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Topic ClosedMy version of axle support plan B

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marwayne View Drop Down
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Direct Link To This Post Topic: My version of axle support plan B
    Posted: 08 May 2019 at 1:50pm


 


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offgrid View Drop Down
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Direct Link To This Post Posted: 08 May 2019 at 2:09pm
That looks good! Are you keeping your plan A piece in place? That will help to carry the moment (torque) created when the axle end pushes up on your new part so your don't bend the trailer frame rail. 
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marwayne View Drop Down
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Direct Link To This Post Posted: 08 May 2019 at 2:42pm
The supporting axle stayed in place, the outriggers are bolted to it with the back of the risers sandwiched in-between.
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StephenH View Drop Down
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Direct Link To This Post Posted: 08 May 2019 at 3:58pm
Plan B looks great!
StephenH
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GlueGuy View Drop Down
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Direct Link To This Post Posted: 08 May 2019 at 4:22pm
I like it. Should boost your axle capacity by a couple hundred pounds per side (there was no calculation involved; it was justa  SWAG).
bp
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offgrid View Drop Down
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Direct Link To This Post Posted: 08 May 2019 at 5:05pm
My swag would be about a 50% improvement, similar to my solution and toyanvil's. That is closer to a couple thousand ponds per side Thumbs Up
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GlueGuy View Drop Down
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Direct Link To This Post Posted: 08 May 2019 at 7:23pm
Originally posted by offgrid

My swag would be about a 50% improvement, similar to my solution and toyanvil's. That is closer to a couple thousand ponds per side Thumbs Up
That would probably be beyond the capability of the torsion axle in the first place. None-the-less, I would think that it would eliminate any issues that might be typical.
bp
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Toyanvil View Drop Down
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Direct Link To This Post Posted: 08 May 2019 at 9:42pm
I really like that, I tend to over think things. If mine starts moving I will add a center bar like yours, only welded to the risers and turned on diamond like the axle.
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Direct Link To This Post Posted: 08 May 2019 at 10:31pm
Originally posted by GlueGuy


Originally posted by offgrid

My swag would be about a 50% improvement, similar to my solution and toyanvil's. That is closer to a couple thousand ponds per side Thumbs Up
That would probably be beyond the capability of the torsion axle in the first place. None-the-less, I would think that it would eliminate any issues that might be typical.


When I did the stress calculation the existing axle capability was about 2.5-3 g, which is about 4000 to 5000 lbs per side at yield. Any of these fixes ought to take it up to about 3.5-4 g. It needs to be able to take that kind of punishment to survive real world bump loads. I read a couple of vehicle design articles that indicated that even 3g wasn’t really considered adequate. As another example, Normal category aircraft are certified to 3.8 positive g’s with a 50% safety factor on top of that. Good thing we don’t also get negative g loading on rPods or we’d really have problems. Our black tank contents would be dripping off the ceiling.   
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Direct Link To This Post Posted: 09 May 2019 at 6:22am
Originally posted by Toyanvil

I really like that, I tend to over think things. If mine starts moving I will add a center bar like yours, only welded to the risers and turned on diamond like the axle. 

Either flat or diamond will work but the tube is 40% stronger in bending if you keep it flat rather than turning it to the diamond orientation. 

For the record, the section modulus of a 3 x 3 x 3/16 tube flat is 1.86 in^3 vs 1.32 in^3 for the diamond.  I got an overhang of 13.75 inches to the center of the wheels (midpoint between the bearings) from the axle frame mounts when I measured mine. That puts the bending moment on the axle tube at the supports (no reinforcement) at 1750 lbs/1.32*13.75=18.2 ksi (18,200 psi), for a safety factor/g loading of 1.98 assuming standard structural steel with a 36 ksi yield.  So the axle is weaker than I was remembering it was from when I last did the calculation. 2g is an inadequate safety margin IMHO.

If someone (StephenH?) were starting from scratch and wanted to do something more elaborate than just u-bolting an angle under the axle like I did, I'd suggest a continuous full length tube with Marwayne's brackets at each end and flanges welded to bolt it to both the frame and the axle (replacing the existing riser). Basically it would be a bolt up combination riser and axle "doubler".  

These would probably sell like hotcakes to a certain segment of rPod owners, but be sure to get one of our resident attorneys to write an ironclad warranty disclaimer for you Tongue

All that aside, I'm still thinking that some of the failures that are being reported are due to bent spindles, torque arms, or compressed rubber cords which reinforcing the axle tube won't help. We'll see. 
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