Driving the Cybertruck

[ajdelange]

What one gets depends entirely on the trip's detailed record of distance and altitude vs time. This is, in turn, dictated by the road ahead and how you drive it. If you want to achieve minimum Wh/mi go slow and don't accelerate. If you can do a drive with regen off without ever touching the brake pedal there is no point in turning it on as it gains you nothing. But if you have to decellerate for whatever reason you will always do better with regen on.

The big advantage of regen is, IMO, one pedal driving. But if you still have hyper miler virus particles in your blood stream you don't get the "damn" reaction that braking used to elicit in your ICE car. Yes, you are wasting a bit of energy but not nearly so much.

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[kpett]

Interesting that your experience is different than mine. I guess it could be the terrain and driving routes. I live in a part of Indiana that has small hills (100 ft elevation change is about the most I usually cover) and lots of curves. I am also driving short distances (7 mile one way commute; most other trips are less than 30 miles).

What difference do you see by breaking vs coasting? I am curious because the math doesn't work in my head. If you use 100% of your momentum in the coast down to 0 mph versus recovering 30% or even 50% of it, how does it result in better MPW?

 

[Crissa]

What difference do you see by breaking vs coasting? I am curious because the math doesn't work in my head. If you use 100% of your momentum in the coast down to 0 mph versus recovering 30% or even 50% of it, how does it result in better MPW?

...Because if you coasted, you would go further. You're only 'recovering' energy by stealing from how far/fast the vehicle coasts. And since regen is recovery% times efficiency%, it's always less than just accelerating and then coasting back down.

-Crissa

PS, if efficiency% changed by acceleration in meaningful way, the amount of time spent coasting being more efficient changes, too. That's why there's an optimum acceleration rate for ICE cars and rockets ^-^

 

[CyberMoose]

...Because if you coasted, you would go further. You're only 'recovering' energy by stealing from how far/fast the vehicle coasts. And since regen is recovery% times efficiency%, it's always less than just accelerating and then coasting back down.

-Crissa

PS, if efficiency% changed by acceleration in meaningful way, the amount of time spent coasting being more efficient changes, too. That's why there's an optimum acceleration rate for ICE cars and rockets ^-^

I don't see how you are coming to this conclusion. Yes you will coast further without regen but to do this you must first accelerate above the speed you want to coast at which will require more energy. A nice option for Tesla that I might use in busy cities is the Chill option which will help from accelerating too much.

If you never accelerate faster than the speed you are driving at, you don't have to worry about the difference in coasting with or without regen. If we are talking about coasting downhill, i'm pretty sure that at an angel that you would be able to coast comfortably, you will also be able to coast with the regen, the difference being that you would regen your battery a small amount and save your brake pads. I enjoy coasting downhill as much as the next person, but I don't really think I would care about highways and city roads, especially with autopilot.

 

[Sirfun]

A couple of problems i have with the coasting only theory. There are hills that if you coast down them, you Will end up going faster then most of us want to go. A couple of hills between Baker, California and Vegas come to mind. Also there was mention of coasting to a complete stop, that would require some serious skills. To be able to calculate in your head at any speed, how far your vehicle will coast to get back down to zero. I used to sail with an Olympic gold metal winning sailor. He was amazing at something similar. Without the use of a motor we would sail back to the dock and he would time exactly when/how far from the dock to drop the sails and come coasting into the slip, bare bones without sails. At times I would guess 100-150 yards, gliding along until we would barely make it to the slip. If you screw up and come in hot, you have no way to jump off and stop a 33ft. sailboat. So, you need to be down to about 1mph to stop the momentum of the boat. Now how you gonna do that in a truck going 70 down the freeway? Start coasting a 1/2 mile from the exit? Then comes the next problem. Coasting, you will spend a lot of time going slower than anybody wants to go. On public roads!
So that takes me back to my idea of a coast button on the steering wheel/yoke. plus regen when you actually want to slow down substantially without using brakes. I agree the brakes are only your friend when you need them.

