Post rigs

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Mystery Steve
Mystery Steve
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Joined: 25 Sep 2009, 07:04
Location: Cincinnati, OH, USA

Re: Post rigs

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Yes, you can simulate a 7-post shaker on a computer, but like with anything in the world of engineering there is a trade-off. To get the most accurate results, you need to use nonlinear models, which are difficult to setup and take a lot of time that some teams do not have. You can linearize the models, but you limit the range of data that you can examine accurately depending on the point in the data about which the linearization is made, and the engineers that are developing the simulations are aware of this. Even if a team does have the capability to develop these models (I know Ferrari has used a computer simulation of a 7-post shaker), they still need to validate. I know this has become a bit of a buzzword around here in the aerodynamics threads, but it is very important. If an engineer thinks that they fully understand every minute element of an evolving system as complex as an F1 car, they are being naive and overestimating themselves, period.

So, let's set the record straight on what is being accomplished with the 7-, or 8-, post rig. They are not replacing track testing, they are supplementing track testing. Additionally, they are not replacing computer simulation, they are supplementing computer simulation. Two areas of the suspension that have a great effect on handling and response are the tires and dampers. Constant efforts go into modeling the effects of variables like temperature, pressure, slip angle, normal load, etc on the lateral and longitudinal forces developed at the contact patch in addition to all of the moments that are produced. It is straightforward to use this tire data to develop a steady-state cornering simulation based on the springs and suspension geometry being used. The variable that is missing is the damper, and this is where the 7-post shaker rig is useful. Dampers are primarily used as control elements. They are used to control the variation in normal load, and thus the variation in lateral and longitudinal force at the contact patch. Additionally, they are used to control pitch and heave of the chassis, which is critical on an aero-dependent car.

The shaker rig is not always used to replicate track data. Engineers can set a plaid of damper settings between the front and rear dampers and see what effect they have on the heave and pitch response resulting from a controlled input. The input can be a swept sine curve or it can be noise with some dominant frequency. Generally, you can either minimize the pitch, or minimize the heave, but you cannot minimize both (see the second paper that I linked previously... "Damper tuning with the use of a Seven Post Shaker Rig"). The setup engineers can then look at this data and determine the "best baseline" setup. In fact, in many cases doing this has produced quicker lap times than driver feedback. The drivers still have some input, though. They can take the car in the baseline setup, and can provide feedback on how controllable the car is in a given track situation. Based on this driver feedback and telemetry data, the engineers can then look at data from the shaker rig and determine how much they may want to change the damper settings, and not just a general direction of the change that needs to be made. This way they are engineering and not tweaking the setup. Doing this minimizes the track time required, which is very important considering the limitations imposed on track testing.

The bottom line is that computer simulation, controlled lab testing, and track testing are not mutually exclusive. They all complement each other, and the whole is greater than the sum of the parts.

F1_eng
F1_eng
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Joined: 05 Aug 2009, 11:38

Re: Post rigs

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Without going in to specific details of our test programs and sequences, there's not much more I can be say than the above post really.

As has been said, you can generate a matrix/map of dynamic response of systems with different settings in their installed condition. For example a damper on a damper dyno will behave different to its installed position. Tyre data supplied is usually poor and not what most teams require, a lot of this can also be collected.
So many uses, its difficult to imagine that there's skeptics.

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Scuderia_Russ
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Joined: 17 Jan 2004, 22:24
Location: Motorsport Valley, England.

Re: Post rigs

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I spent two days on a four post changing dampers and springs on a V8 touring car a couple of years ago. Boring as hell.
"Whether you think you can or can't, either way you are right."
-Henry Ford-

Mystery Steve
Mystery Steve
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Joined: 25 Sep 2009, 07:04
Location: Cincinnati, OH, USA

Re: Post rigs

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Scuderia_Russ wrote:I spent two days on a four post changing dampers and springs on a V8 touring car a couple of years ago. Boring as hell.
No one is claiming it's exciting work :)... but the data is useful if you know how to use it...

