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I"m designing a set of ramps and a travel ramp so i can test and tune my cars suspension as well as have a bit of extra room to move around under my cars while working on them. I cam up with an idea to make a pair of ramps that can be joined via hinge then flipped over to make a ramp
Basically the ramps will be 1500 long and 400 high, when together they will form a 3000mm x 400mm truss that can be leant up against something.
My questions are
I want to make them out of 50x25x2.5 RHS or something close to that. Based on the sketches below, do you think that will be strong enough or should i go heavy wall - say 3.5 mm or summat. obviously i want it strong enough with a safety margin but i also want to be able to move the buggers around. I might put castors on one side so they can be dragged.
i will make the hinge out of sections of 20x 5mm wall tube like a piano hinge that has a removable 10mm rod, i'll brace the tube with a section of 6x 50mm barstock. how do people think this will go as a hinge? strong enough?
Any idea how to work out a formula to determine the tension on the hinge for a given load at a given angle?
Why would you want to put that much stress through a hinge?
I would put the hinge (now simply used to locate the two pieces together) on the floor part of the same end of the ramp (in first diagram), and use steel rope under tension from one pointy end to the other, running underneath when viewed in the second diagram. The cable lengths could be worked so that the cables are tensioned up as you force the two pieces down to place the pin in.
George Carlin, an American Comedian said; "Think of how stupid the average person is, and realise that half of them are stupider than that".
DAMKIA wrote:Why would you want to put that much stress through a hinge?
I would put the hinge (now simply used to locate the two pieces together) on the floor part of the same end of the ramp (in first diagram), and use steel rope under tension from one pointy end to the other, running underneath when viewed in the second diagram. The cable lengths could be worked so that the cables are tensioned up as you force the two pieces down to place the pin in.
I'm no engineer, but from my experience as a rigger/climber the tension that the rope you are talking would have to be under so much tension it's almost incalculable. The way you are talking about having the hinge on top in compression, would mean the bottom would be wanting to open up, and the available leverage on a cable across the bottom would be boggetyteen.
In my example (which is a direct copy of a military engineers transportable bridge), the bending load puts the hinge on the bottom in an outwards tension movement. the longer the vertical separation from the drive platform to the hinge the less the leverage on the hinge. Which is why i made it 400 instead of something smaller like 200
DAMKIA wrote:Why would you want to put that much stress through a hinge?
I would put the hinge (now simply used to locate the two pieces together) on the floor part of the same end of the ramp (in first diagram), and use steel rope under tension from one pointy end to the other, running underneath when viewed in the second diagram. The cable lengths could be worked so that the cables are tensioned up as you force the two pieces down to place the pin in.
I'm no engineer, but from my experience as a rigger/climber the tension that the rope you are talking would have to be under so much tension it's almost incalculable. The way you are talking about having the hinge on top in compression, would mean the bottom would be wanting to open up, and the available leverage on a cable across the bottom would be boggetyteen.
In my example (which is a direct copy of a military engineers transportable bridge), the bending load puts the hinge on the bottom in an outwards tension movement. the longer the vertical separation from the drive platform to the hinge the less the leverage on the hinge. Which is why i made it 400 instead of something smaller like 200
It would be exactly the same tension whether taken by the hinge on the bottom or by several cables placed underneath. You are still talking about the same tensile force along the bottom of the platform in response to a weight on top of it. Cables are designed for tension, hinges are not.
George Carlin, an American Comedian said; "Think of how stupid the average person is, and realise that half of them are stupider than that".
If i make them out of 50x25 RHS i have 3 wall thicknesses to choose from 2.0, 2.5 and 3.0
here are the cost/weight breakdown for them based on the steel prices available to me in Penrith
2.0mm
$114 in materials
55.2kg and 27.6kg for both halves and each half respectively
2.5mm
$135
64.7kg and 32.3kg
and
3.0mm
$156
73.8kg and 36.9kg
So for the engineers out there, will the 2.0 be strong enough not to bend in the middle (i'm talking about the RHS not at the middle joint) because the cost and weight savings for lugging them around the shed are obvious.
If i find i'm breaking the middle hinge i will just use bolts and load spreading plates to hold it all together.
DAMKIA wrote:Why would you want to put that much stress through a hinge?
I would put the hinge (now simply used to locate the two pieces together) on the floor part of the same end of the ramp (in first diagram), and use steel rope under tension from one pointy end to the other, running underneath when viewed in the second diagram. The cable lengths could be worked so that the cables are tensioned up as you force the two pieces down to place the pin in.
I'm no engineer, but from my experience as a rigger/climber the tension that the rope you are talking would have to be under so much tension it's almost incalculable. The way you are talking about having the hinge on top in compression, would mean the bottom would be wanting to open up, and the available leverage on a cable across the bottom would be boggetyteen.
In my example (which is a direct copy of a military engineers transportable bridge), the bending load puts the hinge on the bottom in an outwards tension movement. the longer the vertical separation from the drive platform to the hinge the less the leverage on the hinge. Which is why i made it 400 instead of something smaller like 200
It would be exactly the same tension whether taken by the hinge on the bottom or by several cables placed underneath. You are still talking about the same tensile force along the bottom of the platform in response to a weight on top of it. Cables are designed for tension, hinges are not.
\Big low loaders have ramps that fold in half and do exactly what is shown above.
Big hinge on the bottom takes the weight of a very heavy plant driving ontop of it. (big dozer, 30-50tonne?)
I see no problem with putting 1500kg of 4wd ontop of this design.
Shadow wrote:
\Big low loaders have ramps that fold in half and do exactly what is shown above.
Big hinge on the bottom takes the weight of a very heavy plant driving ontop of it. (big dozer, 30-50tonne?)
I see no problem with putting 1500kg of 4wd ontop of this design.
Thanks for that Shadow, I hadn't thought of that
Yep. 5mm wall tube is pretty beefy. Presuming your hinge pin is solid, a tight fit, and the tubes are arranged such that the pins are in shear with essentially no bending component, I'd say it's a no-brainer that the hinge will be strong enough - if it's welded well enough, so don't ask me to weld it.
-Scott- wrote:
Yep. 5mm wall tube is pretty beefy. Presuming your hinge pin is solid, a tight fit, and the tubes are arranged such that the pins are in shear with essentially no bending component, I'd say it's a no-brainer that the hinge will be strong enough - if it's welded well enough, so don't ask me to weld it.
I was going to weld the tube to the ramps joined together then cut the sections while welded together so it'll be a neat fit except for the 1mm cutting disc gap
