To learn and share about dampers / shock absorbers

[Peter-RC]

Now I did some assumptions for car weight, weight distribution and unsprung weight.
They are probably not 100% correct, but it should be good enough for an "order of magnitude" estimate.

If you can povide some data, for spring rates, sprung and unsprung mass and motion ratios, we can calculate your current "ride frequencies".

darn, that is pretty close for weight and weight distribution...
I have the car in exploded view for the moment (build it up soon) and take some accurate measurements for you. (and me!)

But those calculated springrates looks a tad to soft to me... they usually run around 5n/mm springs, up to 8n/mm at the front. (but with very inclined shocks)

Last season (2010) I ran every race with softer and softer springs, ending up with 1.5N/mm springs in the rear...but felt still too stiff afterwards.
maybe following science will be bettter instead of following the herd

[747heavy]

Thanks for the feedback Peter.
I had a look at the Serpent website, and tried to guess the inclination angle (40-50°) of the dampers, so that the motion ratio is maybe a bit more realistic.
Running the spring rates you provided I end up with this:



If you like PM me with an e-mail adress and I´m happy to send you the spreadsheet, so that you can run your own numbers.

[tomracing]

those numbers for the 1/8th scale are very nice indeed!
i ran numbers for 1/10th scale electric touring a while ago and found similar frequency range.
however considering the scale factor of the 1/8 model
those frequency numbers would put them in the full size range around 3 to 4 Hz.
those are big down force number even higher then my 1/10th scale but expected with the fancy wing bodies that are ran on 1/8th scale


you have to consider the scale when you are deciding spring rates or wheel frequencies.

[gambler]

Have been thinking the perfect shock would have the shaft go completely through the shock body to eliminate the displacement problem. It would still have to run under psi, but with not as many side effects maybe? Other than weight and extended length.

[747heavy]

Have been thinking the perfect shock would have the shaft go completely through the shock body to eliminate the displacement problem. It would still have to run under psi, but with not as many side effects maybe? Other than weight and extended length.

Yes, you are quite right, and this type of damper exists, as TRD/TSD
(Through Rod Damper/Through Shaft Damper), and has become more popular
in the last years in all sorts of racing from F1 to MotoGP.

Another form of an "constant volume" damper would be a rotary damper.

One of the most common non motorsport applications for an TRD/TSD damper is a steering damper for a motor bike.

some examples:

[Formula None]

Are any of the F1 teams using rotary dampers these days? I got the impression they had been abandoned due to cost (I assume due to the high internal pressures they have and the minute amount of angular displacement they operate in). Pretty amazing devices, IMO.

Suzuki had one on a road bike in the 90s:

[747heavy]

AFAIK only MGP at the rear

[marcush.]

ohlins ttx 40 is also different in having two tube design ,it can run with very low gas pressure as it does not lead itself to cavitation .

[DaveW]

AFAIK only MGP at the rear "corners".

"They package well."

The "cost" is compliance, seal friction & leakage across the "piston" (paddles), though Sachs claim to have "solved" friction & leakage problems. If a "real" damper is modelled as a "pure" damper with a spring placed in series with it, then the series spring stiffness of a conventional damper at unity motion ratio will be between 4 & 6 KN/mm. An equivalent rotary damper appears to have a series spring stiffness of around 500 N/mm.

In my opinion, a through rod design makes much sense for "strut" & steering damper applications (for different reasons). Otherwise, the better motion ratio offered (potentially, at least) by a more conventional design has its attractions.

[Belatti]

What do you guys think about using this tool to set dampers...

The technique says it should be done with data of a complete lap... can this achive something else beyond balancing bump/rebound generated ride heights?

[Belatti]

And in case the technique results useful, there is a critical number: what do you consider as slow/fast speed. When you go from 25mm/seg to 50mm/seg (both considered rather slow speeds to me, taking into account damper dyno graphs) the histogram percentages changes significantly... to the point where a contradiction between "suggested" setups appear.

[DaveW]

What do you guys think about using this tool to set dampers...

I don't want to say too much without a context (do you have a reference, Belatti?), but the idea of setting up dampers with no knowledge of the vehicle, its suspension geometry, springs, or tyres does appear to be a little fanciful at first sight.

[Belatti]

Dave, I never said that I had no knowledge of the vehicle, suspension geometry, springs and tyres... just asked if someone is familiar with that analisys technique of damper travel data acquisition...

That particular graph is from a Claude Rouelle vehicle dynamics seminar.

Motec and AIM softwares does that analysis, in Pi you have to buld it for yourself.

[Jersey Tom]

25-50 mm/s is where most shocks transition from low to high speed.

I know Claude likes looking at damper histograms and getting them symmetric and everything... supposedly that's what's worked for him. Doesn't mean it's the only way to do it, doesn't mean it's the best way to do it.

All of Claude's "magic numbers" (TLLTD, etc) are just identification methods.. indicators. Some cars / drivers / tracks are more sensitive to them than others.

[DaveW]

Apologies, Belatti, I questioned the apparent lack of detail in the reference you quoted, not your knowledge & understanding. Anyway, thanks for the steer.

I don't wish to question the wisdom of Claude Rouelle, but to my simple mind dampers are multi-functional. They are responsible for the dissipation of (the major part of) disturbance energy, but they can also help to control the transient response of the vehicle to driver inputs. The first is a function mainly of overall damping, the second depends upon the "shape" or "style" of the load-velocity trajectories. By and large, driver inputs are low frequency, low velocity events. It follows, I think, that damper low velocity characteristics can be used to reduce steering time constant, control transient lateral balance, help braking stability and reduce power on understeer (particularly for "aero" vehicles). Arguably, last two can also be improved by geometry & differential changes, but damper changes are a "quick fix", & manipulating just the low speed characteristics can be effective for transient control whilst minimising the impact on efficient energy dissipation.