Damper set up, analysis and shaker rig work

[Jersey Tom]

Well I'd echo what JT alluded to and say a rig is just a big lifesize model/simulation. The fact that you don't have any lat/long tyre forces, no rotating wheels, no inertial effects and a whole lot of other simplifications means that you are not actually observing what happens on the track but a simplified representation. Rubbish in - rubbish out applies to physical tests too.

I agree with most of that. But there is a big difference between a mathematical model and a rig test. In the first case you are working with the limitations of the model you create and the parameters you adopt. A poor decision often goes undetected. In the second case you are working with (hopefully) a real vehicle, and you have the opportunity to improve your understanding of the vehicle, accepting always the limitations of the test.

I agree with most of that. But I see another big difference between a rig test and a math model. In the first case you are working with the limitations of the test rig and the test methodology you adopt. Poor test procedures often go unnoticed, and often conclusions are drawn or extrapolated from too few data points or an incomplete "big picture". In the second case you are working with (hopefully) a more complete system, and you have the opportunity to improve your understanding of the fundamentals and subtleties of vehicle dynamics, accepting always the limitations of your model fidelity.

[DaveW]

Quick question - is damping a circuit car easier than damping a road car? Or is it just that relatively less time is spent on it due to lack of resources?

In short, yes.

The first is very much concerned with mass and CPL control, the second is rather more interested in comfort (depending on the vehicle class). Having observed (conventionally damped) road cars at various stages through development, I would suggest that structure & overall damping levels are set fairly early, but a lot of time is then devoted to shim builds (essentially setting the frequency at which the dampers loose their structure), top mounts (sometimes - curiously, increasing T/M stiffness often improves ride), and power train mount characteristics.

[DaveW]

I agree with most of that. But ... accepting always the limitations of your model fidelity.

Touché. Forgive me for asking, but Is NASCAR performance still dominated by ride height and aero?

[Jersey Tom]

There are tracks 0.5 mile long with average speeds in the 90-ish mph range... and there are tracks 2.0+ mile long with average speeds exceeding 200 mph. Qualifying record for a F1 car at Monza comes in at a comparatively paltry 160 mph average lap speed (though CART/IRL times around Indianapolis crush all of these being in the 230+ range).

Suffice to say it varies... but there are plenty of places where aero is inescapably a big deal even if by virtue of nothing more than sheer speed.

[Crucial_Xtreme]

There are tracks 0.5 mile long with average speeds in the 90-ish mph range... and there are tracks 2.0+ mile long with average speeds exceeding 200 mph. Qualifying record for a F1 car at Monza comes in at a comparatively paltry 160 mph average lap speed (though CART/IRL times around Indianapolis crush all of these being in the 230+ range).

Suffice to say it varies... but there are plenty of places where aero is inescapably a big deal even if by virtue of nothing more than sheer speed.

Tom, I respect you and most certainly you're knowledge. However I do take issue with your characterization of the "paltry" F1 Monza speeds when the COT wouldn't have the same average speed at the same track. it would be much lower. I'd love to see the COT brake from 210mph in under 400' for T1 at Monza and make it through in half the time(being generous). Furthermore you compare Indy with it's high top speed, another circle/oval track to a track of a completely different nature. SMH. You think the current Indy car would be quicker than 2012 F1 spec car at Monza today? Dream on.

To compare the three IMHO is unfair to say the least. One goes in circles 90% of the time. The other goes in circles 50%(??) of the time while the other does no circle(I really mean oval/4-turn tracks) at all.

This is one of the most asinine comparisons of areodynamics & speed I've ever seen. And this isn't coming from a yankee, it's coming from someone who was born & raised in Charlotte and spent University time in England so I certainly know the difference.

[gixxer_drew]

There are tracks 0.5 mile long with average speeds in the 90-ish mph range... and there are tracks 2.0+ mile long with average speeds exceeding 200 mph. Qualifying record for a F1 car at Monza comes in at a comparatively paltry 160 mph average lap speed (though CART/IRL times around Indianapolis crush all of these being in the 230+ range).

