Yet another grapple project

[davesisk]

OK, I finally got started on this for my old PT1418. The 6' stack of tree limbs and trunks in my back yard after our recent ice storm was the motivation.

Initially, I was thinking of making a really simple grapple attachment that was fixed to the lift arms. You then close the bucket against it. However, it occurred to me that the lift arms actually swing through quite a large angle (like around 90 degrees), so if the fixed grapple were positioned so that there was ample room to close the bucket against it when the lift arms were down, then it would be opened 90 degrees when the lift arms were raised, and vice versa.

I really didn't want to go to the trouble and expense of plumbing in another cylinder, valve, and hoses, so what I've done is designed this grapple attachment almost like an upside down bucket (ie. the same curl pivot point, and a mirror image of the lift pivot point). Essentially (if it works the way I intend after I'm done), when I uncurl the bucket the grapple will open, and when I curl the bucket, the grapple will close against it. I'll post some pics (and maybe even an MPEG) when it's done, which should be possibly today, perhaps tommorrow. Keep your fingers crossed that I haven't made some glaring error in it's geometry!

Dave

 

[MossRoad]

We want VIDEOS!!! /w3tcompact/icons/laugh.gif

 

[Anonymous Poster]

Sounds /w3tcompact/icons/cool.gif and frugal...
We're waiting /w3tcompact/icons/eyes.gif...

 

[waterglyn]

where are the pics?

 

[davesisk]

Patience, my PT friends, patience.../w3tcompact/icons/smile.gif. I finished fabricating the stuff tonight. I've drilled the holes in the attachment where it will hook to the lift arms, and I've got it clamped on the tractor now. I'll drill matching holes in the lift arms probably tommorrow afternoon (I've to crank it up and verify I've got the placement right before drilling, and the neighbors wouldn't appreciate it at 11pm at night...)

It's fairly "light-duty" compared to the PT grapple buckets, but it should suffice for my needs. Plus, since I have to hoist it up onto the lift arms and hold it to put the clevis pins in, I wanted to keep it reasonably light weight...probably should've used square tubing rather than the angle stock I used, but too late now!

I'll warn you ahead of time, it ain't the prettiest thing you'll ever see...but unless I've made some glaring engineering mistake it should work reasonably well.

I'll do my best to post pics and an "operational MPEG" tommorrow...

Dave

 

[davesisk]

Just as a side note, I used an 85 amp 115V stick welder to do all the welding. I was previously using a so-called "gasless MIG" (actually, FCAW, a wire-feed welder that uses only flux-cored wire, a $150 "EasyMIG"), and it's welds are ugly as h*ll AND often don't penetrate well. Didn't appear to be a problem with this little inverter-based stick welder. I actually bought it along with a 90 amp TIG torch to try out it's scratch-start TIG capabilities (I've been looking for a good used DC/AC-squarewave TIG unit for several months, but folks don't seem to ever sell the good ones. I'm really looking for an ESAB Heliarc 161 AC/DC or an HTP Invertig200, if anyone happens to know of a used one for sale at a good price!) Anyway, it's TIG capabilities are just a tad less than satisfactory for what I want (limited duty cycle keeps it in cool down mode half the time), but I was quite surprised how powerful 85 amps is with a 6013 stick electrode. It's still an ugly weld, but not nearly as ugly as the FCAW wire-feed welder, and the penetration is really good even with that small amount of power. Plus, I could see what I was welding much better than with the MIG gun, AND there's no moving wire-feed parts to stick/break/slip/wear/need adjustment/etc. I think I really like stick. Since all TIG machines will also do stick, now I've just got to find that TIG welder at a good price. They're not cheap (like $1K+), but I have a feeling that I'll probably keep it the rest of my life. (I'm returning this little stick unit and the TIG torch, even though the total deal was < $300, it's wasted money if it doesn't do what I need...)

Just thought this might be worth sharing. Welding is one of my other hobbies, although not necessarily one that I'm all that skilled at!

Dave

 

[davesisk]

Grapple pics

The open view

 

[davesisk]

Re: Grapple pics

The closed view...

 

[davesisk]

Re: Grapple pics

A close-up...

 

[davesisk]

Re: Grapple pics

Another closeup...

