Grapple project OPEN SOURCE

[polemidis]

I agree with everything but I think you have an error on the the last picture.

But yes, summarizing, I use this simplified formula. Fin = sin(A) * F * L1/ (L1 +L2)
Fin= the final force
A= the angle
F=the Cylinder force
L1- the distance between the pivot and the end of the cylinder
L2 the distance between the end of the cylinder and the point where the force is acting.

I think you are wrong where you sketched that the 26.25"
It should be like this one correct? (My apologiesm I have removed the outlines of the cylinder base. But is where the red dot is


So in my last picture I get a force of 7850×sin(7.9)×16.24÷(16.24+3.94) = 868lbs

 

[LD1]

Do the method I showed and what do you get for clamp force?

Or give the 4 dimensions and I'll figure it.

I think you are over complicating it. The grapple doesn't care if the lid is curved or how much it's curved. You are already taking it into account when you figure the angle of the cylinder.

If the lid had straight tines going from it's hinge to it's tips, the force would be the same as if they were curved as they are

 

[ovrszd]

LD1, do me, do me!!!!!!

A = 26.5"
B = 24"
C = 4"
D = 30"

Using a 2" x 8" cylinder if that matters.

Thanks!!!!!

 

[polemidis]

Do the method I showed and what do you get for clamp force?

Or give the 4 dimensions and I'll figure it.

I think you are over complicating it. The grapple doesn't care if the lid is curved or how much it's curved. You are already taking it into account when you figure the angle of the cylinder.

If the lid had straight tines going from it's hinge to it's tips, the force would be the same as if they were curved as they are

No, I think there is a misunderstanding here. The 26.25" that you draw is not the distance between the point that the tines apply the force and the grapple pivot point. In vectors, your 26.25 should be a point on the extension of the line between the grapple pivot point and the cylinder rod point. See my last sketch. Your 26.25 should be where the L2 measurement ends. Not at the hypotenuse.
The shape or the lenght of the teeth should not affect the calculation you are right

 

[LD1]

LD1, do me, do me!!!!!!

A = 26.5"
B = 24"
C = 4"
D = 30"

Using a 2" x 8" cylinder if that matters.

Thanks!!!!!

Not good.

Your "c" dimension is pathetic.

Puts your cylinder on a 7.1* angle at full close. Giving 970# cylinder force.

24/30th of that is 776# bite force.

 

[LD1]

No, I think there is a misunderstanding here. The 26.25" that you draw is not the distance between the point the tines apply the force and the grapple pivot point. In vectors, your 26.25 should be a point on the extension of the line between the grapple pivot point and the cylinder rod point. See my last sketch. Your 26.25 should be where the L2 measurement ends. Not at the hypotenuse.
The shape or the lenght of the teeth should not affect the calculation you are right

Yes. But reality vs practical.

I am giving two known fixed points to measure. = EASY

Trying to extend a vector line beyond, and some imaginary point the lines cross, and get a measurement...= Hard.

And in reality....the numbers are close enough to suffice.

In other words, there are other things that are gonna make a large difference in the calculations. Like being 1/2" off on a measurement one way or another. Or 2400 Psi system pressure vs 2600.

Just trying to keep things as simple and easy as possible and still get a pretty accurate real world number

 

[polemidis]

1957lbs , made it class 2 lever, so end up 2100lbs on the teeth! Wtf that stuff are so fun!
And since you say the 2" cylinder is too quick, replace it with a 2.5" and we have 3280lbs...:cool2:

Thats the proof!

 

[LD1]

Ain't math fun

It's amazing what just a few inches here and there make in overall performance? It's a good thing you are designing and asking questions first rather than just flying by the seat of your pants. Even if in the end I think you will have spent more trying to build.....at least you have a good understanding.

And FYI....these same mathematic principals apply to things like dump trailer design, loader and backhoe lift specs, etc.

 

[LD1]

Just realized I was in too big of a hurry when I posted that last post. You are still using a 4" cylinder.

And to do that and achieve the force you did.....look at your angles when the lid is open.

(Hint: your grapple will never close)

 

[polemidis]

Just realized I was in too big of a hurry when I posted that last post. You are still using a 4" cylinder.

And to do that and achieve the force you did.....look at your angles when the lid is open.

(Hint: your grapple will never close)

hahaha! You are right! Its going towards the opposite direction! hahaha.

I will fix that, and I will redesing it, I think I have to change the shape of the teeth a litte, make the radius more tight and increase the capacity of material that fit in there. I am leaning towards a 2.5" also for reasons:
a) you mentioned that its too fast anyway, so the loss of the speed is a good thing. And the increase in force is a better thing!
b) having that much of a bite force, gives me room to sacrifice a little more force in exchange of some wider angle and more opening. Teeth to teeth in opening (measured from inside) is 29" now. If I can make it to 35" or so it would be perfect.


And yes, I like learning stuff!! Forums, google, videos are my friends!

Anyway, there is a lot work more to be done. BoM, links, cost, figuring out these annoying pins....