Suffice to say it varies... but there are plenty of places where aero is inescapably a big deal even if by virtue of nothing more than sheer speed.

Tom, I respect you and most certainly you're knowledge. However I do take issue with your characterization of the "paltry" F1 Monza speeds when the COT wouldn't have the same average speed at the same track. it would be much lower. I'd love to see the COT brake from 210mph in under 400' for T1 at Monza and make it through in half the time(being generous). Furthermore you compare Indy with it's high top speed, another circle/oval track to a track of a completely different nature. SMH. You think the current Indy car would be quicker than 2012 F1 spec car at Monza today? Dream on.

To compare the three IMHO is unfair to say the least. One goes in circles 90% of the time. The other goes in circles 50%(??) of the time while the other does no circle(I really mean oval/4-turn tracks) at all.

This is one of the most asinine comparisons of areodynamics & speed I've ever seen. And this isn't coming from a yankee, it's coming from someone who was born & raised in Charlotte and spent University time in England so I certainly know the difference.

I didnt read that he meant it like that. To me it seemed like he was just talking about the aero dependance due to the velocity through the fluid.

[Tim.Wright]

Tom, I respect you and most certainly you're knowledge. However I do take issue with your characterization of the "paltry" F1 Monza speeds....

Let not start this shitfight please, the discussion on speeds was for aero relevance, not penis size comparison.

The difference between 160mph and 200mph is pretty massive in terms of aerodynamic forces is what they were getting at.

[Jersey Tom]

Tim gets it.

You think the current Indy car would be quicker than 2012 F1 spec car at Monza today? Dream on. [...] To compare the three IMHO is unfair to say the least. One goes in circles 90% of the time. The other goes in circles 50%(??) of the time while the other does no circle(I really mean oval/4-turn tracks) at all. [...] This is one of the most asinine comparisons of areodynamics & speed I've ever seen.

Well.. let's not get all bent out of shape here. Who said anything about an Indycar or Gen 6 Cup car being faster around Monza? That's not the point. I think framing cars or series in their operating environment is actually a much better and fair comparison for the original question of aero dominance in setup, than would be if comparing different vehicles all on the same circuit.

Otherwise one might look at a stock car and ask why aero would be a big deal - and I would say that with aerodynamic forces growing with the square of velocity... 200 mph average speed at a place like Michigan will make aero a big deal regardless of what the car looks like.

[Crucial_Xtreme]

Tim gets it.



Well.. let's not get all bent out of shape here. Who said anything about an Indycar or Gen 6 Cup car being faster around Monza? That's not the point. I think framing cars or series in their operating environment is actually a much better and fair comparison for the original question of aero dominance in setup, than would be if comparing different vehicles all on the same circuit.

Otherwise one might look at a stock car and ask why aero would be a big deal - and I would say that with aerodynamic forces growing with the square of velocity... 200 mph average speed at a place like Michigan will make aero a big deal regardless of what the car looks like.

Apologies, wasn't trying to come off like a dick. I just take issue when comparing a car's (average)speed that is going through various turns & chicanes, versus a car that is essentially making 2-4 (long) turns a lap. I think the average speed comparison is misleading.

Again, my apology JT, the "paltry" comment didn't sit well.

[Jersey Tom]

I just take issue when comparing a car's (average)speed that is going through various turns & chicanes, versus a car that is essentially making 2-4 (long) turns a lap. I think the average speed comparison is misleading.

Depends what your mindset is or what you're trying to compare. If we were making the case for "Is Racecar A better than Racecar B" (quite a can of worms!) then yes.. we would want to consider how well they are balanced and can perform any array of maneuvers. But if we're just asking, "How much does aero matter?" (which was Dave's inquiry) then to me it's irrelevant whether the circuit is oval or road course, whether it has chicanes or any of that - the raw speed is what it is, and maybe makes people think about things from a different perspective.

