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Author: Subject: Usign Rod Ends and Spherical Joints
liam.mccaffrey

posted on 11/4/11 at 10:11 AM Reply With Quote
Usign Rod Ends and Spherical Joints



I have a question which has had me thinking for quite a while. Its where spherical bearings or rod end are used as inboard suspension pivots and specifically whether they are used with their orientation as in the left picture or with the right.

A lot of fast single seat hill climbers tend to have at least one wishbone bearing as in the left picture. Obviously in this configuration its easier to push the bearing past its vertical ROM especially if the wishbone radius is small. To me it seems as though the forces are fed better fed into the chassis pickups this way and without trying to pop the sphere out of the joint.

That said Ive seen an awful lot of cars with inboard pickups with the joint as in the picture on the right.

Can anyone shed some light on what is the right or accepted way to use rod ends/sphericlsl in this way. Or point me in the direction of some relevant reading.

Thanks

I've tried to find a good actual picture of what I'm talking about but I'm struggling.

[Edited on 11/4/11 by liam.mccaffrey]





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designer

posted on 11/4/11 at 10:18 AM Reply With Quote
The left hand is the correct way to mount spherical joints.
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hellbent345

posted on 11/4/11 at 10:24 AM Reply With Quote
the correct way is the one on the left, lots of cars have it arranged like the pic on the right and normally its down to bad design. if you are designing and making from scratch, always arrange them like on the left.
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liam.mccaffrey

posted on 11/4/11 at 10:39 AM Reply With Quote
that was easy, I thought this was going to be a hornets nest





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hellbent345

posted on 11/4/11 at 10:41 AM Reply With Quote
This is the wrong way to do it



And the bottom wishbone in this pic is the right way



Like you said, its right this way because the forces aren't trying to pop the ball out of the housing.

As an aside, its generally bad practice to use rod ends (as in these pics), as unless they are used very carefully, they are normally loaded in bending and the threaded shank is very prone to breakage.






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mangogrooveworkshop

posted on 11/4/11 at 11:10 AM Reply With Quote
quote:
Originally posted by hellbent345
This is the wrong way to do it



And the bottom wishbone in this pic is the right way



Like you said, its right this way because the forces aren't trying to pop the ball out of the housing.

As an aside, its generally bad practice to use rod ends (as in these pics), as unless they are used very carefully, they are normally loaded in bending and the threaded shank is very prone to breakage.



Top photo is a beetle pan .






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Fred W B

posted on 11/4/11 at 11:27 AM Reply With Quote
quote:

The left hand is the correct way to mount spherical joints.




quote:

that was easy, I thought this was going to be a hornets nest



Until you try to get enough articulation, if this is for a road car. I tried, and gave up eventually. Their is a reason most cars are done the "wrong" way. I used 12 mm ends to compensate.

Cheers

Fred W B





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Mr Whippy

posted on 11/4/11 at 11:55 AM Reply With Quote
just to put a spanner in the works of you logic... the correct way with it horizontal does produce a very small contact patch within the bearing for sideloads, where as having the joint the wrong way i.e vertical would produce a larger ring shaped contact area. I suspect that would make the joint last longer or would would mean it was less likely to be damaged. Plus the forces required to extract that ball from the housing would probably destroy the suspension in the process.






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onenastyviper

posted on 11/4/11 at 12:13 PM Reply With Quote
quote:
Originally posted by Mr Whippy
just to put a spanner in the works of you logic... the correct way with it horizontal does produce a very small contact patch within the bearing for sideloads, where as having the joint the wrong way i.e vertical would produce a larger ring shaped contact area. I suspect that would make the joint last longer or would would mean it was less likely to be damaged. Plus the forces required to extract that ball from the housing would probably destroy the suspension in the process.


I do not understand this? Are you talking about the difference between the alignments in the original post picture?

With regard to mounting sperical rod ends, is it not best to align the shank with the direction of applied loads and use wishbones that are more triangulated so that where the rod end meets the chassis it is at an appropriate angle rather than normal (i.e. 90deg) from the chassis?

Yeesh, my head hurts.

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coyoteboy

posted on 11/4/11 at 12:25 PM Reply With Quote
Even on a track car it's pretty hard to achieve sufficient suspension articulation with them mounted in the "correct" way. FWIW they're mounted in the "wrong" way on my tin top road car from the factory.
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liam.mccaffrey

posted on 11/4/11 at 12:35 PM Reply With Quote
I'll be able to get enough articulation on the front of my car but the back may take some thinking about.

