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Angular Force Required
7

Angular Force Required

Angular Force Required

(OP)
Hi all,

I am new here and was hoping that someone would be able to help me with a problem that you will probably find simple.

Looking at the image, how would I go about calculating the force required to equal the applied load?



I am struggling to get my head around calculating angular forces!

Thank you in advance for your help,

Regards,

Adam
 

RE: Angular Force Required

That was just sum of forces equal zero in the vertical direction. Sorry for the confusion witb the wrong title.

RE: Angular Force Required

(OP)
Thanks for your help Renderu, much appreciated,

I wasn't too far off the right line then, but doesn't the 0.25 mtr moment further increase the force required?

RE: Angular Force Required

Sorry. I'm at work and messed that all up. You need moment around hinge. I'll send update very shortly.

RE: Angular Force Required

(OP)
Thanks mate, really appreciate your help

RE: Angular Force Required

Is the cylinder end inline with hinge? Doesn't look like it. What's that offset distance?

What did you mean by mtr moment?

RE: Angular Force Required

(OP)
Your right, it isn't completely inline, the cylinder end is 12.5mm higher than the hinge point,

I mean't 0.25 metre distance horizontally from hinge point to cylinder end, sorry I'm probably not using the correct terminology.

RE: Angular Force Required

(OP)
It is almost inline so that is fine, that was the figure I was coming out with basically as per your first calculation multiplied by the moment around the hinge.

Great clarification though, as I don't really do many of these calculations very often I have gotten really rusty with it.

Thanks again for your help,

Adam

RE: Angular Force Required

(OP)
Brilliant info, thanks again

RE: Angular Force Required

Foxhole:
To completely define the problem you have to add vert. dimensions from some datum, say the top of the deck plate, down to the hinge pin center and to the two pin centers on the hydraulic cylinder. Then think of it this way: the gravity loads always act vertically and the lever arm to them, the point load and/or the dead load of the machine is horiz. or perpendicular to their line of action; the lever arm btwn. the cylinder and the hinge pin is always the perpendicular distance from the hinge pin to the center line axis of the cylinder. This is a kinematics problem, and you see that the lever arm to the cylinder is increasing, while the lever arms to the loads are decreasing, with any lifting rotation. So, your sketch shows the highest cylinder force. You do not want the cylinder axis to get much closer to the hinge pin or you will have an unstable system which could experience snap through. So, provide a solid stop under the platform so it can’t go below the horiz. position shown.

RE: Angular Force Required

This can be solved quite easily with a scale.
First get the vertical reaction at the left end of the piston using the ratio of lever arms ( 1000 / 250 )
Then find the lengths of the legs of a right triangle formed by the piston's two ends.
The vertical force is proportional to the length of the vertical leg of this triangle.
The force in the piston is proportional to the diagonal length of this triangle.
Note that the sine in the previous answer is the opposite over the hypotenuse which is the same as the vertical side of the triangle divided by the diagonal length, so the answers come out the same.

RE: Angular Force Required

5141 N at 11 degrees.

Nobody ever answers the question in this forum, just hand waiving arguments.

Regards,
Cockroach

RE: Angular Force Required

We teach fishing

RE: Angular Force Required

Dave:
Very nice, that says it all.

RE: Angular Force Required

Before getting really serious about your solution, you should investigate the motion and look at the cylinder you have drawn. The cylinder looks like it has been cartooned in, and does not reflect actual cylinder dimensions.

RE: Angular Force Required

I'm just going to give the OP a star for providing a proper drawing & explanation of his problem. This is more rare then it should be.

NX 7.5.5.4 with Teamcenter 8 on win7 64
Intel Xeon @3.2GHz
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Nvidia Quadro 2000

RE: Angular Force Required

"Cockroach (Mechanical)
11 Mar 13 15:08
5141 N at 11 degrees.

Nobody ever answers the question in this forum, just hand waiving arguments"


Now, now, Cockroach, give the guy a break.
He gave enough geometry to do the problem, notwithstanding some poor nomenclature.
Compared to most other posters, the guy deserves an A.

RE: Angular Force Required

(OP)
Thanks again all for your help, much appreciated.

Just to clarify a few points...

dhengr, as you rightly stated regarding snap through, there is (in the final design) a physical stop so the axis of the cylinder does not get any closer to the hinge pin, so the geometry is in it's worst condition in the diagram shown.

dvd, at the time of posting I hadn't yet modeled a cylinder within the assembly but was well aware of the actual cylinder dimensions. The 'cartoon' cylinder was just representative to help clarify the mechanism for my post. I took an educated guess at a 32mm bore cylinder, operated at 120 bar system pressure (= 9650 N), I would be easily able to amend the design should a larger force be required, this was just a starting point.

dhengr & IFR, thanks, your explanations are helping me to understand how to calculate the solution to my problem, I will keep at it!

Walterke, thanks for the star!

