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FORUMS Photography Talk by Genre Transportation Talk 
Thread started 21 Apr 2008 (Monday) 10:35
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Official Automotive Rigs - DIY Thread

 
steelbluesleepr
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May 13, 2012 16:00 as a reply to  @ post 14425786 |  #6946

Round tubing has a much higher strength to weight ratio than square tubing. Square is much easier to find, but is only strong in 4 directions, round tubing has the same strength in all directions. These two reasons are why roll cages in race cars are made from round instead of square tubing.


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VisualEchos
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May 13, 2012 16:07 |  #6947

steelbluesleepr wrote in post #14425956 (external link)
Round tubing has a much higher strength to weight ratio than square tubing. Square is much easier to find, but is only strong in 4 directions, round tubing has the same strength in all directions. These two reasons are why roll cages in race cars are made from round instead of square tubing.

Great info! I would have thought that square tubing would be stronger up-to-down, which is how we need it for booms.


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BlackerPhotos
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May 13, 2012 16:47 |  #6948

steelbluesleepr wrote in post #14425956 (external link)
Round tubing has a much higher strength to weight ratio than square tubing...

Nope.

From an engineering site, this question was posed:

If for example I had some 50mmx50mm box 3mm thick (1.96" square with a wall thickness of 0.118"), and some scaffold bar 49mm (1.9" OD) x 3mm (0.118") thick which would be the strongest?

The scientific answer is with 0.5kn (approximately 112lbs of force) point loading applied to the centre of a 2.5m (8.2 feet) length of each of your materials, 6.6mm (0.259") deflection on the round tube, and 4mm (0.157") deflection on the square.

Riddle me this; If round is better, why is this 42 foot(!) carbon fiber boom square?

http://www.move-n-shoot.com/us_rig_inven​tory_g1.html (external link)


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Ando27
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May 13, 2012 19:47 |  #6949

[QUOTE=BlackerPhotos;1​4426131]Nope.

From an engineering site, this question was posed:

If for example I had some 50mmx50mm box 3mm thick (1.96" square with a wall thickness of 0.118"), and some scaffold bar 49mm (1.9" OD) x 3mm (0.118") thick which would be the strongest?

The scientific answer is with 0.5kn (approximately 112lbs of force) point loading applied to the centre of a 2.5m (8.2 feet) length of each of your materials, 6.6mm (0.259") deflection on the round tube, and 4mm (0.157") deflection on the square.

Riddle me this; If round is better, why is this 42 foot(!) carbon fiber boom square?

Riddle me this , Since when is 4mm greater than 6.6mm ???

Even in way down under Australia its deflecting less....


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BlackerPhotos
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May 13, 2012 21:15 |  #6950

[QUOTE=Ando27;14426688​]

BlackerPhotos wrote in post #14426131 (external link)
...The scientific answer is with 0.5kn (approximately 112lbs of force) point loading applied to the centre of a 2.5m (8.2 feet) length of each of your materials, 6.6mm (0.259") deflection on the round tube, and 4mm (0.157") deflection on the square.

Riddle me this , Since when is 4mm greater than 6.6mm ???

Even in way down under Australia its deflecting less....

What are you talking about? Read it again - I stated that square tubing deflects 4mm. Round tubing deflects 6.6mm. Square tubing deflects less.


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Spikeydevilbandit
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May 14, 2012 00:01 |  #6951

OK. My Turn.

Riddle me this.

If square was stronger than round, why are trees round and not square?
Nature knows you know ...


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Johandyman
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May 14, 2012 06:31 |  #6952

Spikeydevilbandit wrote in post #14427641 (external link)
OK. My Turn.

Riddle me this.

If square was stronger than round, why are trees round and not square?
Nature knows you know ...

to make sure all of the water is absorbed equally fast?

however i must say that im on the round is better boat, the reason a piston in an engine is round is because of the "perfect shape" a circle is, there are prob. reasons why the carbon monster from move'n'shoot is boxed, i think price, stackability and easiness when working with it.
also, from a quick google search ive come across the idea that bigger needs boxed and smaller needs round?
http://image.shutterst​ock.com …control-room-71262412.jpg (external link)
this is a big MF crane, and its all boxed.
this smaller - very very awesome - crane is with round.
http://farm5.static.fl​ickr.com …51680522_f5af16​9362_o.jpg (external link)


