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Feature request: one-shot speed limiter
- Thread starter jgs
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- Driving Dynamics Model S
Johan
Ex got M3 in the divorce, waiting for EU Model Y!
Yeah that was sarcasm.
Point is that if there's enough demand for the feature why not do it? They did make the Ludicrous mode after all? Who on earth "needs" to go 0-60 mph in 2.8 seconds, even if it's legal on some roads??? I guess as many people that need to go 0-55 in the shortest possible time.
Not at all, although that was how I described it, so I guess I was asking for it. One could just as easily describe the feature as providing driver assistance to accelerate optimally to a setpoint while avoiding energy loss due to exceeding the setpoint.
While I appreciate your offer to engage in a ritualized exchange of pleasantries, I'm just here to talk about cars, thanks.
As described above, I disagree. Just as with many other features of the car, the described feature could be used quite legally, and without straining credulity too.
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Quite.
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This is intuitively obvious. As with other intuitively obvious things, it is however not necessarily true, and must be proven or at least convincingly argued before being accepted. And actually, from what I know about Newton's laws of motion, I'm not sure why the statement would be true. Consider: Newton's laws tell us that an object's speed will increase for as long as the object is undergoing acceleration, as a function of the acceleration. Equally, an object that is not undergoing acceleration will not see a change in speed. Now, consider what we know about electric drivetrains. It's possible to apply full power to them rather suddenly, hence the famous insane and later ludicrous modes. I don't see any reason why it shouldn't also be possible to completely remove power from them rather suddenly.
If you put these two facts together, one would imagine it ought to be possible to apply full power to the drivetrain right up to the setpoint (or very close) and then just as quickly remove power from it. If I remove power from the drivetrain, why would the car keep accelerating? What magical force would do it? If there is some way to make a Tesla Model S continue to accelerate without draining power from the battery pack, I bet Tesla's engineers want to know about it! (So does the USPTO, although it might fall afoul of their automatic rejection of perpetual motion filings.)
I do realize that the world is analog, not digital, so it's not possible to actually remove power instantaneously. Not literally instantaneously, but compared to the reflexes and reaction time of a human driver, it might as well be instantaneous.
So I submit that the intuition of you and several other posters, while perfectly reasonable, may be wrong. If I'm mistaken, I'd be interested in knowing which premise I got wrong. I'm pretty sure I got Newton's laws right.
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Johan
Ex got M3 in the divorce, waiting for EU Model Y!
Jgs: you're right about Newton's law, but you underestimate the lag in removing acceleration. Yes the motor is electric so "instantaneous" but the entire drive train has many mechanical linkages that will react far from instantaneously. I.e. you'll have to start throttling acceleration quite a bit before you reach 55 mph on order to hit 55 mph and never surpass it. So the option wouldn't be all that fun but it would be useful if you really wanted to go as quickly as possible to the legal speed without any overshoot.
It does have non-trivial mechanical linkages but anyone who has read any Tesla propaganda knows, a whole lot fewer than in an ICE vehicle. So without more evidence I'm still optimistic that the described feature could deliver some smiles. (I'm not a complete purist, I'll accept argument from authority as long as the authority being asserted is more like "I'm an automotive engineer and I do this for a living" and less like "I'm a clever chap and it stands to reason" -- I can assert the latter authority myself, after all.)
Let me make one more try at waving my hands at an argument: the Model S is renowned for being very responsive. That responsiveness clearly has to reflect the costs of all the mechanical linkages -- the car doesn't respond until the driver's input is reflected by power being transferred into the wheels, and the road. Why should it be that the drivetrain would be radically slower at removing power from the wheels than it is at pushing it there? I can imagine some asymmetry but worse than a 2:1 asymmetry?
To put it a different way, just how much energy do you think the mechanical drivetrain is capable of storing? And just how slowly is it capable of releasing it?
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I can see some desire to have this option, but I think it's better to learn how to do that on the fly by yourself. It's like anything else with a car, spend enough time playing with the limit and how it reacts and you ultimately have more control over what you can do.
If you launch frequently enough you will learn how the car behaves and you can let off so that it "stops" around the speed limit. It takes some practice, but I do it all the time because I love launching, but I see cops everywhere. Regen will help with keeping it around the target speed. You don't need to fully let off the pedal for that to happen you just need to learn the timing so that when you let off enough the regen will provide resistance to limit further acceleration beyond the target.
If you're doing a full launch and are worried going 75 in a 65 will get you in trouble then that would mean the police were watching you do the launch the entire time. Don't think a feature like this would help then. Tesla has so much more that needs to be done before something like this is tackled.
swaltner
Active Member
I'll reference the (in)famous thread here on TMC regarding why you don't want this feature.
Cops don't like losing to a Model S!
