Dual Stage Spring Setup ?

[Matt49]

I'm glad you responded, even though condescendingly. You are taking my remarks out of context. I made the remark simply because of a simple concept. Understanding one is much easier than understanding two. Hooke's is reliant and is only a 1st order operation. A very generic way of looking at things. Why do we check springs to see if they have maintained their dimension? I will suggest that we test them because during dynamic operation the first order operation variables may change. For how long? When? How?Your spring lasts forever, but my spring doesn't. Whose right?Let's now get away from the simple Hooke's and move to the second order operations:Newtons second law: mx" + cx' +kx = F(t)forced, unforced, damped, or undamped.Do these two different spring rate springs have different frequencies? Different dynamic forces upon them?Here is an important question for you:I build a coil spring suspension for a highway pickup. I use a 800 pound 8" spring and a 700 pound 4" spring stacked on the right rear. Which one will wear out first? The short or the long? Now an 800pound against a 200 pound? Which one is doing more work or risks moving outside the 1st order?That question will never be answered by a first order operation. My point is that formulas that relate springs of different rates in the 1st order often don't tell the whole story. But since you already knew that it doesn't really matter in this conversation does it?

I think the condescension started when you said that anyone who thinks there is an equation for this or that is foolish. Now here you are trying to lecture me on second order linear equations (or operations as you like to call them). I took a little math in engineering school but thanks for the refresher on Newton's second law.
If it happens in physics, it can be explained with math. Your original post seemed to imply that wasn't the case and anybody that thought it was the case was foolish. I obviously misread or misunderstood something. I'm moving on.

If you agree that all thing in physics can be explained using math, then I think we're on the same page albeit not necessarily speaking the same language.

[let-r-eat]

I apologize if my remarks were out of context. If equations were the rule of the world we wouldn't have tests.........We would already know the result. There would be no reason for trial and error.

[Ghopper]

I apologize if my remarks were out of context. If equations were the rule of the world we wouldn't have tests.........We would already know the result. There would be no reason for trial and error.

I am a simulation guy, but -

We are looking at low frequency applications, with low velocities........so heat and fatigue in the life of a dirt springs is not that big of a deal. Also this is a passive system! So I think we can keep it simple.

I suggest using a spring rate machine that tests the whole spring/damper system and take good notes in your testing.



Ghopper

[Matt49]

I apologize if my remarks were out of context. If equations were the rule of the world we wouldn't have tests.........We would already know the result. There would be no reason for trial and error.

I agree...there is no reason for trial and error. That is a completely unscientific problem solving methodology. The only reason to test anything is to verify or nullify a hypothesis. We try/test things on race cars not because we don't know the result of one change but because we don't know if that one change will improve an overall situation (i.e. a larger more complex system with external variables (e.g. track conditions and driver input)).
I guess I would still like for you to provide me with an example of when a spring (or combination of springs) would provide a non-linear rate without some type of coil bind or other external forces being introduced.
You said that stacked spring was not cut and dry. I'm simply saying that it is. Provide me with an example of when it isn't and I'm all ears. Otherwise, I think we're going in circles here.

[drtrkr244]

Hmmmmm! I wondered why alot of the super dlm drivers have a Gale Force in their hauler!

[let-r-eat]

I agree...there is no reason for trial and error. That is a completely unscientific problem solving methodology. The only reason to test anything is to verify or nullify a hypothesis. We try/test things on race cars not because we don't know the result of one change but because we don't know if that one change will improve an overall situation (i.e. a larger more complex system with external variables (e.g. track conditions and driver input)). I guess I would still like for you to provide me with an example of when a spring (or combination of springs) would provide a non-linear rate without some type of coil bind or other external forces being introduced. You said that stacked spring was not cut and dry. I'm simply saying that it is. Provide me with an example of when it isn't and I'm all ears. Otherwise, I think we're going in circles here.

