Dual Cam Setup

JBarca wrote:
Here I need some help understanding why TW is not a factor. I do not understand how you can discount it. The hitch was adjusted because of the TT TW. TW is one of the forces pressing down on the WD bars creating tension in them. The more down force, the more tension and less down force is less tension. So far so good? Agree?

I agree the WDH was adjusted to redistribute load which was imposed on the TV by the TT's TW.
I do not agree that TW is pressing down on the WD bars creating tension in them.

It would be entirely possible to use a WDH to transfer load even if the TW were zero. The bars transfer load because the lift chains are pulling up on the bars and the chains are pulling down on the TT's A-frame. This can happen with zero or negative TW.

When one WD bar lost tension due to hitch head roll and the tilt is relaxed, the WD on the other side of the hitch head truck can still be under tension and in most cases is. When the back of the truck drops in height due to loss of 1 entire WD bar going to zero, the angle of the hitch head is tilted back towards the TT by the truck dropping height. Similar to a back flex when the truck goes up hill just not as pronounced.

I agree 100%, and I think it might be helpful to expand on this scenario by using a numerical example.

The TV has a 130" wheelbase, 65" ball overhang, front axle spring coefficient of 400 #/inch, and rear axle coefficient of 500 #/inch.
The TT is 195" from ball to midpoint between axles.
The the WD bar length is 32" and its cantilever stiffness is 300 #/inch.

The two WD bars have been adjusted give a combined 500# restored to the front axle and 750# removed from the rear axle.
The two bars each contribute 50% of the load transfer.

The TV/TT are travelling straight ahead and one of the lift chains breaks.
The load on the front axle immediately decreases by 250# and the load on the rear increases by 375#.
The front wheelwell rises by 250/400 = 0.625" and the rear wheelwell drops by 375/500 = 0.75".

The front rise of 0.625" combined with the rear drop of 0.75" over the 130" wheelbase gives a frame slope change of 0.61 degrees
Extending that slope to the ball causes the ball to be 1.44" lower than with both bars active.

Having the nose of the TT 1.44" lower gives the TT an angle change of 0.42 degrees.
The resulting change in vertical angle between TV and TT is 0.61+0.42 = 1.03 degrees.
This means the rear end of the remaining WD bar is effectively raised by 32*sine(1.03 degrees) = 0.57".
The corresponding increase in load on the remaining WD bar is 0.57*300 = 172#.
The base load on each bar to generate the initial load transfer was 762#.

The 172# increase in bar load would cause 57# to be added back to the front axle and 71# to be removed from the rear axle.
These load transfers would cause the slope of the TV to decrease from 0.61 degrees to 0.56 degrees.

The increase in load on the remaining WD bar would end up at 159#.
The ball height would be 1.32" lower than when both bars were attached.
The primary effect of having one bar with no load is to cause a drop in ball height due to decreased load transfer, rather than causing a significant increase in bar load.

The TW of the TT is still pressing down and more TW mass is available to be resisted by the only remaining WD bar which has tension. While the head roll angles play a large role in how much weight is added to the one remaining WD bar, the head now has more rear tilt then it did before, the rear of the bar is rising up the cam and more mass available to load on the one tensioned bar then when the loads were shared by both bars.

Adding the effect of a sharp turn complicates matters. It'll take a bit more time to come up with the numbers for this scenario.

My point is, TW does play a role in this, it cannot be discounted. In order to bend the snap up, the bent snap up side of the A frame had to gain more chain tension and the WD bar had to have an increased tension in order for the chain to have more. I do not think you are disputing the fact the WD bar tension had to rise in order to increase the chain tension.---

IMO, the snap up damage is not due to an increase in vertical force produced by the WD bar. As I tried to show in the my Dual Cam free body diagram, I believe the damage is caused by a large increase in chain load resulting from the friction force between bar and cam and the increased compression in the cam bar.

