Rotating Lunette (1 Viewer)

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It was a true pintle connected to a reciever. I was backing up, cruiser was level, trailer was jacknifing up a hill. when i tried to go forward trailer didnt straighten out . That was because it had bound up and bent 1/2" thick steel that the pintle was attached to as well as bending the attachment point of my reciever hitch. trailer acted as a huge lever. I really dont care if you agree or disagree. I field tested the rotating lunette and this happened. I have read that it also happens in some multi-axis hitches. MrPepper was there. Take it for what its worth. My opinion is worth what you paid me for it. :flipoff2:
CIMG0185%20(2).jpg
DSCF0598[1].jpg
 
Easy there, all that I said was that I couldn't imagine how it could happen in my head. My plan to try to figure it out with the real parts got derailed, but I can see exactly what happened from your pictures.

Seems to me that some simple limit tab(s) on the pintle could prevent that from happening again w/o reducing the useful range of motion in the coupling. I think that I'll try to have a look at that tomorrow evening. Hopefully that won't get derailed too.
 
The pintle limits twist to ~45 degrees when everything is in line, but there is no limit to the approach/departure angle of the trailer. To visualize the problem, turn the lunette 90 degrees to the pintle (as if trailer was jackknifed) and try to push the pintle with the side of the lunette. That is essentially what happens when you back a trailer up in a hard turn. The axis the lunette rotates on will want to get ahead of the "axis" of the pintle around the lunette by rotating the lunette 180 degrees either over or under the pintle.
 
On my pintle anyway it can't go over the top because the gate is too big to fit thru the lunette very far. Under the pintle is a different story. Right now I'm thinking that a simple, robust tab welded to the underside of the pintle that would stop the lunette from being able to get it's axis of rotation forward of the "hole" that the lunette rotates thru the pintle in might prevent a next occurrence.
 
That sounds like a reasonable solution, and easy enough to implement. Just make sure that the lunette can't rotate so far that when you go to pull forward and straighten things out the lunette will always want to rotate back into the correct position. Also, the tab you are welding onto the pintle will end up being what pushes the trailer, so make it beefy enough to do that and you should be fine.
 
Got the chance before dark to hook the pintle into the lunette and rotate things around to create the arrangement that caused Volcanic all of the trouble. I verified that the lunette cannot go "over the top" due to the size of the gate, but it can go "under the bottom" and end up locked-up like the pictures above.

My idea looks like it will work. The tab would need to extend down to slightly below the point of contact with the lunette and the limiting face should be, at the closest to the vehicle, at the center of the opening in the pintle as viewed from the side. That keeps the lunette's rotational axis from ever getting directly under the center of that opening. If it can go past that point it essentially goes over-center and you'll end up with bent/broken parts.

The tab will split the pushing duty in backing up (assuming that the lunette rolls around that far) with the normal surface the the lunette is pushed by.
 
My idea looks like it will work. The tab would need to extend down to slightly below the point of contact with the lunette and the limiting face should be, at the closest to the vehicle, at the center of the opening in the pintle as viewed from the side. That keeps the lunette's rotational axis from ever getting directly under the center of that opening. If it can go past that point it essentially goes over-center and you'll end up with bent/broken parts.



Won't this try to stop the lunette from rotating far enough in an incline and then quick decline situation? Seems the tab would limit the angle between the tow vehicle and trailer as it comes over the crest and try to lift the trailer.Seems this would bend or brake something, or if it is srong enough to lift the the trailer it will come around and could cause a scary situation.


Matbe you could come up with a removable tab or stop to be used only in situations where you do not want the rotation.
 
At work, where everything is a pintle hitch setup, our Lunettes have a metal tab welded to the bottom that limits the rotation. This tab goes into a cage that limits the rotation to say about 30 degrees to prevent the above scenario from happening. I can snap pictures next week... I was wondering why your pics looked weird, like something was missing.... The cage also keeps the lunette off of the ground when not connected.

---------[[[[[[[[[[[[[[ (rotating Lunette and trailer tongue)
\---------[---- (metal tab welded to the lunette)
(Cage that limits the rotation and is welded to the tongue)
http://www.eielson.af.mil/photos/mediagallery.asp?galleryID=2384&page=64 top row picture on right and bottom row picture on the left....
 
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jagota said:
ntsqd said:
My idea looks like it will work. The tab would need to extend down to slightly below the point of contact with the lunette and the limiting face should be, at the closest to the vehicle, at the center of the opening in the pintle as viewed from the side. That keeps the lunette's rotational axis from ever getting directly under the center of that opening. If it can go past that point it essentially goes over-center and you'll end up with bent/broken parts.
Click to expand...



