Dual Cam Setup

Nice looking work. Knowing what you you where up agasint, this would of done a lot of prevention had this been on since new. How would one have known this though? They always say, hind site is 20/20.

Have you resolved yet, the long term approach?

Thanks for sharing.

John

Here's a little update. I've made a few parts for a bolt on repair. 1/4" outer plate, 3/16" inner plate, 1/4"x2" "clamps". The 1/4" plate is threaded for studs (grade 5 bolts with head cut off). Right now there are two dual cam studs and one snap up stud per side. I may add two more studs per side for the snap ups.








Still to do:

* Weld the clamps to the large plates. Just a 1" bead at the center. This will prevent the clamps from bowing out. Hopefully it will help distribute some of the clamping force over a larger area too?

* Weld the studs in from the back side.

* The passenger side only has 3 clamps due to the spare tire mount. I may just put a clamp on the other side of the bar for raising/lowering the spare. I liked the idea of the clamp being against the cross tube for the battery/spare tire mount, but not enough to try to redo the spare tire mount.


* Deal with mounting the propane tanks. They don't quite fit between the middle two mounts. Maybe a 1x1x1/8 "L" on the inside and the outside mounted to the 1/2" bolts. That would raise the tanks about 1". Something like this:

Ron Gratz wrote:

For Christmas, I would like to ask the Data Santa Claus (a.k.a. "JBarca") if he could find time to measure the bar lift versus turn angle when the bar moves rearward relative to the cam. This would give us a better handle on how the inside bar unloads.

Thanks in advance, Santa. :)

Ron

Gee Ron, Thanks for the good words. Much appreciated. :)

Super job on the graphs, analysis is your specialty! :C

On the next data finding mission... we need to request some "heat" from Santa. Suppose to go to 5F tonight and even worse tomorrow... and this "white stuff" seems to be coming too... We lucked out the last few years not having much in this area. Hope this is not catch up time... I'll connect with you when the weather breaks and the next data opportunity presents it self.

Thanks again

John

Effect of TV/TT Angle on Dual Cam Bar Loads – Bar Tip Elevation vs Bar Swing Angle

The second of John's previously mentioned studies was to measure the tip height of an unloaded WD bar as the bar swings on its trunnions when the TV turns relative to the TT.
Part of John's experimental setup is shown here:



The rearward tilt of the bar's trunnion axis (15 degrees in this case) causes the bar tip to rise as the bar swings away from being parallel to the TV's longitudinal centerline.
In effect, the "rearward" (directed from front of bar to rear of bar) tilt of a bar's trunnions decreases from 15 degrees when the bar is straight behind the TV to a tilt of zero degrees when the bar is at a right angle to the TV. This will cause the bar to unload as it swings away from a zero-degree relative angle.
Results from John's measurements are shown below.



These data are for the right-side bar and the swing to the left was limited to 60 degrees due to contact between socket and ball nut.

It is important to note that, when the TT is straight behind the TV, each bar will be swung about 25 degrees away from the TT's centerline -- i.e. the left bar swing angle is -25 and the right is +25 degrees.
This means the load on the right-side bar initially will increase as the TT turns left.
Maximum load on the outside bar will occur at a turn angle of about 25 degrees when the bar becomes parallel to the TV's centerline -- i.e. its swing angle becomes zero.

If the TV turns 50 degrees left, the outside (right) bar will swing from +25 degrees to -25 degrees and its trunnion-tilt induced load will end up at the same value at which it started.
The inside bar will swing from -25 degrees to -75 degrees. This would cause the tip to rise about 5.6" -- more than enough to unload this bar.

Ron

Effect of TV/TT Angle on Dual Cam Bar Loads – WD Bar Lift vs TV/TT Angle

Thanks to John Barca’s mastery of experimental design and measurement, we now are able to calculate the effect of TV/TT angle on dual cam bar loads.
John’s recent studies have measured 1) WD bar lift when sliding over the cam and 2) the effect of TV/TT angle on the tip height of an unloaded bar.
The first of these relationships is shown below as a function of TV/TT turn angle.



These data are for the outside WD bar at three TV/TT angles of 15, 30, and 45 degrees.
The bar tip is being pulled forward relative to the cam and slides up over the cam as it moves.
The lifting of the tip increases the curvature of the cantilever bar which, in turn, causes the bar to exert greater downward force on the cam.

