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Comment by virtue3 | Hacker News Reader

So if you operate a bicycle you might understand what's actually going on here a bit more.

The first parts of the movement are actually quite responsive but don't result in a huge change.

If the wheels moved as the drive dictated the car would flip over. You can't just magically make all the forward momentum go lateral without relying on road and tire friction to get the job done. This can hit limits / you just end up skidding the tires and going ass over end instead of turning because you yanked the wheels too dramatically.

It would be like riding a bicycle and then turning the handlebars completely to one side while going at a good pace forward.

You could argue why isn't the car just doing it because they're at a standstill and it should be safe to do so? It's probably a sane default in case there are no sensors / no velocity reading / etc.

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> The first parts of the movement are actually quite responsive but don't result in a huge change.

> If the wheels moved as the drive dictated the car would flip over.

Non drive by wire cars react instantly by virtue of having wheels and steering physically linked. One can tip over such a car in the same way as you describe, the only thing preventing it is a) physics which makes it a bit harder to apply enough force and b) physics which gives the driver feedback that they're doing it wrong.

Which leads us to the crux of the issue here: this DBW implementation decouples the steering device not just physically in action but in dynamics and feedback as well: It's literally a joystick masqueraded as a steering wheel, with apparently little to no force feedback, and very obviously force feedback completely decorrelated from the actual angle of the wheels.

Taking a side road through the bicycle example: one doesn't turn a bicycle by turning the handlebar, one turns a bicycle by angling the whole apparatus, and the front end follows due to its geometry.

The same principle applies to a car's front suspension: the geometry of it makes it resist being turned, which provides quintessential feedback to safe operation. Without this, a critically important signal is removed. A second one is removed as there is jo way to know how angled wheels are relative to the car's body. Throw in latency into the mix and you get a surefire way to create an overcorrection feedback loop and be completely unable to react in even slightly non-ideal situations.

This means that for any sort of safety that should be by design of the chassis and suspension the vehicle relies entirely on ESP, when ESP should be a last resort fallback when the normal mode of operation fails. Instead there is no fallback nor redundancy and ESP MUST work or this vehicle becomes a death machine at the slightest sideway skid that would be perfectly manageable otherwise, even without ESP.

> sane default

This means the vehicle changes its dynamic reaction to driver input. Training aircraft pilots about normal law vs alt law is already quite something, I don't think training drivers about similar things is going to be very successful.

Would it be possible to force the front wheels to turn fast enough when the truck reaches high speed to cause an accident?

That's a bit morbid, but if you can hack the computer or manipulate sensor input to change the car comportement, it'll be easier, more effective and more stealthy for assassination.

The wheels move exactly as the driver wants in any vehicle with a mechanical steering rack. It's not a problem. Lag due to poor drive-by-wire implementation however is most definitely a problem and not a small one, it's a significant safety hazard.

> The wheels move exactly as the driver wants

If I try to turn the front wheel of my bike too far left or right it does not let me. Further, this is accomplished by a rubber bumper that continues to push for a short time after I let up, but it would be absurd to call this "lag." Normal operation of the bicycle never gets close to those limits.

The question is whether this video is showing typical system lag -- in which case, yeah, I agree, it's a problem -- or whether it is showing limiting behavior in which case getting upset about it makes as much sense as getting upset over the rubber bumpers on my bike.

>If I try to turn the front wheel of my bike too far left or right it does not let me.

Not sure what you're referring to here - I've got multiple bicycles and the headset bearing allows them to spin around 360 degrees, the only thing preventing them from going further is the cables and hydraulic hoses.

>Further, this is accomplished by a rubber bumper that continues to push for a short time after I let up

What bumper do you mean? Your handlebars, stem, and fork should be moving as a solid unit, with minimal deformation under any reasonable conditions. There's very little elasticity in the system, perhaps the biggest source is just the spokes (or the grips if they're quite thick). The behavior exhibited in the video is way more than any properly operating bicycle.

Your bike is different than mine. Shrug. It is not beyond my imagination to imagine the free-spinning mechanism you have described, so I cannot imagine that it is beyond yours to imagine a bumper. Try, and you will succeed.

I seriously have no idea where such a bumper would even go, let alone what it would look like. And it's not my bike, it's dozens of ones that I have owned or seen. It's also far easier to imagine the lack of something rather than the existence of something you've never even heard of. A simple link to a photo would be quite helpful.

If you ditch the cables altogether it's a blast: https://www.youtube.com/watch?v=lqCyTM1bF6Q

I am not upset by a bike behavior because I know exactly what my wheels are doing just by holding the bars. Same in a mechanical steering rack. This here seems more like a guessing game

> The wheels move exactly as the driver wants in any vehicle with a mechanical steering rack.

Your rims might, your tires don't. Check out about halfway down this page:

https://ciechanow.ski/bicycle/

Yes there's a bit of slack and elasticity all the way including in metal parts, not just in tires. Still, even though the tire tread doesn't move right away the moving rims are immediately exerting force on the tire interior, and thus there's an instant converse force from the tire interior which resists the movement.

In any case, this vehicle has rims and tires; what's being discussed here only adds lag to the existing system, which appears to be several orders of magnitude higher than the above physical process.

But what's apparently worse here is that there's no link (whether physical or digital): the video shows the driver has moved the steering device all the way to lock yet the wheels are only halfway through and then continue moving towards lock in spite of the steering device being completely still.