Won't this try to stop the lunette from rotating far enough in an incline and then quick decline situation? Seems the tab would limit the angle between the tow vehicle and trailer as it comes over the crest and try to lift the trailer.Seems this would bend or brake something, or if it is srong enough to lift the the trailer it will come around and could cause a scary situation.


Matbe you could come up with a removable tab or stop to be used only in situations where you do not want the rotation.
Click to expand...

You would have to back the trailer straight back off a cliff before the lunette would contact my proposed tab in a simple pitch angle situation. That was one of my first concerns with the design.

I don't want to limit the rotation about the centerline, the idea is that if the trailer's going to flop that it doesn't take the tow rig with it. There have been instances of exactly that happening. One on my own family involving an Airstream and a ball coupler.
 
Ok. I think I understand it more now. The tab will be much lower on the pintle than I was thinking.Enough so it can't go past a point of no return and binds up.
 
I can take some pics next week, their is another design that has steel straps bolted to the sides of the shaft to prevent pintle bind/rotation angles. Perhaps a system could be engineered so that the tabs "could" break in case of a turnover to allow full rotation?
 
Just added 4 pics of a rotation "limited" lunette to prevent the binding issues. I guess this design could be modified to allow trailer rollover without taking the tow vehicle with it with a lighter weight tab or breakaway bolts to hold it?
http://s946.photobucket.com/albums/ad306/JamesD-/FJ80/
 
I played with variations on that theme in CAD, but being an anal Engineer type I wanted something that was immediately re-usable w/o needing tools to do anything more than twist the lunette around enough that it would re-couple with the pintle (assuming that the up-righting process required uncoupling). I also didn't want to do the math to figure out how much inertia was needed to overcome such a limiter, meaning I needed a design where the "break-away" point was more easily tuned.
Does all of that matter? Probably not.....

"Shark Fin" with the root pass weld done, need to wash-weld it and get some paint on it:
IMG_0550.jpg
 
Volcanic Iceberg said:
It was a true pintle connected to a reciever. I was backing up, cruiser was level, trailer was jacknifing up a hill. when i tried to go forward trailer didnt straighten out
Click to expand...
looks to me like the pintle has too much free space
even see some plate welded in to fill ?
or maybe it's the lunette ring that is too small ?

I personally think the mismatch between the lunette and pintle
look culprit to me.

I never had any issue pulling my M100 with an appropriately sized pintle.
Pushed and pulled mine on more then a few tight rocky trails... no hint of any bind.

IMO: you either need a larger lunette ring diameter
or a smaller ID pintle hitch.

I wheel my junk off road...
trailer has got to rotate the whole 360*
not good if it's pulling my hauler over, just for a trailer save
 
The MIL 1/4t's that I've seen all have some variation on a spring loaded taper attachment for the lunette. That adds a friction brake function to the rotation. V.I.'s system doesn't appear to have that function, his looks free to rotate at will. Some rotational friction may have prevented it from happening and may not have. Push the system far/hard enough and rotational friction won't mean much of anything.

Friction braked or not, the ability for the lunette to get past center was the Root Cause. Even with my well fitting couple this could have happened so long as the lunette had any rotational ability. Basically, if your lunette can rotate you could find yourself in V.I.'s shoes.
 
this is the first time I've ever read about binding problems like this. Likely very uncommon and I kind of doubt the military would have gone pintle if there was much/any chance of this happening with their systems.
 
They don't look as good in person, and given the 1/2" thickness of the plate and the mass of the pintle I think a second, "wash-weld" pass is called for. Not too happy about how low it had to go to be effective. I'm sure that it will mark my passing when I'd rather that it did not.
 
ntsqd said:
The MIL 1/4t's that I've seen all have some variation on a spring loaded taper attachment for the lunette. That adds a friction brake function to the rotation. V.I.'s system doesn't appear to have that function, his looks free to rotate at will. Some rotational friction may have prevented it from happening and may not have. Push the system far/hard enough and rotational friction won't mean much of anything.

Friction braked or not, the ability for the lunette to get past center was the Root Cause. Even with my well fitting couple this could have happened so long as the lunette had any rotational ability. Basically, if your lunette can rotate you could find yourself in V.I.'s shoes.
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True. I am currently looking for ways to imobilize the lunet. The problem came from the lunet rotating instead of the trailer. I now have a combination pintle so I am thinking of putting a sleave on the ball that will effectively take up most of the slop in the lunet and make it so it cant rotate nearly as much. The trailer would still be able to rotate.
 
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e9999 said:
this is the first time I've ever read about binding problems like this. Likely very uncommon and I kind of doubt the military would have gone pintle if there was much/any chance of this happening with their systems.
Click to expand...

The military tends to not back up as much as most off-roaders -- unless they're French -- except with spotters.
 
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