has overhead lines on some bus routes and I think some other cities have similar setups. There are some stretches of urban freeways where overhead lines could be strung in a way that accidents were unlikely to take them out.

Where things are already built up, it wouldn't be all that expensive to put in overhead lines, but in rural America, that can get expensive very fast. During the 1930s the Rural Electrification Administration was started to have the government get power to far flung communities in rural areas. It was cost effective to run power lines by private companies in urban areas, but rurally it wasn't worth it for companies to do it, so the government had to.

North America and Australia have countries just as developed and sophisticated as much of Europe, but conditions through large swaths of both continents are very different than Europe. Europe is a compact continent with a large population. The distance from London, UK to Moscow,Russia is 300 KM less than the distance from where I am near Portland, OR and Chicago, IL. And Chicago is only a little over halfway across the continent from here. If you draw a box from the SW corner of Oregon to the Canadian border and stretch that to Minnesota, there are only three metro areas in that box with populations greater than 1 million people and all of them are near the edges of the box. That box is 2200 KM wide.

As far as deserts go, western North America has 4 of them and three of them are over 300,000 sKM.

In Europe smaller batteries with charge on the fly might be feasible, but there are large swaths of the US and Canada where any big rig needs to carry it's own energy. If the government was willing to build the infrastructure it could probably be done, but in the current political climate, it's an incredibly low priority even among those politicians who would like to see it happen.
 
This is a picture of a stretch of interstate near the Utah/Wyoming border, but there is lots of highway just like this all over the western US. A really long stretch of I-5 through California looks like this. You find yourself looking forward to driving past the cattle feedlot and the stink because it's something a little different, even if it's unpleasant.
http://www.aaroads.com/west/utah080/ut-172_at_i-080.jpg

While you paint a pretty good picture with your words, your photo doesn't quite match. That picture is on I-80, just outside of Salt Lake City. Actually, you're barely passed the Salt Lake City International Airport there. You can see the Kennecott smelter (Kennecott Garfield Smelter Stack - Wikipedia) in the distance to the left. Go another 30 miles outside of town, and you get to the salt flats, where it's literally a straight road that goes for like 50 miles of absolutely nothing (there is one exit for a Morton Salt plant, and a weird concrete art sculpture thing that I can't even remember if it has a proper exit for). Once you get to Nevada, it's not as straight, but it's like an hour and a half of driving between each town of any consequence, and even then they're fairly small, with the exceptions of Elko and Winnemucca.
 
While you paint a pretty good picture with your words, your photo doesn't quite match. That picture is on I-80, just outside of Salt Lake City. Actually, you're barely passed the Salt Lake City International Airport there. You can see the Kennecott smelter (Kennecott Garfield Smelter Stack - Wikipedia) in the distance to the left. Go another 30 miles outside of town, and you get to the salt flats, where it's literally a straight road that goes for like 50 miles of absolutely nothing (there is one exit for a Morton Salt plant, and a weird concrete art sculpture thing that I can't even remember if it has a proper exit for). Once you get to Nevada, it's not as straight, but it's like an hour and a half of driving between each town of any consequence, and even then they're fairly small, with the exceptions of Elko and Winnemucca.

I was Googling for pictures that painted what the interior west's highways look like and Googled Wyoming. I noticed that said it was in Utah so I assumed it was around the Utah-Wyoming border, but of course SLC is very close to the Wyoming border. But I guess it kind of further illustrates my point that you get just outside one of the largest cities in the region and the highway looks like that.

Most of the interior west is a giant slab that was pushed up by tectonic forces. In New Mexico and Arizona, the slab is pretty much intact. In Utah it got eaten down by Lake Bonneville during ice ages. Most of Utah was a massive lake as large as some of the Great Lake today. In Nevada, the underlying structure was more fragile, so as it lifted up, it broke and it ended up looking like a rumpled carpet with one N/S mountain range after another.

One summer I worked in Milwaukee, WI and took Amtrak back to Seattle. The train goes through the prairies of North Dakota and Montana and it's the flattest place I've ever been. The prairies were a vast shallow sea before the ice age started about 2 million years ago. It's basically sea bottom. Riding the train I could look out over the vast plains and marvel, but driving through that is some of the dullest highway in the world.

