2lMan
Brewer, ME
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To quote Tim...
Exactly! The force must be applied in a direction that complies with the tightly restricted elliptical-like path of the linkage in order to get it to move. Any other direction and/or combination will be met with incredible resistance, making many conclude that it is "locked" or rigid. It's not, but good luck ever getting a trailer to apply force and direction needed to pivot the hitch
Tim,
I believe that this was similar to what I spoke about a few posts back, likening the Hensley's "eliptical" (your word, and you explained it better than I) to a motorcycle swingarm suspension. Remember, the swingarm follows the same direction as the obstacle in the road.
Without following the same direction, it must overcome incredible force. The swingarm still can pivot, however, much more force is required. This would be followed if you were going on a motorcycle very fast in reverse and hit a bump. The arcs are in opposite directions, and would tend to resist movement.
So, I would venture that this resistance in movement would render the connection "virtually solid." Even though movement might be possible, the amount of force required to overcome this would probably be enough to destroy the TT.
2003 GMC Yukon XL 2500 8.1L 4.10 Axle - 2002 Sprinter Quad Bunkhouse
Home is where you bring it!
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ttsr4us
Florida
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Joined: 10/17/2003
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Just to be clear, I can move my hitch, the non orange bit which the stinger docks into, from the TV end with the stinger in place but not attached to the TV. It rotates and moves in an eliptical path. Also the angle of the hitch relative to the TV can also be changed. But you have to push rather than pull.
Brian and Esta
previously 2 Trailers and 2 Motorhomes, back in the trailer game.
GMC Sierra 3500HD 2WD, SLT Crew Short Bed. Duramax. 2014
Airstream 2016 Flying Cloud 30 RB with 2 a/c + Window Awnings
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Stressor
Whitefish Bay, Wisconsin
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![[image]](http://home.ripway.com/2005-1/238631/Folder%20Name/Hensley.JPG)
![[image]](http://home.ripway.com/2005-1/238631/Folder%20Name/Hensley2.JPG)
![[image]](http://home.ripway.com/2005-1/238631/Folder%20Name/Hensley3.JPG)
And that is how it works. No magic at all. ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/biggrin.gif "biggrin")
Milton Findley (and Kerene)
A small piece of my mind...
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BurbMan
Indianapolis, IN
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Ok, if Milt had posted this last week, this thread would only be one page long.....looks like he's got it figured out. When does that patent expire????
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tluxon
Kirkland, WA
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Thank you for chipping in, Ron. You're absolutely correct about the direction of the force vector being critical. Thinking of the boy in "The Sword and the Stone", it wasn't how hard he pulled that got the sword out of the stone, it was the direction he applied the force.
If anyone has watched their Hensley in action they would note that it translates significantly from side to side on even very slight angulation between the TV and TT. If anything is done to keep it from translating through its restricted path of freedom, it will appear to be - for all intents and purposes - locked up. When either end of the hitch is securely attached to a fixed object (stationary vehicle), the linkage at that end is NOT free to move and all the other parts of the hitch will have to move differently to accommodate that restriction. When a TV/TT combination is at speed, however, the attachment at either end of the hitch is only anchored down as much as the rolling friction of the tires and the inertia of the vehicle force it to be. That's why I introduced the hockey puck on ice analogy. Given just the right amount of freedom (lack of anchoring) and the perfect direction and force of input (inertia or otherwise), the Hensley will allow an angle between the vehicles. When that degree of freedom (extremely low friction, etc.) is reached, it won't matter whether the TV or TT initiated the motion, the angle will still be generated, some of the required translation occuring at the TV end and some of it at the TT end. All the while there is no change in the angle of the tees formed by the TV and the "front bar" of the linkage and the TT and the "rear bar" of the linkage.
Another thing you can do to observe the interactions between each linkage "end bar" is to have someone drive straight slowly and then begin to initiate a turn. You will note that when the TV turns one way (translating the front bar tee), the front of the TT (rear bar tee) simultaneously moves off-center significantly to accommodate a change in angle between the TV and TT. If you remember the little video I linked to a few days ago, you will remember that it translated from rotational inputs on each of the "end bars", as long as the opposite end bar was given freedom to move. That is why I claimed that the hitch could be reversed (provided the necessary attachments could be made) and still allow the TV to turn the TT.