Excellent photo documentation of John's data collection project is presented in this thread.

As shown in the last image of John's thread, the inside bar initially will lift and then will begin to drop until it becomes completely unloaded if the turn is sharp enough. We just don't know how far it will lift and drop.

For Christmas, I would like to ask the Data Santa Claus (a.k.a. "JBarca") if he could find time to measure the bar lift versus turn angle when the bar moves rearward relative to the cam. This would give us a better handle on how the inside bar unloads.

Thanks in advance, Santa. :)

Ron

mrekim wrote:
As the turn starts, the inside bar needs to ride up the cam before it unloads. It seems like this would have the effect of tightening the chain some.

From the chart, it looks like the reduced slope of the inside bar load line from 0 to -10 degrees may be due to this riding up effect. If that's the case, hopefully you can describe why it initially decreases slowly rather than increasing a little first.

That's one of the details I hope to get properly documented later today.

Yes, the inside bar does ride up the cam before it unloads.
I assumed the front slope of the bar detent is the same as the rear (although it appears to be less).
From John's data, the rear slope produced bar lift of about 0.04" per degree of turn for small angles -- corresponding to a bar load increase of about 12# per degree.

John also has provided data which shows the effective rearward tilt of the WD bar trunnion changes with turn angle.
For the inside bar, the trunnion tilt effect will cause the bar to unload at a rate of about 24# per degree of turn as the trailer begins to turn.

The cam rise effect of plus 12# per degree and the trunnion tilt effect of minus 24# per degree gives an initial net effect of about minus 12# per degree of turn.

As the turn angle increases (becomes more negative on my chart), the cam rise effect reaches a maximum and then decreases slightly, while the trunnion effect continues to unload the bar at a rate which increases as the TV/TT angle increases.

For my example, the trunnion effect causes the inside bar to completely unload at a turn angle of about -34 degrees.

Ron

As the turn starts, the inside bar needs to ride up the cam before it unloads. It seems like this would have the effect of tightening the chain some.

From the chart, it looks like the reduced slope of the inside bar load line from 0 to -10 degrees may be due to this riding up effect. If that's the case, hopefully you can describe why it initially decreases slowly rather than increasing a little first.

JBarca wrote:
I may be using a wrong word or words trying to explain to not “yet” discount that the loaded weight of the TT tongue is a factor in the bent snapup situation. If I am understanding your point correct, you are stating TW has nothing to do with the bent snap up. Is this a correct assumption? Yes/no?

Keeping an open mind that I may have a wrong thought pattern going on here, I concentrated on the zero TW example to try and prove to myself where my thought process is coming from on why TW matters OR to possibly help me understand why TW has nothing to do with it…

John, here's another way to look at the influence of TW on WDH bar loading.

Using the TV/TT/Bar configuration from my previous post:
Assume the TT has a 1000# TW. Assume the TV and TT are connected but the coupler is held just off the ball by the tongue jack. Assume the lift chains have zero twist and are adjusted to the load on each bar is just slightly above zero.

Now raise the tongue jack so the full tongue weight is carried on he ball.

If the bar load remained at zero, the front of the TV would rise about 1.25" and the rear would drop about 3".
However, the bar load does not remain at zero. The load in each bar increases to about 403#, the front rise decreases to about 0.59", and the rear drop decreases to about 2.3".
If the owner were willing to settle for that much front end rise and rear end drop, one could say that the WD bar load of 403# was directly determined by the 1000# tongue weight.

If the owner desires more load transfer, the WDH must be adjusted to give more bar curvature.
If the owner wants to return the front to its unhitched load, the load on each bar needs to be increased to about 840#.
In this case the bar load is directly determined by WD bar and TT dimensions combined with how much load transfer is desired. The tongue weight is simply a factor which helps to determine how much load transfer is desired. Other factors are TV wheelbase, ball overhang, and owner's FALR philosophy.

However, I'm afraid our tongue weight debate is clouding the real issue which, IMO, is: What is causing the failure of the Dual Cam brackets?
I think one thing we can agree on is the fact that the tongue weight is not changing as the OP's combo is being driven down the road.
Therefore, I suggest we focus on the things which are changing during a turn such as: bar lift due to riding up over the cam, bar unloading due to trunnion tilt and bar swing, unloading of inside bar, and hitch pitch-axis rotation due to TV slope change.

