What is the formula for calculating force in a crank and slider mechanism?

[ShaiNaveh]

Hi all,

I have a question regarding a simple crank and slider mechanism, but I'm not a mathematician. This means that long formulas scare me... (: I've been searching around and haven't found anything I can really understand.

I'm trying to get a "ball park" formula to calculate the amount of force I'll need to push plate B at a given angle between the two plates in order for them to fold. I suppose that when the angle is 180 deg., no force would do the trick, but at 0 deg it would be the easiest. I'm also sure it's not linear, but that's as far as my knowledge takes me for this kind of linkage...

For this example let's say the the plates weigh 1kg each, and there is no friction involved. It's probably something you guys blurt out in your sleep, for me it's voodoo...Any help would be appreciated.

Many thanks, and happy September 1st holiday for us parents... (:

 

[Bystander]

Lengths of the plates?

 

[ShaiNaveh]

Lengths of the plates?

Ohhh dear, you're right, that IS important... It's 0.5m each.

Thank you.

 

[Bystander]

Are you familiar with trig functions?

 

[ShaiNaveh]

Are you familiar with trig functions?

The basic stuff I suppose

 

[Bystander]

Give you any ideas?

 

[ShaiNaveh]

Give you any ideas?

Not sure I understand what you mean...
Do trig functions give me any ideas, or are you asking me if I want you to give me any ideas...

 

[Bystander]

Do trig functions give me you any ideas

 

[ShaiNaveh]

Yes, they give me an idea, but only an idea regarding the non-linear fashion of the force I need. As I said, I have a real problem with understanding formulas, all the way back to my school years. I've been designing and building machines for years using my experience and gut feeling when it comes to selecting motion components. So far nothing has crashed... but sometimes my gut feeling is not enough and I need to go back to school.

The way I see it, the mass is centered in the pivot. It should be half of each plate's mass when the angle is 180 deg., so there's 1kg to lift there. I also know that the pivot point gets easier to lift in a non-linear manner. It should be half the mass at 60 deg. if I'm not mistaken.

 

[Bystander]

https://www.physicsforums.com/threads/man-climbing-a-ladder.884019/
Watch this thread for hints. You'll need to include a ninety degree rotation of the coordinates.