[simonR]

Thanks for the input - i just want to try summarise what this means to me...

i accept and completely agree with the point that simulation and physical tests both have limitations. i like the hardware in the loop point as i have already got a basic 1/4 car model and i guess i feel more comfortable with the triangle of simulation, physical rig test and circuit test analysis - each contributing something and the correlation then providing some validation or reason to investigate anomalies.

Bear in mind that i dont have the undoubted experience that you will have - JT might do the simulation over a beer at lunchtime - i'd just sit and drink the beer so for me a physical test still has something to offer.

I'm pretty comfortable building the physical rig and systems to run and log - i'd appreciate any thoughts on parameters such as frequencies and amplitude and anything else i should be thinking about.

incidentally if you know people who have done this then please feel free to pm me with suggestions to contact if you think they be willing to offer advice.

thanks

[Tommy Cookers]

I was thinking of a scotch yoke thing putting in say 10mm amplitude and going from say 1 to 15hz with a load cell between the input and the tyre. So it would record tyre contact patch load, position and also damper displacement (pot on the damper). Its not too hard then to do a wealth of analysis with this raw data.

it sounds as if you would be doing all the things that should not be done with a load cell !

load cell output is a measurement of the cells own deflection with load, certified for steady loads
your load cell will be effectively a rather stiff spring cyclically driving rather substantial masses
unless the natural frequency of this system is maybe 10 times higher than your eg 15 Hz forcing frequency
the load cell deflection will not be proportional to the load ie there will be load measurement errors
signal filtering may also be a factor eg these errors could be masked by any filtering built in to the load cell

your 'cheap and cheerful' approach may benefit from using quite a large load cell, to give a higher system natural frequency

[DaveW]

Simon: We use hydraulic actuators to power the wheels. For a variety of reasons we normally use a "logarithmically" swept sine input with roughly constant peak velocity. This allows us to sweep over a wide frequency range without encountering problems.

The generator is implemented as constant amplitude sine wave generator feeding into a first order, unity gain low pass filter with a 1 Hz cut-off frequency (though this is ajustable). The output of the filter is then switched appropriately (heave =1/1/1/1, pitch =1/1/-1/-1, warp =1/-1/-1/1, etc), before being used to drive the four wheel actuators. Typically, we sweep up to 40 Hz with a sweep rate of approximately 9 octaves/minute.

Peak velocity depends on the context and the "mode" being excited, but will asymptote to values of between 70 & 180 mm/sec.

[simonR]

Simon: We use hydraulic actuators to power the wheels. For a variety of reasons we normally use a "logarithmically" swept sine input with roughly constant peak velocity. This allows us to sweep over a wide frequency range without encountering problems.

The generator is implemented as constant amplitude sine wave generator feeding into a first order, unity gain low pass filter with a 1 Hz cut-off frequency (though this is ajustable). The output of the filter is then switched appropriately (heave =1/1/1/1, pitch =1/1/-1/-1, warp =1/-1/-1/1, etc), before being used to drive the four wheel actuators. Typically, we sweep up to 40 Hz with a sweep rate of approximately 9 octaves/minute.

Peak velocity depends on the context and the "mode" being excited, but will asymptote to values of between 70 & 180 mm/sec.

Dave - thanks for this. i think this is the nub of my problem really. i have a good appreciation of the reasons for keeping the peak velocity constant and this demand conflicts with a "simple" mechanical rig where the amplitude would remain constant and we vary the frequency. The complexity/cost of a hydraulic rig would put this project outside my reach.

The 1/4 car rig was never going to cover the heave, pitch, roll modes but i did hope that it would yield some information about the unsprung mass control at higher frequencies - i guess i have much more doubt about it's value now although it might be something to build as a personal learning tool and to correlate with my 1/4 car model results rather than having any great expectatations.

Again many thanks to all for advice.

[DaveW]

The complexity/cost of a hydraulic rig would put this project outside my reach.

For ideas, you might try looking at machines that are used to test damper performance in situ. I believe that testing dampers in this way is now a requirement in most European countries.