Stolen from http://forum.ih8mud.co​m …square-vs-round-tube.html (external link)

The size square tube you are using will hold up, but on a geometric consideration, no other shape dissapates forces and is stronger than a circle. That is why almost everything is made out of circular tube instead of square. The bending rigidity of a tube is radius to the 4th power so even a thinner gauge metal can be stoopid strong

Again, i know jacksh*t about this stuff, im just a FF from denmark lol :D but this could be why the bigger stuff is made from boxed stuff and the smaller is made from round.
get it? :)


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VisualEchos
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May 14, 2012 07:42 |  #6953

Had a chat with a guy last night that has used the MNS system several times, and was told by MNS that the reason it's square is because it's easier to manufacture CF that way for strength.


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spb
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May 14, 2012 12:01 |  #6954

For structural beams, what matters in their resistance to deflection is their second moment of area (often referred to as moment of inertia) or "I".
If you have two beams that are made of the same material same length, all you have to do to compare their stiffness is compare their I's.

For a square hollow beam with cross section dimensions
a=outer side,
b=inner side:
I=(a^4-b^4)/12

For a round hollow tube with cross section dimensions
a=outer diameter,
b=inner diameter:
I=(a^4-b^4)*(π/64)


Now if you want to take in account the length and material, you need to introduce:
L=length,
E=modulus of elasticity (property of material, may be found on matweb.com)
q= lb/ft weight of the beam per foot (approx. cross sectional area * density)
P=load due to camera mounted.
δ1=max deflection (at the end of the beam) due to the weight of the beam.
δ2=max deflection (at the end of the beam) due to weight of the camera.
δt=max total deflection

δ1 = (q*L^4)/(8EI)
δ2 = (P*L^3)/(3EI)
δt = δ1+δ2

Assumptions:
-Camera is mounted at the end of the beam.
-Weight of the beam is uniformly distributed.
-Cantilever beam.


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p27rpy
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May 14, 2012 13:44 |  #6955

Haven't posted in here in a while! Recent rig shot:

IMAGE: http://civitello.smugmug.com/Cars/Lotus-Elise/i-xGdPg7T/0/XL/Lotus-Rig-XL.jpg

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VisualEchos
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May 14, 2012 16:33 |  #6956

spb wrote in post #14429813 (external link)
For structural beams, what matters in their resistance to deflection is their second moment of area (often referred to as moment of inertia) or "I".
If you have two beams that are made of the same material same length, all you have to do to compare their stiffness is compare their I's.

For a square hollow beam with cross section dimensions
a=outer side,
b=inner side:
I=(a^4-b^4)/12

For a round hollow tube with cross section dimensions
a=outer diameter,
b=inner diameter:
I=(a^4-b^4)*(π/64)


Now if you want to take in account the length and material, you need to introduce:
L=length,
E=modulus of elasticity (property of material, may be found on matweb.com)
q= lb/ft weight of the beam per foot (approx. cross sectional area * density)
P=load due to camera mounted.
δ1=max deflection (at the end of the beam) due to the weight of the beam.
δ2=max deflection (at the end of the beam) due to weight of the camera.
δt=max total deflection

δ1 = (q*L^4)/(8EI)
δ2 = (P*L^3)/(3EI)
δt = δ1+δ2

Assumptions:
-Camera is mounted at the end of the beam.
-Weight of the beam is uniformly distributed.
-Cantilever beam.

Dude, just tell us which is stiffer up-to-down lol.


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StE823
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May 14, 2012 16:44 |  #6957

What the hell, I'm not an engineer and I never calculate the stiffness when I built my rig four years ago.


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Spikeydevilbandit
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May 14, 2012 23:52 as a reply to  @ Johandyman's post |  #6958

QUOTE=Johandyman; to make sure all of the water is absorbed equally fast?

LOL .... OMG, I don't know what you were doing in your biology class at school ... looking out the window maybe?


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spb
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May 15, 2012 08:38 |  #6959

just wanted to get it out of my system.


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Johandyman
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May 15, 2012 11:52 |  #6960

Spikeydevilbandit wrote in post #14433190 (external link)
QUOTE=Johandyman; to make sure all of the water is absorbed equally fast?

LOL .... OMG, I don't know what you were doing in your biology class at school ... looking out the window maybe?

take a joke dude ;)


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