Grapple project OPEN SOURCE
- Thread starter polemidis
- Start date
Also, look up "sum of moments around a point".
You will mostly be avoiding having to get into "beam bending moment and shear diagrams" by copying existing designs, building them, and fixing what breaks. And the lessons stick better.
You will mostly be avoiding having to get into "beam bending moment and shear diagrams" by copying existing designs, building them, and fixing what breaks. And the lessons stick better.
I'll assume you simply misquoted. The distance between the pins isn't the problem exactly. I'll let you correctly describe what needs changed.
Sorry guys my English is not my mother language. I mean I will increase the distance between the base pin and the pin that pivots the grapple. So the force will by applied with bigger angle.
Or in other words I will increase the distance between the pivot point and the l line that passes between the cylinder pins. Did I pass the test??
I know that my lack of knowledge gives you comfort (I am just joking), but I do not qualify not even as a user yet (21hours on a tractor in my lwhole life
, and definitely not as a designer!!!! Been able to press the buttons to draw lines in the CAD does not make me a designer!! Btw, what is a desent clamping force in a grapple that a 40hp tractor should have? I will do the calculations (Middle school physics if I recall!!!!) to get that force
ovrszd
Epic Contributor
- Joined
- May 27, 2006
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- 32,195
- Location
- Missouri
- Tractor
- Kubota M9540, Ford 3910FWD, Ford 555A, JD2210
I'd rather let LD1 explain this, he's much better versed than I. I tend to talk in layman's terms. But I'll give it a go and he or others can feel free to add what I miss.
My point about the amount of cylinder stroke to open/close the claw has little to do with the distance between the two cylinder pins in one position. But it has everything to do with the difference in distance between the cylinder pins when the claw is open versus that distance when the claw is closed.
Here's where I fail verbally. Any tractor has a given hydraulic capacity. That's determined by GPM (gallons per minute) of flow and PSI (pounds per square inch) of maximum pressure. To result in greater force the amount of fluid required to complete the action needs to increase.
This can be accomplished in two ways. Increase the bore diameter of the cylinder or increase the distance of cylinder travel to complete the action. You don't have space for a large diameter cylinder. So you must design the triangle mentioned above to increase the cylinder travel length. Your design of 4" cylinder travel to complete the action isn't enough when using a 2" or 2.5" bore diameter.
My homemade grapple has nil clamping force when the claws are wide open. That clamping force increases dramatically as the claw closes peaking in the last inch of movement. I wasn't smart enough to design that into the plan. It just happened that way. If that situation were reversed my grapple would be worthless. I use 8" of cylinder travel.
My point about the amount of cylinder stroke to open/close the claw has little to do with the distance between the two cylinder pins in one position. But it has everything to do with the difference in distance between the cylinder pins when the claw is open versus that distance when the claw is closed.
Here's where I fail verbally. Any tractor has a given hydraulic capacity. That's determined by GPM (gallons per minute) of flow and PSI (pounds per square inch) of maximum pressure. To result in greater force the amount of fluid required to complete the action needs to increase.
This can be accomplished in two ways. Increase the bore diameter of the cylinder or increase the distance of cylinder travel to complete the action. You don't have space for a large diameter cylinder. So you must design the triangle mentioned above to increase the cylinder travel length. Your design of 4" cylinder travel to complete the action isn't enough when using a 2" or 2.5" bore diameter.
My homemade grapple has nil clamping force when the claws are wide open. That clamping force increases dramatically as the claw closes peaking in the last inch of movement. I wasn't smart enough to design that into the plan. It just happened that way. If that situation were reversed my grapple would be worthless. I use 8" of cylinder travel.
LD1
Epic Contributor
Do the math with the angles I mentioned, and try to get as long of a stroke as possible.
Think of it this way......It dont matter if you use a 4", 6" or 10" cylinder.
The distance the grapple must travel from full open to full closed is gonna be the same. So if that given distance can be accomplished with a 4" cylinder.....you have a clamp force of x.