I have thought really hard on this and I want to adjust my comments because of it. See if you agree. I’ll start with some of the actual factors (my assumed factors that is).

I agree with all of the following. I'll add some brief comments in

blue

The bent snapup has several factors associated with the snap up failure when using the DC.

Some of these factors are: (Note: FALR = Front Axle Load Restoration)

1. Starting with a heavily loaded trailer TW creates the need for the user to adjust the WD hitch to have a higher starting tension in the WD bars as opposed to a lighter TW trailer.

2. The WD adjusting method of returning the TV front axle back to unhitched weight (100% FALR) creates a certain tension in the WD bars and chains. The WD bar and chain tension will be higher using this method then if only 50% FALR or other method less than 100% FALR was used.

3. The actual loaded TW of the trailer is a factor in the failure of the snapup bracket due to creating a need for the user to adjust a higher starting tension in the WD bar resulting in a higher chain tension than a lighter TW trailer.

Yes, TW is one of several factors.

Some attributes of the snapup failure:
1. The snapup will fail (stressed to the point of permanent deformation) when a certain chain tension is exceeded.

2. By bolting the snapup to the trailer frame, the snapup bracket has shown to be able to resist higher chain tensions before permanent deformation occurs.

3. The tension in the lift chain attached the outside turn WD bar “has the ability” to increase above the starting tension required to achieve FALR when the TV was straight ahead on level ground with the TT when larger degrees of a turn are experienced.

Lifting of the bar by the cam will lead to increased chain tension for a wide range of turn angles.

4. Compound angle turns classified as the TV and TT are on uneven ground during a turn, the hitch head can roll and result in the inside turn WD bar loosing tension and at times going to zero tension. During this event, the outside turn WD bar has the potential to have increased tension in the WD bar due to the increase of rearward tilt of the hitch head.

Even on a simple turn where the TV and TT remain on the same plane, the inside bar can completely unload resulting in some increase in load on the outside bar. This effect varies with turn angle.

5. In a compound angle turn, the potential exists for increased lift chain tension when the outside turn WD bar is rising up the cam.

Also in a simple angle turn.

6. Chain tension is a result of WD bar tension created by the WD hitch and the friction forces generated by the WD bar dragging (WD bar in motion) across the cam.

Also is a result of compression in the cam arm.

7. As shown in this reply a magnification of chain tension has the potential to increase 4.3:1 times the pre-existing normal chain tension during the motion of when the TV is turning.

After thinking on all this, I still believe TW is still a factor in the failure of the snap up bracket however the reason has shifted. The reason being the person adjusting the WD hitch created more “starting tension” in the WD bars and lift chains as a result of the TW. TW is a factor. Heavier TW’s require higher starting tension to achieve the same FALR then lighter TW’s. Once the WD is adjusted, the starting tension is preset and as long as the TW does not change, the balance of increased WD bar and chain tension is a result of the mechanical action of the WD hitch and the friction added by the DC system when the TV is in motion.

Yes, TW is one of the factors which determine the "base load" on a WD bar. And, we have made good progress in defining the effects of hitch kinematics and friction.

And yes I can now see how once the system is preset, as long as the TW does not change, the physical TW will not increase the WD bar or chain tension. Thinking through the hypothetical zero TW trailer helped show me the light. Mechanical action of the hitch head, WD bar and cam can increase the tension in the WD bar and lift chain. Now we just need to sort out that mechanical action. My belief, aka hunch, is it is in middle of the moving motion of the compound angle turn.

I think we now have a good handle on the simple angle turn. Sorting out the compound angle effects might require some more experimentation and analysis.

Yes, please do. Helping solve the combination of events behind this issue now has my curiosity at an all time high. If was not snowing and 23F out, I would hitch up and go create the WD bar pointer in a compound angle turn.

Following is a preliminary result from the simple angle study which might satisfy your curiosity while waiting for the weather to improve.
Details of the chart will have to wait until tomorrow. :)


Ron

Ron, Some added thoughts,

Ron Gratz wrote:

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.

I almost mentioned in my last post, “if” a trailer TW was zero, (in pure theory only) one could adjust a WD hitch to apply tension in the WD bars due to the mechanical action of the hitch. I was going to head that one off at the pass before it surfaced, however I should of better predicted that it would…

I may be using a wrong word or words trying to explain to not “yet” discount that the loaded weight of the TT tongue is a factor in the bent snapup situation. If I am understanding your point correct, you are stating TW has nothing to do with the bent snap up. Is this a correct assumption? Yes/no?