Regards,

Foxhole



RE: Angular Force Required

Foxhole:
I also congratulate you for your original sketch, but think through the whole problem so you include all the needed info. in the future. Note that if you could change the 250mm horiz. dimension to 300mm and still get the total platform rotation you wanted, the kinematics problem again: you would improve the angle and the lever arm from the hinge pin to axis of cylinder, and thus reduce the cylinder force req’rd.; you would lessen the shear on the hinge pin; and you would reduce the bending and shear stresses in the platform structure. Maybe not a bad trade off, and 325mm would be even better.

RE: Angular Force Required

I'm really baffled at some of the comments here. The OP asked a question, and I answered. Then people question the design. He/she, simply asked a question. Leave it alone.

RE: Angular Force Required

You somehow conjured up an answer without sufficient information. Any competent engineer would examine and question.

RE: Angular Force Required

TheTrick, Foxhole had a question and I answered the question and he is satisfited with the response because it answered his question. I provided the textbook solution to the problem and noted that it didn't take into account the mass of the object. Your attack concerning my competence as an engineer is unwarranted . You don't have enough information to draw such a conclusion. An engineer should make comments based on facts.

This forum should be about helping people and I've done that. This attitude can only discourage newcomers from contributing.

RE: Angular Force Required

Your answer expresses force in units of mass. BIG RED FLAG! Not questioning your competence, only your solution, which makes no sense and was arrived at with too little information to fully solve the problem.

As for Foxhole, if he knew how to get the answer, then he would also be able to better evaluate what we are saying.

RE: Angular Force Required

You see red flags where there isn't none. If he had provided lb I would have used lb, if it were slugs I would have used slugs. For that matter, I also wouldn't mind using cherries if that's what was provide.

RE: Angular Force Required

By not including gravity, your "solution" is off nearly 10x. Kg is not force. Newtons is force. Force is not mass.

g = 9.8 m/s^2
force: Newtons = kg*m/s^2

RE: Angular Force Required

I think we are getting petty here.

It is not uncommon to state "kg" with the understanding that weight is the product of mass and acceleration due to gravity. But as with other references to a clean workable diagram to outline the problem, yes, it was well done and buddy deserves the star for being precise and explaining his problem clearly.

To point out cylinder dimensions and scale relative to the drawing is pointless. It's a sketch to illustrate the problem at hand and not a print worthy of manufacturing. The problem was to determine cylinder load based on the geometry of the scissor lift, not design the entire system noting stops and such. I'm surprised that nobody commented on hydraulic pump requirements and some other off the wall remark that has nothing to do with the question at hand.

Again, few solutions and just a lot of verbal nonsense. So good job Renderu, you are one of the few who answer a question.

Regards,
Cockroach

RE: Angular Force Required

I think one of the problems here (and I am often guilty of this as well) is that some of us do nor read ALL of the posts before commenting on the problem posed and the solutions offered. In this case, the OP failed to give the complete geometry in his sketch which he subsequently corrected by adding the "offset" value.
Renderu correctly solved the problem but all of the negative comments that followed showed that those posters hadn't taken the time to follow the thread.
I think we should be more careful before judging others.

RE: Angular Force Required

I suppose a little contrition is in order. I was being nitpicky. Renderu's solution is fine, at least in a mathematical sense.

I do think it was reckless to just throw up the first solution and fill in assumptions where information was missing. I think the OP needed to be made aware of the need for the info before being offered a solution.

We don't necessarily need to "teach everyone to fish". However, I do think the OP benefited from being compelled to get more information, as it would help him see the problem more clearly

Using mass for force is plain sloppy. Gets under my skin. In my day, it meant 11 points lost on a 10 point problem. To me, being an engineer means being keenly and instinctively aware of such things.

RE: Angular Force Required

"Using mass for force is plain sloppy. Gets under my skin. In my day, it meant 11 points lost on a 10 point problem. To me, being an engineer means being keenly and instinctively aware of such things."

With all due respect, since we are not working on Mars, everybody I know knows what 1Kg of mass weighs. It weighs 1kg. If they never invented Newtons, it would still weigh 1kg.

RE: Angular Force Required

I've made a good living cleaning up after people like you. Don't quit until my kids are through college.

RE: Angular Force Required

This discussion on units of force is plain ridiculous. Reminds me of my 12th grade teacher (where this kind of critismsm was actually relevant).

RE: Angular Force Required

If your 12th grade teacher (physics) was anything like mine, compliment accepted.

RE: Angular Force Required

"I've made a good living cleaning up after people like you. Don't quit until my kids are through college. "

It's a wonder how I sent my kids to college WITHOUT somebody like you "cleaning up after me".
Do you really believe what you are writing?

RE: Angular Force Required

Speaking of gravity, has anyone considered the weight of the platform being lifted?

RE: Angular Force Required

sum moments about the pivot ...
F*sin11*250 = (25*9.81)*1000
F = 5141N

Quando Omni Flunkus Moritati

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