Tim
Tim -
wife Beverly & 2 boys who love camping
2002 K2500 Suburban 8.1L 4.10 Prodigy
2005 Sunnybrook 30FKS HP Dual Cam
Replaced 2000 Sunnybrook 26FK on 8/6/04
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tluxon
Kirkland, WA
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Stressor wrote:...images...
And that is how it works. No, no, no. I'll explain later today.
Tim
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Ron Gratz
full time RVer
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Stressor wrote:
The diagram is meaningless unless you specify some point of fixity. Lets assume that A-C and B-C are pinned at C. Then, if you push UP at B, without any lateral restraint at B, B-C would simply rotate clockwise about C. There can be no lateral force applied at C unless there is a corresponding lateral force applied at B.
Quote:
Again, the diagram is meaningless unless you specify some point(s) of fixity. If points D and E are fixed in space and length A-B is constant, then pushing UP at B would cause the following:
1. B-E will rotate CCW about E, causing B to move right and forward.
2. A must remain at fixed distance from B, so A moves right and rearward. A-B rotates CCW.
3. A-D pivots CCW about D.
The linkage is not "locked". D-E is fixed in space and all three other links are free to simultaneously translate and rotate.
Quote:
Another meaningless diagram. Point C is not the Virtual Pivot Point. The VPP is the point of convergence for one line projected through points A and D and another line projected through points B and E.
Sorry, Milt, but your depiction is NOT how it works.
Ron
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tluxon
Kirkland, WA
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Milt, in your first image you made the statement,Stressor wrote:Hooking a come along to between point B and a Willow tree would result only in a lateral load being applied at point C. This is not correct. Since you can't move C without trying to shorten or lengthen segment AC, there is also a vertical component to the load at C.
The case presented in your second illustration is not clear to me, but if "there is no place for the force to go" for a force applied to A or B, how can there be a lateral load at C if there is no impetus for movement? Are you fixing point C or any of the lengths AD, DC, BE, or EC? Fixing either the points or the segment lengths is redundant and simply results in a truss structure.
In your third illustration you try to convert your truss structure to a Hensley analogy, but it doesn't work that way. First you sayStressor wrote:distance C-E and C-D must remain the same Since there is no physical point C, what exactly can possibly constrain those segments to be equal?
You also said Stressor wrote:C is what has been called the Virtual Pivot Point This is incorrect. Up to date in this thread, the Virtual Pivot Point has always been described as the imaginary point at which segments AD and BE would intersect if they were extended to their point of intersection. In theory, this is also termed the Instantaneous Center of Rotation. Instantaneous because no two angles between AD and BE ever intersect at the same point.
When you say Stressor wrote:In the Hensley, we do not actually extend the legs to point C, because we hold distance D-E and A-B constant it is incongruent since making segments DE and AB fixed lengths has nothing to do with enabling the omission of fixed-length segments to a point C.
Point C as you describe doesn't ever exist on a Hensley application nor is it useful for any purpose.
Tim
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tluxon
Kirkland, WA
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Milt, I'm sorry I had to disagree with the presentation you made to illustrate your point. I know it took some time and effort to put together and I want to thank you for the investment you're putting into this thread. It is certain there are others who have perceptions of how the HA works that are very similar to yours, so it is very valuable to have these types of ideas scrutinized. By the time we're done with this give-and-take I believe many people will see this hitch in a new and hopefully clearer light.
Tim
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Stressor
Whitefish Bay, Wisconsin
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Tim,
If it can be demonstrated empirically, the theory needs to accomodate what is actually happening to be a valid theory. That is what theories do.
The point of fixity when towing is point C, representing your tow vehicle with all of its mass and resistance to changing direction. Holding DE and AB to a fixed length makes them rockers in 4-bar parlance, and while C does not exist physically, except as the entire mass of the TV as it is attached at the hitch receiver, the linkage acts as if it is a rigid connection. That the legs are fixed, rigid entities to a pulling force was demonstrated by a come-a-long and a willow tree.
In operation, if a force is applied to the travel trailer sufficient to move C, the entire rig moves to the side. This is something no Hensley owner will argue.
That the links pivot as demonstrated if point C is moved, by turning a steering wheel for example, is what you are all calling translation. The links move to the side.
At approximately 30 degrees angular difference between the TV and the TT, the links are fully extended, translated if you will, and continued turning beyond that causes the links to rotate until they run into themselves at about 75 degrees TV/TV angular difference in the real world.
There ain't no magic.
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