bayshine wrote:i wished i had 4 legs on mine as she tips over real easy if you move it around when full
A Three-Legged Stool
Subject: Re: Why is a 3-legged stool always steady?
Think of it this way:
(1) If you hold a cane in the air, you can move it in any direction,
twirl it, and so on. Its motion isn't constrained at all. That is,
the top of the cane can move freely in three dimensions.
(2) If you put (and keep) one end on the ground, now its motion is
constrained: you can't lift it, or rotate it... although you can
swing the top around in a variety of different arcs. That is, the
top of the cane can move freely in two dimensions.
(3) If you connect the tops of two canes together and place the other
ends on the ground, you can still move the tops, but only along a
single (straight) arc, back and forth. That is, the tops of the
canes can move freely in one dimension.
(4) If you try the same trick with three canes, now you can't move the
tops at all. This is basically what's happening with a three-
legged stool. The tops of the cans can move in zero dimensions...
which is to say, they can't.
Each time you add a cane, you remove one dimension in which the top
can move freely - that is, each new cane removes one 'degree of
freedom'.
Now, what happens when you add a fourth cane? Well, now you have too
many constraints. This means that there are multiple ways that the
stool can 'solve' the problem of which legs to use for support.
Wobbling occurs when the stool can't 'decide' which solution to use,
or, more precisely, when it's changing its mind about which solution
to use.
In effect, during the time that the stool is actually wobbling, it's
really a two-legged stool, with one degree of freedom - which is the
direction of the wobble.
In math, we see this kind of behavior in systems of equations. If I
have two variables, one equation will give me a whole range of
solutions:
y = 2x + 3 Solutions include (1,5), (2,7), (3,9)
In fact, the range of solutions is just the graph of the equation. If
I add another equation, I can have at most one solution:
y = 2x + 3
Solution is (2,7)
y = 4x - 1
That is, each new equation removes a 'degree of freedom' from the
system. With two variables, I need two equations to lock things down.
With three variables, I need three equations. And so on.
Now what if I add a third equation?
y = 2x + 3
y = 4x - 1 No solution
y = 4x + 1
There is no pair of (x,y) values that will satisfy all three of these
equations simultaneously. Of course, I can _choose_ any two of the
equations and get a solution for that pair, and then I could switch to
another choice, which would be quite a lot like what happens when a
four-legged stool wobbles.
So, the 'mathematical' answer to your question is: A 3-legged stool
'solves' a system of three equations in three variables, while a four-
legged stool changes its mind about which three of four equations to
solve for the same three variables.
MacStill wrote:I'll take 3 legs any day thanks ;-)
4 legs just gives you an extra direction it can tip & does nothing to alleviate the centre of gravity.A Three-Legged Stool
Subject: Re: Why is a 3-legged stool always steady?
Think of it this way:
(1) If you hold a cane in the air, you can move it in any direction,
twirl it, and so on. Its motion isn't constrained at all. That is,
the top of the cane can move freely in three dimensions.
(2) If you put (and keep) one end on the ground, now its motion is
constrained: you can't lift it, or rotate it... although you can
swing the top around in a variety of different arcs. That is, the
top of the cane can move freely in two dimensions.
(3) If you connect the tops of two canes together and place the other
ends on the ground, you can still move the tops, but only along a
single (straight) arc, back and forth. That is, the tops of the
canes can move freely in one dimension.
(4) If you try the same trick with three canes, now you can't move the
tops at all. This is basically what's happening with a three-
legged stool. The tops of the cans can move in zero dimensions...
which is to say, they can't.
Each time you add a cane, you remove one dimension in which the top
can move freely - that is, each new cane removes one 'degree of
freedom'.
Now, what happens when you add a fourth cane? Well, now you have too
many constraints. This means that there are multiple ways that the
stool can 'solve' the problem of which legs to use for support.
Wobbling occurs when the stool can't 'decide' which solution to use,
or, more precisely, when it's changing its mind about which solution
to use.
In effect, during the time that the stool is actually wobbling, it's
really a two-legged stool, with one degree of freedom - which is the
direction of the wobble.
