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Author Topic: Breaking Wind  (Read 88269 times)
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Rex Schimmer
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« Reply #90 on: January 07, 2015, 06:49:32 PM »

The purpose of this "A" arm is to locate the rear end laterally in the horizontal plane. If you look at the position of the mounting bracket and the heim joint the load is then from side to side on the joint, not trying to pull the ball vertically out of  its' race, which is the direction that a joint has the least strength. The four bars take all of the axle over turning load and because the lateral locator A frame has a slide function in it, it will never see any appreciable  load in the vertical direction. Also Javajoe has used a joint with a 3/4 inch shank and 5/8 diameter pin hole and he has the pin/bolt in double shear and he is using a very high quality joint. Personally to me it looks perfect!

Rex
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manta22
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« Reply #91 on: January 07, 2015, 07:19:00 PM »

JJ;

If you are satisfied with it, that's what counts.

Regards, Neil  Tucson, AZ
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Regards, Neil  Tucson, AZ
javajoe79
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« Reply #92 on: January 07, 2015, 10:37:20 PM »

I am satisfied but am still considering an upper wishbone. Also waiting to hear from Lafevers. Thanks Rex
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jl222
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« Reply #93 on: January 08, 2015, 12:42:32 AM »

 Seems like there would not be much movement with the rod ends mounted that way.

  Jerry Bickle's book Complete Guide To Chassis Performance has a good picture of what he likes and the rod ends
are turned 90 deg to what you have, also has the slider.

  Good book for chassis tuning and setup.

   Good luck JL222
  Yeah there isn't much movement but it is enough. Where the single rod end attaches to the rear end bracket, it has around 6" of travel. Do you mean the 2 forward rod ends are 90*? I don't have much room to work with as we are planning on a 6" exhaust passing through this area on the passenger side but I am considering an upper wishbone as well.

I see the sliding feature now which would eliminate the bind, but I would still have approval in writing on side loading of the Heim ends. Be a shame to get there and have an inspector say "no run".

Ron
I will send an email to Lefevers. Hard to imagine this not being approved.

Although they ran two wishbones, Speed Demon used rod ends side loaded just like this. Maybe I will add an upper wishbone too?



 Similar to Speed Demon but bolts parallel to cross member mounted in double shear and mounted to bottom of rear end
further back. Rod ends mounted  same as 4 link rod ends. Not sure of rod end mounting at rear end but probably like Speed Demon.

          JL222
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« Reply #94 on: January 08, 2015, 09:48:16 AM »

From Aurora FAQ:
· What direction is a radial load applied?
· The radial load is applied through the axis of the shank of the male or female body.

Note that it says nothing about loads applied that would produce bending in the shank, and no capacities are cited for that type of load, since the bearings are not intended to be used in that manner. 

Assuming a 1.5” overhang, 0.625” minimum diameter of the shank, and 60 ksi yield strength of the material, only about 960 lb side load would produce yield.  And this not taking into account the stress concentration factors of the thread roots, fatigue, and any degradation or propensity for hydrogen embrittlement/stress corrosion cracking.

Yeah, people get away with a lot of things, but it doesn’t make it a sound or defensible engineering approach.  Getting an inspector’s approval is basically meaningless.  Is he going to do a complete analysis and take on the liability for the results?  No.  He is just going to say there are no obvious reasons to reject the arrangement and that you are on your own with it. 

A diagonal bar with rod ends used in the manner they are intended to be used (as in the 4-bar links) is a far superior structural arrangement, uses fewer simpler components, and does away with the monkey-motion maintenance headache sliding interfaces.

Speed Demon was on very thin ice with their double wishbone arrangement.  The only thing that kept them from snapping the rod ends as a result of the driveline torque was the monster anti-roll bar and the slop and flexibility of the wishbones.

But, as Neil said, “If you are happy with it . . .”
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javajoe79
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« Reply #95 on: January 08, 2015, 10:13:27 AM »

Did any of those rod ends in question on speed demon break during the crash?

From Aurora FAQ:
· What direction is a radial load applied?
· The radial load is applied through the axis of the shank of the male or female body.

Note that it says nothing about loads applied that would produce bending in the shank, and no capacities are cited for that type of load, since the bearings are not intended to be used in that manner. 


So they give a radial load rating of 10% of 40,000lbs+   How does that not include the bending strength of the shaft? How can you apply that force without also putting that load through the shaft?

 We used the same rod end on the fleet of formula mazdas that were constantly being crashed. This was the upper, outer rod end on the front suspension. This was a rocker arm type suspension if you are familiar. So for starters the whole weight of that corner of the car was applied through it as a bending load on the shaft. We got to see countless examples of how they yielded when crashed. They pretty much never broke and they would normally destroy whatever they were attached to, before they bent.

 In your opinion would you be happier if those 2 rod ends were turned 90* so the load was through the housing of the rod end rather then the ball race?
« Last Edit: January 08, 2015, 10:25:13 AM by javajoe79 » Logged

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« Reply #96 on: January 08, 2015, 12:55:06 PM »

Aurora is a bearing company.  Their 10% rating of their “radial”, that is, the sideways load of the ball against the socket and housing is the limit they are comfortable with to keep their bearing/seat/housing from undue suffering.  It has nothing to do with, and clearly does not imply, that that much sideload is acceptable in the shank.  If you don’t believe it, do the calculations yourself.  They have no control over what people might do with the rod ends.  They just don’t want their bearing to come apart.

