Grapple Design Ideas

[WhiteRock]

I am designing a grapple/rake bucket for my tractor (Kubota M9000, FEL LA1251A). The doesn't matter, but it will give folks an idea where my thoughts are coming from. Yes, I could buy one, but I wanted to design and build one.

I started this thread for design discussion (in the event any folks are interested) and to not hijack other project progress discussions

I am currently working on the rake/bucket portion and doing the grapple arm and hydraulics design in my spare time (near 0).

I am not as skilled as the TBN'er here so I have to design and draw. But I enjoy that. I am drawing in a way that I can post on the web. I do not have the skill to totally engineer a grapple, but you never know what one can learn here. I might before it is over.

I have done some work on the geometry of the grapple arm and cylinder pivot locations. I wrote a simple spread sheet to allows me to plug in placement values and it will compute my cylinder stroke. If there is interest I can try to post what I have.

Additions I intend to add to the spread sheet are:
- specify open close angle, have it compute stroke
- specify cylinder diameter and psi, have it compute closing/open force
- other associated grapple design info

Currently I would like to dig up some mechanical physics concepts and compute the pinching force of the grapple while being pushed by a cylinder at an angle.

If this stuff is already out there, maybe I just need pointers.

I will stop here to see if there is any interest in this sort of thing. I just thought it might generate some interesing ideas and reference material for build-it-yourself grapple folks.

 

[DanR67]

WhiteRock -

Reading your post and the other recent grapple post got me thinking "lever calculator"...one google search later - first hit:
Engineers Edge There are 4 different lever calculators - if you go searching through the site there are also hydraulic calculators, and info on types of weld joints! What a great site!

I have been toying around with the idea of a "compound lever" system to change the lever relationship between cylinder stroke and grapple jaw opening (angle) - but nothing firm yet. I am somewhat familiar with this concept because the plastic processing equipment I work with has (toggle-) lever mechanisms.

I'm planning on making some scale "2D" lever models using cardboard cutouts and varying the hinge point distances to get a feel for the required cylinder stroke - or better said: cylinder / hinge placement to get the necessary grapple jaw opening angle. I'd be interested in any lever calculations you had worked out to help with my first draft.

As far as hydraulics go - I simply have a beefy 3" bore / 6" stroke hydraulic cylinder already purchased - if I can use the "big side" of the piston for making the closing force (at the expense of *speed* - which isn't an issue for me) - I don't think I'll have anything to worry about - other than to make sure the grapple can endure pressing against the stops! /forums/images/graemlins/grin.gif But then I think the hydraulic / force calculations are fairly easy.... /forums/images/graemlins/wink.gif

Hoping to get started cutting steel (have some 1 1/2" x 3" x 1/4" rectangular tube that I'm thinking of for the grapple "fingers" - I also have some HEAVY 2" x 1" flat stock - I'm thinking of making the hinge assembly out of the heavier flat stock - and then make two sets of "fingers" that could be removed simply by pulling a pin - the rectangular tubing slides almost perfectly onto the flat stock!

I'd like one heavier set of grapple fingers for lifting rocks, logs and brush - and another set with sort of a coarse mesh / screen (3" x 3" grid") that I could use to sift rocks and other debris from soil and compost.

Looking forward to seeing what everyone is brewing up! /forums/images/graemlins/grin.gif

Dan

 

[WhiteRock]

Good stuff already. /forums/images/graemlins/cool.gif

That is a big cylinder. For the 7610, I believe your hydraulics are about 2,000 psi max. That would give you around 14,000 lbs of force. The actual pinching force will be much less with the levers in the closed position. I plan to add this math to my spreadsheet.

I would recommend your design allow you cylinder to fully extend and contract. I think this is better for your implement.

Even with a 3" cylinder, I would be surprised if you have any speed problems. I know some folks have had to add restrictors to slow the operation down. I think they may be using smaller cylinders though. There is another idea. It should be easy to add the open and close times to the spreadsheet as well.

I don't know how much pinching power a grapple should have. I have seen some hold pretty heavy stuff hanging out the bottom of the grapple (WR Long I think).

I have thought about the compound lever as well. It would be neat if a design would allow the grapple to fold into the bucket out of the way, or ...