I agree high friction is in the middle of this. When the load goes up, the friction goes up and as you have shown, the friction load is large multiplier, possibly 4.3 to 1 if I understood correctly. However my recollection of the laws of friction remember that to increase the friction force we have to change 1 or both of 2 things. The coefficient of friction has to change to a larger value (not likely in this case) or the force applied has to increase. (most likely in this case) If we have no force increase, how can the friction force increase? That remains the question, how did the force increase?….:h

The normal force increases because the turning hitch head is trying to pull the rear slope of the outside bar through the cam. This increases the friction force which, in turn, increases the normal force. The end result is the force magnification shown in my free body diagram example.
Without this force magnification -- the Dual Cam doesn't work.

If the rear slope of the bar were horizontal, the friction force would simply be equal to the vertical force from the WD bar times the coefficient of friction.
Since the rear slope is not horizontal, the normal force is greater than the bar force.
Imagine what would happen if the rear slope were vertical -- the force magnification would be enormous.

I will see if I can hunt up some kind of load cell for the chain and or the load pointer on the WD bar. However I do not have a way to record the constant travel under tow. Yet anyway. Also need a positive way to hold the hitch head still while measuring load applied to the end of the WD bar for the spring constant data. I'm a think'in.

Shouldn't be necessary to be under tow. You should be able to measure the effects using a slow forward turn in your driveway.
I'll see if I can come up with some ideas for measurements.

Ron

I love the cold weather and wintertime "non camping" time. It gets our engineer members time for thinking and posting interesting stuff! :B :W
Keep at it guys! I love it! :)
Barney

Ron, Sorry this has took so long, been tied up. A few comments.

Ron Gratz wrote:

JBarca wrote:

Now enter the compound angle turn. When the hitch head rolled and unloaded the inside turn WD bar to zero or near zero, there is only the outside turn bar left to provide any level of WD. If the outside bar load stayed the same, then the truck would of lost 1/2 the WD and the front of the truck would of came up enough the driver “may” feel it. Lighter suspension trucks would fell it more so then stiffer suspension trucks.

For reference, the OP's Excursion rose 0.44" in front and dropped 1.38" in rear with no WD applied.
Using 800# bars, he was able to drop the front 0.31" and raise the rear 0.62".
If the WD bar load were reduced by 50%, the front would go back up about 0.15" and the rear would go back down by about 0.31".
Therefore going from the full WD bar load to 50% bar load would change the slope of the TV by about 0.46" over a distance of 137" corresponding to an angular change of 0.7 degrees.
My point is that reducing the WD bar loading by 50% might not make a noticeable difference in the stance of the TV.

I think if we really want to know how the WD bar loading is affected by different simple or compound angles, we need to come up with a method for directly measuring or calculating the load on a WD bar.

Something is not totally adding up with the fenders and weights of an 1,100# loaded TW when mrekim’s had his frame issues. My 2003, K2500 Suburban gasser front end rose 1 1/8” with a 1,200# loaded TW and no WD. However mrekim has the heavy diesel up front and the fender rise effect may be less for rise even if the weight is moving. We can let this go for the moment that not all TV’s may notice the shift in 50% loss of WD.

And I totally agree we need a way to directly measure or calculate the load on the WD bar. More on the loss of one WD bar to zero later in this response.

Ron Gratz wrote:

JBarca wrote:


Since the TT TW did not change, it is still providing a constant force down on the only WD bar that can produce tension. Since the same TW mass is available to only 1 WD bar it comes down to, will the hitch head angle and the rising rear of the WD bar allow an increase in tension?

The tongue weight does not determine how much load is generated by a WD bar. Hold that thought.
The load on the bar is a function of height difference between front and rear of bar, slope of the front end of the unloaded bar, and bar stiffness.
The user determines how much load is generated by changing some or all of those parameters.
If you simultaneously raise the rear of a bar and decrease the front slope (e.g. decrease the head tilt), you can have an increase in bar load, no change in load, or a decrease in load.