In math, we see this kind of behavior in systems of equations. If I
have two variables, one equation will give me a whole range of
solutions:
y = 2x + 3 Solutions include (1,5), (2,7), (3,9)
In fact, the range of solutions is just the graph of the equation. If
I add another equation, I can have at most one solution:
y = 2x + 3
Solution is (2,7)
y = 4x - 1
That is, each new equation removes a 'degree of freedom' from the
system. With two variables, I need two equations to lock things down.
With three variables, I need three equations. And so on.
Now what if I add a third equation?
y = 2x + 3
y = 4x - 1 No solution
y = 4x + 1
There is no pair of (x,y) values that will satisfy all three of these
equations simultaneously. Of course, I can _choose_ any two of the
equations and get a solution for that pair, and then I could switch to
another choice, which would be quite a lot like what happens when a
four-legged stool wobbles.
So, the 'mathematical' answer to your question is: A 3-legged stool
'solves' a system of three equations in three variables, while a four-
legged stool changes its mind about which three of four equations to
solve for the same three variables.
I did my research before designing boilers :D
A Three-Legged Stool
Subject: Re: Why is a 3-legged stool always steady?
Think of it this way:
(1) If you hold a cane in the air, you can move it in any direction,
twirl it, and so on. Its motion isn't constrained at all. That is,
the top of the cane can move freely in three dimensions.
(2) If you put (and keep) one end on the ground, now its motion is
constrained: you can't lift it, or rotate it... although you can
swing the top around in a variety of different arcs. That is, the
top of the cane can move freely in two dimensions.
(3) If you connect the tops of two canes together and place the other
ends on the ground, you can still move the tops, but only along a
single (straight) arc, back and forth. That is, the tops of the
canes can move freely in one dimension.
(4) If you try the same trick with three canes, now you can't move the
tops at all. This is basically what's happening with a three-
legged stool. The tops of the cans can move in zero dimensions...
which is to say, they can't.
Each time you add a cane, you remove one dimension in which the top
can move freely - that is, each new cane removes one 'degree of
freedom'.
Now, what happens when you add a fourth cane? Well, now you have too
many constraints. This means that there are multiple ways that the
stool can 'solve' the problem of which legs to use for support.
Wobbling occurs when the stool can't 'decide' which solution to use,
or, more precisely, when it's changing its mind about which solution
to use.
In effect, during the time that the stool is actually wobbling, it's
really a two-legged stool, with one degree of freedom - which is the
direction of the wobble.
In math, we see this kind of behavior in systems of equations. If I
have two variables, one equation will give me a whole range of
solutions:
y = 2x + 3 Solutions include (1,5), (2,7), (3,9)
In fact, the range of solutions is just the graph of the equation. If
I add another equation, I can have at most one solution:
y = 2x + 3
Solution is (2,7)
y = 4x - 1
That is, each new equation removes a 'degree of freedom' from the
system. With two variables, I need two equations to lock things down.
With three variables, I need three equations. And so on.
Now what if I add a third equation?
y = 2x + 3
y = 4x - 1 No solution
y = 4x + 1
There is no pair of (x,y) values that will satisfy all three of these
equations simultaneously. Of course, I can _choose_ any two of the
equations and get a solution for that pair, and then I could switch to
another choice, which would be quite a lot like what happens when a
four-legged stool wobbles.
So, the 'mathematical' answer to your question is: A 3-legged stool
'solves' a system of three equations in three variables, while a four-
legged stool changes its mind about which three of four equations to
solve for the same three variables.
bac206 wrote:Looking good. Can't beat a well set up boiler. Where's you score your SG from? I'm also doing up a new boiler and have a 3" Ferrule welded there for a sg.
As for controller, I used an aluminium project box. Leccy mate said it'd also act as a bit of additional heat sink. Not sure if it does for sure but sounded good to me. And not to mention the earthing issue. But I'm no leco
Sg glass from... fsd mate.
Cheers
Yummyrum wrote:Well yes smb...pleasd you are sus .....sorry this my soap box.
The main thing is will you contact any metal protruding from that plastic box ? If you can then that metal be it a switch or potentiometer shaft or the grub screw in the knob that is attached to it or any shit that accumulates in the hole where the grub screw is or any screws that are holding shit inside...then all these points newd to be earthed......If there are too many that your sparky can't be botheted to individually address than you newd to either
1. Get another sparky
2. Get an earthed metal case
bac206 wrote:Wouldn't that piss ya. Might be time for me get some glasses. Didn't even notice them there
Thanks
Brad
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