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Old 07-01-2019, 07:25 PM   #11
Bus Geek
 
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Join Date: Dec 2017
Location: Dawsonville, Ga.
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Year: 1999
Coachwork: Genesis
Chassis: International
Engine: DT466/3060
Rated Cap: 77
Oops, after pulling the rear windows from the surplus pile I found them both broken. It was then that I remembered these were the 2 I broke before I learned how to remove them properly.
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Old 07-02-2019, 10:47 AM   #12
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Join Date: Oct 2018
Location: Ogden utah
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Year: 2002
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Chassis: Tc2000
Engine: 5.9 24v
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Ah,

Well thank you for the offer marc!
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Old 07-02-2019, 10:49 AM   #13
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Join Date: Oct 2018
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Year: 2002
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Follow up with the FEA and design that went into this.
Figured someone might find it valuable.

https://imgur.com/a/rDTER2F#MmO8h0F

----


See entire album but highlights are below.

The FEA is done in solidworks using the SimulationXpress Analysis Wizard. This is a " Demo" tool and doesn't allow you to perform FEA on an assembly, so the calcs were done for a single beam and modeled as a distributed load. Note that the A/C is held up by TWO brackets so double any forces that you see and double the factor of safety to get an idea of the strength of the assembly. Dimensions of the brackets are shown in the hand calcs, steel was assumed to be low carbon/mild steel, cold rolled based off it's texture and smooth finish. I got the steel from the junkyard for free so I do not have it's exact specifications.

Major props to our mechanical engineering Co-Op who had some downtime at work and modeled this for me & did the hand calcs. Im an electrical engineer so not as versed in the mechanics & materials.

Note the deflection in these models is exaggerated for scale. The max actual deflection shown is 2.05mm

Stresses at 2.05mm of endpoint deflection within beam, 1000N force ( 225 lb ). ONE BEAM



Zoomed in view of the fatigue location. Calculated factor of safety for a 1000N force ( 225 lb ), FOS2.4 ( 4.8 for entire assembly of two beams )



I found this model to be the most valuable since it shows where the likely failure point would be. Now I can add it to my list of monthly inspections to inspect this area of the bracket for any bending or deflection. Among others I inspect the battery terminals for corrosion or loose connections, check fluids, air brake bleed-off rate, etc. The monthly inspection list is rather long but necessary to stay ahead of untimely failures and breakdowns.

Hand calcs to backup / confirm model



View inside

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Old 07-07-2019, 12:24 PM   #14
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Join Date: Aug 2018
Location: Rhode Island
Posts: 143
Year: 1980
Coachwork: Crown Coach
Chassis: Supercoach
Engine: Detroit 671T
Quote:
Originally Posted by Rivetboy View Post
OK, lets say you weigh 160 pounds. The hammock is supported at either end so the end that is tied to the unit weighs 80 lbs. Now that 80 lbs is tied to either bracket so the static load is only 40 pounds on each bracket. Now imagine that you hit a big bump and now the accelerated mass of that hundred pound condenser is headin down hard. I do not know... but the mount is built for static load. gussets would help immensely IMHO
Splitting hairs here, but the load on the anchors is significantly higher than a simple division of the load on the line. In this case it looks like the angle of the hammock is about 120* so the load on each anchor would be approximately 160lbs. If you split that on the a/c side then each connection is seeing at least 80lbs of force. Itís tough to wrap your head around at first but its very easy to generate massive anchor loads with highlines, and rigging like that. Here is good guide to help explain https://roperescuetraining.com/physics_angles.php
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