The Limiting Factor - How the Tesla Semi “Broke the Laws of Physics”

firsttruck

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If Tesla Semi is so ground-breaking how much more will the Cybertruck be??

Would the longest range Cybertruck be trimotor configured like the Tesla Semi.

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How the Tesla Semi “Broke the Laws of Physics”
When Tesla unveiled their Semi 5 years ago, auto industry was skeptical to say the least. As Daimler put it, Tesla must be defying the laws of physics.
Jan 23, 2023
The Limiting Factor

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DMC-81

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That video is fascinating. Good information. I wonder if and how much of the Semi tech ( besides the 1,000 volt architecture ) will be leveraged for the Cybertruck's towing capabilities.
 

JBee

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It won't have a clutched drivetrain to disable motors, to many parts and extra cost for a comparitively low load CT.
 
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DMC-81

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It won't have a clutched drivetrain to disable motors, to many parts and extra cost for a comparitively low load CT.
Yeah, I really just want the plaid motor. 😁
 

kbolt

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If Tesla Semi is so ground-breaking how much more will the Cybertruck be??

Would the longest range Cybertruck be trimotor configured like the Tesla Semi.

----------------------------------------------

How the Tesla Semi “Broke the Laws of Physics”
When Tesla unveiled their Semi 5 years ago, auto industry was skeptical to say the least. As Daimler put it, Tesla must be defying the laws of physics.
Jan 23, 2023
The Limiting Factor

--------



----------------------------------------------
That was a really good video that made some good points about why the semi has the engineering decisions it does.
 


electricAK

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The video raises an interesting point. Re-gen rate (and therefore total range) is limited by the battery capacity, (more so than the number of motors). So when comparing a dual-motor model Y to a dual-motor Cybertruck with twice as much battery, the Cybertruck should have a significantly higher capacity for re-gen braking.

That makes me feel better about buying an EV truck, which is sure to be heavier and less efficient than a smaller EV like the Y. Maybe the CT is more efficient than we are expecting.

Really, the takeaway from the video is that we should not automatically think adding mass = bad. Because adding battery mass is less-bad.
 

Ogre

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Really, the takeaway from the video is that we should not automatically think adding mass = bad. Because adding battery mass is less-bad.
Interesting thought here.

Cybertruck battery: 180-210 kWh
Semi battery: 850 - 1000 kWh (4-6x the capacity)

Cybertruck weight with trailer: ~20,000 pounds
Semi weight with battery: 81,000 pounds (Roughly 4x the weight)

Hmm. Coincidence?

But that’s kind of where it ends. The Cybertruck won’t need 3 motors to max out regeneration, in fact I think just 1 motor will be enough regen to max out the ability of the Cybertruck’s battery even towing.
 

Luke42

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The video raises an interesting point. Re-gen rate (and therefore total range) is limited by the battery capacity, (more so than the number of motors). So when comparing a dual-motor model Y to a dual-motor Cybertruck with twice as much battery, the Cybertruck should have a significantly higher capacity for re-gen braking.

That makes me feel better about buying an EV truck, which is sure to be heavier and less efficient than a smaller EV like the Y. Maybe the CT is more efficient than we are expecting.

Really, the takeaway from the video is that we should not automatically think adding mass = bad. Because adding battery mass is less-bad.
The 1-pedal driving setup communicates this to the driver really well.

The amount of regen available on my Model Y varies depending on the situation (mostly the battery temperate), and you can really feel the difference through the 1-pesal driving.

Having a higher regen-ceiling is great, but the driver can adapt quickly and easily if the vehicle provides proper feedback.
 

JBee

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Regen is the worst option to increase range, unless you can't stop in time by coasting, or need it to reduce speed going down hill.

Coasting to a stop is much better because it has no conversion loses from charging/discharging the battery and increases cell life by reducing cycling. But this requires people to change their driving styles and actually look further ahead.

One of the main reasons why semi gets its range is that the primary energy consumption is aerodynamic drag. Per ton of vehicle and load, semi has less drag because its displaces less air because of its frontal surface area is small compared to it overall body mass. This offsets it's higher rolling resistance and energy requirements for altitude change.

