Does a bend in a link effect the geometry of the suspension?

[tom@vp]

he just said the same thing.

Originally Posted by DeoreDX

Now my engineering expertise is in seismic rated industrial structural systems not suspension geometry but physics is physics and it should hold true here as well. Looking at the video it looks like you are picking the truck in in a way to load the rear axle in a way that would simulate the load the rear axle sees under acceleration. From a rotational mechanics perspective what is between the ends of the link isn't important, the geometry is defined by the distance between the connection/end points of the link. As long as the end to end link distances are the same the shape of the link is totally irrelevant to the arch the suspension will travel, at least until you start increasing the forces in the system. When loaded as under acceleration bottom link will be in compression while the top link will be in tension to counteract the rotation of the axle. While the forces at the ends of the link are the same with a straight link or a curved link, what is different is the stresses inside of the link itself. A straight bar in tension or compression is much stronger than a bent bar in tension or compression. Draw an imaginary line from the link and to the link end. The farther your link strays away from that line the higher stresses it will see. The higher the stresses the more the link will deform under load. The more the link deforms under load the more the design will stray from the performance of the pretty unloaded engineering drawing someone made. I can't see how just flipping a curved link upside down would change the suspension, but then again I might be missing something since this is the first time I've looked at the physics of a 4 link suspension geometry.

[Duuuuuuuude]

Somebody build this:



This setup will give us repeatability and measure whether there are any lifting/squatting forces applied with a bent lint vs a straight one.

[DeoreDX]

Originally Posted by tom@vp

he just said the same thing.

Well said it much more eloquently and succinctly

[Brandon]

Originally Posted by Erik D_lux

Would this model be hard to setup in CAD? I wonder if it would show similar results?

Extremely easy to setup in CAD. However, I can promise you it wont make a difference.

[tom@vp]

great fixture

eyeball engineering to the rescue ?

need to add a way to measure the compression or decompression length of the bent link

Originally Posted by Duuuuuuuude

Somebody build this:



This setup will give us repeatability and measure whether there are any lifting/squatting forces applied with a bent lint vs a straight one.

[spidr]

In the 1:1 world, the only thing we care about is the end points. Geometry is not effected at all by the shape of the link.
Rcs are a whole differant ball game.The things that you can get away with on small scale would never fly in full scale, and things flex. I can run the RC and watch shocks flex and twist, plastic rod ends flex when maxed, everything moves a whole lot easier. I dont think that the video is a fair comparison though to be completly honest. Run it up a rock, actually drive it up, off camber, wouldnt be too bad to run the exact same line before and after and do the same type of video. I'd bet that it makes zero differance provided that the bends are causing the rod ends to contact anywhere.

[johnnyh66]

an arc is an arc.
I could do a quick test in Maya with different bent links using the same pivot points but it doesn't make any sense to me... so I'm not going to.

[ROWDY RACING]

Ti in first vid, all thread in second?

If so thats apples and oranges and I'd bet the all thread flexes more.

[Duuuuuuuude]

Originally Posted by tom@vp

great fixture

eyeball engineering to the rescue ?

need to add a way to measure the compression or decompression length of the bent link

My cape and superhero mask is in the mail. If it weren't for MLK day it would have been here by now.


Compression/decompression would be easy, though it might require molestation of a digital caliper....ie...drill a hole in each arm and bolt it on with the link. If the link flexes it'll pick it up.

[Duuuuuuuude]

Originally Posted by ROWDY RACING

Ti in first vid, all thread in second?

If so thats apples and oranges and I'd bet the all thread flexes more.

[Harley]

Endpoint to endpoint. #physics

Only variable is material properties.

[Calderwood]

Originally Posted by Harley

Endpoint to endpoint. #physics

Only variable is material properties.

Physics is physics is physics.

