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Uneven suspended load/counterbalance

Uneven suspended load/counterbalance

Uneven suspended load/counterbalance

(OP)
I'm sure this question is easy but I do not remember my statics calculations right now haha. I have a beam that is 79" long and weighs 130lbs. I have a part that weighs 190lbs that will be uniformly suspended by 2 straps 44" apart. The first strap needs to be hooked on the bar started at 4". I can move the pick up spot to practically anywhere along the length of the bar. Where do I need to pick up so that the load is balanced?



Thanks in advance!

________________________________
Ryan M
Quality Engineer
3d Printer Hobbyist

RE: Uneven suspended load/counterbalance

so CG of bar is midspan, CG of "part" is at 4+44/2 = 26,
balance point is at (130*79/2+190*26)/(130+190)

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: Uneven suspended load/counterbalance

Hi rsm7400

Split the 190lb into two forces of 95lb and place them as point loads at the straps 44” apart. Place the 130lb as a point load at the centre of the 79” beam. Take moments about the beam from the left hand end:-

95*4” + 95*48” + 130*39.5” = x * (95+95+130)

X = 95*4” + 95*48” + 130*39.5”
—————————————————————————
(95+95+130)

That should give you the lifting point position X.

From an academic point of view that’s how to solve the problem, however if this is a real life situation I would be concerned about lifting from a single point

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: Uneven suspended load/counterbalance

(OP)
Thank you so much! I havent touched statics in 15 years, the last place I worked we could pick up every part/fixture by hand.

________________________________
Ryan M
Quality Engineer
3d Printer Hobbyist

RE: Uneven suspended load/counterbalance

Hi rsm7400

You’re welcome

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: Uneven suspended load/counterbalance

You may have simplified your description to make your question simple and clear.  However what you have shown is an unstable mechanism.  If (when) your spreader-beam begins to tilt, even infinitesimally, the geometry of the total lifted load (spreader-beam plus straps plus "part") changes because the straps will always be vertical.  The system's centre of gravity moves slightly to the left, so the spreader-bar tilts a bit more to compensate.  Away she goes!

At the very least, you MUST ensure the rectangle in your diagram CANNOT turn into a parallelogram.  Adding a pair of crossed diagonal ties might do the job, but only if they have adequate axial stiffnesses.

RE: Uneven suspended load/counterbalance

(OP)
Yes thank you :) I was aware of that but good to restate it. We just moved the part with the gantry moving very slow. All was stable and flat and loaded up very nicely!

________________________________
Ryan M
Quality Engineer
3d Printer Hobbyist

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