Grapple mathematics

[mroldstyle]

Is there any particular formula for figuring out the placement of the cylinder when building a grapple, or just use a trial and error method?

 

[kennyd]

I am not a math guy...so I take two pieces of PVC pipe-one 1/2" and one 3/4" and make my own "cylinder". The 1/2" will slide in and out of the 3/4 to simulate this and its very easy to mark with pencil. Once you get it close, then only tack-weld the bracket in place to make a real test with the real cylinder.

 

[PapaPerk]

Is there any particular formula for figuring out the placement of the cylinder when building a grapple, or just use a trial and error method?

What are you trying to figure out? Cylinder length, grapple force, etc ,etc?

 

[Brad_Blazer]

I attached a spreadsheet in the first post of the linked thread.

There was a problem attaching a spreadsheet so I renamed as a text file. You have to save it and then edit the suffix from .txt to .xls. Then it should open in Excel.

There is a diagram showing what the dimensions mean. It will graph force and speed at the grapple tip. I designed mine for more force when fully closed and more speed when fully open. There is a tab you can click on along the bottom labeled "Force" where you can calculate the hydraulic force of your cylinder.

http://www.tractorbynet.com/forums/...-grapple-cad-build-geometry-calculations.html

 

[LD1]

What are you trying to figure out? Cylinder length, grapple force, etc ,etc?

Yep, really need more info on this.

Are you trying to find what length cylinder??? Diameter vs Force??? Pivot placements??

Have you already built the grapple??

It is really just simple geometry. You will have 3 pivot pins, 1 on each end of the cylinder, and one where it attaches to the bucket. These three points create a triangle, no matter how far the grapple is open or closed. 2 sides of the triangle are a fixed length and cannot change. The third side can change length (the cylinder) and that will change all 3 angles of the triangle.

All that being said, the formula I would most likely use the most for the various calculations involved with the grapple geometry is the cosine law.

c^2=a^2 + b^2 - 2ABcos(C)

If you are wanting to find the force, that takes a little more math. First you would have to find the force of the cylinder. pi x r^2 x PSI. Then you have to find how much force it is exerting on the grapple in the downward direction ONLY. Cylinders mounted on angles the formula is cylinder force x sin of the angle. That will tell you the force at the cylinder point.

Since the grapple probabally extends beyoned that (think of a lever) the force will be less at the tip of the grapple. How much less depends on the lengths of the grapple, where the pivot is, and where the cylinder is mounted. But it will be a ratio. Think of the pivot as zero. If the cylinder is mounted 12" out on the grapple and the tip is 24" from the pivot (cylinder mounted exactally half way) the ratio is 12:24 or 1:2. You would have exactally half of the force at the tip as you do at the cylinder.

Is this what you are looking for??

 

[Brad_Blazer]

That's exactly what's in my spreadsheet

 

[LD1]

That's exactly what's in my spreadsheet

I am a slow typer I clicked reply before you had posted and didn't see your post until I has submitted mine.

And It might be because I am on the work computer at the moment, but I couldn't get the spreadsheet to open for me. It kept wanting to open in the notepad and not excel.

 

[Brad_Blazer]

Sorry, I added some better instructions for renaming the file to a .xls in post 4.

 

[mroldstyle]

Thanks so far.
I'm trying to figure pivot point location and size. I would think using the two pieces of pvc pipe would be a good way to determine length. First attempt at building a grapple.

 

[LD1]

Thanks so far.
I'm trying to figure pivot point location and size. I would think using the two pieces of pvc pipe would be a good way to determine length. First attempt at building a grapple.

If you havent yet, do a search here on TBN.

There are a bunch of members who have built their own grapples and have some very good photos to give you pleanty of ideas.

And when you do build yours too, I expect you to take lots of pictures through out your build and post them on here as well:thumbsup: