Post Rig References

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LuisAlvesBR
0
Joined: Fri Dec 22, 2017 1:12 pm
Location: São Paulo, Brazil

Post Rig References

Post by LuisAlvesBR » Fri Dec 22, 2017 1:39 pm

Hey guys,

I'm searching for some book or document that explain about Post Rig Tests. I'm looking for a mathematical equations and theory that gives me the knowledge to develop a some models of vibrations (like a simple quarter model of car), how to evaluate a post rig results, how to tune the damper with this results, how to apply this on real cases.

I just found a book a book called "Aerodynamic and Aero Post Rig Analysis Race Cars". I'm going to buy this book but I don't know if this is exactly what I'm searching. I'm from Brazil and I'm waiting the book arrives.

If someone already read this book and can send your review or if someone knows some book or document about this theme, please tell me.

Thank you all,

Luis Alves

WilO
4
Joined: Fri Jan 01, 2010 2:09 pm

Re: Post Rig References

Post by WilO » Fri Dec 22, 2017 9:44 pm

Hi Luis,

You've come to the right place, see for example viewtopic.php?f=6&t=7710

DaveW is the guy to pay attention to in this thread, and any other that he contributes to, for that matter. As you'll see, he's a wealth of information, a brilliant guy. There are some papers referenced at the bottom of the first page....enjoy.

Wil

WilO
4
Joined: Fri Jan 01, 2010 2:09 pm

Re: Post Rig References

Post by WilO » Sat Dec 23, 2017 1:53 pm

Hi Luis,

My first reply was a quick one, as I was on my way out the door, but I think your question deserves a more complete answer.
I would suggest you search this forum for post rigs, and damper tuning, as you'll find a wealth of information. There are three people I pay particular attention to: DaveW, GspeedR, and 747Heavy. These guys really know the subject well, from first principles if you will, and have been generous with their knowledge.

A word of caution, though. I don't know what your level of knowledge is, I don't know if you've taken classical mechanics, system dynamics, etc. If you haven't, I would strongly suggest you establish a background in those topics, and the relevant mathematics. There are several good texts on dynamics and control theory, some of which include quarter-car models as examples. Additionally, a quick internet search will yield MATLAB and Simulink models that you can implement in Octave or SciLab if you don't have access to MATLAB. Just remember, there's nothing magical about the topic just because we're talking about cars, so the same fundamental knowledge applies (vibration theory). Once you've modeled the quarter-car, you can begin to think about the dynamics of front and rear axles being subject to a particular input on a rig, and how the modes of vibration are coupled (does a pure heave input result in a pure heave response from the vehicle, or do we find a pitch response as well?).
It's a really interesting topic, just make sure you begin at the beginning, so to speak. You'll save yourself a lot of time, believe me.......

Jersey Tom
257
Joined: Mon May 29, 2006 7:49 pm
Location: Huntersville, NC

Re: Post Rig References

Post by Jersey Tom » Sat Dec 23, 2017 2:33 pm

There are two halves of this, one of which is more pure theory, the other perhaps more empirical.

Theory
Vibrations and system dynamics - this falls under classical engineering education. I don't have a particular textbook in mind that I'd recommend, I've been out of the classroom for 10 years and didn't feel like I was great with the topic back then!

Something to bear in mind though is that it's relatively easy to have a pure, closed-form solution to a trivially simple system - e.g. quarter car with a constant mass, constant linear spring rate, and constant linear damping rate. It's good for illustrating the general concepts, tinkering around and seeing how forces and displacements change as you alter parameters. In reality though, dampers don't have purely linear responses - nor purely dependent on velocity - so a closed-form solution is probably either impractical or impossible.

If you're an engineering student and have access to something like Simulink or Dymola, you can quickly and easily create a quarter car model as a block diagram - and take advantage of built-in blocks to where you could add a non-linear table damper or other things and see what they do.


Application
Assuming you had mastered the pure science or modeling aspect (a significant venture in itself!) there's then the question of... what do you do with it. How do you know what the results mean? How do you know what's going to be faster on the racetrack?

I would say there is no closed-form obvious answer to this. You need to come up with the answer - often by lots of experimenting and track testing, finding your own rules and recommendations. In my experience, success in pro motorsport engineering is highly contingent on building up a good notebook of your own experiences, particularly between theory and real world measurement. "The answer" doesn't just jump out at you - it's an empirical endeavor that builds on itself over time.

