Balancing a mass within 1 degree?
Balancing a mass within 1 degree?
(OP)
Let's say I have a large structure that weights 100k pounds that is hung from a simple support at the very center (x,y = 0,0). The CG is offset by a few inches, say (6,2). I need the structure to hang within 1 degree of flat.
This seems like a simple trig problem but I am unsure how to setup the equation(s). I can add counterweight to bring it into spec, but need to know how much weight and where to put them ahead of time.
This seems like a simple trig problem but I am unsure how to setup the equation(s). I can add counterweight to bring it into spec, but need to know how much weight and where to put them ahead of time.





RE: Balancing a mass within 1 degree?
another day in paradise, or is paradise one day closer ?
RE: Balancing a mass within 1 degree?
If you are hanging the thing flexibly, the centre of mass should be directly under the hanging point. It is likely that the centre of mass is not located exactly where you think it is.
This setup shows your CofM in X and Y. You need Z as well to do your calculation
Is there any way you can mount this thing on three scales? This will tell you exactly where your CofM is. You can work out the additional masses required to move it to exactly where you want it.
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JHG
RE: Balancing a mass within 1 degree?
You made a great point. It must be too early, yes we have a Z direction component as well, and that makes the problem a lot more clear.
RE: Balancing a mass within 1 degree?
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Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
RE: Balancing a mass within 1 degree?
Ted
RE: Balancing a mass within 1 degree?
I am using Z as the vertical axis, not Y.
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JHG
RE: Balancing a mass within 1 degree?
Ted
RE: Balancing a mass within 1 degree?
RE: Balancing a mass within 1 degree?
RE: Balancing a mass within 1 degree?
TTFN

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Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
RE: Balancing a mass within 1 degree?
Pick counter balance weight = 1000lbs.
The counter balance weight must be located 100000*6/1000 = 600 inches from the suspension vertical to the right for perfect balance.
For 1deg out the cg is about 1.75 inches from the suspension vertical.
100000*1.75/1000 = 175 inches from suspension vertical for 1000lbs to balance offcenter cg.
Ted
RE: Balancing a mass within 1 degree?
Ted
RE: Balancing a mass within 1 degree?
Neither the 100in or the 6in is known from the OP's test. All we have is an angle.
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JHG
RE: Balancing a mass within 1 degree?
Ted
RE: Balancing a mass within 1 degree?
I don't think those are real numbers. The OP made them up to populate his sketch. If he knows X and Z as shown, I am not willing to explain his counterweights to him.
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JHG
RE: Balancing a mass within 1 degree?
That's surely the easiest solution.
RE: Balancing a mass within 1 degree?
RE: Balancing a mass within 1 degree?
RE: Balancing a mass within 1 degree?
do you Know the weight of the object and have an estimate for the CG location ? then you can solve for the rotation and add balance weights if required at a convenient location (away from the suspension axis). then test to confirm.
else test, and that'll show you something about the CG. then add weights to achieve your target. you might use two locations, offset parallel to the suspension axis, since you're supporting the body along an axis, and not at a point.
another day in paradise, or is paradise one day closer ?
RE: Balancing a mass within 1 degree?
RE: Balancing a mass within 1 degree?
Ted
RE: Balancing a mass within 1 degree?
RE: Balancing a mass within 1 degree?
It is done everyday while installing subsea equipment.
RE: Balancing a mass within 1 degree?
is bouyancy an issue ?
is this only assembled underwater ? if so, can you test (with currents and such) ?
or is this "by analysis only" ?
another day in paradise, or is paradise one day closer ?
RE: Balancing a mass within 1 degree?
If the angle is critical (i.e for mating up subsea) then I would suggest using a multi point lift and setting your sling lengths to the give you the angle required.
RE: Balancing a mass within 1 degree?
another day in paradise, or is paradise one day closer ?
RE: Balancing a mass within 1 degree?
Easiest solution is hang it from a second then third points and find the intersecting axis point or use a variable counter weight until the angle meets requirements.
Also weigh it at three points equidistant from the lift point and then counter balance until all three scales are equal.
RE: Balancing a mass within 1 degree?
another day in paradise, or is paradise one day closer ?
RE: Balancing a mass within 1 degree?
My interpretation is that he is trying to hang the object less than one degree from vertical, and he does not know where the centre of mass is.
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JHG
RE: Balancing a mass within 1 degree?
another day in paradise, or is paradise one day closer ?
RE: Balancing a mass within 1 degree?
In the OP, he is trying to set up the calculation, which does require the centre of mass.
--
JHG
RE: Balancing a mass within 1 degree?
another day in paradise, or is paradise one day closer ?
RE: Balancing a mass within 1 degree?
M1 is the block weight
l is the cg distance from the horizontal plan containing the attachment point
M2 is the mass to add
X is the distance from the hook point
vector is opposite to the slope of the block (uphill direction)
Rotation created by M2 * x must equal M1 * (CG offset from vertical) before lifting to keep the block balanced. After lifting the horizontal distance can be found from L * sin (theta). M2 * x is a constant. The vector is reverse of the slope, I believe it was 6,2 for an offset, so the vector would be on the line of -6, -2.
Also if you balance the unit by trial and error you can used these same equations to find the CG of the original block.