 

[ajdelange]

Your car contains energy in three forms: electrical (battery), kinetic (due to speed) and potential (height above sea level). To move the car from point A to point B requires the expenditure of energy, To get the car moving requires battery energy be converted to kinetic. Going up a hill requires battery to be converted to potential. The third energy requirement is for that energy required to overcome friction in the bearings, tires and air. The kinetic and potential energies can, theoretically, be completely recovered by a perfect regeneration system. There is no such system.

Figuring out what actually happens requires some math including calculus so I won't even touch on it here. But I can say that if you ever touch the brake in an ICE car you are wasting energy because the heat produced represents energy that is forever lost. It cannot be used to overcome friction, speed up the car or run it up a hill. Conversely with regen a good part of that energy will be returned to the battery and thus be available for future acceleration, hill climbing or conquest of friction.

"Many researches show that from one third to one half of the
energy required for the vehicle operation is lost during braking
and downhill driving"

That makes no sense to me.

Did you touch the brake when the car was moving? If you did you lost energy - it got turned into heat. Did you feather the pedal in a BEV to the point where the power meter indicated negative? You lost some energy but not nearly as much as if you had achieved the same decelleration from a friction brake.

A couple of problems i have with the coasting only theory. There are hills that if you coast down them, you Will end up going faster then most of us want to go. A couple of hills between Baker, California and Vegas come to mind. Also there was mention of coasting to a complete stop, that would require some serious skills.

Yes, that is tough to do but you can get sort of good at it. The real problem is that it requires deceleration for a long time which annoys the drivers behind. The big advantage with regen is that there really isn't much saving to be gained by doing this. You can come much closer to the intersection at speed and then start to feather the pedal such that you stop at the line. As you never touched the friction brake you didn't lose much energy at all to brake heat but there is a second order effect. You maintained speed for longer and thus had to give up a bit more energy to drag.


At the non mathematical level the whole question comes down to whether you touched the brake or feathered the pedal past the neutral torque point. If you did either you have lost more energy than if you didn't (pure coast). With a friction brake only the energy lost can be appreciable. With regen less so.

 

[Crissa]

If you never accelerate faster than the speed you are driving at, ...

There is no way to drive on public roads in which you do not at some point need to slow back down.

If you slow down via coasting, it's more efficient than slowing down with regen. All energy that can be turned into motion, has been.

If you slow down using regen, you recover some, but not all, of that energy.

If you slow down with brakes, you lose all that energy (but you gain other advantages, like traction for your turning wheels, when slowing quickly.)

Each has its advantages.

A couple of problems i have with the coasting only theory. There are hills that if you coast down them, you Will end up going faster then most of us want to go.

Because no one is saying to not use regen to keep you from going too fast! ^-^

I use coasting primarily but I still use regen when I need to slow down faster.

-Crissa

 

[Ehninger1212]

One of the most efficient options is actually binding regen to the brakes. That gives you more room to coast on the accelerator pedal.

Honda did that in their hybrids. And among the Zero riders, it's been tested to be the most efficient for range.

Tesla may have the option to do that in the future, but they default to make brakes pure.

-Crissa

My A3 E-tron does exactly this. It will coast until you hit the brakes, unless you put it into sport mode... then it regens with skinny pedal modulation. It will not come to a complete stop without hitting the brakes though.

 

[Sirfun]

My A3 E-tron does exactly this. It will coast until you hit the brakes, unless you put it into sport mode... then it regens with skinny pedal modulation. It will not come to a complete stop without hitting the brakes though.

I'm curious with your Audi , does an electric motor have less mechanical drag, so that when you let off the throttle it would feel more like being neutral than an ICE vehicle in drive?

 

[Crissa]

I'm curious with your Audi , does an electric motor have less mechanical drag, so that when you let off the throttle it would feel more like being neutral than an ICE vehicle in drive?

It depends on how it's built and programmed.

