suspension - statics

[GrannySmithApple]

Hi all, I'm fairly new to SAE and I want to understand more on designing and developing calculations for suspension systems. So I hope you can help me.

I want to develop a basic 2D static analysis excel spread sheet that can determine the loads on the upper and lower A-arms (whether they are in tension or compression). The diagram below is a front view of a double wishbone with a pull rod suspension. Just want to check whether I am on the right path. How would I calculate the force loading on the pull rod?

If you could provide some guidance or any help, much appreciated!

[GrannySmithApple]

Hi all, I'm fairly new to SAE and I want to understand more on designing and developing calculations for suspension systems. So I hope you can help me.

I want to develop a basic 2D static analysis excel spread sheet that can determine the loads on the upper and lower A-arms (whether they are in tension or compression). The diagram below is a front view of a double wishbone with a pull rod suspension. Just want to check whether I am on the right path. How would I calculate the force loading on the pull rod?

If you could provide some guidance or any help, much appreciated!

[Nick Renold]

For 3D analysis:

http://fsae.com/eve/forums/a/t...20226151#21020226151

For 2D analysis:
Write force balance and moment balance equations for each point. Solve.

[GrannySmithApple]

Thanks for your quick reply,

I used "method of joints" by taking the moment at B and then found the remaining forces in the members by doing a force balance in each point as you said. Top arm and lower arm is in compression, with the pull rod in tension. But you said to write moment balance for each point? Could you explain why this is necessary?

thanks!

[Nick Renold]

For your simplified front view, it sounds like you did all the necessary steps.

If you wish to move to 3 dimensions it helps to start with the equilibrium equations (force and moment balance). That is all.

[edd_16]

In the above figure Sdyn and Gdyn represent cornering and ground reactions right?
i am also new to FSAE suspension so its all very confusing to me as well
To solve the equation we would need 2 force equations and a moment equation right?
The force equation could be from the ground and cornering but what about moment equation? do we need to take the roll centre distance as well and make a moment equation such that there is no roll over???
Is this making any sense

[Ray19]

http://www.fsae.com/forums/showthrea...ysis+wishbones
This thread will give you a great idea on how to proceed in calculating wishbone forces. (I am getting a 404 error on the page Nick posted above so sorry if it is a repost)

[edd_16]

Thank you for the fast reply ray
But as explained in the link u posted the forces are for static condition right?
What about the dynamics like cornering accelerating etc.???

[Ray19]

Your previous question about moments can be answered by the thread I linked to although it is in 3d. What do you mean by dynamic conditions? In the above method you can input cornering and acceleration forces at the tire contact patch and see the output as forces on the links. Do you mean to say that you want to analyze on moving links? Also a suggestion, the above FBD approach is the best place to start(and in many cases more than enough) and I would like to see you solve that and get some values first before moving on.

[edd_16]

Thank you Ray
Now i have a clear understanding on many concepts of the foorce and moment calculation
I am learning to prepare the matrix and at the same time working out the FBD approach as well.
Just one little question suppose my tire left front contact patch has co ordinates of x=0,y=0.66m,z=0 and origin is the centerline of my vehicle .
Now if i wanted to calculate my moments on the rear left tyre that has corodinates of x=1.62m(wheelbase) ,y= 0.60m(trackwidth) and z=0(vertical height) with Fx=Fy=Fz=1000N (assuming) the calculations will be
Mx = Fz.Ry - Fy.Rz = 1000x0.60 - 1000x0 = 600 Nm
My = Fx.Rz - Fz.Rx = 1000x0 - 1000x1.620 = -1620 Nm,
Mz = Fy.Rx - Fx.Ry = 1000x(1.620) - 1000x0.60 = 1020 Nm
Is the approach correct???
If yes then you have helped me solve a major problem in my understanding of suspension dynamics