Often there's some tradeoff or relative weighting to "mechanical grip" (control of tires) versus the sprung aerodynamic platform. I suppose if you had a target ride height and could get better platform control without a mechanical grip penalty - that's perhaps an obvious free lunch. Of course that assumes your aero data is truly accurate and it's the "right" ride height to be targeting for the right reasons (downforce and drag trade offs, etc). Or you might easily postulate that it's probably not a good thing for a vehicle to be wildly under-damped, that's another freebie you might come up with. Otherwise - it's a compromise. You'll have to find out, for your type of vehicle, what the weighting is for platform vs. mechanical. Or how much front versus rear. Main springs versus the tires as springs. How over-damped or under-damped. Etc. etc.

If it seems like a daunting task with a lot of design space to cover - it is - especially early on when you're starting from scratch and scanning a broad range of things. Eventually though you may find patterns and things that correlate, or tangible measurements you can work with. Maybe you discover, "Okay... at the race track, it seems like X ratio of critical damping is best for speed and driver feel. Now if I want to try Y amount stiffer springs, I'll have to add Z overall damping to get back to X damping ratio since I believe that's a good quantity." Things like that.

Of course, there are those on this forum with a lot more industry experience with this specific topic - but it's my two cents.
Grip is a four letter word. All opinions are my own and not those of current or previous employers.

LuisAlvesBR
0
Joined: Fri Dec 22, 2017 1:12 pm
Location: São Paulo, Brazil

Re: Post Rig References

Post by LuisAlvesBR » Mon Jan 15, 2018 6:52 pm

WilO wrote:
Sat Dec 23, 2017 1:53 pm
Hi Luis,

My first reply was a quick one, as I was on my way out the door, but I think your question deserves a more complete answer.
I would suggest you search this forum for post rigs, and damper tuning, as you'll find a wealth of information. There are three people I pay particular attention to: DaveW, GspeedR, and 747Heavy. These guys really know the subject well, from first principles if you will, and have been generous with their knowledge.

A word of caution, though. I don't know what your level of knowledge is, I don't know if you've taken classical mechanics, system dynamics, etc. If you haven't, I would strongly suggest you establish a background in those topics, and the relevant mathematics. There are several good texts on dynamics and control theory, some of which include quarter-car models as examples. Additionally, a quick internet search will yield MATLAB and Simulink models that you can implement in Octave or SciLab if you don't have access to MATLAB. Just remember, there's nothing magical about the topic just because we're talking about cars, so the same fundamental knowledge applies (vibration theory). Once you've modeled the quarter-car, you can begin to think about the dynamics of front and rear axles being subject to a particular input on a rig, and how the modes of vibration are coupled (does a pure heave input result in a pure heave response from the vehicle, or do we find a pitch response as well?).
It's a really interesting topic, just make sure you begin at the beginning, so to speak. You'll save yourself a lot of time, believe me.......
Hi WilO,

Before all, thanks for you reply.

I will check the post that you recommended and reply you after this.

To be more specific on what I'm working now this is the points:

1 - Quarter car model

I just developed a quarter car model in Simulink with a rig.

So now I can input some frequency at the rig and see how the system works.

About this I wanna validate my model with another one to go to the next step, a half car model.

2 - Half car model

I'm waiting for the quarter car model validation and some examples of half car models to start the development.

3 - Data Analysis

Now I have the data from my quarter car model, but I don't know how to evaluate which setup is better. I'm thinking in reduce wheel load variation, but i don't know if it is simple like this way...

So my main doubts are about my model accuracy and how to use the data to improve my car. I think at the post I will find something, but I still searching for a book.

Thanks for all,

Luis Alves

LuisAlvesBR
0
Joined: Fri Dec 22, 2017 1:12 pm
Location: São Paulo, Brazil

Re: Post Rig References

Post by LuisAlvesBR » Mon Jan 15, 2018 7:05 pm

Jersey Tom wrote:
Sat Dec 23, 2017 2:33 pm
There are two halves of this, one of which is more pure theory, the other perhaps more empirical.