Jersey Tom
Jersey Tom
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Joined: 29 May 2006, 20:49
Location: Huntersville, NC

Re: Post rigs

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F1_eng wrote:I haven't watched the video, no offence but most of the American race car stuff annoys me so I won't watch it, agricultural springs to mind in most cases.
I used to think the same. But after sitting down and watching it, a lot of it is pretty exciting. Moreso than F1 even.
Grip is a four letter word. All opinions are my own and not those of current or previous employers.

marcush.
marcush.
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Joined: 09 Mar 2004, 16:55

Re: Post rigs

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In fact, in many cases doing this has produced quicker lap times than driver feedback.


this is very true for a car which is dominated by a peaky aeromap of course.If your work on the seven poster will produce the numbers and settings needed to keep the car in the sweet spot window for most of the time ,of course the car will be a lot quicker.To find this window by driver response I honestly have to say I cannot imagine anyone out there being able to give that sort of feedback....
You still can off course look into the data after a days running and try to find settings to achieve neerly the same ....but then you are already one day behind...

F1_eng
F1_eng
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Joined: 05 Aug 2009, 11:38

Re: Post rigs

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I watched it as per your recommendation.
It was twice as boring as I though it was going to be.

That is not what is usually thought of as an 8 post rig, plus contraining the chassis with the "aero loaders" positioned where they are is not very good practice.

autogyro
autogyro
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Joined: 04 Oct 2009, 15:03

Re: Post rigs

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Validate
Definitely a buzz word and not just on here.
Sounds more like an excuse to me.

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Fil
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Joined: 15 Jan 2007, 14:54
Location: Melbourne, Aus.

Re: Post rigs

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F1_eng wrote:..plus drives will lie very often, we need to tell them which set-up will be quickest very often, not just listen to their feed-back.
:lol: i love this quote!
you make it sound like drivers are more like a burden of necessity! :lol:
Any post(s) made by this user are (semi-)educated opinion(s), based on random fact(s) blurred by the smudges of time.
Any fact(s) claimed by this user will be supplemented by a link to the original source of said fact(s).

F1_eng
F1_eng
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Joined: 05 Aug 2009, 11:38

Re: Post rigs

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Drivers are a huge burden. They unpredictable and illogical, they will also lie about the car if they're having a bad day, their performance can be up and down. None of the designed systems on the car are like that, unpredictability is something we can't deal with.

We should have a robot driver so it's all about the cars, I could not care less about the drivers to be honest.

Perhaps you have something a little more constructive towards the thread?

autogyro
autogyro
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Joined: 04 Oct 2009, 15:03

Re: Post rigs

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F1_eng wrote:Drivers are a huge burden. They unpredictable and illogical, they will also lie about the car if they're having a bad day, their performance can be up and down. None of the designed systems on the car are like that, unpredictability is something we can't deal with.

We should have a robot driver so it's all about the cars, I could not care less about the drivers to be honest.

Perhaps you have something a little more constructive towards the thread?
Robot drivers, hmm
There is little risk in driving F1 cars anymore, so why not.
Mind you if you just turned it all over to computers, there would be little need to 'validate' anything or use rigs either.
All it would become is already here, a computer game.
Welcome to the 21st century. All virtual reality with no value.
If it gets any better, IMO the human race has little more than a few decades.
What ever happens somebody will still put Ferrari badges on some of it.

Jersey Tom
Jersey Tom
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Joined: 29 May 2006, 20:49
Location: Huntersville, NC

Re: Post rigs

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autogyro wrote:Validate
Definitely a buzz word and not just on here.
Sounds more like an excuse to me.
If I'm not mistaken, you claim to have a fair amount of engineering experience in mechanical design. I don't see how this concept is so alien. Hell it's even driven into FSAE students by design judges (and for good reason!).

A design process isn't that complicated.
  1. Come up with a concept. A theory, draft, sketch, whatever.
  2. Use predictive tools (FEA, CFD, or non-computer tools etc) to guide the design process and narrow or eliminate certain options.
  3. Prototype
  4. Do physical validation testing
  5. Use the above to refine the design, and pass the data back into the design process
That's pretty standard for what I've seen.. in aerospace.. in motorsports.. and product development.