If you can squeeze a 8" stroke cylinder in there of the same bore diameter (same hydraulic force acting on the grapple) You have essentially doubled your mechanical advantage. So thats like going from a 2" cheater pipe on your wrench to a 4' cheater and still applying the same force.
If you look at your design and draw the triangle....it looks like maybe a 7.5 degree mounting angle for the cylinder looking at the second drawing. I am sure you can confirm that with the software you are using.
Most grapples us a 2" bore cylinder, and most tractors run ~2500psi. So that cylinder is capable of pushing with a force of 7850 lbs.
But that cylinder mounted on a 7.5 degree angle....only ~1000 lbs of force trying to close the grapple.....the rest of the force is trying to rip the whole thing apart. Now since the cylinder mount is about half way back the grapple lid....you can cut that in half yet again. and you will have a meager 500# of bite force. Is that enough to "contain" a log or some brush....sure. Is that enough to clamp a rock or clamp anything and actually rely on the clamp power to hold.....absolutely not.
Think of it this way......It dont matter if you use a 4", 6" or 10" cylinder.
The distance the grapple must travel from full open to full closed is gonna be the same. So if that given distance can be accomplished with a 4" cylinder.....you have a clamp force of x.
If you can squeeze a 8" stroke cylinder in there of the same bore diameter (same hydraulic force acting on the grapple) You have essentially doubled your mechanical advantage. So thats like going from a 2" cheater pipe on your wrench to a 4' cheater and still applying the same force.
If you look at your design and draw the triangle....it looks like maybe a 7.5 degree mounting angle for the cylinder looking at the second drawing. I am sure you can confirm that with the software you are using.
Most grapples us a 2" bore cylinder, and most tractors run ~2500psi. So that cylinder is capable of pushing with a force of 7850 lbs.
But that cylinder mounted on a 7.5 degree angle....only ~1000 lbs of force trying to close the grapple.....the rest of the force is trying to rip the whole thing apart. Now since the cylinder mount is about half way back the grapple lid....you can cut that in half yet again. and you will have a meager 500# of bite force. Is that enough to "contain" a log or some brush....sure. Is that enough to clamp a rock or clamp anything and actually rely on the clamp power to hold.....absolutely not.
Even the best calculations can steer you wrong. Sometimes you just have to cut metal and see what happens.
For example, here is the original version of my garden tractor front loader:
Here is the redesign I came up with later:
Both versions used scrounged cylinders in nonstandard sizes. One has far fewer parts and weighs 70 lbs. less. This is also why I say sometimes you throw away half your materials. Sometimes whole parts of your design have to be cut off and set to one side.
70 lbs. at the far end of the loader boom makes a lot of difference to the operating performance of the machine. For both, the calculations on the range of motion and dump force on the actual bucket were correct. It is not always the things you measure and calculate that will be a problem, but aspects you did not even know to consider.
Sometimes what breaks won't even be on the parts you make. (my loader is now on a heavier tractor, and has had yet other things fixed and modified)
For straight out saving money and getting the job done, though, this was the actual best solution:
I finished building my machine because I am stubborn, and it was fun (for me, not everyone finds this type of design iteration work fun).
Have you had a chance to watch videos of people using a grapple to do what you are thinking of doing?
For example, here is the original version of my garden tractor front loader:
Here is the redesign I came up with later:
Both versions used scrounged cylinders in nonstandard sizes. One has far fewer parts and weighs 70 lbs. less. This is also why I say sometimes you throw away half your materials. Sometimes whole parts of your design have to be cut off and set to one side.
70 lbs. at the far end of the loader boom makes a lot of difference to the operating performance of the machine. For both, the calculations on the range of motion and dump force on the actual bucket were correct. It is not always the things you measure and calculate that will be a problem, but aspects you did not even know to consider.
Sometimes what breaks won't even be on the parts you make. (my loader is now on a heavier tractor, and has had yet other things fixed and modified)
For straight out saving money and getting the job done, though, this was the actual best solution:
I finished building my machine because I am stubborn, and it was fun (for me, not everyone finds this type of design iteration work fun).
Have you had a chance to watch videos of people using a grapple to do what you are thinking of doing?
I only know practical application. They know "why".
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.