One of these days I do want to take a road trip through Utah. My mother's father is from Nephi and his family were among the town's founders, I'm probably related to half the town. I also have friends in Boise and SLC I'd like to see again. I just haven't gotten around to getting that way yet.
 
Drag is an issue at higher speeds like freeways for sure, but not an issue at slow speeds. Weight is the opposite, no issues at high speeds but a huge issue when you are starting and stopping a lot. I can assure you that the Tesla semi will not have a 1000KWh battery. There is enough information out from JB and Elon to glean that it will be more like 400KWh max.

You may have your physics confused. Friction is friction no matter what speed you're going. Yes you have to use a boat load of energy to get a vehicle up to speed, but once you're cruising you're still using a ton of energy to keep the car moving from rolling resistance alone. You just add on top of that with aero drag the faster you go.

From your earlier analysis in the thread I'm going to have to disagree. I just don't see how a 400kWh battery can get the job done for long haul. You mentioned regen, but regen only works in the mountains. It's not like you're gaining and losing a ton of elevation going across Kansas or Oklahoma. Even basic matlab code can show you'd need a ton more energy than 400kWh just to maintain trucker highway speed (55-65).

Like I said I think they have a product, but I'm guessing it'll be more short haul than actual long haul. You still need class 8 in city situations. If they do pull it off I'll be just as astounded as everyone, and then immediately get my hands on their tech so I can then found an electric airplane company. If you can pull off long haul trucking with electric, then aerospace isn't that much further away.
 
You may have your physics confused. Friction is friction no matter what speed you're going. Yes you have to use a boat load of energy to get a vehicle up to speed, but once you're cruising you're still using a ton of energy to keep the car moving from rolling resistance alone. You just add on top of that with aero drag the faster you go.

From your earlier analysis in the thread I'm going to have to disagree. I just don't see how a 400kWh battery can get the job done for long haul. You mentioned regen, but regen only works in the mountains. It's not like you're gaining and losing a ton of elevation going across Kansas or Oklahoma. Even basic matlab code can show you'd need a ton more energy than 400kWh just to maintain trucker highway speed (55-65).

Like I said I think they have a product, but I'm guessing it'll be more short haul than actual long haul. You still need class 8 in city situations. If they do pull it off I'll be just as astounded as everyone, and then immediately get my hands on their tech so I can then found an electric airplane company. If you can pull off long haul trucking with electric, then aerospace isn't that much further away.

I'm not arguing with you, I'm just trying too make sense of what JB and Elon have already stated. Assuming you have 2 vehicles and one is an EV and one is an ICEv. What makes the ICE so much better at highway speeds and the EV so much better in traffic. Assuming both weigh the same. Is it as simple as the transmission? Allowing for different hearing at higher speeds. Could the talks semi have some kind of hearing that makes it more efficient at higher freeway speeds similar to an ICE. I know cost and complexity with little gain is why they don't used gearing for the cars, but could the semi be a place where that makes sense? Again, I'm no expert, but Elon and JB seem very confident and 200 miles of range is not very confidence inspiring. BTW, byd has a class 8 semi with 188kwh pack and gets 94 miles of range I think:

TRUCK – BYD USA
 
You may have your physics confused. Friction is friction no matter what speed you're going. Yes you have to use a boat load of energy to get a vehicle up to speed, but once you're cruising you're still using a ton of energy to keep the car moving from rolling resistance alone. You just add on top of that with aero drag the faster you go.

From your earlier analysis in the thread I'm going to have to disagree. I just don't see how a 400kWh battery can get the job done for long haul. You mentioned regen, but regen only works in the mountains. It's not like you're gaining and losing a ton of elevation going across Kansas or Oklahoma. Even basic matlab code can show you'd need a ton more energy than 400kWh just to maintain trucker highway speed (55-65).

Like I said I think they have a product, but I'm guessing it'll be more short haul than actual long haul. You still need class 8 in city situations. If they do pull it off I'll be just as astounded as everyone, and then immediately get my hands on their tech so I can then found an electric airplane company. If you can pull off long haul trucking with electric, then aerospace isn't that much further away.