There are some things that you either can't do on a computer, or it's a waste of time. For example, with a very elaborate, explicitly solved FE model of the whole chassis, you might be able to get realistic "virtual 7-post" results. However, even with cluster computing, I'd imagine it would take days or weeks and immense storage space (already being eaten up by CFD) to solve EACH run. And even then you're stuck with the question, "Is this accurate? Does it capture everything?"

Inevitably there are things you know you've accounted for. Then there are things you know you've had to ignore, or assumptions you've made. Then, there are the physical things acting that you're not aware of (the surprises). Since computational modeling is whatever reality you program it to be, that can really bite you in the ass.

By comparison, you can run through heaps of runs in a day on a 7-post, on a true physical model. Does it have limitations? Certainly. But if you're smart, you can use just the right amount of virtual and physical testing to meet your goals. For example, 7-post data in conjunction with rolling, loaded tire data. Relying ENTIRELY on one or the other (Campos?) will not get you to the front of the pack.

Bottom line, many people think computational tools are a lot more mature than they really are.

Edit - Having now read Steve's post above.. I believe he is saying a lot of the same things..
Grip is a four letter word. All opinions are my own and not those of current or previous employers.

marcush.
marcush.
159
Joined: 09 Mar 2004, 16:55

Re: Post rigs

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haha drivers are lying drivers are a burden..
sorry guys ,you are catching the cow at the wrong end.
It should read:
Drivers are the most tuneable device on any racecar.Your input to them will help or worsen the performance of the whole package.
If you are aproaching the situation with something like:
look here my data says this nut here should make the whole shitbox 1tenth faster and the driver comes back to you telling you the shitbox turned into something worse ..you are in the middle of a problem not asociated with engineering but more what is needed to make your hero tick..
I really and honestly think the approach of :hey i know the numbers ,if it don´t work the driver is a girl and I will not trust his words will never ever lead to success.at least not with this guy.Or not with you .It`s your choice.

As for everything you try to simulate ,the story is never complete as you may not
be able to even see all variables affecting your sim.So maybe on certain sims you are very close to getting the correct answer but maybe tomorrow you suddenly start to simulate in an area were all your calculation is overcast by a factor you are not taking into account and from one second to the other your results will go from correlation to useless crap .that is why the actual verifying of the sims in real world is so important.Of course you can verify during race weekends but then you are back to the early days in Motorsport ,empirical ways of approach.With a bunch of expirenced guys this will of course also have its place.

autogyro
autogyro
53
Joined: 04 Oct 2009, 15:03

Re: Post rigs

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marcush. wrote:haha drivers are lying drivers are a burden..
sorry guys ,you are catching the cow at the wrong end.
It should read:
Drivers are the most tuneable device on any racecar.Your input to them will help or worsen the performance of the whole package.
If you are aproaching the situation with something like:
look here my data says this nut here should make the whole shitbox 1tenth faster and the driver comes back to you telling you the shitbox turned into something worse ..you are in the middle of a problem not asociated with engineering but more what is needed to make your hero tick..
I really and honestly think the approach of :hey i know the numbers ,if it don´t work the driver is a girl and I will not trust his words will never ever lead to success.at least not with this guy.Or not with you .It`s your choice.

As for everything you try to simulate ,the story is never complete as you may not
be able to even see all variables affecting your sim.So maybe on certain sims you are very close to getting the correct answer but maybe tomorrow you suddenly start to simulate in an area were all your calculation is overcast by a factor you are not taking into account and from one second to the other your results will go from correlation to useless crap .that is why the actual verifying of the sims in real world is so important.Of course you can verify during race weekends but then you are back to the early days in Motorsport ,empirical ways of approach.With a bunch of expirenced guys this will of course also have its place.
My point I think Markus. We can all guess but let's use the word 'Validate' as it should be used and not as an excuse for bad guesses.

F1_eng
F1_eng
4
Joined: 05 Aug 2009, 11:38

Re: Post rigs

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Do you recommend creating a simulation model of a system and trust it fully without any comparison to real world data autogyro? You are much more confident than I am if this is true.

I will end my posting on this thread here, there doesn't seem to be any direction.

Regards