3 ms·
This reminds me of an article I read about the Space Shuttle's flight control system. Five computers on board, with 4 running redundantly and the fifth on backu
by chaz 13y ago
This reminds me of an article I read about the Space Shuttle's flight control system. Five computers on board, with 4 running redundantly and the fifth on backup.
> Q. How are actuators controlled?
> A. For the aerosurface actuators, each of the four computers sends out an independent command on an independent bus. With no failures, the commands should be identical. The voting is done at the actuator using a hydraulic voting mechanism, called a force-fight voter. In it, there are four hydraulic ports called secondary ports, each commanded by one of the four GPCs. The secondary ports go into the primary ports, which are heavy-duty actuators that connect to what's called a "summing bar," which is no more than a massive steel rod. If there are three good computers and one bad one, the three good commands physically out-muscle the fourth. This limits the control authority a little bit--we don't get the total force we'd like to get, but there's still enough power to control the vehicle. If you have a large enough pressure differential for a large enough time, the port is hydraulically bypassed, which relieves the pressure in that one port. The remaining three ports then regain their full authority.
The whole article is worth a read: http://klabs.org/DEI/Processor/shuttle/shuttle_primary_computer_system.pdf http://klabs.org/DEI/Processor/shuttle/shuttle_primary_compu...
- qwerty_asdf 13y agoHomer: Well, today's the day for Homer J. I know I'm gonna win this time. Lenny: Yeah? How come? Homer: Union Rule 26: "Every employee must win Worker of the Week at least once regardless of gross incompetence, obesity or rank odor." Mr. Burns: Compadres, it is imperative that we crush the freedom fighters before the start of the rainy season. And remember, a shiny new donkey for whoever brings me the head of Colonel Montoya... Hmm? What? Oh! ...and by that I mean, of course, it's time for the Worker of the Week Award. I can't believe we've overlooked this week's winner for so very, very long. We simply could not function without his tireless efforts. So, a round of applause for this inanimate [steel] rod.
- qbrass 13y agoIt was a carbon rod. That was the episode where Homer went into space, where another carbon rod became a hero. http://simpsons.wikia.com/wiki/Inanimate_carbon_rod http://simpsons.wikia.com/wiki/Inanimate_carbon_rod
- qwerty_asdf 13y agoYes, I am aware of that. Hence the brackets.
- jonmrodriguez 13y agoThat "force-fight voter" concept is pretty cool.