There are actually two types of friction, static and dynamic. Static friction is always higher and is the major factor when trying to get something moving, and it diminishes as speed increases and dynamic friction becomes more of a factor as speed increases. In a car dynamic friction becomes the primary friction factor at around 25 mph, though the speed where static friction is not a factor anymore varies from car to car.
 
There are actually two types of friction, static and dynamic. Static friction is always higher and is the major factor when trying to get something moving, and it diminishes as speed increases and dynamic friction becomes more of a factor as speed increases. In a car dynamic friction becomes the primary friction factor at around 25 mph, though the speed where static friction is not a factor anymore varies from car to car.

Static friction is the force is takes two objects which are not initally moving relatively to each other to start sliding relative to each other. Dynamic friction is the force required to keep them moving.

For tires, normal driving is basically static friction, the tire is not moving relative to the road at the point of contact. If you exceed the static friction, you transition to dynamic friction aka skidding (much less friction).

In terms of energy usage, there is loss in the deformation of the tire, friction in the bearings through the drive train, motor/inverter/battery losses. I think most of these are fairly linear with speed, but wind resistance changes by the square of speed, so it dominates high speed operation.
 
Static friction is the force is takes two objects which are not initally moving relatively to each other to start sliding relative to each other. Dynamic friction is the force required to keep them moving.

For tires, normal driving is basically static friction, the tire is not moving relative to the road at the point of contact. If you exceed the static friction, you transition to dynamic friction aka skidding (much less friction).

In terms of energy usage, there is loss in the deformation of the tire, friction in the bearings through the drive train, motor/inverter/battery losses. I think most of these are fairly linear with speed, but wind resistance changes by the square of speed, so it dominates high speed operation.

You guys are silly, why are you arguing about physics that applies to both Diesel and EV semis. Can anyone answer why the ICE vehicle can be so much more efficient at higher speeds. Is it simply just the gear box? Why couldnt a Tesla semi with more HP, more Torque just add a gear box for higher speed cruising. Assuming that it will be more efficient at stop and go speeds because EVs are more efficient then ICE in that scenario today.

If you just scale up the BYD T9 188KWh/94Mi range by 4x and add some for Tesla being more efficient with lighter batteries and better motor/inverters, you get 400 miles on less then 600KWh:

http://www.byd.com/usa/wp-content/uploads/2016/08/T9-final.pdf
 
I just don't see how a 400kWh battery can get the job done for long haul. You mentioned regen, but regen only works in the mountains. It's not like you're gaining and losing a ton of elevation going across Kansas or Oklahoma. Even basic matlab code can show you'd need a ton more energy than 400kWh just to maintain trucker highway speed (55-65).


Certainly at steady highway speeds the energy needed can be expressed in watts, regardless of the propulsion. I agree that 400 kWh seems low for a generic class 8 truck. But the first trucks will probably be designed to run specific routes. There must be may thousands of class 8 trucks that run no more than 200 miles per day.

400kWh replaces maybe 30 gallons of diesel when idling and energy recapture is considered.
 
You guys are silly, why are you arguing about physics that applies to both Diesel and EV semis. Can anyone answer why the ICE vehicle can be so much more efficient at higher speeds. Is it simply just the gear box? Why couldnt a Tesla semi with more HP, more Torque just add a gear box for higher speed cruising. Assuming that it will be more efficient at stop and go speeds because EVs are more efficient then ICE in that scenario today.

If you just scale up the BYD T9 188KWh/94Mi range by 4x and add some for Tesla being more efficient with lighter batteries and better motor/inverters, you get 400 miles on less then 600KWh:

http://www.byd.com/usa/wp-content/uploads/2016/08/T9-final.pdf

I'm not in the EV vs diesel debate, (if I were, I'd be talking about the energy required to more load being the same (and apply 1 HP = 750 watts), but ev's have regenerative braking, and no idle restrictions).
I was intending to correct what I interpreted as an incorrect description of static friction.
 
I'm not in the EV vs diesel debate, (if I were, I'd be talking about the energy required to more load being the same (and apply 1 HP = 750 watts), but ev's have regenerative braking, and no idle restrictions).
I was intending to correct what I interpreted as an incorrect description of static friction.