The problem is not determining when a bind may occur. The problem is in determining when the next one will, or the next one, or the next one, or the next one, along with what direction the forces are moving. The problem is this often creates a strain beyond the modulus of elasticity of the material. Here is a short explanation: Lets take a sudden jounce:Using this formula shown here:http://mathworld.wolfram.com/QuarticEquation.htmlYou One can take the modulus of the material and calculate the first, second, and third orders and find that many times during a suspension event the modulus of the material may be exceeded when bind occurs using the wrong combination of parts. Such as placing too much burden on the first stage. I could do some of the math for you but that's what we have computer programs for. The modulus of elasticity depends on how much of the grain structure of the material suggests an isotropic or anisotropic structure. Young's is dependent on this and determines a materials response in Hooke's The more one can understand the directions, the more one can use the dampening to control them or understand when you are "out of bounds" with a particular application. Such as a 50# spring stacked on a 2000# spring, not that you would or anything but using as an example. Placing 2 springs on top of each other can make it a two-fold problem in determining when these events that strain the modulus the most occur. The linear portion of the stress or strain curve, although linear in slope, will depend on the isotropic structure of the material.The bottom line:The quality of the material matters and a basic assumption about the material is all a man has with the spring, a rater or calculator. The average Joe, experimenting as they do, may create a combination that is *out of bounds* Just like a valve spring or any other spring. That reason is what I was trying to explain. A person must know when they are putting themselves in a position that places their arrangement "out of bounds." Much easier to get out of bounds with 2 than with 1................................................. .................................................. ........................................Ghopper,An ything that has a frequency is doing work. Work creates heat. What happens when you warm something you are measuring 10 degrees? It expands < modulus of elasticity on carbon steels. Although may seems trivial but really matters more than one may think. ***********************************Summation****** ***************************** There is also strains that are not along the major movements. We control this buy understanding what we are working with and the dampening of those forces. Let's go back to the, 150# spring against a 2000# spring................= 193# spring. Anyone see a problem if the dampening isn't controlled precisely or the crossover point isn't controlled appropriately?That is the reason why you need trial and error.

[let-r-eat]

Gale Force is a nice piece of equipment for its purpose.

[Matt49]

You might want to check your math on what the resultant spring rate is when combining a 150 pound spring with a 2000 pound spring. Based on what you typed and what it actually is I'll give you the benefit of the doubt and assume it was a typo.
You think trial and error has its place and I call it guessing. Let's agree to disagree.

[Ghopper]

Ghopper,Anything that has a frequency is doing work. Work creates heat. What happens when you warm something you are measuring 10 degrees? It expands < modulus of elasticity on carbon steels. Although may seems trivial but really matters more than one may think.

Really. How much? I think your sensitivities are off. You are focusing on details that pertain to .01% usage in our dirt car application.

Question - Did you ever change your springs at the track because of the grain structure or operational spring temperature was not within your tolerance?



Damping:
These folk are combining 200-800lb/in springs with a 0.5-1" gap. We are not really concerned with the damping for the travel range that is outside of 95% usage. Example is that we spend 95% of the time within 3-4" of damper travel. Look at the spring rate at this point and set your damping (or overdamping) for this state.....which is most likely on the primary spring.


The question that we all are trying to master is having the right dynamic wedge for our combination. That is a much more simple quest than writing a Matlab program to study temperature/friction/noise/vibration/impacts of the spring on the damper. We can figure this out without textbooks on Mechanics of Materials or Mechanics of Vibrations.

The spring and damping combinations discussed is just not at any component extremes.



Ghopper

[let-r-eat]

You might want to check your math on what the resultant spring rate is when combining a 150 pound spring with a 2000 pound spring. Based on what you typed and what it actually is I'll give you the benefit of the doubt and assume it was a typo. You think trial and error has its place and I call it guessing. Let's agree to disagree.

You would be kind enough to check it for me and show your work so I might be able to understand it?

