Dual Cam Setup

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