tluxon
Kirkland, WA
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bettered wrote:That's sort of the problem. It's very difficult to discern exactly what's happening with the side links because you can almost never see them. I was running my hitch back and forth and trying to determine exactly what the links were doing when I concluded that they (being shorter than the distance between the bearings) can and do fold over each other (the lines of action cross) during the last (tightest) part of the turn. That's what gives the hitch the 165 degrees of travel.
Clearly the front and rear bars overlap at this point, but it's the action of the side links "meshing" that makes it possible.
Ed
Unless some of the links extend considerably beyond the points at which they're pinned, I don't believe the side links can ever cross over each other, or "mesh" as you say. To help illustrate my point, I put together a sketch in AutoCAD and that shows a progression of the linkage positions in different colors as the rear bar rotates clockwise. Very shortly after the furthest rotation shown is when the side bar lengths limit any further rotation.
!!!!!!!
NOTE - This image in incorrect - I'll be replacing it shortly
!!!!!!!
![[image]](http://home.comcast.net/~tbluxon/Hensley_Fig4.jpg)
Does that help?
BurbMan wrote:...I think we pretty much beat the concept of the 4-bar linkage to death. I'll go out on a limb and say that we all agree that the creation of the VPP by the linkage is the cornerstone of the HA design and largely responsible for its effectiveness. Recent conversation has largely been focused around the specifics/details of this. I was hoping we wouldn't have to linger quite so long on the concept of the 4-bar linkage either, but understanding it was at the core of the answer to the original post. There was more resistance to some aspects of the linkage than I expected to find, but it took a while to figure out the nature of the resistance and what kind of information would best clear it up. That path ended up taking a few side-trails and a fair amount of interest kept it going perhaps longer than was best for captivating everyone's interest.
BurbMan wrote:We did start to touch on a secondary component of the hitch, a point that you brought up Tim, about the HA's ability to reduce lateral forces on the TV based on the moments created by the 4-bar linkage. I think we got off track before we sufficiently quantified that concept.
All we need now is a little differential calculus to show that the 4-bar linkage not only changes the force moments, but also affects that rate at which those forces build on the TV in response to forces applied to the TT. (dv/dt=?) I agree that there is more good stuff to delve into regarding lateral forces, resultant moments, and the various reactions required. I think we might lose a few people if we try to find problems that require differential equations to solve, but I believe there are plenty of real-life scenarios that would be quite interesting to look into and quantify that wouldn't require differential equations to solve. In fact, I was considering making a type of spreadsheet where people could plug in the known values for their particular setup, and it would show the leverage advantage that a Hensley would give them.
BurbMan wrote:I would also suggest that we could summarize for the Les the Moderator the relevant posts to keep in the thread and condense to a sticky. Les is already helping me get started in that direction. It may involve creating a new cleaned-up post/thread that links to this one for those who want all the skinny.
Tim
* This post was
edited 06/10/05 12:59pm by tluxon *
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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BurbMan
Indianapolis, IN
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Tim, I was kidding about the differential calculus!
Don
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bettered
UpCountry SC
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Tim, I'll bet he wasn't. Just trying to see whether you'd take the bait. (You did..)
There's a helluva lot of good information in these 27 pages. But there's too much information for some (we could think of at least one..)
I'm still thinking about the side links (maybe I should call them the short links for clarity). I'll go have another look, but it's not them that interfere at the limit of travel, it's those ears in the middle of the front link that bump the links on either side at the limit. I think there is a point when the two links are either at or nearly at right angles to each other near the limit of travel. The T formation, The last 30 degrees or so of front link rotation are what's bringing me to that conclusion. Otherwise the ears in the center of the rear link couldn't be the stop...
Like I say, this fellow was pretty clever. The story is that Hensley discovered him, and saw what he was doing -- bought one, liked what it did and so then bought him out and started a company to manufacture and market the product.
Ed
BetterEd
DW + 2 grandkids + Mini Schnauzer
2005 Chev 3500 Crew D/A 6.6L LLY, 6 x 6 DRW, 3.73
Tru-Flow + Banks, 2005 Flagstaff 831FKSS
Hensley + Prodigy
"Genius may have its limitations...." E. Hubbard 1856 - 1915
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BurbMan
Indianapolis, IN
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Geez, it didn't take you long to give me up, Ed.....![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/biggrin.gif "biggrin")
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tluxon
Kirkland, WA
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[quote=tluxon][quote=bettered]That's sort of the problem. It's very difficult to discern exactly what's happening with the side links because you can almost never see them. I was running my hitch back and forth and trying to determine exactly what the links were doing when I concluded that they (being shorter than the distance between the bearings) can and do fold over each other (the lines of action cross) during the last (tightest) part of the turn. That's what gives the hitch the 165 degrees of travel.
