Driving the Cybertruck

[ajdelange]

I love it that the car comes to a complete stop and now I count on it.

Absolutely agree with that. Much safer than creep.

I agree about the nosediving...you do have to get used to driving an EV including how to stop accelerating, etc.

What nosediving? Regen is no different than using the friction brake in the sense that development of the retarding torque requires a counter torque which "transfers weight to the front wheels" but that's what the adaptive suspension is for. No? I have never noticed nosediving with regen. I will look for it next time I take the car out.

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[Daweism]

As a Raptor driver, I also try to drive without braking as much as possible. And even so, I would call it Braking De-gen as it still uses an obscene amount of gas even when not on the gas hahaha.

 

[Jhodgesatmb]

Absolutely agree with that. Much safer than creep.

What nosediving? Regen is no different than using the friction brake in the sense that development of the retarding torque requires a counter torque which "transfers weight to the front wheels" but that's what the adaptive suspension is for. No? I have never noticed nosediving with regen. I will look for it next time I take the car out.

Perhaps nosedive is an imprecise term. If you take your foot off the accelerator the first few times it is really noticeable.

 

[Scot Kiser]

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?

It’s true when you break you are converting motion into heat energy. So that is energy lost. With regeneration back to electrical energy that is greatly reduced but loss is not eliminated. You are doing what is called hyper mileage. You may annoy others just don’t be dangerous about it please.

 

[Crissa]

Ugh, don't use Creep Mode. It's like a crappy automatic car.

Cars shouldn't move unless you specifically push a button.

Of course, I drive stick so... Biased.

-Crissa

 

[ajdelange]

Without regen if you accelerate uniformly to some maximum velocity Vm, hoild that for some time and then slow back to 0 you will consume energy

E = 0.5*m*Vm^2 + 0.5*Cd*dens*Area*∫V(t)^3*dt

The first term in the sum is the kinetic energy in the vehicle at Vm. If you don't know what all the symbols in the second term mean don't worry about it. Just appreciate that the magnitude of the second term depends on speed at each instant of time. The longer you spend at higher speed the bigger it will be.

Consume means just that. Use it up. Lost. Deducted from the battery's charge. It all gets converted to heat whether you take your foot off the accelerator and let drag slow you or step on the brake and let the brake slow you. if you decide to use drag (hyper-miling) you take your foot off the accelerator well before the desired stopping point gradually slowing and, quite probably, annoying the people behind you. If you maintain speed until closer to the stop point and then step on the brake you don't annoy the people behind but you use more energy overall because V, your speed, stays higher for a longer part of the total journey and the second term in the sum is consequently larger. That's a major part of the concept of hyper miling.

With regen you do the same thing but you skip the brake pedal. A retarding torque is then developed by the motor rather than by friction of a brake pad against disc and the dissipating kinetic energy of the vehicle (first term) gets converted to electrical energy rather than heat. A substantial fraction (f ~ 0.75) of that gets returned to the battery and the rest (1 - f) gets converted to heat. Your total energy consumption then is

E = 0.5*m*Vm^2 + 0.5*Cd*dens*Area*∫V(t)^3*dt - f*0.5*m*Vm^2
= (1 - f)*0.5*m*Vm^2 + 0.5*Cd*dens*Area*∫V(t)^3*dt

To the driver behind nothing seems unusual. The brake lights even come on and so he isn't annoyed unless you have a bumper sticker advocating one or the other of the presidential candidates on the back of the car.

Just as the friction brake isn't an on/off proposition neither is regen. You don't have to take your foot off the accelerator to get it. As soon as you back it off past the "neutral" point the motors will start to generate negative torque. Thus you can modulate your regen braking just as you can your friction braking and go between positive and negative torque in an instant because you don't have to shift to another pedal. Note that you have some of that in an ICE vehicle with compression braking. In any case you soon learn to feather the single pedal to smoothly approach a stop sign or light and accelerate out of it with the single pedal. If you have the auto transfer to hill hold mode on it is quite possible to make entire trips without ever touching the brake pedal.

Finally, it is quite possible with regen to hyper-mile in a manner that annoys the drivers behind you. It's done the same way as in an ICE vehicle. Just back off the pedal way before you get to the intersection. The big difference is that in the Tesla you have all kinds of nifty displays to show you how much energy you are saving.

Almost forgot. One can "coast" in a Tesla. It is done by feathering the pedal to the point where the power consumption meter reads 0. At this point the motors are generating no torque. They are coasting. There is really no reason to do this other than to see if you can. It's not easy.

 

[Crissa]

Almost forgot. One can "coast" in a Tesla. It is done by feathering the pedal to the point where the power consumption meter reads 0. At this point the motors are generating no torque. They are coasting. There is really no reason to do this other than to see if you can. It's not easy.

It's more energy efficient to bleed speed off with coasting than active regen.

But also,I do this on my Zero. We get to choose how much regen is applied when braking and off-throttle in the app (tho it's capped as it's easy to lock the wheel on a bike.)

-Crissa

 

[VolklKatana]

It's more energy efficient to bleed speed off with coasting than active regen.

