Angular Force Required 7

[Foxhole]

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

 

[Foxhole]

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

 

[dhengr]

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.

 

[renderu]

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.

 

[TheTick]

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

 

[renderu]

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.

 

[TheTick]

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.

 

[renderu]

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.

 

[TheTick]

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

 

[Cockroach]

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

 

[zekeman]

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.

 

[TheTick]

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.

 

[zekeman]

"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.

 

[TheTick]

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

 

[renderu]

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

 

[TheTick]

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

 

[zekeman]

"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?

 

[flash3780]

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

 

[rb1957]

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



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