 

[WhiteRock]

I did a little more work on the spreadsheet tonight. I am including the following picture in the spreadsheet in an attempt to make it more usable. I am not a great spreadsheet writer.

I am setting it up to allow entry of distances by letter to letter (A-B, B-C, etc.) and various information will be calculated.

None of this math is particularly complicated, but hopefully this sheet will collect a lot of the math necessary for various hydraulic projects. It is causing me some thinking cramps to set the formulas up to work in anyplace someone wants to put a component.

Currently computing:
- cylinder push and pull force, oil capacity, extension and retraction speed
- cylinder length and stroke to open and close grapple
- grapple pivot placement
- cylinder pivot placement

Work in progress:
- Expanding angles that the grapple can open and close
- grapple load pinching force
- grapple bucket pinching force
- grapple pinching force at specified angle

Anything else I should compute?

 

[jmc]

Whiterock,

Seems like most of the forces are going to change as the jaw position changes. Are you going to calculate those as a function of opening distance and possibly plot them?

The maximum open dimension may be more useful than the maximum open angle.

You may want to confirm that @ max opening, the movable jaw can still touch the ground for back dragging when you uncurl the loader.

Its interesting to see how different TBN people approach the same problem. One guy will do it this way (my tendency) while the next guy will build it, tack it, try it, relocate it...

John

 

[WhiteRock]

Yes the forces will change with the jaw position. I had planned to allow the entry of position and show the force. It would be easy to display a table of positions. Its not to difficult to plot as well. I am just worried about making the sheet to complex. I am a low level system programmer and not good with GUI's. Good idea though, I will try to add it. I think folks might be surprised at how these forces change.

I can also add the maximum open dimension. Another good idea.

Confirming the grapple will touch the ground is an interesting one. I will be asking for user input for the vertical dimension of C-E and maybe horizontal dimension of C-E (picture above). Since I expect the user to design the frame, it can be put at the location of choice. I will just help with cylinder choice and forces. This may be all backward...??

It is interesting to see the different approaches. I was amazed with my initial spreadsheet as to how easy it was to manipulate the positions and avoid a big wart on the top of your grapple. This is why I wanted to share it. With all the different ways to do it, it may be more work that I can do. But I am going to give it a try. I will learn something....

 

[DanR67]

WhiteRock -

KubotaBillys pics in the other thread helped me clarify the general location of the hydraulic cylinder mounting - I took a look at my FEL this morning and I don't see any clearance issues (I had originally thought of mounting "behind" the bucket to protect cylinder - way too complex / low on clearance).

I made a quick sketch (attached) of what I have in mind:

- 1" x 2" bar stock will be used for the "hinge" mechanism that the cylinder mounts to, and to in turn - create the jaw opening / closing movements.

- 1 1/2" x 2 1/2" x 1/4" rectangular tubing will be use to fabricate the "jaws" of the grapple. Reinforcement plates / gussetts will likely also be 1/4".

The basic concept is that the hinge mechanism will have two male posts (1" x 2" bar) that will slide into a female receiver (1 1/2" x 2 1/2" tube) on the grapple jaw itself. The grapple jaws and posts will be cross-drilled to allow for a quick-release fixing pin attachment - so that the jaws can quickly be removed - or more importantly - alternate jaw configurations - could be attached.

Initially, I plan a simple, "two-claw" grapple - to be used for moving some brush piles, logs, and mid-sized rock landscaping placement.

I took some pics this morning also - I'll post them later today while at work - but the fit between the bar stock and the tubing is nearly perfect! /forums/images/graemlins/laugh.gif

Hope that helps....

Dan

 

[WhiteRock]

DanR67, nice drawing! That sure is a quick way to convey you ideas.

Here are some alerts to me that I would like to here your thinking on:
- I think a 3" cylinder is way to big for a B7610
- Your high cylinder mount is worrisome and problematic, I think
- Think grapple weight.

I have a B7500, so I think I understand what you are working with. I don't have the hydraulic relief valve pressure here, so maybe I can get it when I get home.

I think a 3" cylinder will "beer can crunch" you bucket and equipment. If you don't already have your cylinder, I would look at something like a 1" cylinder that is short. I will be lighter, easier to work with, and probably pinch all you can pickup. It is good for over a 1,000# extension force.