Here I need some help understanding why TW is not a factor. I do not understand how you can discount it. The hitch was adjusted because of the TT TW. TW is one of the forces pressing down on the WD bars creating tension in them. The more down force, the more tension and less down force is less tension. So far so good? Agree?

I agree that “The load on the bar is a function of height difference between front and rear of bar, slope of the front end of the unloaded bar, and bar stiffness.” are factors in bar tension and so is TW. In this case, the hitch was adjusted for a given TW where the user adjusted the head tilt and or chain length to compensate for a given TW. Both WD bars once the hitch was adjusted with the TV and TT straight in line on level ground are close to equal tension in the bars along with equal loads on both sides of the A frame from the WD bar chain loads.

When one WD bar lost tension due to hitch head roll and the tilt is relaxed, the WD on the other side of the hitch head truck can still be under tension and in most cases is. When the back of the truck drops in height due to loss of 1 entire WD bar going to zero, the angle of the hitch head is tilted back towards the TT by the truck dropping height. Similar to a back flex when the truck goes up hill just not as pronounced.

The TW of the TT is still pressing down and more TW mass is available to be resisted by the only remaining WD bar which has tension. While the head roll angles play a large role in how much weight is added to the one remaining WD bar, the head now has more rear tilt then it did before, the rear of the bar is rising up the cam and more mass available to load on the one tensioned bar then when the loads were shared by both bars.

My point is, TW does play a role in this, it cannot be discounted. In order to bend the snap up, the bent snap up side of the A frame had to gain more chain tension and the WD bar had to have an increased tension in order for the chain to have more. I do not think you are disputing the fact the WD bar tension had to rise in order to increase the chain tension. TW is still a mass regardless of head roll angle and can create more load in only one WD bar pending how the head angles end up. Granted the head angles may allow one bar to go to zero and the other bar be less, however if the head angles line up, the one tensioned bar now has more downward mass only held by 1 WD bar and the bar tension can go up. It is a combination of the angles, the TV turn and the mass pressing on the bar to create the tension.

A normal way I have seen both WD bars unload is when the truck goes over steep hill heading downhill while the TT is still on a more level ground or still going uphill. Like the TT going uphill on a steep RR track crossing when the truck is over the hump going down hill. The bars unload when the TT is going up the hill and then heavily load up when the TT is coming down off the hill.

Ron Gratz wrote:

JBarca wrote:

In order for the snap up to fail like they do, an increased force presents itself to one side of the WD hitch at the WD chain that overloads a non bolted snapup. A hypothesis is, that the outside WD bar rose enough in tension from the compound angle turn to cause the snap up failure. Now the task is, how to quantify that? If this compound angle turn is not creating the force, then what other combination of actions is?

My current thinking is that the friction force between bar and cam results in an amplification of lift chain tension, and it is that which is causing the problems.
Of course, I always reserve the right to change my mind. :)

Ron

I agree high friction is in the middle of this. When the load goes up, the friction goes up and as you have shown, the friction load is large multiplier, possibly 4.3 to 1 if I understood correctly. However my recollection of the laws of friction remember that to increase the friction force we have to change 1 or both of 2 things. The coefficient of friction has to change to a larger value (not likely in this case) or the force applied has to increase. (most likely in this case) If we have no force increase, how can the friction force increase? That remains the question, how did the force increase?….:h

I will see if I can hunt up some kind of load cell for the chain and or the load pointer on the WD bar. However I do not have a way to record the constant travel under tow. Yet anyway. Also need a positive way to hold the hitch head still while measuring load applied to the end of the WD bar for the spring constant data. I'm a think'in.

mrekim wrote:
I'm expanding on a previously posted suggestion for measuring the bar load...

What if a rigid bar ( a dowel or maybe a fiberglass rod) where taped to the the bar near the trunnion and some measuring scale was fixed to the bar at the other end - maybe to the chain.

If we had such a setup, then measurements could be taken for various scenarios. And, possibly, these loads could be captured via a camera (like a gopro) so the dynamic/"in motion" forces could be captured as well.