 

[davesisk]

Design flaw

Btw, I tried to post an MPEG video clip, but it's too large...

There's a design flaw in this contraption that I didn't consider. The bucket is self-levelling (when you raise the lift arms, the geometry of the lift arms and curl arm are such that the bucket stays parallel to the ground). The grapple is based on an upside down mirror image of the same geometry, so when you raise the lift arms the grapple opens and vice versa. However, it has enough motion about the pivot point to still be useful for what I intended, I just have to compensate by changing the bucket curl when raising or lowering the lift arms.

I can't think of a mechanical fix for this. I think the best way is MossRoad's design that uses the additional hydraulic cylinder (just like the PT grapple bucket).

Enjoy the photos, and let me know if you have any suggestion about where I could post the MPEG's (largest is about 550KB, other two are around 300-400KB).

Dave

 

[MossRoad]

Re: Design flaw

HOLY COW DAVE!!! /w3tcompact/icons/laugh.gif

How did you figure out the geometry?

Private e-mail me here at TBN and I'll give you a different e-mail address to send me the MPEGs and I'll post them at my web site until I run out of space or you find a differnet host.

Cool!!

 

[bubenberg]

Great job, and allot cheaper than my pt grapple. on suggestion i have is to add an angle iron of your choice, mine was bedframe size, to the front of the teeth, if not they will bend every which way. additionally the angel iron will help you grab more firmly on to your debris. logs etc

 

[davesisk]

Hans: Good suggestion...actually, I made the forks out of 1/2" rod so they would be springy (just in case I encountered a "design flaw".../w3tcompact/icons/smile.gif).

Dave

 

[davesisk]

Re: Design flaw

My email address is davesisk@ipass.net...

 

[davesisk]

Re: Design flaw

MossRoad:

<font color=red>How did you figure out the geometry?</font color=red>

Essentially, the only important pieces (to my thinking) where these:

1) the pivot point of the grapple needs to be on the same vertical line as the pivot point of the bucket.

2) On my bucket, the point where the curl arm connects is 6 vertical inches from the bucket's pivot point (ie. where the lift arms connect). So, the curl connection on the grapple needed to be 6 vertical inches below it's pivot point to get the same leverage and speed but opposite direction.

Of course, as I stated earlier, this ignores the fact that the bucket is self-levelling, so the bucket curls down by geometry when you raise the lift arms, and vice-versa. So, this means that the grapple curls up at the same speed when you raise the lift arms, thus the design flaw.

This would have been a case where some sort of mechanical design/solid modelling tool would have been really helpful to design it detail first. (I was pretty much working from a mental picture.) I've got a copy of AutoCAD, but you (AFAIK) can't "animate" mechanical parts without some pretty fancy and expensive plug-ins. I have copy of something called FreeCAD that lets you do that animation (plus other solid modelling analysis) with basic geometric shapes (freeware), but I couldn't figure out how to use it (it documentation is pretty much non-existent) and it doesn't appear to support drawing solid to specify dimensions...? Something in between would be really nice....if you know of anything (particularly freeware or shareware, please post it!)

Dave

 

[MossRoad]

Here's a link to Davesisk's grapple video.
<A target="_blank" HREF=http://users.beanstalk.net/godollei/pt425/othertractors/grappledemo.mpg>Right click here and choose save target as,</A> then save it to your PC and watch it there.

Gotta say, pretty cool, Dave /w3tcompact/icons/smile.gif

 

[Anonymous Poster]

Re: Design flaw

davesisk,

Is geometrician a word?...I hope so, 'cause I think you're one.../w3tcompact/icons/smile.gif

Just slap some black paint and a Pat.Pend. sticker on it and you're finished.

That baby will work way better than teenagers/w3tcompact/icons/smile.gif

 

[davesisk]

Re: Design flaw

He he...don't do this at home! (In other words, stick with MossRoad's design, it is the more conventional idea and will work much better.) This will do, until I get the gumption to plumb in another cylinder and valve, though...

 

[Spencer]

Re: Design flaw

It may not be the conventional way to do it but it opens and closes. I say you get an "A" for effort. Some sort of grapple is better than no grapple at all. Thanks Mossroad for making the mpeg available to us.