That's awesome, do you need more HP to propel the semi down the road with a single gear or less based on how many gears you have? I thought the whole point was that ICE fuels have a ton of stored energy, way more then an EVs battery by like 10 fold or more, but that they are extremely inefficient at converting that stored energy to propulsion. Why is it more efficient at higher speeds? Why cant you just make an EV with a transmission, is that not a solution?
 
What I am unclear on is how the Tesla semi with fixed gearing is going to out pull a standard semi that has a 17:1 (T310M) or 27:1 (T310MLR) first gear along with a 2.7 or so rear axle. Total torque multiplier of ~50 or 70x the engine. A Mack MP8 puts out 1500 lb-ft of torque, so the total is > 75,000 lb-ft to the rear axle. With a 6 motor Tesla tractor, each would need ~12,000 ft-lb to match. The P100D puts out ~900, double the gear ratio to sacrifice top speed and that only gets you to 1,800 each.

Even with one axle with a much lower gear ratio (80 times lower ratio than the P100D to cover the smaller motor of the 3 [450*2*80 = 72k]) and over running (sprag) clutch, it would top out at 2-3MPH, and it wouldn't help with regenerative braking.

On the side of Tesla is that the torque is available from 0 RPM.

What am I missing?
  • Model 3 weight around 3,600lbs?
  • 40 ton truck 80,000lbs, fully loaded. Unladen it should be half, so 20 tons.
  • 22 Model 3's worth of weight fully loaded.
  • Top speed of Model 3 is ~130mph?
  • 65mph would have /2 the gearing, allowing:
  • 11 Model 3's worth of weight loaded at 65MPH.
  • Conveniently, a standard 40 ton truck (for comparison) already has 10 wheels using fat wheels (or 18 skinny wheels if you double up everything but front); one Model 3 motor per wheel (or wheel set for dualies). (By the way, I always include the trailer in all of my calculations. I'm not sure why anybody wouldn't, except for a local tractor.) ((I think Tesla Truck might only be a trailer with builtin mini tractor with no driver's seat, or at least one version like that.))
  • Using Model 3 equivalency, that would be 750kWh battery for 300 mile range.
  • A 40 ton truck has a huge wall moving through the air, but it also has a huge amount of truck behind it that slithers through the air tunnel made by that wall. I wonder how much efficiency comes from that tunnel. Of course, the tunnel sides are still made of air. If it is properly wind-tunneled, perhaps some sort of aerodynamic tunnel could be created by the shape of the front.
I'd like to see aero drag numbers 40 ton truck vs model 3.

The key problem with what I described is that a 40 ton truck isn't built to carry Model 3 passengers (typ. 1) times 10 (so 10 people): it's designed to carry 20 tons cargo. That means the weight of the vehicle unladen needs to be 20 tons, not 40 tons; laden, 40 tons.

How much of that is battery?

Tesla Model S Weight Distribution

Tesla-Model-S-Weight-Distribution-Chart.png


Well, how much of it is battery and motor? Apparently, motor is a huge amount. Anyway, battery + motor for Model 3 must be around part of that.

So, battery + motor for Model 3 is wild ballpark ~1,800lbs*10=18,000lbs, or only 9 tons. That leaves 11 tons for skeleton, skin, and brain power, and that seems all quite reasonable. Remember, we can go all the way up to 40,000lbs for an empty tractor-trailer combination as long as it can carry another 40,000lbs inside its cargo hold.

But all of this is using Model 3 and Model S as comparison. Once you get to truck size, you have all sorts of size advantages and disadvantages that make all the numbers way different. You have places to put a huge amount of stuff that you don't with a car. And, you have huge amounts of air to push out the way since you want all of that space available to put pallets into with proper weather protection and security. Also, you have constraints of road weight limits, so that puts a big hamper on reducing wheels.

Perhaps Tesla could be kind and program in some aerodynamics that lifts the truck off the road so it weighs less at top speed, but to do that, it would need rudders and great computer steering. This would save the cost of rolling on the roads. I wonder how much lift a truck can develop in its shape. It would also need flaps to give down-pressure in curves and high winds so it doesn't float off the lane and/or tip. The rudders could help in the wind, too.

