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
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
RE: Angular Force Required
RE: Angular Force Required
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
RE: Angular Force Required
RE: Angular Force Required
What did you mean by mtr moment?
RE: Angular Force Required
This assumes it's inline. Also neglets the weight of the structure.
RE: Angular Force Required
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
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
http://www.imgur.com/fzginfI.jpeg
RE: Angular Force Required
RE: Angular Force Required
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
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
Nobody ever answers the question in this forum, just hand waiving arguments.
Regards,
Cockroach
RE: Angular Force Required
RE: Angular Force Required
Very nice, that says it all.
RE: Angular Force Required
RE: Angular Force Required
NX 7.5.5.4 with Teamcenter 8 on win7 64
Intel Xeon @3.2GHz
8GB RAM
Nvidia Quadro 2000
RE: Angular Force Required
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
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
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
RE: Angular Force Required
RE: Angular Force Required
This forum should be about helping people and I've done that. This attitude can only discourage newcomers from contributing.
RE: Angular Force Required
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
RE: Angular Force Required
g = 9.8 m/s^2
force: Newtons = kg*m/s^2
RE: Angular Force Required
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
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 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
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
RE: Angular Force Required
RE: Angular Force Required
RE: Angular Force Required
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
RE: Angular Force Required
F*sin11*250 = (25*9.81)*1000
F = 5141N
Quando Omni Flunkus Moritati