Thanks for all the input so far

[Edited on 11/4/11 by liam.mccaffrey]





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blakep82

posted on 11/4/11 at 12:36 PM Reply With Quote
^ yep, and on my pickup, chassis built by SHP, who have been building track and oval race cars for ever lol. they know a thing or two about suspension i'd say

i agree with whippy though. think mounted the 'wrong' way may well mean they last a bit longer.
i'm not sure theres really a huge problem with being the 'wrong' way round. i appreciate that the loads may well be trying to pop the ball out of the joint, but i wouldn't think its a huge issue. i would think it works more like trying to pull the suspension out on the front joint, and pushing the rear joint in, bearing in mind that if you didn't have a steering rack on a car, and try driving it forward, both front wheels are trying to point outwards

like this

Description
Description


i think, but just an opinion, no scientific fact

[Edited on 11/4/11 by blakep82]





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hughpinder

posted on 11/4/11 at 12:37 PM Reply With Quote
Both ways could be correct. The key point is to work out the direction/magnitude of the applied forces, and the the amount of articulation required. Rod ends are supposed to be set up so they are in tension/compression along the thread. Since this is probably impossible to achieve for this use, you just need to decide which orientation gives least force trying to push the ball out. This will depend on suspension geometry/bumps in the road producing forces in odd directions. Personally I'd go for the right hand picture for a road car, because of the large movement of the wheel up and down. In a track/race car, this movement is much less, so it could be either way, and the lower photo with the thread straight down the suspension arm would certainly resist forwards/backwards (extreme acceleration/deceleration) forces better, but worse in the up/down direction.

All my opinion of course, I'm not a mechnaical engineer.

Regards
Hugh

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coyoteboy

posted on 11/4/11 at 12:39 PM Reply With Quote
In mine the sphericals normally mount where the two cross-axle red bushes have been placed here:

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onenastyviper

posted on 11/4/11 at 12:53 PM Reply With Quote
Still confused, pictures please?
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adithorp

posted on 11/4/11 at 03:12 PM Reply With Quote
I think a lot of kits have them mounted the "wrong way" because then one chassis can be made with one set of brackets but assembled with either metalastic bushes, poly bushes or rod ends.





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Volvorsport

posted on 11/4/11 at 04:14 PM Reply With Quote
ideally , you need to buy high articulation joints , but these can run into 70-80 a pop for a 5/8 joint .

again , you need to work forces out to specify a joint properly .

our tarmac chapionship winning darrians had them mounted the 'wrong' way ...........

you could always specify inner joints with poly bush the outer joint in high articulation rose joint for some adjustment .

im interested in that beetle front end ? where did it come from ?





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getting dirty under a bus

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Doctor Derek Doctors

posted on 12/4/11 at 07:11 AM Reply With Quote
They may be the 'wrong way' but in a decade of running all sort of race cars I have never seen a car manage to pop the ball out its socket.

I have seen rod ends so badly worn that the have at least 3mm of float but still hanging together and cars utterly obliterated in crash with the wishbone torn clean off the rod ends but the rod end undamaged.

Using a bit of common sense with this sort of car on the inner wishbones were you have two rod ends they are plenty sufficient to do the job even if they are mounted the 'wrong way' on the outer front were you only have one rod end it will need to be mounted in the horizontal plane.

The other advantage of mounting the inner rod ends vertically is that you can adjust the caster angle easily by moving the wishbones back or forth with different length spacers.

Something I have noticed in building a 'Locost' is that many people try force very high end design criteria onto a car that doesn't really need it that would be driven by a driver who wouldn't be able to tell any difference and I think this is one of those times.

I work in F1 as a designer and my Race Car has its inner rod ends mounted vertically because that is the best way for that car.

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liam.mccaffrey

posted on 12/4/11 at 09:46 AM Reply With Quote
All very interesting, thanks guys





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mrwibble

posted on 12/4/11 at 10:09 AM Reply With Quote
very interesting. can i just ask a noob question and determine if a spherical bearing is the same as that used in a rose joint, and if rod end is also the same thing. ta
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Bluemoon

posted on 12/4/11 at 10:48 AM Reply With Quote
quote:
Originally posted by mrwibble
very interesting. can i just ask a noob question and determine if a spherical bearing is the same as that used in a rose joint, and if rod end is also the same thing. ta


Yes (that's my understanding).

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designer

posted on 12/4/11 at 10:56 AM Reply With Quote
Yep, they are the same.

Rose is a trade name, just like a vac. is called a Hoover.

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b14wrc

posted on 12/4/11 at 11:20 AM Reply With Quote
coyoteboy

'posted on 11/4/11 at 01:39 PM

In mine the sphericals normally mount where the two cross-axle red bushes have been placed here: '


Is your car a Celica GTfour? The hub in your photo looks like the rear end bit!

Going back to polybushes and what the average driver can feel, are rose joints better (per ) than polyurethane bushes??

Cheers, Rob





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coyoteboy

posted on 12/4/11 at 11:36 AM Reply With Quote
quote:
Something I have noticed in building a 'Locost' is that many people try force very high end design criteria onto a car that doesn't really need it that would be driven by a driver who wouldn't be able to tell any difference and I think this is one of those times.

I work in F1 as a designer and my Race Car has its inner rod ends mounted vertically because that is the best way for that car.

Yep, you see it's properly engineered. There's no "correct" way to mount things if they function in many ways, there's jsut a correct usage and design which could be one of many ways.

b14 - good eye
Rose joints are infinitely better than polybushes if the suspension was designed without compliance in the joint. If the suspension was designed to squish a bit the rose joints would cause issues.

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adithorp

posted on 12/4/11 at 12:33 PM Reply With Quote
quote:
Originally posted by Doctor Derek Doctors
They may be the 'wrong way' but in a decade of running all sort of race cars I have never seen a car manage to pop the ball out its socket.




... and if they did, whats going to happen? At worst there'll be a lot of play and change in geometry, but the arm won't escape off the bolt. The consequenses of a track rod end or ball joint poping out are far worse.





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