So let’s just recap:  Formula Mazda---You have had previous first-hand experience with bending loads applied to rod end shanks that resulted in bending and breakage of the shanks, yet that kind of intentional loading doesn’t give you pause?

Nothing about a wishbone/rod end arrangement would make me happy when there are other superior methods to be used.

Not that it has to do with anything, but the Speed Demon joints were not broken, but until I verified that it was a serious concern.  Simply having survived a crash doesn’t validate the methodology used.
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« Reply #97 on: January 08, 2015, 01:24:55 PM »

First choice was an X link like this but there is no room for that. You can see all the rod ends are side loaded like mine. That is a picture of a very high hp drag car.



 Then I considered a diagonal but it won't fit as the pinion is so low and this differential is huge in general. No room for a watts link and I don't care for a panhard bar.

So I ended up with this. This wishbone allows the suspension travel I need, and will easily unbolt to allow enough droop to remove the wheels so that we don't have to have fender arches that are cut away to allow tire removal. This setup is very similar to many very high HP drag cars that are much more violent in their behavior.

 Yes I have seen the strength of these joints survive heavy contact with walls that don't move and other cars. That, along with the strength rating of these joints gives me confidence in this setup. Again I am happy with it.
 
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Rex Schimmer
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« Reply #98 on: January 08, 2015, 07:58:59 PM »

Note that Javajoe said:


 Those are 3/4" shank x 5/8" bore rod ends from Aurora. This is a common setup on many drag cars, street cars and off road machines. Google wishbone locator.

This means that the shank of the rod end is a 3/4-16 threaded, the root diameter for this thread is .6891 inches not, as IO stated, .625. As the moment of inertia of a circle is based upon the diameter to the fourth power this would make the moment of inertia of the 3/4-16 tread 1.48 times larger than the .625 diameter and using the same yeild strength of 60,000 psi and the 1 1/2 inch lever arm, the max load at yield would be 1290 lbs. A secondary point is that IO assumed the material to be something like 4130 as rolled which has a tensile strength of 100,000 psi and a yield of 60,000 psi but in reality these rod end bodies are heat treated and a simple quench and temper will easily increase the tensile strength to 144,000 psi with a yield strength of 130,000 psi which would, along with the increased root diameter, raise the load, at yield, in bending to approx 2800 lbs.

I maintain my opinion that the set up is more than strong enough for a car that is designed to go in a straight line with a traction coefficient  (on salt) of  less than .5.

Rex

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javajoe79
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« Reply #99 on: January 08, 2015, 11:07:19 PM »

 cheers
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Peter Jack
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« Reply #100 on: January 08, 2015, 11:41:35 PM »

Knowing the beating those rod ends take in oval track applications I have no fear that those in the salt car will last forever. If they're deformed in any way it will have happened in the process of the car being much more deformed and the rod ends will not be the cause.

Pete
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« Reply #101 on: January 09, 2015, 01:58:10 AM »

The fact that I never furthered my education is irrelevant.

On landracing.com I just know I'll get educated. If you
don't learn anything here you've got yourself to blame.

Thanks all. cheers
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« Reply #102 on: January 09, 2015, 07:41:01 AM »

Mikey and all,

Tauruck, you have taught us all quite a bit.  So have many others taught me over the years. Keep it up I have much to learn.

Thanks also.

Geo
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« Reply #103 on: January 09, 2015, 10:11:39 AM »

Rex,
The purpose of my earlier, almost off-hand calculation was to disabuse the notion that the 10%/4000 lb load could possibly apply to the shank capacity.  It seems to have done that.  I knew the diameter was slightly small so as to include something of a stress concentration factor, however an actual factor would likely be even more severe.  Even with your unfounded speculation as to the yield strength, the result confirms that the 4000 doesn’t apply.

I suspect Aurora builds their stuff to perform adequately for their envisioned application.  Given the 40,000 lb rating, it appears the material is probably in the 105,000-110,000 psi yield range, a fairly common mid-level fastener material.  But there are many ways to get there that may or may not include some hidden pit-falls.  Perhaps when you confirm the actual shank chemistry, heat treat, tensile properties, hardness, Charpy values, geometrical concentration factors, residual stress, and hydrogen embrittlement/stress corrosion cracking propensity of the steel in a marine environment, a more accurate assessment could be made.
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« Reply #104 on: January 09, 2015, 10:22:44 AM »

Perhaps....

 Heard back from Lefevers. He likes it. Also had another trusted racer stop by the shop and he likes it too.   

 
 May be a few more days before I have more progress but I will have more updates soon.

I should have the rear coilovers today. Planning on a screw jack arrangement for the upper mount so as to allow easy ride height changes just by opening the hatch. Front ride height will also be on a screw jack as we will be using nascar style upper spring perches with large diameter springs.

 Anyone have any thoughts on front spring rate?  Thinking 1500+ lbs of weight on each corner. I have seen surplus nascar springs in the 2000lb/in range and that is what I was considering.
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