If you're proposing something as shown below -- I think that's a great idea.

Since the scale would be fixed vertically, the pointer would move along the scale as the tilt of the trunnion changes.
If the rearward tilt increases, the load on the WD bar increases and the pointer moves down the scale.

If the bar rides up the cam, a reference mark on the side of the bar could be compared to the bar scale for a measure of the added curvature.

This system would give a very good indication of trunnion tilt relative to A-frame orientation and WD bar load could be estimated from the trunnion tilt data and bar-lift data.

Ron

Ron Gratz wrote:
we need to be able to measure the bar load directly or calculate it from curvature measurements.

I'm expanding on a previously posted suggestion for measuring the bar load...


What if a rigid bar ( a dowel or maybe a fiberglass rod) where taped to the the bar near the trunnion and some measuring scale was fixed to the bar at the other end - maybe to the chain.

If we had such a setup, then measurements could be taken for various scenarios. And, possibly, these loads could be captured via a camera (like a gopro) so the dynamic/"in motion" forces could be captured as well.

JBarca wrote:
From mrekim’s thread and other recent hitch head and trunnion bar interaction investigation, I no longer can be sure that the WD chain tension will increase as the WD bar rides up the cam pending what the hitch head is doing. There is a hitch head component to this that is still in the discovery stage.

I agree there's more to be learned about what happens to the WD bar when the TV swings relative to the TT.
And, I thank you for the work you're doing to quantify some of the effect.

However I still have a “belief” that in a compound angle turn when the inside turn WD bar can unload to zero or closer to zero, there is “some” level of increased tension in the outside turn WD bar. How much tension increase is still unknown. Here it the thought path (may be flawed, but this is how I came to it).

I think your current study will go a long way toward eliminating some of the unknowns.

When the TV and TT are on level ground and straight ahead, both WD bars have very close to equal loads. Those WD loads came from the setup of the WD hitch. As a result of this, both left and right WD chain loads are close to the same and the trailer A frame is close to being equally loaded both left and right. So far so good and I think we all agree on this.

Yes, I completely agree.

Now enter the compound angle turn. When the hitch head rolled and unloaded the inside turn WD bar to zero or near zero, there is only the outside turn bar left to provide any level of WD. If the outside bar load stayed the same, then the truck would of lost 1/2 the WD and the front of the truck would of came up enough the driver “may” feel it. Lighter suspension trucks would fell it more so then stiffer suspension trucks.

For reference, the OP's Excursion rose 0.44" in front and dropped 1.38" in rear with no WD applied.
Using 800# bars, he was able to drop the front 0.31" and raise the rear 0.62".
If the WD bar load were reduced by 50%, the front would go back up about 0.15" and the rear would go back down by about 0.31".
Therefore going from the full WD bar load to 50% bar load would change the slope of the TV by about 0.46" over a distance of 137" corresponding to an angular change of 0.7 degrees.
My point is that reducing the WD bar loading by 50% might not make a noticeable difference in the stance of the TV.

I think if we really want to know how the WD bar loading is affected by different simple or compound angles, we need to come up with a method for directly measuring or calculating the load on a WD bar.

I do compound angle turns all the time, and in none of my trucks, 1/2, 3/4 or 1 ton I do not recall the front end going extremely light. We know the WD bar is riding up the cam and we know the rear of the WD bar is rising. We know the trunnion lug on that side is at a down hill angle due to the roll axis. We do not know what the trunnion lug angle in the hitch head did to this equation. That is still an open topic.

I agree. We need to be able to measure the amount of trunnion lug tilt change.
Or, we need to be able to measure the bar load directly or calculate it from curvature measurements.

Since the TT TW did not change, it is still providing a constant force down on the only WD bar that can produce tension. Since the same TW mass is available to only 1 WD bar it comes down to, will the hitch head angle and the rising rear of the WD bar allow an increase in tension?