As dsm says, this feature won't keep you from getting a ticket, so what's the point? If a police officer see you do a launch, they'll most likely pull you over, even if you never broke the speed limit. Speed limits aren't the only laws on the books covering acceleration.
Cops don't like losing to a Model S!
As dsm says, this feature won't keep you from getting a ticket, so what's the point? If a police officer see you do a launch, they'll most likely pull you over, even if you never broke the speed limit. Speed limits aren't the only laws on the books covering acceleration.
From my understanding the CA law is about the intent to show off or attract attention. They would need to prove that and if you are the only car involved it is harder to do.
If it is about unsafe starts I think you could argue about what the definition of an unsafe start is. Every car has a different rate of acceleration and how would they determine unsafe. Unless a rate of speed (ft/s) is documented for what is considered unsafe I'd fight it.
In my opinion, you are all wrong.
If you stop supplying current to the motor, the car will stop ACCELERATING almost immediately. There will be NO overshoot - the car's momentum will keep it moving, but the acceleration will cease almost instantly (and that's WITHOUT regen or braking or anything else).
The reason we all go over is because we don't cut petrol to the ICE or current to the Tesla motor immediately (throttle doesn't close instantly), plus the fact that the instruments don't tell us our speed instantaneously and we can't perceive what they tell us instantaneously and react instantaneously.
So if the car can stop current flow to the motor very fast (I'm certain the throttle bouncing back up is the major delay here) it wouldn't need to back off on current flow AT ALL until the speed limit is reached.
EDIT: ok so jgs above has this right- no ongoing force, no ongoing acceleration....
Johan
Ex got M3 in the divorce, waiting for EU Model Y!
Thinking more about this you're likely correct. Law of preservation of energy and all that.
ra-san
Member
This is what I think too. Seemed obvious. The opposite seems to seem obvious to many other posters. Can't wait to hear why I'm wrong :tongue:
I don't doubt it's possible to learn how to do a pretty accurate launch-to-speed manually (pedally?), although automation will always be able to do it better. The same is true of a great many driver assistance features, such as stability control, antilock brakes, and so on – a highly-trained, highly-experienced performance driver will do as well, and in some cases better. However, plebes like me won't. The thing is, I don't have any interest in spending my time becoming a highly-trained, highly-experienced performance driver. Most of the time, I'm happy being a competent, normal driver. I'm also happy to have so many specialist skills embedded in the electronic reflexes of my car, though. Some of them make driving safer, some of them make it more fun.
So, possible? Yes, pretty much. "Better", as you put it? "Better" is subjective, and from my keyhole, I don't think it would be better. You should also keep in mind that I don't want to "launch frequently enough". I mostly don't want to launch at all, I just want to pull away from the stoplight smartly but without giving anyone whiplash. Every now and then, I want to show what the car can do, and that's when the feature would come into play.
I should also explain for all those who've been bringing it up (at least Pete90D, dsm363, swaltner), that I'm not worried about cops. I'm not reckless enough to do this next to a cop car, or in the presence of one, even if I'm 100% guaranteed that I won't exceed the posted speed limit. It's simply that I don't want to exceed it. My target is to reach a certain speed, and I view it as sloppy to go past it. There's also a big element of being interested in the feature simply because I find the "programmable electromechanical platform" aspect of the car intriguing.
Actually, apart from the fact that it's self-evidently a low priority feature compared to (for example) getting Autopilot shipped, the biggest impediment I see to implementing it is getting the UI right. I bet the car dynamics are not terribly hard, given the amount of intelligence that must already be embedded in the software about that. However, it's clear that Tesla is trying hard to avoid exposing every possible nerd knob just because they can. So as much as I would like a CLI on my car to let me tweak every possible parameter, I don't see it happening. And I don't have a good UI to suggest for this feature.
It is possible to do, but to do it right every time is very hard. If you understand what your reaction time is and the reaction of the car to letting go of the pedal then you can time it right so that when you see 4X on the speedo, you will not accelerate past 45 if you let go right then. I say it is better because you are learning how to control the car yourself instead of relying on software and until we have true self-driving cars, we are still responsible for knowing how to control the car.
I agree that automation and electronic features do make cars safer and can do a better job than a human will. I do not feel this makes the car safer. Launch control did make cars safer because it helped keep traction. So here's my rant for the day on why I really dislike this feature at a lower level, which is that I don't like the direction it takes drivers.
I agree that at times it would be nice to have a hard limit on the speed that stays on until disabled... especially on the highway. I do not agree that a feature should be added that is directed more at one-time use (primarily launching) and makes people avoid learning to control their velocity. It promotes having anyone propel a 2.5 ton car to 60 in less than 4 seconds without worry of tickets, which is not something everyone should be doing. It makes fast acceleration a novelty without making light of the responsibility and danger that comes with it.