Theory
Vibrations and system dynamics - this falls under classical engineering education. I don't have a particular textbook in mind that I'd recommend, I've been out of the classroom for 10 years and didn't feel like I was great with the topic back then!

Something to bear in mind though is that it's relatively easy to have a pure, closed-form solution to a trivially simple system - e.g. quarter car with a constant mass, constant linear spring rate, and constant linear damping rate. It's good for illustrating the general concepts, tinkering around and seeing how forces and displacements change as you alter parameters. In reality though, dampers don't have purely linear responses - nor purely dependent on velocity - so a closed-form solution is probably either impractical or impossible.

If you're an engineering student and have access to something like Simulink or Dymola, you can quickly and easily create a quarter car model as a block diagram - and take advantage of built-in blocks to where you could add a non-linear table damper or other things and see what they do.


Application
Assuming you had mastered the pure science or modeling aspect (a significant venture in itself!) there's then the question of... what do you do with it. How do you know what the results mean? How do you know what's going to be faster on the racetrack?

I would say there is no closed-form obvious answer to this. You need to come up with the answer - often by lots of experimenting and track testing, finding your own rules and recommendations. In my experience, success in pro motorsport engineering is highly contingent on building up a good notebook of your own experiences, particularly between theory and real world measurement. "The answer" doesn't just jump out at you - it's an empirical endeavor that builds on itself over time.

Often there's some tradeoff or relative weighting to "mechanical grip" (control of tires) versus the sprung aerodynamic platform. I suppose if you had a target ride height and could get better platform control without a mechanical grip penalty - that's perhaps an obvious free lunch. Of course that assumes your aero data is truly accurate and it's the "right" ride height to be targeting for the right reasons (downforce and drag trade offs, etc). Or you might easily postulate that it's probably not a good thing for a vehicle to be wildly under-damped, that's another freebie you might come up with. Otherwise - it's a compromise. You'll have to find out, for your type of vehicle, what the weighting is for platform vs. mechanical. Or how much front versus rear. Main springs versus the tires as springs. How over-damped or under-damped. Etc. etc.

If it seems like a daunting task with a lot of design space to cover - it is - especially early on when you're starting from scratch and scanning a broad range of things. Eventually though you may find patterns and things that correlate, or tangible measurements you can work with. Maybe you discover, "Okay... at the race track, it seems like X ratio of critical damping is best for speed and driver feel. Now if I want to try Y amount stiffer springs, I'll have to add Z overall damping to get back to X damping ratio since I believe that's a good quantity." Things like that.

Of course, there are those on this forum with a lot more industry experience with this specific topic - but it's my two cents.
Hi Jerson Tom,

Thanks for you replcy.

As I spoke to WilO, I just developed a quarter car model in Simulink. The theory I wanna just to check my equations and results.

About the application you told what I was thinking, the methods to improve the car at the racetrack are normally achieved by testing and enginner experience.

I work with race cars for seven years, but just at last year I have the opportunity to tune the dampers. Because of this I don't have expericience or tests in this area so I was searching for some book to put me in some way.

For now I wanna start with two basic setups: One for tracks that needs more mechanical grip and other to benefit more aero grip.

Did you think that is a good start?

Thanks for all,

Luis Alves

LuisAlvesBR
0
Joined: Fri Dec 22, 2017 1:12 pm
Location: São Paulo, Brazil

Re: Post Rig References

Post by LuisAlvesBR » Wed Feb 07, 2018 6:14 pm

I have found a good one.

In the 2nd edition of Jorge Segers book the chapter 12 have a very powerful information about this, this chapter was written by Josep Fontcaba and explain how to create a model and how to use the information.

Sandra04
0
Joined: Mon Feb 12, 2018 2:15 am

Re: Post Rig References

Post by Sandra04 » Mon Feb 12, 2018 2:19 am

WilO wrote:
Fri Dec 22, 2017 9:44 pm
Hi Luis,

You've come to the right place, see for example viewtopic.php?f=6&t=7710 Rachat de crédit

DaveW is the guy to pay attention to in this thread, and any other that he contributes to, for that matter. As you'll see, he's a wealth of information, a brilliant guy. There are some papers referenced at the bottom of the first page....enjoy.

Wil
Hello, thank you very much for the link :)