>Your rims might

If they don't something is broken.

>your tires don't.

I did say "wheels", which generally speaking means the rim. Yes, I'm well aware of tire deformation and contact patch mechanics, but that's not the issue here - the rims on the truck are not moving in sync with the wheel. It's just not acceptable.

> If they don't something is broken.

The speed of sound in steel and roughly 1m of steering column put the theoretical minimum latency at 0.2ms. Manufacturing tolerances and material strain put minimum bounds on accuracy as well. Your entire suspension, down to the rigidity of the individual linkages, influences the steering of your vehicle.

> Yes, I'm well aware of tire deformation and contact patch mechanics, but that's not the issue here...

I think it's very relevant to know that cars already take the direction of the tires/rims/wheel as more of a suggestion. The "tightness" of the steering and the suspension varies drastically between vehicles. So what is the issue here? How it drives. I don't have one, but a common comment I've found in reviews is that it's "too sensitive." I think this is an imagined problem.

> The "tightness" of the steering and the suspension varies drastically between vehicles

I could push your argument forward a bit more: the same vehicle can have tightness change as speeds goes up: electric power assistance progressively reduces as speed goes up. Why? because electric power steering is so powerful that it would be too easy to quickly turn wheels at speed. So the helper reduces, making it harder to turn the wheel in the same way that it became harder before power steering because physics.

I needs more force, but the lag doesn't change, and neither is the gear reduction ratio, nor the absolute angle of the steering wheel to the actual angle of the wheels relative to the body.

> I think it's very relevant to know that cars already take the direction of the tires/rims/wheel as more of a suggestion.

I see this vehicle as introducing a fundamental breaking change in how automobiles are being operated:

a) previously: you the driver physically control the car parts. You drive, operating the car by transforming high level intent to low level commands. You're the pilot sitting at the helm and your job is made easier with some helpful systems (ABS, ESP, cruise control, automated transmission, lane assist, what have you) that you can shunt.

b) this vehicle: you communicate intention "I want to go in this general direction" / "Set a course to Rigel VII. Maximum warp" and someone else follows your instruction and drives the car for you. The physics is abstracted away. You're not the pilot, you're the captain, and captains don't go to helm.

Up til now we've seen a) being progressively automated, working up towards full automation.

This vehicle instead appears to be designed to be designed downwards from full automation, offering a degraded mode of operation from full automation that looks like a) but is fundamentally different from a).

You can't shunt systems because that would prevent the actual pilot from operating the vehicle. In fact the pilot could very well do things that would be surprising and you would not be able to override it because your role is higher up.

I fully expect this design to lead to the cap'n turning the wheel slightly left but the pilot "refuses" to comply and slaloms around a bunch of pedestrians.

You're correct that nothing can move instantaneously, at a maximum it's bounded by the speed of sound in the material. But can you detect a 0.2ms delay? Probably no human can. What about a 2ms delay? Potentially some people can. What about a 20ms delay? Probably, although it's still very small.

Perhaps saying that the wheels move "exactly" as the driver intends in a rack and pinion system is too absolute, but if you can't see or feel this delay then I'd argue that to the human driving it's irrelevant. You can see the lag in the video, which admittedly is slowed down, but if we assume the original frame rate was 60fps then there's a minimum of a 16.7ms lag and I'd estimate it's at least 3-4 frames so more like 50.0-66.7ms, which is absolutely noticeable. Why should we accept performance which is clearly worse than a mechanical system? This is a delay that exists on top of all the other factors you've mentioned, not in lieu of them. It casts doubts on the functional safety of the system.

> You could argue why isn't the car just doing it because they're at a standstill and it should be safe to do so? It's probably a sane default in case there are no sensors / no velocity reading / etc.

So the argument is that even with critical sensors offline or not providing meaningful data, the automation should continue to operate as normal? I believe Boeing has said much the same. The outcomes they've had by it lead me to doubt the merit of the argument.

A cybertruck can put the front wheels in a 90° angle? What is this, a professional drift car?

By the way, if this is true, it is beyond stupid...

> If the wheels moved as the drive dictated the car would flip over.

Do you mean “… at high speed?” To me, it looks like the person just wants this car to steer the way literally every other car does. Your bicycle analogy — yes, that’s how they work, so pretty quickly you learn how to do that.

Satirical post I assume?

The demo shows the person stearing couldn't apply urgency in directing the wheel, sounds dangerous. Onus should be on the driver being capable of making the steering angle appropriate for the conditions, defending eventually consistent steering is comical, now drivers must account for where and by what speed the wheel angle reaches the desired position?

> defending eventually consistent steering is comical

That's how things work though. Momentum and material strain mean that nothing reacts instantly, and that changes with your speed, steering angle, and rate of change in speed and steering angle. So yes, all drivers must account for the where and by what speed the wheel angle reaches the desired position.

I'd honestly class that as reductio ad absurdum, quantum mechanics dictates it is a probability my car might spontaneous become a pink elephant.

I'm all for evidence showing the latency shown on the video is comparable to competing implementations, but I'm not interested in lazy arguments that all momentum is eventually consistent as a defence.

> I'm all for evidence showing the latency shown on the video is comparable to competing implementations...

It's a vehicle you can buy right now, and this clip comes from a review (thanks rainbowzootsuit).

https://www.youtube.com/watch?v=TeqE1kOO3dE&t=709s

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