Another issue with regen is that especially in cars and trucks, most of the regen is needed on the front axle, especially so at high regen rates. So RWD vehicles will physically have less regen capability in comparison to a FWD or 4WD.
 

Ogre

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Regen is the worst option to increase range, unless you can't stop in time by coasting, or need it to reduce speed going down hill.
This is one of those times where you are techically correct, but wrong in real world application.

For the majority of drivers, having regen be on consistently is the best idea.

Coasting to a stop requires you know where you are going to stop and how far out it is. Trying to scrub speed via coasting is tedious and the average driver will almost always get it wrong.

Keep in mind 50% of drivers are worst than average. Whatever small amount of energy you gain from enabling coasting for the better drivers will be lost twice over by those below average drivers.
 


JBee

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This is one of those times where you are techically correct, but wrong in real world application.

For the majority of drivers, having regen be on consistently is the best idea.

Coasting to a stop requires you know where you are going to stop and how far out it is. Trying to scrub speed via coasting is tedious and the average driver will almost always get it wrong.

Keep in mind 50% of drivers are worst than average. Whatever small amount of energy you gain from enabling coasting for the better drivers will be lost twice over by those below average drivers.
I think you underestimate how much better coasting is, let alone the safety implications of forward looking driving habits. There's no reason to continue ICE driving habits in a EV. (Although hypermiling techniques work in ICE too)

The main reason for this is that regen reduces in effectiveness at slower velocities that you decelerate from. So you don't recover as much energy at city driving speeds, or stop and go in traffic, as you do from decelerating off a highway offramp etc.

Ideally, the Autopilot distance ranging on Teslas would auto adjust braking rate to optimise efficiency between coasting, regen and the identified point in front of you you are slowing down for. So assisted braking when you are off throttle but not on the brake yet.
FBW regen.
 

Ogre

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I think you underestimate how much better coasting is, let alone the safety implications of forward looking driving habits. There's no reason to continue ICE driving habits in a EV. (Although hypermiling techniques work in ICE too)

The main reason for this is that regen reduces in effectiveness at slower velocities that you decelerate from. So you don't recover as much energy at city driving speeds, or stop and go in traffic, as you do from decelerating off a highway offramp etc.

Ideally, the Autopilot distance ranging on Teslas would auto adjust braking rate to optimise efficiency between coasting, regen and the identified point in front of you you are slowing down for. So assisted braking when you are off throttle but not on the brake yet.
FBW regen.
If you are talking about AP or FSD, then yes, implementing smart coasting into the driving algo is a great strategy. If you are talking about normal people driving the car, regen is going to win every time. Trebly so in city driving or hill country.
 
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Bill906

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Coasting also significantly lengthens your travel time. If you want to go that slow through the city, get a bike. The majority of people will not tolerate other drivers hyper-miling during rush hour in the city, let alone actually do it. I bet any Uber driver who hyper-miles gets low ratings. Driving fast and braking hard costs more for fuel and brake maintenance, yet every taxi I’ve ever ridden in does just that, accelerates hard, and decelerates hard. Gas and brakes are expensive, but time lost by driving slowly apparently is more expensive.
 

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On hilly terrain, the impact of regen is significant.

"Physics is the law; everything else is Elon"
 

Sirfun

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I think you underestimate how much better coasting is, let alone the safety implications of forward looking driving habits. There's no reason to continue ICE driving habits in a EV. (Although hypermiling techniques work in ICE too)

The main reason for this is that regen reduces in effectiveness at slower velocities that you decelerate from. So you don't recover as much energy at city driving speeds, or stop and go in traffic, as you do from decelerating off a highway offramp etc.

Ideally, the Autopilot distance ranging on Teslas would auto adjust braking rate to optimise efficiency between coasting, regen and the identified point in front of you you are slowing down for. So assisted braking when you are off throttle but not on the brake yet.
FBW regen.
How about this option? You take your foot off the pedal the vehicle coasts, then when you want to slow down you hit the brakes which is actually regen except in hard braking or the maybe 8mph to stop.

Just coasting can't possibly work. Coasting, you would spend WAY too much time going between whatever the speed limit is, and zero mph. Take for example a 55mph main road with traffic signals. Won't work.

 

 
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