+++

Advertising will be easy: load up an uncovered flatbed with metal-I beam and something in front that's the full height of the legal height limit with everything weighing 79,975 pounds with proper axle distribution with driver, make sure they don't eat, drink or purchase more than 20 pounds net at rest stops, and drive it up every mountain with heavy truck traffic passing every truck at the full car-pulling-trailer speed limit. 55MPH up the Grapevine. 50MPH up Hwy 17. 55MPH up Windmill Hill. 55MPH up 156 toward the reservoir. 55MPH up I-80 into Nevada (there must be a mountain there -- I don't know but I presume). Just do that all day long for 3 days going up every mountain with a Tesla logo on the tractor and on the trailer passing every other fully loaded truck and advertising for the next quarter century is done. (Must follow 35MPH speed limit downhill for legal reasons; braking will be the ultimate limit, so I don't know how good regen is downhill for braking.) Carry sales business cards for fleet managers and indies and advertising budget is spent and done and never to be used again. If anything, the trucks will be a sales profit center, since they will earn sales for the brand that way, not spend on sales. (Tesla will say "we rid the world of polluting trucks!" as a brand positive.)

Tesla doesn't have to do any other reveal.

---

The tractor-only electric with traditional non-electric trailer will be a short range non-hill variety, with less power and less range. It would be for in-town and short haul in flatlands. Basically, anything pulling old stock up hills that's electric would have to have some sort of oversized motors and alternate battery implementation. I consider that a side case, something ungermaine to the main product line; it can be done, but with tighter constraints. The main product line in my view integrates the whole combined vehicle for electric propulsion and operation (batteries, regen, motive, aero, etc.).

This is what makes the reveal exciting to me: what will Tesla actually do?

And, as I said above, why do they even need a reveal? Maybe to score brand points more than anything, and keep businesses appraised of what's happening, spurring both innovative competition and regulatory innovation (e.g., allowances in the form of demands).
 
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That's awesome, do you need more HP to propel the semi down the road with a single gear or less based on how many gears you have? I thought the whole point was that ICE fuels have a ton of stored energy, way more then an EVs battery by like 10 fold or more, but that they are extremely inefficient at converting that stored energy to propulsion. Why is it more efficient at higher speeds? Why cant you just make an EV with a transmission, is that not a solution?
More brainstorming:

Multiple motors allow the possibility for some motors being geared differently than other motors without switching gears. In my 10 motor idea, at least 5 pairs of motors would be symmetrically geared, and overall almost all the power would be needed for all speeds (low and high), but there could be a slight distribution of their gearing so that some of the motors would pull harder in lower speeds and other motors would pull harder in higher speeds, allowing for a greater overall power and efficiency, maybe. I don't really know. It must be fun to play with the numbers. We already know Model S & X do this in their dual motor systems for at least some of their setups (I think all dual motor Teslas are geared differently in front and back).

Similarly, even with just two gear ratios (2 speed transmission) per motor, they could slightly offset all the motors gearing so that no two pairs of motors are switching gears at the same time, and the other motors could make up for the hiccup of gear switching; that void would be difficult to handle, though, so perhaps it's better just not to have more than one ratio per motor (savings on gear switching weight, motor gap filling, etc.).
 
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More brainstorming:

Multiple motors allow the possibility for some motors being geared differently than other motors without switching gears. In my 10 motor idea, at least 5 pairs of motors would be symmetrically geared, and overall almost all the power would be needed for all speeds (low and high), but there could be a slight distribution of their gearing so that some of the motors would pull harder in lower speeds and other motors would pull harder in higher speeds, allowing for a greater overall power and efficiency, maybe. I don't really know. It must be fun to play with the numbers. We already know Model S & X do this in their dual motor systems for at least some of their setups (I think all dual motor Teslas are geared differently in front and back).

Similarly, even with just two gear ratios (2 speed transmission) per motor, they could slightly offset all the motors gearing so that no two pairs of motors are switching gears at the same time, and the other motors could make up for the hiccup of gear switching; that void would be difficult to handle, though, so perhaps it's better just not to have more than one ratio per motor (savings on gear switching weight, motor gap filling, etc.).