But also,I do this on my Zero. We get to choose how much regen is applied when braking and off-throttle in the app (tho it's capped as it's easy to lock the wheel on a bike.)

-Crissa

Unless Im misunderstanding you, that is incorrect.

Any power going back to charge the battery with regen is going to be more efficient than coasting, in all cases.

Initial energy usage	Regen recharge to battery	Total energy used
-100	+3	97	Regen
-100	0	100	Coasting

 

[MUSK007]

Guys. Regen helps with braking but doesn’t really add any substantive range. I drive down the mountain from 5200 feet and then it adds about 12-16 miles of range but that depends on your SOC when you leave. The more range you have at the start, the less it’s adds

 

[Crissa]

Unless Im misunderstanding you, that is incorrect.

Any power going back to charge the battery with regen is going to be more efficient than coasting, in all cases.

No. When you coast you don't have the conversion loss the motor and friction adds twice to every regen. Just rolling resistance.

No motor is 100% efficient. The Model 3 is the most efficient Tesla as 97%. So when you regen, you can't recover more than 97% of the energy. And then when you use those watts to move the wheels again, only 97% is turned back into motion. So 97% * 97% = 94% (There is also loss from resistance in the wiring, capacitance, battery, even the tires' rubber, too)

But with coasting you don't have those conversion losses.

Tesla is getting really good at evening out human inputs, but there's lossiness there, too.

-Crissa

 

[VolklKatana]

Guys. Regen helps with braking but doesn’t really add any substantive range. I drive down the mountain from 5200 feet and then it adds about 12-16 miles of range but that depends on your SOC when you leave. The more range you have at the start, the less it’s adds

I agree, its negligible, probably no more than a mile or two between charging sessions. but it is still more efficient than no regen at all. Over years, that does add up

If it was more efficient to coast and brake, they wouldnt bother putting regen in the vehicles at all.

I assume you are meaning that in every scenario, you are not using the brake pedal at all, that you are able to gauge the coast to stop distance perfectly each time? If thats the case, I can see your argument. In real life usage, the odds of being able to do that every time is slim in my experience.

 

[ajdelange]

Regen recaptures the mass related energies that is the inertial (0.5*m*v*v) and gravitational (m*g*v*grade) loads. How much you recover depends, thus, on the size of these loads. If you smoothly accelerate to 70 mph and drive for hours at that constant speed on level ground then your biggest load will be the drag load. The inertial load will be relatively small and regen doesn't buy you much. If, conversely, you are driving in stop and go traffic or on a winding road in hilly terrain both the inertial and gravitational loads will swamp the drag load and regen can extend your range appreciably (which is, of course, why it is offered). Consider the following picture:

Probably hard to read but the first part of the drive was on busy highway (NJ Rte 17) then onto the NY Thruway and then the last third crossing hilly Vermont. The measurements are of power flowing from (above 0 on the kW scale) or to the battery (below 0). The energy recouped is the proportional to the area between the 0 line and the curve. On Rte 17 the curve dips below the 0 line fairly often as one has to slow for traffic and traffic signals. On the Thruway one doesn't have to do this nearly so often and so there is very little area below 0 and not much recovered. In the hilly terrain, clearly, the power curve spends, relatively, lots more time below the curve and, therefore, quite a lot of energy is recouped under such conditions. I'll note that I have had trips, one of about 22 miles duration, in which all the energy required and then some was recovered. The SoC at the end of the trip was higher than at the beginning.

The amount of range recovered from a given amount of energy recovered has nothing to do with the battery SoC. If I recover 270 Wh I get additional rated range of 1 mile from that whether the battery is at 4% or 84%. Do be aware, however, that if SoC is 90% or more regen is disabled and I will not recover 270 Wh even if going down hill.

The car clearly knows how much energy it has taken from the battery and how much it has put back in. Evidently you can access that info if you tap the CAN bus and know how to interpret the fields. It would be pretty nifty, IMO, if Tesla displayed that info or at least made it available through the API.

 

[ldjessee]

If Tesla let you turn regen off like some other EVs do, you would see a big difference in your mileage in stop & go (ie, city) traffic.

On the highway/freeway not as big of a difference (assuming the speed stays the same over most of the trip).

I almost always drive our Leaf in B and Eco mode.
B has the most Regen and starts as soon as you lift off the gas... but my Leaf is older and did not get the one pedal driving update. Eco mode limits acceleration and top speed, but since we almost never leave town and the short stints on the highway (where it is easier to get from one spot to another in town to use the highway). This gives us the most range.

 

[ajdelange]

If Tesla let you turn regen off like some other EVs do, you would see a big difference in your mileage in stop & go (ie, city) traffic.

Don't forget hilly terrain. As the record in #28 shows that's where the major benefit is obtained.

Tesla won't let you turn it off but they will let you turn it down. Clearly someone who understands how it works would not want to do that as by so doing you would lose some of the benefit. Also, with it in max you can effectively turn it down as much as you want by keeping the pedsl close to the neutral point.

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