[DeoreDX]

I made a quick model of a link. 4" (101.6mm) from eyelet to eyelet. I picked an arbitrary number of 10lbs in the X axis for the load which was applied to one eyelet. I measured the reaction forces at the other eyelet.



This first analysis is with 15 degree bend. It's hard to see when resized @ 800pixels so click the link for the full size. Reaction @ the eyelet in the X direction is 10lbs. Reaction in the Y direction for all intents and purposes is zero. FEA solvers have a problem calculating Zero so you will have to trust that 0.0000000002 is as close to zero as you will get from this particular solver.

https://lh6.googleusercontent.com/-7..._15_Degree.jpg



Here is a link with a 30 degree bend. Same eye to eye dimension of 101.6mm and same 10lbs load. Reaction forces are the same, zero off axis and 10lbs in the X axis. Displacement has jumped 239% under the same load. Stresses has increased 203%.

https://lh3.googleusercontent.com/-e..._30_Degree.jpg



Finally I did a sensitivity study and varied the angle of the bend in the link from 1 to 40 to see how the stresses and displacement behave when the angle of the link is varied. The stresses in the link behave in a linear fashion while the displacement behave non-linearly.

https://lh5.googleusercontent.com/-P...ensitivity.jpg

[The Violator]

Should be required reading for getting a vendors star.

[Erik D_lux]

Originally Posted by tom@vp

the major difference between a straight link, and an extremely bend link is,

the straight link does not change in length.

the bent link is now a spring, and unless you used precise bending technique, your springs are different even if they are the same length.

even with a precise bending technique, the springs would vary tremendously, especially with extreme bends.

Another way that a bend could affect the geo....

Originally Posted by Calderwood

Well I was just trying to say that if you take a straight link and bend it than the length changes which I turn changes the geometry. If the bent link is the same length and the straight link it replaced than nothing changes.

Originally Posted by ROWDY RACING

Ti in first vid, all thread in second?

If so thats apples and oranges and I'd bet the all thread flexes more.

Originally Posted by Erik D_lux

Between the two videos not a thing changed other then the bends. I didnt even take the links off, I just turned them around.

Originally Posted by ROWDY RACING

Did that screw the rod ends in or out changing the length?

One end should have threaded in, the other should have threaded out. Should not have changed other than where the bend lies, slightly.

Originally Posted by spidr

Run it up a rock, actually drive it up, off camber, wouldnt be too bad to run the exact same line before and after and do the same type of video. I'd bet that it makes zero differance provided that the bends are causing the rod ends to contact anywhere.

Good idea. I might have to go do that.

Originally Posted by The Violator

Should be required reading for getting a vendors star.

Are bent links covered in that book? I have not read it. If it is, do you have a page reference?

[Erik D_lux]

The reason I am holding the rear axle is because its the only idea I have of simulating the axle rotation. I do know that it shows accurate affects on my chassis when I move them up/down at the chassis so that is why I took the assumption when I did it this way too. If anybody has a better simulation, other than driving, which I plan to do, I am all ears.

[SkaldidDog]

From the other thread.

Imagine one of those crazy straws, the liquid still goes from your cup to your mouth. Same as a straight straw. Two points lie on a line, independent of how you get there.

J

[Duuuuuuuude]

Originally Posted by DeoreDX

I made a quick model of a link. 4" (101.6mm) from eyelet to eyelet. I picked an arbitrary number of 10lbs in the X axis for the load which was applied to one eyelet. I measured the reaction forces at the other eyelet.

Just for giggles, can you do it again with the bends near one end of the link?

[Erik D_lux]

Just more food for thought...

My bends are pretty impractical in the video, but what about a bent rod end? I would guess it should have the same impact on a smaller scale?

[ROWDY RACING]

Originally Posted by Erik D_lux

Just more food for thought...

My bends are pretty impractical in the video, but what about a bent rod end? I would guess it should have the same impact on a smaller scale?

I'm guessing it works the same way as those uppers are physically in the center of the axle, but not bolted directly to it.