Clearly the front and rear bars overlap at this point, but it's the action of the side links "meshing" that makes it possible.
Ed[/quote]
Unless some of the links extend considerably beyond the points at which they're pinned, I don't believe the side links can ever cross over each other, or "mesh" as you say. To help illustrate my point, I put together a sketch in AutoCAD and that shows a progression of the linkage positions in different colors as the rear bar rotates clockwise. Very shortly after the furthest rotation shown is when the side bar lengths limit any further rotation. If the left side link was allowed to continue any further clockwise (links in red illustrate furthest rear bar rotation), it would push the right side bar far enough to result in the rear bar beginning to turn counterclockwise.
[img]http://home.comcast.net/~tbluxon/Hensley_Fig4.jpg[/img]
Does that help?
[quote=BurbMan]...I think we pretty much beat the concept of the 4-bar linkage to death. I'll go out on a limb and say that we all agree that the creation of the VPP by the linkage is the cornerstone of the HA design and largely responsible for its effectiveness. Recent conversation has largely been focused around the specifics/details of this.[/quote]I was hoping we wouldn't have to linger quite so long on the concept of the 4-bar linkage either, but understanding it was at the core of the answer to the original post. There was more resistance to some aspects of the linkage than I expected to find, but it took a while to figure out the nature of the resistance and what kind of information would best clear it up. That path ended up taking a few side-trails and a fair amount of interest kept it going perhaps longer than was best for captivating everyone's interest.
[quote=BurbMan]We did start to touch on a secondary component of the hitch, a point that you brought up Tim, about the HA's ability to reduce lateral forces on the TV based on the moments created by the 4-bar linkage. I think we got off track before we sufficiently quantified that concept.
All we need now is a little differential calculus to show that the 4-bar linkage not only changes the force moments, but also affects that rate at which those forces build on the TV in response to forces applied to the TT. (dv/dt=?)[/quote]I agree that there is more good stuff to delve into regarding lateral forces, resultant moments, and the various reactions required. I think we might lose a few people if we try to find problems that require differential equations to solve, but I believe there are plenty of real-life scenarios that would be quite interesting to look into and quantify that wouldn't require differential equations to solve. In fact, I was considering making a type of spreadsheet where people could plug in the known values for their particular setup, and it would show the leverage advantage that a Hensley would give them.
[quote=BurbMan]I would also suggest that we could summarize for the Les the Moderator the relevant posts to keep in the thread and condense to a sticky.[/quote]Les is already helping me get started in that direction. It may involve creating a new cleaned-up post/thread that links to this one for those who want all the skinny.
Tim[/quote]
[edit] - image corrected
Note: Due to invalid formatting, all formatting has been ignored.
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bettered
UpCountry SC
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Hey Burb, that's cuz I'm not the one yawning and snoring..
ROFL
Ed
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tluxon
Kirkland, WA
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Oops, somehow my edit turned into a brand new post. Oh well, probably just had too many things going on at once here.
Tim
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bettered
UpCountry SC
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I see what you're saying Tim. I'll go have another look, now that I see what I'm looking for. The fact that the short links can rotate over 180 degrees really has me going here..
Ed
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bettered
UpCountry SC
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Tim, that's a good thing. I was having trouble anyway. For a time I couldn't even see the red bar position (old age, I suspect). The new post called my attention to itself.
Besides, how else are we going to get this thread to 30 pages?
Ed
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tluxon
Kirkland, WA
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bettered wrote:...I'm still thinking about the side links (maybe I should call them the short links for clarity). I'll go have another look, but it's not them that interfere at the limit of travel, it's those ears in the middle of the front link that bump the links on either side at the limit. I think there is a point when the two links are either at or nearly at right angles to each other near the limit of travel. The T formation, The last 30 degrees or so of front link rotation are what's bringing me to that conclusion. Otherwise the ears in the center of the rear link couldn't be the stop... If you take the "entertaining" popsicle stick model and rotate the rear bar clockwise while fixing the top bar in place, you'll see that as the rear bar approaches its "limit" the side link on the right is starting to come back down. This will begin to bring the rear link back down in a counterclockwise direction. I would guess that the "stop" is there to prevent the side link from continuing any further in that direction. Otherwise the rear bar would just continue doing figure-8s.
Note that the position of the red links are at the extent of clockwise rotation the rear bar can achieve.
Tim
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