4 ms·

Sending uncontrollable accelerations for hundreds or thousands of feet is safer than a maximum of 11 ft of coasting? Yes, there are always trade offs to be mad

by RogerL 13y ago

Sending uncontrollable accelerations for hundreds or thousands of feet is safer than a maximum of 11 ft of coasting? Yes, there are always trade offs to be made. But a corrupted system is utterly unpredictable - if a control port can do something, it eventually will, at the speed of electronics. On the other hand, a shutdown is entirely predictable. We design for it, because every system does eventually fail and shut down. It's a 'normal' mode of operation in this sort of system design. That tends to weight the design heavily towards very fast resets and redundancy in mission critical (people die if you mess up) systems. I can design a system to handle a shut down control board (limit the robots arm's travel, etc). I often can't do anything if the arms are waving about randomly, under power. I'm not opining randomly; I've worked in flight control, robotics, UAVs, and factory machinery. Until my current job, I've always had to worry about killing somebody. You really can't let software that controls dangerous equipment continue to run in a damaged state unless the rest of the system has a supervisor mode that can override and limit the system's behavior. Even then, I'm having trouble thinking of a scenario where I would prefer to leave that process running vs shutting it down.

dspeyer 13y ago
What does it even mean to shut down the control systems on a moving car? All stop? Coast? What's the physical behaviour that isn't likely to kill someone?
- aaronem 13y ago
  At most, it means you're coasting with no power assist for steering or brakes -- you'll need some extra braking distance, but that's what the shoulder is for, and it'll take a bit more than the usual effort to turn the wheel, which means that getting onto the shoulder, especially if you're in a middle lane when all this goes wrong, is going to need to be smartly done. Taken all together, the impression I get is of a problem in driving skill that's roughly as difficult as a blown tire at highway speeds -- possibly a bit easier, actually, considering the deleterious effect a blown tire has on steering control. An alert and competent driver should be able to handle either situation without posing a deadly danger to herself or anyone else. The same, I think, cannot reasonably be said of uncommanded acceleration. With a blown tire or a failed ECU, all you have to do is use your ordinary driving controls to get off the freeway and bring the vehicle to a safe stop. With a throttle stuck wide open, you are suddenly a race car driver, only you're neither in a race car, nor in a race. You can't bring the vehicle to a stop with the ordinary driving controls, at least two of which -- the accelerator and the brake -- are no longer responding properly or at all, which is itself frightening and disorienting to the driver. In order to bring the vehicle to a stop, the driver must shut off the engine with the key, at which point the problem reduces to our failed-ECU worst case above, just with some more speed to burn off. But there is no circumstance, in either the normal driving regime or even any other abnormal one, where turning off a moving car is a proper or safe response to any situation, which is why almost no driver has ever given the slightest thought to doing so -- and when your car's speeding up past ninety all of a sudden, and you're not telling it to, is maybe not the best time to be thinking up new ways to interact with your car that you've never thought of before. At a guess, I'd say some people whose Toyotas ran away on them were able to come up with the idea in time, and they mostly survived. Others ran out of time before they thought of it, and those unlucky souls mostly died.
  - scj 13y ago
    I agree with most of what you've said. But point out that you didn't go with the worst case example, loss of steering / brakes on ice. Unwanted acceleration on ice would be worse though. I can't imagine, in rush hour conditions, being unable to control my acceleration. At best, you'd rear-end someone, and their car would stop you.

by RogerL 13y ago

dspeyer 13y ago

What does it even mean to shut down the control systems on a moving car? All stop? Coast? What's the physical behaviour that isn't likely to kill someone?

aaronem 13y ago
At most, it means you're coasting with no power assist for steering or brakes -- you'll need some extra braking distance, but that's what the shoulder is for, and it'll take a bit more than the usual effort to turn the wheel, which means that getting onto the shoulder, especially if you're in a middle lane when all this goes wrong, is going to need to be smartly done. Taken all together, the impression I get is of a problem in driving skill that's roughly as difficult as a blown tire at highway speeds -- possibly a bit easier, actually, considering the deleterious effect a blown tire has on steering control. An alert and competent driver should be able to handle either situation without posing a deadly danger to herself or anyone else. The same, I think, cannot reasonably be said of uncommanded acceleration. With a blown tire or a failed ECU, all you have to do is use your ordinary driving controls to get off the freeway and bring the vehicle to a safe stop. With a throttle stuck wide open, you are suddenly a race car driver, only you're neither in a race car, nor in a race. You can't bring the vehicle to a stop with the ordinary driving controls, at least two of which -- the accelerator and the brake -- are no longer responding properly or at all, which is itself frightening and disorienting to the driver. In order to bring the vehicle to a stop, the driver must shut off the engine with the key, at which point the problem reduces to our failed-ECU worst case above, just with some more speed to burn off. But there is no circumstance, in either the normal driving regime or even any other abnormal one, where turning off a moving car is a proper or safe response to any situation, which is why almost no driver has ever given the slightest thought to doing so -- and when your car's speeding up past ninety all of a sudden, and you're not telling it to, is maybe not the best time to be thinking up new ways to interact with your car that you've never thought of before. At a guess, I'd say some people whose Toyotas ran away on them were able to come up with the idea in time, and they mostly survived. Others ran out of time before they thought of it, and those unlucky souls mostly died.
- scj 13y ago
  I agree with most of what you've said. But point out that you didn't go with the worst case example, loss of steering / brakes on ice. Unwanted acceleration on ice would be worse though. I can't imagine, in rush hour conditions, being unable to control my acceleration. At best, you'd rear-end someone, and their car would stop you.