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Topic ClosedMy version of axle support plan B
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marwayne View Drop Down
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Posts: 1002 		Direct Link To This Post Topic: My version of axle support plan B
    Posted: 09 May 2019 at 5:27pm

Huskers, your plan is not going to work, you either have to make it in 3 pieces or drop the axle because you never be able to put it together.
If you want something done right, do it yourself.
2011 RP172, 2016 Tundra 5.7 Litre, Ltd.


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marwayne View Drop Down
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Posts: 1002 		Direct Link To This Post Posted: 09 May 2019 at 4:13pm
The tubing between the risers is 3x3 1/4" wall, The out riggers are 2 1/2 x 2 1/2 1/4" wall. I needed the extra space to get a washer and a nut in-between the axle and the outrigger.
If you want something done right, do it yourself.
2011 RP172, 2016 Tundra 5.7 Litre, Ltd.


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SC for Huskers View Drop Down
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Posts: 144 		Direct Link To This Post Posted: 09 May 2019 at 4:05pm
Marwayne,  do you remember the size of the tube you used on the out rigger?  Im thinking of getting a 2x4 riser and punching a diamond shape in it  so as "Offgrid said"  to go from  end to end one piece.  Then place all the hardware in the middle and ends.  Input anyone?
Happy Traveling,
Tom
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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Posted: 09 May 2019 at 9:38am


[/QUOTE]Since I don't have the skill to do this myself, I would be a customer for such an item. As for other points of failure, in my case it was the loss of camber. Bearing wear might have also had some part but the symptoms (excess wear on the inside edge of the tires and visual tilt of the tires when viewed from the front or back) led me to feel the problem was not in the spindles, rubber cords, or torque arms. If I had a good line-up on a place that could have fixed the axle for less than I had to pay for replacing it, I would have done that instead, but I still would want some sort of reinforcement. to help prevent the problem from happening again.
[/QUOTE]

Neither do I. The u-bolted 3x3 angle is about my limit. It does the same job, just doesn't look as pretty.

Your failure was almost certainly the axle tube. The giveaway is not having any crown left in the tube. That is a bent axle tube. I'm not sure some of the other possible failure scenarios (say a bent torque arm) couldn't also cause negative camber though. And we have a couple of cases floating around where the tube doesn't appear to be bent or decambered but the trailer is sitting much lower on one side than the other. Those sound like maybe damaged rubber cords.  The majority seem to be bent tubes though. 

 
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StephenH View Drop Down
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Posts: 6289 		Direct Link To This Post Posted: 09 May 2019 at 8:18am
Originally posted by offgrid

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.
What about a round tube as opposed to either flat or diamond?

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".
If a round tube were used, could one drill through the existing riser and then weld the tube to the riser instead of building a new riser?
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.
Since I don't have the skill to do this myself, I would be a customer for such an item. As for other points of failure, in my case it was the loss of camber. Bearing wear might have also had some part but the symptoms (excess wear on the inside edge of the tires and visual tilt of the tires when viewed from the front or back) led me to feel the problem was not in the spindles, rubber cords, or torque arms. If I had a good line-up on a place that could have fixed the axle for less than I had to pay for replacing it, I would have done that instead, but I still would want some sort of reinforcement. to help prevent the problem from happening again.
StephenH
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offgrid View Drop Down
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Posts: 5290 		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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offgrid View Drop Down
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Posts: 5290 		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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Toyanvil View Drop Down
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Posts: 157 		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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GlueGuy View Drop Down
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Posts: 2630 		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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offgrid View Drop Down
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Posts: 5290 		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
1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
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