[let-r-eat]

Really. How much? I think your sensitivities are off. You are focusing on details that pertain to .01% usage in our dirt car application.Question - Did you ever change your springs at the track because of the grain structure or operational spring temperature was not within your tolerance? Damping:These folk are combining 200-800lb/in springs with a 0.5-1" gap. We are not really concerned with the damping for the travel range that is outside of 95% usage. Example is that we spend 95% of the time within 3-4" of damper travel. Look at the spring rate at this point and set your damping (or overdamping) for this state.....which is most likely on the primary spring.The question that we all are trying to master is having the right dynamic wedge for our combination. That is a much more simple quest than writing a Matlab program to study temperature/friction/noise/vibration/impacts of the spring on the damper. We can figure this out without textbooks on Mechanics of Materials or Mechanics of Vibrations. The spring and damping combinations discussed is just not at any component extremes. Ghopper

I agree its a little deep. But you have to know where the bottom of the hole is if your going to jump.

[Matt49]

You would be kind enough to check it for me and show your work so I might be able to understand it?

The combined spring rate of two stacked springs is the product of the two spring rates divided by the sum of the two spring rates. Or (A*B)/(A+B)
(2000*150)/(2000+150) =
300000/2150 =
139.5

Now...would you be kind enough to check your math again and show me your math along with the work and you figured 193 so I might be able to understand how you could possibly combine two springs and end up with a rate that is greater than the lesser of the two originals. Because I'm pretty sure it's physically impossible.

[let-r-eat]

I transposed the numbers. Sorry about that. I didn't double check. Of course there is no math that will reach a higher rate than the lowest rate of the stack. Our problem is determining the work on that 4" spring with the 150# rate.Now that we have a 4" 150# spring.atop a 8" 2000# spring. How much weight to reach coil bind on that 150# spring? 139/150 = .926 Assuming below parameters for 4" spring we have 398 is .926 of 427# as the rate at which coil bind of 150# spring occurs. So now we need to consider the ratio of rates when doing the calculations. Assume spring parameters are .341 wire, 4" free length, and 3.5 outside diameter..........The answer is the point I'm trying to make. The ratio of rates matter and coil binding the spring often without control the dampening properly can make the handling erratic. Why? What happens after the spring binds. What does the rate go to then?

[Matt49]

Yeah...I know you didn't double check...that's why I suggested that you do so. And even suggested that you may have made a typo. But you ignored that suggestion and instead asked me to "show my work" as if I'm your student here or something. ha ha ha.

I KNOW that the rate will change when coil bind starts to occur. I've been saying that since LITERALLY three days ago on this thread. Coil bind is not occurring on any stack spring setup I have seen on a late model which is why I refuted your comment that "equations for this or that is foolish" in the first place. The equations work. Period.

The first time I see a 150 pound spring stacked with a 2000 pound spring on any type of race car I will let you know.
In fact when I see a 300 with a 1000 I'll let you know.

[let-r-eat]

Yeah...I know you didn't double check...that's why I suggested that you do so. And even suggested that you may have made a typo. But you ignored that suggestion and instead asked me to "show my work" as if I'm your student here or something. ha ha ha.I KNOW that the rate will change when coil bind starts to occur. I've been saying that since LITERALLY three days ago on this thread. Coil bind is not occurring on any stack spring setup I have seen on a late model which is why I refuted your comment that "equations for this or that is foolish" in the first place. The equations work. Period.The first time I see a 150 pound spring stacked with a 2000 pound spring on any type of race car I will let you know.In fact when I see a 300 with a 1000 I'll let you know.

I was being sarcastic of course because you knew that I knew that you knew..............lolBut back to the topic:Now, Why was the stacked spring created for left rear applications? Could it be because the desired rate/dimension would bow? Bowing doesn't occur with a traditional spring within traditional parameters? What is the bow's effect on rate?You are still dealing with trivial elements that I assume we both know about. How does your equation predict bowing or I assume you think it doesn't matter?The rub marks created from coil springs just happen......?? That pitch I talked about earlier doesn't have a thing to do with bowing?I'm waiting on your equation for that?Could this be another reason for testing?HMMMMMMMM>