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Admin
still waiting for a concrete example of a situation where this is the case. you have not provided.
Admin
You can't imagine a situation where "hella complicated", "complexity would rise in a superexponential manner" might put you outside of the allowable design requirements, even given unlimited time and money? Which, by the way, I thought was plenty generous, given that you're intentionally ignoring what's physically possible for all practical purposes?
Fine. You already agreed that, for practical purposes, it's totally impossible. So this argument is really a moot point.
At this point I feel like the burden of proof is on you to show that, for every imaginable system, a physical interlock would be possible for every motion such that it's failsafe. That's a rather incredible claim that you've made.
Admin
no. i said for practical purposes it can be impractical, even extremely impractical.
it is not however, impossible.
you might not be willing to spend the money or time to implement it, but that does not make it impossible. Design requirements restrict the problem space and in any case are most useful as a description of what the customer wants, they often don't care how you get from A to B so long as you do.
I stand by my statement. A system of physical interlocks is possible and in cases where we're dealing with the safety of humans that is a very good thing indeed.
Admin
"Impractical" and "for all practical purposes, impossible" mean basically the same exact thing. Especially when calling it "impractical" is more of an understatement than it is even the tiniest bit hyperbolic.
Admin
Definition 1 does not imply impossible. Not sensible, yes. Not a good idea, yes. impossible, no.
as for Definition two, that would be a coloquialism, or at best a regionalism (see the North Ammerican notation) which means that definition is to be avoided in technical and international writings as context can, and probably will, be lost due to the coloquial or regional nature of that definition.
Admin
Not disagreeing with what you're saying, but if you're gonna pick up on dictionary usage, it would be useful to be able to spell.
Admin
There are 2 types of "not sensible or realistic". There's the type where someone tells you that and you prove them wrong. And there is the type where someone tells you that and they're right.
Admin
and which one is this pray tell?
Admin
If you re-read what I said, you'll see that you're the only person who gets to decide that. You get to prove me wrong, and I get to assume it's the latter until you do.
And you basically claimed that all robots can be built in such a way that it has physical interlocks to prevent it from doing anything dangerous. I feel pretty justified in thinking that you'll never prove me wrong.
Admin
FTFY, HTH, HAND.
Admin
-_-
you asked foir a way to prevent the robot from harming itself by attempting to move part of itself through itself.
now you're trying to twist my argument to be me arguing that physical interlocks, a thing that can be used to prevent a robot from damaging itself, can be used to prevent any dangerous behavior.
Margelous :moving_goal_post: there Blakey.
:rolleyes:
Admin
Nice job mixing your TV shows.
He's Blakey, he's Blakey, you're Blakey, I'm Blakey. Are there any other Blakeys I should know about!?
Admin
Okay... you still basically claimed that all robots could be built in such a way that they have physical interlocks to prevent any part of it from damaging itself or another part of it... without adding enough size/weight to make the robot no longer capable of performing its intended function(s).
That's a pretty radical claim.
Admin
well the physical interlock does not have to witstand the force of the actuator, it could instead physically remove power from the motor.
granted that does mean it requires manual intervention to unstick but it massively reduces the size of the interlocks.
so yes i do claim that the physical interlocks can be created to do that.
Admin
Well there is that thread....
Filed Under 7826
Admin
But "impractical" is often used as hyperbole for, "We'd rather not spend that much money." In fact, I think that is the most common use.
Admin
Admin
There should be three more, I think?
Admin
So which one is Avon? Or for that matter, who is Servalan around here?
Admin
That's still only half a solution... you'll still have an arm in motion, and possibly carrying thousands of pounds of metal.
Admin
This thread needs some guidance in objective:
[image]Admin
If you do 1 - 3 - 2, you end up with a system that's running out of control, usually backwards. That looks something like this (go to about 4:25 for the money shot):
https://www.youtube.com/watch?v=u4WPSZojtyE
Admin
That wasn't what I was thinking of but it still made me LOL.
Admin
I'm sure he's some sort of sick hybrid of the two, like the guy they stole Slave from wanted to do with the crew.
Admin
There are a lot of variants on that theme:
https://itshambles.files.wordpress.com/2013/01/tree-swing.jpg
Admin
Admin
What if you do 1 - 3 - 2 but change 3 to
Admin
A physical interlock need not be a mechanical brake that has to stop hundreds or thousands of pounds. It can be a switch that cuts power to the motor that is moving the robot arm. It's an electrical interlock, but it's still hardware, not software, and it can be tiny (with a big relay to control the big motor, if necessary; still hardware).
:hanzo:
Edit to address this:
However, using the motor itself as the brake for an emergency stop need not (necessarily) involve the normal control system; it can still be a fully hardware thing. For a small-scale example, consider power tools that have a brake to stop the blade when you turn the tool off. A single switch disconnects power to the motor and shorts the motor terminals. The spinning motor acts as a generator/alternator, and the short is a very heavy load on the generator. Kinetic energy -> electrical energy -> heat. That can reduce the kinetic energy to zero pretty quickly. It might not be suitable for every conceivable system, but it covers a lot of them.Admin
Which can still fail. Very early computers used relays for a lot of their logic, and their failure rate was much higher than the solid state systems we've used in my lifetime.
Admin
Of course. We're talking about a safety mechanism to protect against damage due to software failure or operator error, not something to reduce the failure probability to 0.0000000000000000000000000000000000000000000000000000000000000%; nothing can do that.
Not really the same sort of thing, though. A relay that is switching at a very high rate is going to have a higher failure rate that one only switches rarely when an operating limit is exceeded. Also, solid-state relays are a thing, with current ratings up to ~150A readily available. That might not be enough for @anotherusername's scenario of a motor moving many thousands of pounds, but it's adequate for a heck of a lot of uses.Admin
The reason you don't do 1 - 3 - 2 is that you end up with, between 3 and 2, an unbraked system which is usually heavily loaded on one side. The emergency brake should catch that situation pretty much as soon as the lift starts rolling back, but even a 50cm rollback is noticeable and scary (for the passengers as well as the driver). I've seen a 2m rollback on a "live" lift before, and I don't want to see it again.
Some lifts have mechanical antirollback. Effective, but brutal.
Emergency stop is, at least for chairlifts, an entirely separate system, decoupled from the motor. You have a big fuckoff brake on the bullwheel. Discordance between motor speed and cable speed (might be a broken gearbox)? Brake slams shut. Lift stops. Cable catcher security break? Brake slams shut. Lift stops. Rollback? Brake slams shut. Lift stops. You get the idea.Admin
I'd be more worried that the system would fail-closed and nobody would notice.
(I did like the shorting of the motor terminals approach. A nice, physical “stop now means STOP NOW!”)
Admin
Let's say that in that situation the arm in question is moving a 5 ton load when you cut the power. What's stopping the momentum of the load after the power is cut? Your fail safe just failed.
Admin
bang chair destroyed bang chair destroyed bang chair destroyed bang chair destroyed Hey guys, where are you going? I can keep this up all day...
Admin
va'e is lojban for "nth position on a scale".
Admin
Here's the idiomatic Esperanto for Santayana's famous quote
[spoiler]Hej , ni lernas lobjan![/spoiler]
Admin
Admin
It couldn't, though... mangled chairs getting stuck in the mechanism was what eventually stopped it.
Admin
I don't know why they stood there that long. I'd have run or taken cover behind something strong and heavy much earlier. Maybe the perspective on the shot is misleading though and they were further away than they look.
Admin
The real WTF here is calling clamp when comparisons are already done in the assertion...
Admin
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