Keeping an open mind that I may have a wrong thought pattern going on here, I concentrated on the zero TW example to try and prove to myself where my thought process is coming from on why TW matters OR to possibly help me understand why TW has nothing to do with it…

I have thought really hard on this and I want to adjust my comments because of it. See if you agree. I’ll start with some of the actual factors (my assumed factors that is).

The bent snapup has several factors associated with the snap up failure when using the DC.

Some of these factors are: (Note: FALR = Front Axle Load Restoration)

1. Starting with a heavily loaded trailer TW creates the need for the user to adjust the WD hitch to have a higher starting tension in the WD bars as opposed to a lighter TW trailer.

2. The WD adjusting method of returning the TV front axle back to unhitched weight (100% FALR) creates a certain tension in the WD bars and chains. The WD bar and chain tension will be higher using this method then if only 50% FALR or other method less than 100% FALR was used.

3. The actual loaded TW of the trailer is a factor in the failure of the snapup bracket due to creating a need for the user to adjust a higher starting tension in the WD bar resulting in a higher chain tension than a lighter TW trailer.

Some attributes of the snapup failure:
1. The snapup will fail (stressed to the point of permanent deformation) when a certain chain tension is exceeded.

2. By bolting the snapup to the trailer frame, the snapup bracket has shown to be able to resist higher chain tensions before permanent deformation occurs.

3. The tension in the lift chain attached the outside turn WD bar “has the ability” to increase above the starting tension required to achieve FALR when the TV was straight ahead on level ground with the TT when larger degrees of a turn are experienced.

4. Compound angle turns classified as the TV and TT are on uneven ground during a turn, the hitch head can roll and result in the inside turn WD bar loosing tension and at times going to zero tension. During this event, the outside turn WD bar has the potential to have increased tension in the WD bar due to the increase of rearward tilt of the hitch head.

5. In a compound angle turn, the potential exists for increased lift chain tension when the outside turn WD bar is rising up the cam.

6. Chain tension is a result of WD bar tension created by the WD hitch and the friction forces generated by the WD bar dragging (WD bar in motion) across the cam.

7. As shown in this reply a magnification of chain tension has the potential to increase 4.3:1 times the pre-existing normal chain tension during the motion of when the TV is turning.

After thinking on all this, I still believe TW is still a factor in the failure of the snap up bracket however the reason has shifted. The reason being the person adjusting the WD hitch created more “starting tension” in the WD bars and lift chains as a result of the TW. TW is a factor. Heavier TW’s require higher starting tension to achieve the same FALR then lighter TW’s. Once the WD is adjusted, the starting tension is preset and as long as the TW does not change, the balance of increased WD bar and chain tension is a result of the mechanical action of the WD hitch and the friction added by the DC system when the TV is in motion.

And yes I can now see how once the system is preset, as long as the TW does not change, the physical TW will not increase the WD bar or chain tension. Thinking through the hypothetical zero TW trailer helped show me the light. Mechanical action of the hitch head, WD bar and cam can increase the tension in the WD bar and lift chain. Now we just need to sort out that mechanical action. My belief, aka hunch, is it is in middle of the moving motion of the compound angle turn.

Ron Gratz wrote:

JBarca wrote:
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

Yes, please do. Helping solve the combination of events behind this issue now has my curiosity at an all time high. If was not snowing and 23F out, I would hitch up and go create the WD bar pointer in a compound angle turn.

JBarca wrote:

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.

I'm not sure what the difference is. I guess the heavy engine could be part of it. I have some front fender rise measurements with no WD below. I can't explain why the passenger rises more than the driver side, but at least it's consistent.

Driver Front___Passenger Front_____Avg
.5_____________.75____________.62
.5_____________.69____________.59
.625___________.875___________.75
.44_____________not taken


I'm pretty sure the first two were on the same day so they were close. It's possible the trailer was a little more packed on the 3rd one.

The last one there was some gear removed from the trailer and some additional gear in the back of the Excursion. The propane tanks were off too. I don't think I ever recorded a large raise in the front.

I think I had a 1/16 rise on the driver side and 1/8" on the passenger side when the scale had me 340lbs light in the front. I was surprised that such a small measured change represented such a large weight difference.