smart51
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| posted on 2/6/10 at 05:57 PM |
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How big should the triangles be in a triangulated chassis?
I'd guess that there's a ratio of tube size to triangle size. Does anyone know what it is? Too small and you're adding metal for
no real gain. Too large and I suppose the tubes would buckle. What's the ideal ratio?
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mcerd1
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| posted on 2/6/10 at 06:10 PM |
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depends on what size/type of tube your using 
[Edited on 2/6/2010 by mcerd1]
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smart51
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| posted on 2/6/10 at 06:19 PM |
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quote:
Originally posted by mcerd1
depends on what size/type of tube your using
Yes, I believe I said that.
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Alan B
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| posted on 2/6/10 at 06:30 PM |
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A lot depends on the specific loading of the tubes more than anything. A tube loaded in tension can be much smaller in section and longer in length as
it wont see a compressive load. However, the same load in the opposite (compressive) direction will have to be much shorter and/or bigger in section
to resist the bucking tendencies that a long thin tube will have.
Check out slenderness ratio....
http://en.wikipedia.org/wiki/Buckling
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Alan B
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| posted on 2/6/10 at 06:30 PM |
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A lot depends on the specific loading of the tubes more than anything. A tube loaded in tension can be much smaller in section and longer in length as
it wont see a compressive load. However, the same load in the opposite (compressive) direction will have to be much shorter and/or bigger in section
to resist the bucking tendencies that a long thin tube will have.
Check out slenderness ratio....
http://en.wikipedia.org/wiki/Buckling
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mcerd1
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| posted on 2/6/10 at 06:38 PM |
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I've not designed a chassis before so take this with large pinch of salt (but I do design steel structures for a living)
from the chassis I've seen I'd guess its more about getting the angle of the bracings right, most seem to have the bracing doen the sides
at 30-40 deg. from the horizontal
if they are too shallow then they will just act like another beam/ rail, too steep and they might as well be vertical
whats right for your one will depend on what load it needs to carry, what direction that acts in and the proportions of your main chassis rails (i.e.
lenght vs gap between them)
personaly the size of the tubes is the last thing I decide - I'll guess a geometry and rough tube size, play with the geometry a bit till the
loadings work out about right, then do the final size up on the tubes based on the loading in each one
of course if you were designing a robin hood then you don't need may bracings at all
[Edited on 2/6/2010 by mcerd1]
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smart51
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| posted on 2/6/10 at 07:06 PM |
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quote:
Originally posted by Alan B
Check out slenderness ratio....
http://en.wikipedia.org/wiki/Buckling
Perfect, thanks.
For those who are interested, a 1" 16 SWG tube up to 206mm long is considered a short tube and should not fail by bucking. Up to 825mm is an
intermediate tube and will fail partly by buckling and above this is a long tube and will buckle as it's primary failure mode (general guide of
course).
A 3/4" 16 SWG tube is the same up to 173mm and 692mm. Most tubes on a locost are intermediate but there are a couple that are a bit long I
should think.
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zilspeed
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| posted on 2/6/10 at 07:25 PM |
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Of course,all dependent on the point of triangulation being otherwise supported.
I M H O
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Fred W B
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| posted on 2/6/10 at 08:01 PM |
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quote:
Of course,all dependent on the point of triangulation being otherwise supported.
I like to consider it by imaging that the structure is a pure pin jointed frame, that all the joints are free to pivot in any plane. A true space
frame will still be rigid in this state.
Cheers
Fred W B
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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