Damper Histograms

The reasoning behind having the symmetrical damper histogram is to be able to compare the balance of the vehicle. By comparing oversteer/understeer of the car, the weight transfer is usually easily monitored with the histogram. You can make adjustments easier when you know which damper is spending the most time in a certain range. Also, with dampers spending the majority of their time in the low speed section of the histogram, a symmetrical motion is often preferred to control weight transfer. Weight transfer issues can usually be traced to the damper/dampers which are spending an uneven amount of time between low speed bump and low speed rebound. On a side note, low speed is the most important area of damper control, and also the most easily controlled by the damper.

First off, if you email Claude and don't get a response, it is not because you are being blown off.

Claude gets so many emails with technical questions everyday it's not even funny. If he answered all of them, he wouldn't have time to give any seminars. You'd be surprised how much time we spend at OptimumG answering technical questions.

The symmetrical damper histogram question has come up quite a few times. There's a short explanation in a previous tech tip:
Tech Tip

This looks like a good topic to bring up at the FSAE seminar next month for those that will be there.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by mtg:
First off, if you email Claude and don't get a response, it is not because you are being blown off.

Claude gets so many emails with technical questions everyday it's not even funny. If he answered all of them, he wouldn't have time to give any seminars. You'd be surprised how much time we spend at OptimumG answering technical questions. </div></BLOCKQUOTE>

I totally appreciate that, I wasn't taking it as getting blown off, I was just interested in getting an answer.

I hadn't seen the Tech Tips on the website before. Would it be better to put the spreadsheets and other things that he says he'll send people on the website? Would it also be possible for you to post the more detailed explanation of why the histogram should be symmetrical somewhere?

I can see that a simple 1dof vibrating system with some damping will exhibit this exponential decay, but I'm not willing to make the leap to saying I should want that on a race car without knowing what assumption are being made about the tyre.

A good example is Claude's explanation of load sensitivity in the seminar, which is based on Schallamach's work as presented in the DOT tyre design book. If assumptions like that are part of the damper histogram philosophy I'd be interested to know.

Ben

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
Dampers are "crutches" that you put on a car when its suspension is not quite right.
</div></BLOCKQUOTE>

Z,

I think you're off on this one. Dampers are necessary to "damp" oscillations of the sprung and unsprung mass (wheel hop). For FSAE cars dampers should be used to minimize grip disturbance over bumps. For aero cars there is the addition of maintaining a flat ride (minimizing aero disturbance). This is a big part of why race teams use 7-post test rigs- they can quickly measure the effects of damping on contact patch grip disturbance.

If anyone is interested in using their dampers "properly" there are some great SAE papers on the topic.

I think Z's trying to point out, please correct me if I'm wrong, features of active suspensions, like the Bose suspension.

There's no dampers in that suspension. Just high speed control processing and high force linear motors that keep the wheels planted and the car flat. Energy put into the suspension from a bump generates electricity in the linear motors/generators that is collected by the power amplifiers, kind of like a Class D audio amp. Class D audio amps are super efficient, like 97%. They're not wasting that energy by dumping it into a resistor.

He said "damping". That system has damping, it's just built into the control algorithm. An active suspension still behaves like a spring-mass damper system, just with variable spring and damping rates.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ben:
I totally appreciate that, I wasn't taking it as getting blown off, I was just interested in getting an answer.

I hadn't seen the Tech Tips on the website before. Would it be better to put the spreadsheets and other things that he says he'll send people on the website? Would it also be possible for you to post the more detailed explanation of why the histogram should be symmetrical somewhere?
A good example is Claude's explanation of load sensitivity in the seminar, which is based on Schallamach's work as presented in the DOT tyre design book. If assumptions like that are part of the damper histogram philosophy I'd be interested to know.

Ben </div></BLOCKQUOTE>

The spreadsheet will probably be emailed out. Part of why it takes awhile to get this stuff out is because we'll be in the middle of working on it, and then you split town for the majority of a week to go do consulting for a raceteam, or we have a seminar coming up that needs preparation, etc. Those type of things take the priority, so sometimes the question answering takes awhile.

Ironically, the guy that's been working on the spreadsheet is out of town right now working with a raceteam.

If you have burning questions, the monthly Tech Tips are a good thing to check- a lot of times popular questions are answered there.

Re: Dampers as crutches.
=======================

Angry Joe,

Actually I am being serious. There is nothing wrong with friction in itself. But when you use it to dissipate expensively acquired kinetic energy, which is what dampers do, then I think you should be looking for a better alternative (rather than looking for more expensive dampers http://fsae.com/groupee_common/emoticons/icon_wink.gif). You probably won't feel it on the millpond smooth FSAE tracks, including Detroit http://fsae.com/groupee_common/emoticons/icon_smile.gif, but high damping forces on off-road cars cause a noticeable drag, and they also wear out the car faster. Since dampers increase the tyre-to-road normal force on the uphill side of the bump, and reduce it on the downhill side, they also lessen overall grip (as well as increasing drag).

Schumi-Jr,

Chris has got the idea. I am not familiar with the Bose system, but it sounds like the type of thing I was thinking of. "Dampers", as usually defined, give a force that is ALWAYS in the opposite direction to the motion. So they always dissipate energy. (Whereas springs absorb and then give back the energy.) If you have clever springs (ie. "active") then by varying their rate the control system can suppress oscillations WITHOUT DISSIPATING ANY ENERGY. Smart springs can also maintain more even tyre loads than spring/dampers, because, as mentioned above, dampers always make tyre loads less even over bumps (ie. less even than the ideal case of no damper and no oscillation). As I said, dampers are fitted to cars because the springs are not smart enough to suppress oscillations by themselves. The dampers suppress oscillations (sometimes, if done right...) and help the car go faster. So they are sort of like crutches... http://fsae.com/groupee_common/emoticons/icon_smile.gif

It bemuses me that for most of the history of suspension design, the designers have used very simple (dumb) springs, and then tried to compensate for the simple spring's inadequacies with either complicated control arm systems (for camber compensation, etc. - eg. see "Dax" thread), or complicated dampers (eg. some modern active dampers). The suspension is there to let the wheel move up and down, so, to me, it makes most sense to concentrate the development on finding the best "springs" to control the up-and-down motion, and then use simple control arms and as little damping as possible. Multi-rate and fully-interconnected springing goes some way towards that, with relatively simple, passive components that don't waste energy.

Ben,

I guess the goal of "minimum damping" (also held by some other people!) goes some way to explaining the symmetrical histograms. You get the most damping (area under curve), with the lowest peak damping force, if the curve is symmetrical. This applies to a single wheel's curve and also to all four wheels (ie. you don't want one stiff damper trying to do all the work).

Z

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Schumi_Jr:
If anyone is interested in using their dampers "properly" there are some great SAE papers on the topic. </div></BLOCKQUOTE>

care to recommend a few, as well as any someone might have on damper design?

If anyone wants proof of dampers causing "drag" like Z mentioned, go ride a full suspension mountain bike. Then ride a rigid one.