Zeros kind of default to a little bit of drag, but that's programming. It also doesn't allow all the regen the motor is capable of, so you don't lock the wheel (which is possible to do!)

Tesla does a ton of magic here.

-Crissa

 

[CyberMoose]

I still don't think coasting will have any benefit over regenerative braking. sure you need to slow down before stopping and I don't know the exact math of the energy used in the few seconds that you will be staying at a constant speed before regen braking to slow down than if you started coasting a few seconds earlier. But I don't see how coasting would ever be more beneficial unless you coasted to nearly a complete stop and if you did that than there is some time that you are just going to slow. At least Regen braking is similar to regular breaks that you can 'regen coast' to a stop without coasting at such a minimal speed that other people behind you would be annoyed.

I would assume that the very minimal benefit you could ever attain (if any at all) of coasting wouldn't be worth as much to most people as saving them a trip to get new brake pads. I can't wait to see how little I have to put my truck up and change something. i've heard stories of people driving 100-150k miles and still having life on their brake pads.

 

[Crissa]

I don't know the exact math of the energy used in the few seconds that you will be staying at a constant speed before regen braking to slow down than if you started coasting a few seconds earlier.

A) Coasting doesn't preclude using regen to slow down faster. Coasting is for one speed of slowing down. There's only one speed your vehicle will coast at - it's set by environmental factors.

B) Regen doesn't recover 100% of the energy, nor can 100% of the energy recovered be returned to motion. Coasting recovers as much as possible.

C) Staying at a higher speed longer, given a flat surface, uses more energy for longer.

D) Coasting has nothing to do with brake pads.

That said, I do usually stay at higher speeds longer, because I value my time (and others'). But I coast whenever I can.

-Crissa

 

[Ehninger1212]

I'm curious with your Audi , does an electric motor have less mechanical drag, so that when you let off the throttle it would feel more like being neutral than an ICE vehicle in drive?

The electric motor is sandwiched between the ICE engine and a dual clutch transmission. So It feels just like the clutch is released and you are coasting in neutral, the electric motor is probably engaged but just freewheeling until you hit the brakes to engage regen. It’s really fun to play with driving around in different modes.

 

[Sirfun]

The electric motor is sandwiched between the ICE engine and a dual clutch transmission. So It feels just like the clutch is released and you are coasting in neutral, the electric motor is probably engaged but just freewheeling until you hit the brakes to engage regen. It’s really fun to play with driving around in different modes.

Wow, that sounds like fun. I bet it doesn't take much of a hill for that thing to accelerate while coasting. It also sounds more efficient to me. At times you could coast for a long ways I'd bet. Then when you want to actually slow down in a "normal" way you touch the brakes and regen some of the energy you used to get up to speed. This reminded me of in my youth, I raced bicycles and used to love bombing down mountain roads. I would imagine it would be a similar experience. Except, you wouldn't actually need to use the brakes hardly, I cooked a lot of brake pads. On the right mountain road the car behind you could possibly not even know that you're coasting without the motor on (well I guess it's on but just freewheeling). There were times on mountain roads, where I would catch up to motorcyclist and join them for miles.

 

[Rockvillerich]

Not sure if the right category, but I want to ask about driving the truck. My current habits might seem strange to some. I try to not use the brake, ever. I am only partly successful. Using the brake is a sign of defeat. All that energy to gain momentum and you just put it into waste heat in a conventional truck. So I lag in traffic (I am sure some hate me) so I do not have to brake often, if at all. A good trip is where I use a brake only once. So my question is do i have to change these habits with the CT? It does have regenerative braking, so am I saving nothing by forgoing the brake petal? Will other drivers like me more now?

I adjust my driving to the situation. If there are vehicles behind me I use the regenerative braking more aggressively, and coast up to red lights and traffic if I'm on my own. In the past three years I've only used the service brakes on a few dozen occasions where hard braking was required. At 35,000 miles the pads look like they just came out of the box.