If you already have the cylinder and must use it, I would consider an adjustable relief valve in the circuit.

The high cylinder mount will increase your exposure to cyl damage. If you are interested, I can propose some placement numbers that will keep the cylinder close. Then you can build a cover over it for protection. This will prevent damage in the event you are ever tempted to close the grapple and push into a pile.

I am not sure, but you may be over designed on strength. We don't have to fly, but excessive weight will tax your implement performance. If the cyl size is reduced, you don't have to worry as much. I had rather bend my grapple that my bucket. I know I tend to design around the materials I have.

I think you will need some kind of reinforcement bar on the top of your bucket.

Good stuff, I will try to think some more about this. Your ideas may work just fine. This is just some of my input for what it is worth.

 

[DanR67]

WhiteRock -

I understand where you are coming from and am in agreement with regards to the 3" cylinder - it is definitely "overkill" for grapple needs.

Having said that - I purchased it last fall along with another 3" x 6" cylinder. The 3" x 6" ended up working out better for me as my 3PH Tilt Cylinder - I thought the 8" stroke would have gone there.... I was just trying to get the shortest - but beefiest - cylinders.

So....yeah this cylinder really is overkill - I was thinking about adding a pressure relief / limiting valve also to keep the forces in check. At full pressure - I would worry about A) tearing the hinge assembly off the back of the bucket or B) "beer can crushing" the bucket as you put it. One way I intended to prevent that would be to have the piston bottom in the cylinder before the claws if the grapple touch the front edge of the bucket...just by playing aroung with the lever geometry.

As I said in my last post - my first grapple is for brush, log and rock moving. The rock moving is what I'll probably get the most use out of - at least initially: brush moving (hopefully) is a once or twice / year affair.

Having moved the "raw steel" around this morning - and throwing in the weight of the hydraulic cylinder - I'd guess that the entire grapple mechanism will add @ 125 lbs to the FEL weight - not an issue for brush and most logs - and I think I should be OK with all but the largest rocks.

Specific to rock moving - I don't think I need that much "force" to hold a rock in the bucket / grapple - I just need enough force to "hold it in place."

I know what you mean about the cylinder mount - Kubotabillys' solution is nice from an open / close geometry standpoint - but the forces that get generated will be *interesting* to tame. That's why I made the note in the sketch I attached: cylinder mount design not completed! /forums/images/graemlins/grin.gif

Finally - I've attached a pic showing the nice fit between the 1"x 2" bar stock and the 1 1/2" x 2 1/2" tube stock - plus a pin for reference. I'm thinking 8-10" of engagement between the two pieces should provide the necessary support to prevent the "claw-tubes" from folding (assuming of course, that I get my big cylinder force under control! /forums/images/graemlins/wink.gif )

I'm still chewing on ideas....but having someone else going through the same exercises is definitely a help! /forums/images/graemlins/cool.gif

Dan

 

[WhiteRock]

DanR67,
That does fit nice. I like that. I think that will work out well for you. You may find all sorts of things you can do with that attachment.

I like your toplink too. I have never noticed a bar being used like that on the tractor side. Neat.

A little clarification on the crushing issue. I think the design should be done such that the cylinder bottoms just as the arms snugs up tight. This still will not prevent the item you pick up (non-compressible like a log) from crushing your implement. So, IMHO you must have strength to use the tractor's relief valve or add a lower pressure one on the cylinder.

I wonder if you could use a 4 x 3 piece of angle iron attached to the top of the bucket's folded lip. Put the 4" inside the bucket. Put your grapple pivots on the 3" vertical side. Build your rear cylinder support on a plate that bolts on the back of the bucket and through to the angle iron along the top. If the 3" cyl strength is controlled, that should be strong enough and give a very low profile. The next time I am by the B, I'll have to look and see if I think this will work. This is all probably as clear as mud. /forums/images/graemlins/confused.gif /forums/images/graemlins/smile.gif

BTW: I think 125# is a reasonable weight.

Another note, you get better open/close geometry with closely mounted pivots. When you spread them apart, it limits how much you can open. Not good in my opinion.

Good stuff, hope you don't mind my opinions...