Not a control engineer

PhysicsGenius wrote:
...


In the real world, events happen simultaneously. In software that runs on one processor, that can sometimes be an illusion, but never real.
Jerry
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Engineering is the art of making what you want from things you can get.
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I'm sure everyone here will agree. No matter how much you test software, it never works quite that way in the field.
sQuick..
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sQuick wrote:

DO-178B, which regulates flight software certification in the US, has 5 levels of criticality, from level E (the software could fail and the pilot wouldn't even need to be told) to level A (the software fails and the pilot is part of a smoking hole in the ground). Fly-by-wire systems, needless to say, are considered to be level A criticality.
I used to work for a guy who managed a team that wrote some fly-by-wire software for a Saab jet fighter. That's not a civilian application, but the level of testing and certification was equivalent to the DO-178 procedures. He had the "honor" of watching a video of the jet, with his software, crashing at an airshow.
It turned out that it wasn't the fault of his team -- someone had given them an incorrect specification, and that's what they tested to.
So it bears out your point, even though line for line you spend about 2500 times more effort and money on DO-178B level A rated code than you do for code for a windows application.
--

Tim Wescott
Wescott Design Services
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That Saab fighter is the Grippen (originally known as the Jars 39). I remember that crash very well. As I recall, during a landing sequence the aircraft cart wheeled on it's wings and burst into flames. The cause was determined to be an overly sensitive aircraft control system. The pilot survived the crash. Spent a lot of time on that application during the aircraft development program. If you want to see a control system that will boggle your mind this is one of them. Share a patent on the control system that puts an imaginary line in the sky--Altitude and Mach No. and then modulates several engine parameters (when left of that line) to prevent engine stall after it has been commanded to decelerate to Idle. Single engine application so there are a number of control system fail safe, backup modes. MLD
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MLD wrote:

As related to me it was the chief test pilot, either for Saab or for the program, who had never flown the aircraft before and didn't listen closely enough to the guy wha actually _had_ flown the thing when told it was really sensitive on the controls. It went into pilot-induced oscillations on the landing pattern -- they guy walked away with a broken arm.
It's one of those "multiple failures" scenarios that so often result in death & destruction -- the boss wants to fly even though he's not checked out on the aircraft, the runway's short and surrounded by viewing stands (did I say it was an airshow?), the guy who _had_ been flying it knew about the control problem and gave warning, and finally the controls themselves were set up to be very sensitive. The result? Boom.
Incidentally, the fellow who related this story was also responsible for recoding the software with the new control laws that made the aircraft less sensitive -- after that was changed the thing flew just fine.
As a side note, you can search on the Gee-Bee R1 & R2 racers from the 30's -- the air-race historians are divided on whether it's a mankiller or the worlds best racer. The most balanced opinion I've seen on it points out that all the air-race pilots believed that they had Really Big Balls and wanted an aircraft that was maneuverable to the point of instability. Whenever the aircraft builders caved in and delivered a plane with an itty bitty tail and a rearward center of gravity the resulting aircraft was an absolute world-beater until it fell out of the sky -- so it's not just software.
--

Tim Wescott
Wescott Design Services
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Tim Wescott wrote:
[%X]

Which should indicate to all System Developers that the initial specifications need as much, if not more, effort expended in testing before the design and coding is instigated.
--
********************************************************************
Paul E. Bennett ....................<email://peb@a...>
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A device designed by a team that I managed (20 years ago) caught fire, and destroyed a major refinery, burning two people to death. Turned out to be the fault of a bad hose fitting (and not on "our hose"), but I didn't sleep for a few weeks afterward. It COULD HAVE BEEN the software.
This was for an application that knowone had really thought of a safety critical. Since then, I see almost every piece of "industrial" code as capable of killing a human being.
-Hershel Roberson
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I clinched up a bit when I saw the recent thread about guiding a wireless unit capable of moving 2 tons.
Scott
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Scott,
That was my question... and rest assured that project is not going to happen unless and until we qualify it every which way possible.
The project proposal was originally hard rail guidance, but the organization writing the spec. is one of those always reaching for new innovation and versatility.
AGV's actually pull as much, or more weight in a lot of applications... they just don't lend themselves to operation in a foundry environment.
In this project I believe we'll probably end up with festooned break-away control cabling,dead-reckoning and a accepted, fail safe bumper safety. Wireless is just a little to extravagant for the benefits involved.
Jake
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On Mon, 27 Dec 2004 15:30:03 GMT, "Hershel Roberson"

Similar experience: As the instrument tech at a new production facility, I was on a wee-hours trouble call that required massaging one line of PLC code in each of twelve units to fix the problem. At the very moment (it seems) I completed the edit on the last unit, a large fireball erupted in the production area. It was immediately outside of the window in the office where I was sitting. Fortunately no one was injured.
In the end, the investigation concluded the event had absolutely no connection to my work. But the timing, and the fact that the systems I was working on were loosely interfaced to flame control systems, resulted in a few weeks of sleepless nights. Happened right before a week long vacation, too.
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PhysicsGenius wrote:

So when the error is .001, what is the integrated increment in one sample period? It has to be a tiny fraction of that. Can you specify double precision for the integrator and see if anything changes?
--
John Popelish

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I can see several places to put the pid loop in a simple remote controlled car.... pid the steering position to the commanded angle, pid the speed to the commanded speed, and finally, in autonomous mode, pid the position to the waypoint.
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As I've said before: In theory there's not difference between theory and practice but in practice there is.
Walter.
I'm testing my Google Posting access so I'm not sure where this will pop up, if at all. I note there is no spell checking. That is going to be tough.
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