This is a once and a while feature, which means those that use it will be less interested in launching and doing it less frequently. A driver that launches less frequently is not going to be as familiar with the excessive power at low speed and potential torque steer. They will also be less familiar with the shorter reaction times, effect of road conditions, going 0-60-0, etc. The weight and traction control of the MS has made fast acceleration simple, so lots of people do it because it's easy and fun, but it's a huge amount of mass hitting a high rate of speed in a short period of time and a lot can go wrong. People should be less concerned with exceeding the speed limit and more concerned with what else can go wrong in <4 seconds, and how to react to it. A car that has 400hp+ or can do 0-60 in <4s is a responsibility. More so than slower cars. So I feel that people should be learning how to control the velocity and power on their own.
It isn't about being a performance driver, or the need to launch all the time or anything of the sort. It is about understanding how a car really handles, which is something everyone should know. Denmark and Norway have low automotive fatality rates, and both countries require drivers to learn skid control and take tests on a slippery track (AFAIK). They aren't learning to be performance drivers, they are learning how to handle a car in real life situations before they are in them. We don't require that in the US and very few people do it on their own, and our automotive fatality rate is 4x (per 100k) as high. There are obviously other factors there, but knowing how to handle a car reduces accidents. Velocity is just one aspect of how a car handles.
People should buy the car they want whether it has 20hp or 800hp. However, if you are going to have 400hp+ you should learn to control it properly or not make use of the power. A 2.5 ton car with 400hp is not a toy, regardless of how safe the car is. I'm not saying don't launch the car, but I really question how much thought goes into it before slamming the pedal to the floor.
To me this feature just means people will say "well I don't have to worry about the speed limit anymore so there's nothing to worry about if I can't see a cop".
I think that most people here would not intend to launch in front of a police officer, but in my experience you don't always know they are there. It gets dark, they switch vehicles, sit behind a line of cars, pop out of a parking lot, come around a corner, etc. Stuff happens.
I don't think that the UI is the limitation. Elon said himself that one of the things they were dealing with was faded lane markers and situations where the lines lose contrast. Our cars do not have the level of technology that self-driving cars have. Watch the talk in this thread Google's head of self-driving cars' case against driver assistance (AutoPilot))
OK, although it was you, not me, who said "If you launch frequently enough you will learn..." so I think you're changing your story a bit.
I disagree with your evaluation. I think I will just have to leave it at that.
You have misunderstood me, conflating two different points. One point is that UI for the proposed speed-limiter feature is hard(er than some things). The other, independent, point is that Autopilot hasn't shipped yet and is self-evidently a much more important feature. I didn't suggest that UI is holding up Autopilot.
Oh, one further point to this -- I'm not reckless enough to launch where, in my judgement, to do so would be ill-advised for any reason, including but not at all limited to the old "don't taunt cops" rule. So, in a sense I don't care if there's a cop I don't see, because I'm going to be able to pass the red-face test regardless. (And if I do suffer a breakdown in judgement and launch where/when I shouldn't have -- well, I deserve the ticket, if I get one.)
Possibly this falls under "it goes without saying" but different people clearly have different assumptions and lines they don't cross.
Mike Tuccelli
Member
Try it sometime. You'll find yourself a good 10 mph over the speed limit by the time the first chime sounds and you get your foot off the go pedal and onto the brake. It's not like on the rare occasions when I do this, I'm not watching the speedo. I'm just not accomplished enough to both punch the acceleration as much as I want, for as long as the car is capable, and back off sufficiently before crossing the line. I either taper acceleration before I have to (almost always that), or exceed the limit and have to decelerate (and waste energy). For that matter, don't get the wrong idea, I seldom punch the acceleration out of a stoplight at all, I just pull out sedately (or sedately for a Model S, anyway.
As with other maneuvers of this sort, I think it's almost indisputable that the car's software is potentially more capable than all but the most accomplished human driver of executing it without violating either the "don't exceed the limit" or "give it all you've got" parameters.
And yeah, I don't really expect the feature to be implemented, but I bet I'm not the only one who would find it fun.
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That's a really good point. For exactly the same reason, I can't imagine Tesla shipping a vehicle that can greatly exceed the speed limit in the region it's sold in. That's why no Model S can exceed 100 mph in North America. And it would take a real madman to imagine a car company shipping a vehicle with an "insane" or "ludicrous" acceleration mode. Talk about features that promote irresponsible acceleration! No, you're right.
Where did you see “no Model S can exceed 100 mph ...”
It’s a joke, son, a joke. I was replying to @CmdrThor who said “A feature that promotes irresponsible acceleration? I can just imagine the lawsuits now.” My comment was an ironic way of pointing out that it was a bogus point — if “oh no, can’t, mustn’t be irresponsible” was actually a restriction, well, Tesla wouldn’t be Tesla.
I had forgotten about this thread, but you know, I still want this feature!
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