Watts linkage. What sort of forces involved?

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PietereQ
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Watts linkage. What sort of forces involved?

Post by PietereQ » Sat Feb 05, 2011 5:08 am

A question to you engineers out there (Maurizo, Mats, others???) I made adjustable watts linkage for my GTV6, and before taking the setup to the track I would like to make a static test of the likage (longitudal direction ofc) So how many Newtons do you suggest?
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Re: Watts linkage. What sort of forces involved?

Post by Maurizio » Sun Feb 06, 2011 11:20 pm

Well that is a good one....
As I'm not an automotive engineer I'm not that good in predicting loads on a suspension. And a static load is not the problem, the dynamic loads are the killing ones.

I did the watt linkage story myself, so this is what I did.

First note is that a 75 has straight watt linkage beams which are parallel to the road.
The curved gtv6 linkage is a no go for me! I don't want buckling forces in a curved beam.
If the rods are under an angle (I guess, that a gtv6 has....?) you need to compensate that in the calculation.

What I did was some reverse engineering.
A 75 has hollow rod as linkage tubes 25.4 x 21.1 [mm] about 500 [mm] long.
If you calculate that back: the buckling strength is ~26 [kN]

With that in mind and while load testing at work we always put a 1.5 margin on top of the normal load.
So that would give a testing load (btw Not pull, but push load!!!) of at least 39 [kN].

It's your life, so take these numbers and interpret them wisely :roll:
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Re: Watts linkage. What sort of forces involved?

Post by PietereQ » Mon Feb 07, 2011 2:08 am

Thanks Maurizio,
No bent bars. Only straight ones. I know it's all about safety that's why I wanted them to break rather during a test than taking a corner. I know rsr stuff is the way to go but you see a lot of racers with diy watts linkage, and 429E for race version is a bit too much for me atm. Only pushing forces involved? I thought there is some pulling (tearing) too.
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Re: Watts linkage. What sort of forces involved?

Post by Maurizio » Mon Feb 07, 2011 2:22 am

The pic looks a bit to flimsy for my liking....

There is both pulling and pushing involved, both in the same magnitude.
But the pushing forces (buckling) are the forces to be afraid of wrt to tube diameters!
So without an engineering back ground: I would at least use the same diameter (preferable larger), wall thickness and material as the oem tubes

As an extra note: The weld, thread/bushing, uniball have also the same forces going through....

So yes: The welds, thread etc are best tested under worse case for them read during a pull test.
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Re: Watts linkage. What sort of forces involved?

Post by Zamani » Sun Nov 27, 2011 2:06 pm

Is the goal to make sure the pivot piece is 90 degrees to the dedion? Right now since the car is lowered, the pivot piece is not perpendicular anymore. What if I cut the watts linkage rod and weld it? Keeping in mind the weld has to be strong of course.
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Re: Watts linkage. What sort of forces involved?

Post by Mats » Wed Nov 30, 2011 1:45 pm

The tube will never be the problem, the thread on the joint will be the breaking point.
I would forget about the adjustable var and just make one that is the right length at ride height, it will never be a problem with adjustments, just think about the travel on a stock suspension compared to a race car. Almost zero...
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Re: Watts linkage. What sort of forces involved?

Post by 75evo » Wed Nov 30, 2011 5:47 pm

Sweet thanks! I think my MIG welder should be able to do it. Ill bring a spare watts to the track in case mine breaks! :)
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Re: Watts linkage. What sort of forces involved?

Post by GTV27 » Thu Dec 01, 2011 3:23 am

should have a bend in it like the gtv6

more seriously, per Mats comment, the weakest link is the issue - i'd expect the body mounts to give before the tubes broke (unless you follow the works and allowed a bend .... :wink: )
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Re: Watts linkage. What sort of forces involved?

Post by squadragrunn » Thu Dec 01, 2011 10:12 am

on my gtv turbo i used hollow aluminium rods ca 15mm dia. with uniballs as watts. never had any problem on or of the track!! the car was driven hard!
Last edited by squadragrunn on Thu Dec 01, 2011 10:15 am, edited 1 time in total.
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Re: Watts linkage. What sort of forces involved?

Post by squadragrunn » Thu Dec 01, 2011 10:13 am

rods were straight, the aluminium special tough kind, also used it as a bracing for the enginecompartment and will do that also with my current gtv
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