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Comment by vitus | Hacker News Reader

I think that's an oversimplification, and helps mainly in the case where one sensor is totally offline.

If you have two sensors, one says everything's fine but the other says you're about to crash, which one do you trust? What if the one that says you're about to crash is feeding you bad data? And what if the resulting course correction leads to a different failure?

I'd hope that we've learned these lessons from the 737 Max crashes. In both cases, one sensor thought that the plane was at imminent risk of stalling, and so it forced the nose of the plane down, thereby leading to an entirely different failure mode.

Now, of course, having two sensors is better than just having the one faulty sensor. But it's worth emphasizing that not all sensor failures are created equal. And of course, it's important to monitor your monitoring.

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> If you have two sensors, one says everything's fine but the other says you're about to crash, which one do you trust?

Neither. You stop the car and tow it to the nearest repair facility. (Or have a human driver take over until the fault is repaired.)

The Elon magic is getting people to bikeshed bullshit like this and ignore the bigger issues.

You don’t gouge out your ears because you hear something walking around at night that doesn’t appear to be accurate. As a human, your executive function makes judgements based on context and what you know. Your eyesight is degraded in the dark, so your brain pays more attention to unexpected sound.

The argument for lidar, sonar or radar isn’t that cameras are “bad”, it’s that they perform very well in circumstances where visual input may not. As an engineer, you have an ethical obligation to consider the use case of the product.

It’s not at all like the 737max issue - many companies have been able to successfully implement these features I have a almost decade old Honda that uses camera and radar sensors to manage adaptive cruise and lane keeping features flawlessly.

In the case of Tesla and their dear leader, they tend to make dogmatic engineering decisions based on personal priorities. They then spackle in legal and astroturf marketing bullshit to dodge accountability. The folly of relying on cameras or putting your headlights inside of a narrow cavity in the car body (cybertruck) is pretty obvious if you live in a place that has winter weather and road salt.

What? I was responding to the specific claim that two independent sensors always make your failure rates go down. Not that any particular source of sensor data is strictly inferior.

I agree that optimizing for vehicle cost and shipping shoddy software at the expense of human lives is the wrong tradeoff, and having different sensors that provide more coverage of situations is generally preferable if you can afford it.

But suppose you have a radar sensor that's faulty, and so it periodically thinks that there's something right in front of it, and so it causes the car to slam on its brakes. That's likely going to cause an accident if you're traveling at highway speeds. Does that mean that we shouldn't use radar in any circumstances? Of course not. But sensors are not infallible, and we need to keep that in mind when designing these systems.

If you’re Tesla, the answer is going to treat it as a driver assistance tech… turn off the automatic feature and throw an alarm. Hopefully the driver has time to reorient, if not, his problem.

If you’re Waymo, you’ve built in a higher standard of sensor and diagnostics, at the expense of the aesthetic.

That’s always been the issue with Tesla… they push 99% solutions for 99.99% problems.

The difference with the 737 Max crashes is that there was only one sensor feeding data to the system, not two. If there's a discrepancy between the two sensors, disconnect the automation and let the human take control. And unlike planes, you can safely stop a car in almost all scenarios.

> The difference with the 737 Max crashes is that there was only one sensor feeding data to the system, not two.

That's fair. I was likely remembering that there were two sensors, since there's one for the pilot and one for the copilot, but not remembering that only one of them was in use.

The other lessons worth noting are that 1) you need to give the human some indicator that something's wrong, and 2) you need to give the human some way of overriding the system.

> And unlike planes, you can safely stop a car in almost all scenarios.

Agreed, mostly. We do have to be careful about how the vehicle disengages and comes to a safe stop, or else we risk repeating the incident where Cruise hit a pedestrian, then pulled to the side of the road while dragging the pedestrian under the vehicle.

Let's also keep in mind that a few poor executions implementing control systems doesn't mean all of control system theory is bad...

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