The tongue weight does not determine how much load is generated by a WD bar.
The load on the bar is a function of height difference between front and rear of bar, slope of the front end of the unloaded bar, and bar stiffness.
The user determines how much load is generated by changing some or all of those parameters.
If you simultaneously raise the rear of a bar and decrease the front slope (e.g. decrease the head tilt), you can have an increase in bar load, no change in load, or a decrease in load.

While the trunnion lug angle in the hitch head may have relieved some of the WD tension, more of the existing TW is available to be held by the outside turn WD bar. An unknown is, did the hitch head angle change enough to not allow more WD bar tension on the outside turn bar and did the rear of the bar riding up the cam over come the loss in the hitch head?

I agree we don't have enough information to answer that question.

The following image shows WD bar curvatures for a TV/TT in three different WD bar loading orientations.
I don't know if the WD bars are the same in all three photos.
If they are the same, we can estimate the relative amounts of bar loading from the relative amounts of bar curvature.
I changed the zoom on the photos to try to keep the vertical scales the same.
As a very rough estimate, I would guess the bar load at bottom left (sharp turn) might be about 15% greater than the load at top left (zero turn).
I see nothing to indicate the load on bottom left is anywhere close to twice the load on top left.
I would expect the bar load at bottom right to be much greater than the load at top left -- maybe twice as much. However, my measurements indicate an increase of about 30%.

In order for the snap up to fail like they do, an increased force presents itself to one side of the WD hitch at the WD chain that overloads a non bolted snapup. A hypothesis is, that the outside WD bar rose enough in tension from the compound angle turn to cause the snap up failure. Now the task is, how to quantify that? If this compound angle turn is not creating the force, then what other combination of actions is?

My current thinking is that the friction force between bar and cam results in an amplification of lift chain tension, and it is that which is causing the problems.
Of course, I always reserve the right to change my mind. :)

Ron

JBarca wrote:
We need mrekim to confirm his loaded TW and how he had the WD adjusted at the time the snap up and frame damage occurred. I was under the impression that he had an 1,100# loaded TW and had adjusted the WD hitch to return the front axle very close to unhitched fender height. I may have mixed that up, we need him to confirm. If all his damage came from only a 500# per side load down onto the WD bar, that is not a comforting thought.

I based the 500# per bar estimate on the scales data reported in this thread.

I neglected to read all the way to the end of the post where I would have seen:
"The above measurements are before my last hitch adjustment. Which was to return the front axles to unhitched weight. This was done by going one notch on the hitch head after the above weights were taken."

Due to my oversight, I used the wrong value for amount of load restored to the front axle.

If the WDH actually returned 560# to the front axle, the estimated bar load would be approximately 1000# per bar.

Ron

JBarca wrote:

How did you have the WD hitch adjusted? Was the TV front end close to unhitched fender height or better, weight?

TV front was adjusted to unhitched fender height.

This is how that came about:

When I went to the scale I was 340 lbs light in the front end. The hitch head tilt was adjusted down one more notch to add the 340 back to the front. Fender measurements had me at zero change on one side a 1/16" heavy on the other.

JBarca wrote:

Ron Gratz wrote:

In this post, I attempted to address the increase in WD bar load for a sway angle of 5 degrees.

I cannot get the link to fire. Is the link OK or it my PC?

Thanks

John

I'll deal with the easy part first.

I don't know what happened to that link -- but I think it's fixed now.

Thanks for pointing out the problem.

Ron

mrekim wrote:

JBarca wrote:

We need mrekim to confirm his loaded TW and how he had the WD adjusted at the time the snap up and frame damage occurred. I was under the impression that he had an 1,100# loaded TW and had adjusted the WD hitch to return the front axle very close to unhitched fender height. I may have mixed that up, we need him to confirm. If all his damage came from only a 500# per side load down onto the WD bar, that is not a comforting thought.

My scale TW, which should be close to what I was when the damage occurred (could be less, but not more), was 1080.

How did you have the WD hitch adjusted? Was the TV front end close to unhitched fender height or better, weight?