Grapple project OPEN SOURCE

[GLyford]

There was a guy on another forum who made all his machines using "cardboard assisted design."

He would make all his parts full size, on the machine, with light weight boards, cardboard, and nuts and bolts. For a cylinder, he would have two boards, one with holes at the "retracted" distance, and one with holes at the "extended" distance. He would take notes with a marker directly on the parts. You can learn stuff from doing that that you might miss other wise, like "will the bucket hit the hood when the boom goes up?"

Computers are fun, but they are not always the best way, or the only way.

 

[GLyford]

Another example:

I had one set of pins that I did not have grease fittings on. Sure enough, at some point later I was working with jacks, chain, and torches after it stopped working so I could get it apart, drill, thread and add fittings.

Speaking of fittings, they can either go into the side of a bushing, or into the end of a pin with a hole drilled down the middle to a cross-drilled hole that comes out in the middle of the bushing. But one way or the other, every part that moves should have a way to get grease. If you look at the other parts of your tractor, you should see this.

 

[ovrszd]

Sometimes the why is meaningless without knowing more about the "the theory is this, but when you actually use them...what everyone does is this" that you only get from a lifetime of running machines. You really need both, or a team of people that collectively know both.

Nicely stated.

No offense intended in this statement. All designers need to also be operators/fabricators.

 

[polemidis]

Thank you guys. Your comments directed me to what to research. Feel free to correct me if I am wrong, no offense taken on construtive critisim.
So, you end up with 7500lb of force by using the formula for the force acting on the opposite side of the rod F2 = (π* d^2 / 4)* P2 ==> (3.14*2^2/4)*2500 ==> 7853lb
Meaning a 2.5"dia cylinder will produce 12271lb!!

And then you used the 7850lbs * sin(7.5ｰ) = 1024lbs. Got it so far. I didn't get the argument that the cylinder is half way back, but there is so much waste anyway
The actual angle in the 2nd design is 10.79ｰ, resulting only 1470lbs at the closing end with 2500lb at the opening place (18.67ｰ). still not good.

I was struglling figuring out why the length of the rod is important as its not included in the calculations but I got it.

So it looks like I have to find a balance. Larger bore, means more force, but slower acting cylinder, while larger rod can achieve more applied force but also takes more time to full extend/retract.

What is an acceptable clamping force? (Don't tell me it depends what I want to use the grapple for!!! I know that! Considering that a compact tractor cannot lift more than 1800lbs on the front pivot, does the target of 2000lbs sounds good enough?

These formulas are really interesting, I will stay up tonight to finish that!
These are the CAD files that I am making on Freecad 0.17 if you want to see them. You only need the "Master CAD" file if you do not want to edit. This is just temporary, the final will go to the GrabCAD

Quick question: These are the hydraulic specs of my tractor. Which number do I use for the calculations? The total flow (13.7) of the implement pump (8.2)??
Implement pump (gpm): 8.2
Steering pump (gpm): 5.5
Total flow (gpm): 13.7
Category, 3 pt hitch: CAT 1
Hitch Lift capacity (lb): 1,808
Lift control type: Manual

 

[polemidis]

Nicely stated.

No offense intended in this statement. All designers need to also be operators/fabricators.

I totally agree!

 

[LD1]

The comment about the rod half way down the lid....

The lid is a simple class 3 lever. ( Google that)

It has a fixed pivot, a point at which force is applied (where rod connects), and the teeth.

You are applying 1024# of force at a point roughly half way between the teeth and the pivot. That means the teeth are gonna have roughly half the force.

Get to around a 20 degree angle and I thin it will be fine

 

[texasranger556]

Use the implement pump numbers. The other pump is usually just for steering and transmission charge if it's hydro.

 

[LD1]

Why do you need pump flow for any calculations?

 

[texasranger556]

Cycle time...

 

[ovrszd]

Cycle time...

Yeah, that's how I took your comment. As well as clarifying which flow rates he needed to pay attention to.