Uneven suspended load/counterbalance 1

[rsm7400]

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

 

[rb1957]

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.

 

[desertfox]

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

 

[rsm7400]

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

 

[desertfox]

Hi rsm7400

You’re welcome

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

 

[Denial]

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.

 

[GregLocock]

I'm glad someone mentioned that.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[rsm7400]

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