LFS Forum - Engineers, math help needed (spring forces)

#1 - JTbo

Engineers, math help needed (spring forces)

Fri, 9 Nov 2007 12:54

Parabolic assymetric leaf spring:
Length:1250mm
Width: 60mm
Thickness: 9mm (average, varies between 0.8mm(ends)-1.0mm(middle) ).

Now I have done bit of research and I have come up with only one formula that gives me 104.21kN/m which I find rather wrong.

I'm not an engineer, I don't even understand whole formula, so help would be appreciated

I put formula in a program quite some time ago and can't remember it too well, but maybe helps someone:

Val sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Dim LWmm As Double = txtLW.Text
        Dim LC As Double = txtLC.Text
        Dim LTmm As Double = txtLT.Text
        Dim LLmm As Double = txtLL.Text
        Dim LW As Double = (LWmm / 25.4)
        Dim LT As Double = (LTmm / 25.4)
        Dim LL As Double = (LLmm / 25.4)
        Dim Result2 As Double = FormatNumber((LW * LC / 12 * (1000 * LT / LL) ^ 3 - 14.09), 2)
        'FormatNumber(Result, 2)

        lblResult2.Text = FormatNumber((Result2 * 0.0178890876565295 * 10 * 9.81), 2)

#2 - tristancliffe

Fri, 9 Nov 2007 13:20

I've never calculated stuff about leaf springs - when we get them retempered we tend to tell the company the static distances we want it altered to rather than a rate.

But I found this http://therangerstation.com/tech_library/leafspringrate.htm. Does it help?

And

http://www.thedirtforum.com/leafspringrate.htm
http://www.hexagon.de/fed10_e.htm <- looks interesting, but only glanced at it
http://books.google.com/books? ... 95j1bfvHBW_yM3YLE144YNThA

Hope they help

What are you trying to do?

#3 - JTbo

Fri, 9 Nov 2007 13:51

Some of pages looks familiar, I believe I have nicked formulas from some of those

This same old rTracktor mod (Volvo), I become suspicious about rear spring stiffness and have been doing some more research and testing, seems to be that rear springs are actually stiffer than front :o
So need verification, however handling seem to be more accurate with new values, but it is rather subjective again and specially when there is no good tracks where I have driven etc.

That Google book link looks to be gold, I'm sure that helps even more in future

edit: Oh yes, have you got time to make some measurements of formula car?

#4 - tristancliffe

Fri, 9 Nov 2007 13:56

If it's your own car you are modelling, can you do it practially? i.e. put a known weight in the car (like a brother or parent after weighing them) and measure how much the spring compresses. If it's a solid rear axle, then rim to wheelarch measuring would be even easier, because most solid axles have a 1:1 motion ratio with the spring.

Might not be totally accurate, but maybe close enough.

I should have time soon

#5 - JTbo

Fri, 9 Nov 2007 14:08

That would be of course one method, I just try to avoid physical work and do things in my brain, however my brain is so small

Perhaps I need to get a scale, then I could weight my own weight, put video camera and measure tape in proper place and check how much there is difference, why would I do things simple way?

But I don't think it will be huge problem if I get it off by 5kN/m as even doubling spring rate seemed not to be major effect in rTractor, maybe my tires are just so bad, must try few different tyres, I have come up with some plan with those