Yeah, I had the same thought, but I dont know how any of this would work. I know the original idea was to have 2 gears in the model S but it was scrubbed long before it became a reality. Elon already stated that the semi would use a "bunch" of model 3 motors. What a bunch is is an interesting question. How did you come up with 10? I got 6, two for each axle in a traditional tractor. Now the back wheels are duly so you could have 2 + 8, but how would that work with a drive shaft? You would have to have a 2 layer driveshaft with the outer layer controlling one wheel and the inner controlling the other wheel. Is that even possible? I think 6 is a safer bet, also be they are going to be roughly 300hp per motor, so that's 1800HP, which would make it the most powerful tractor around and would also have about 2800ft lbs or torque which would dominate Again, I am working from what JB and Elon have said, which is a bunch of model 3 motors and JB clearly said that the semi is basically a scaled up model S, which would equate to 3x S 100D in terms of battery and weight, which would be the same weight as the average class 8 semi. If you look at the BYD T9, you have a real life example of a 188KWh - 94 mile range Class 8 Semi.

If the issue is high speed performance only, meaning EVs are already better at 0-30 and with 2800lbs of torque, you have more then enough to get the vehicle up to 30 with no gears. Maybe the back wheels are traditional motors and rive like an S/X to get the vehicle moving with a much more responsive and agile acceleration (also stated by Elon) and the front wheels could be geared much higher and used only to maintain 60-65MPH on the open roads. In theory, the back wheels could be geared differently as well, to allow a bigger range, but you would only need a couple of motors to maintain the speed limit. Again, I know I am like a broken record, this is all based on what Elon and JB have already stated publicly. If we are to have a theory, it should not contradict what we already know and a scaled up Model S does not point to 1200KWh pack, which would weigh so much that it would cut the load the truck could transport in half.
 
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Yeah, I had the same thought, but I dont know how any of this would work. I know the original idea was to have 2 gears in the model S but it was scrubbed long before it became a reality. Elon already stated that the semi would use a "bunch" of model 3 motors. What a bunch is is an interesting question. How did you come up with 10?

I include the trailer in a tractor-trailer combination:

four-common-types-of-american-big-rigs-or-eighteen-wheeler-tractor-trailers.jpg


Apparently, that USA variety is rare Earth-wide; a search of "tractor-trailer combination truck" in DuckDuckGo returned a bunch of other numbers of wheels:

tractor-trailer combination truck at DuckDuckGo

In my view, every wheel (either single or dual tire) gets one motor.

Including the trailer for consideration of the motors, batteries, and total weight totally changes all the math. This is the obvious way to go medium and long term.

I also think at some point the tractor is reduced to being integrated with the trailer or essentially almost dolly-sized.

A current dolly, for reference:
2AXLE_DOLLY_SEMI_TRAILER.jpg


A future self-driving dolly could affix to the trailer with hooks that keep the dolly straight, and the dolly would have builtin steering wheels and self-driving electronics. Alternatively, the dolly could continue to swivel, but would still need to affix to the trailer for the steering swing arms (messier, I think, but might be easier to mount the motor axles to the wheels?).

Both types, especially the first type could hook up easier to the next in a train such as with the above tow bar. Self driving truck trains could save on space and aero problems. If each trailer steered, that would allow the electronics steering each unit to compensate for train waves, and keep the train lined up (a huge problem with truck trains); that seems easier in the former variety (fixed dolly with independent steering wheels).

Another idea is every wheel could turn. In most concrete pump trucks, all wheels can turn. I see them all the time on construction sites here, but for some reason, can't find any pictures online. Here's a Chinese one that gives some idea:
images.duckduckgo.com.jpeg
 
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I include the trailer in a tractor-trailer combination:

View attachment 233890

Apparently, a search of "tractor-trailer combination truck" in DuckDuckGo returned a bunch of other numbers of wheels:

tractor-trailer combination truck at DuckDuckGo

In my view, every wheel (either single or dual tire) gets one motor.

Dont see more then 6 and dont see them messing with the trailer at this point. Maybe in the future they could make an autonomous trailer system to move loads around the loading docs to be queued up for a Semi. Actually had an idea that these trailers could become almost like a range extending hybrid system for existing semis, helping push along the tractor while driving and responding to breaking with regen. The loads would be much safer with all the torque vectoring and the ability to stop themselves.