no function represents C.
youre a physics major and have not taken any vibrations courses im sure, so please dont post irrelevant information.

its all based on a long "general" equation mxdoubledot+cxdot+kx=f(x)

basically.

you are simply wrong and cannot accept it, im sorry.

ill goto the smartest professor on capus monday, and even my vibrations teacher tuesday to confirm this.

but its not a complicated fact that C is constant, and only velocity(xdot) changes which is based on sin(theta) of that damper.

go buy a book, ive looked at 3 books, one of which is SAE published shock absorber handbook tonight, and all tell me your perception is incorrect. draw a FBD. figure it out for yourself if you have any clue whats going on.

if not, then ill post monday my findings by two ME doctorates....

 

"In order for this to be true, .707*[c*xdot]=.707"

this is very incorrect. i never ever said cxdot was 1, lol. read again, then go back and get some ME classes under your belt.

like i said, based on the longer eqn above which has many more variables involved.

 

it doesnt matter how long someones been doing whatever, if theyre wrong, theyre wrong. numbers do not lie. "sense" doesnt mean anything to those who do not understand the math involved. a lot of things in engineering are not common sense and would go against a lot of what you would think to be true.

 

I need some diagrams

Post your Free Body Diagrams (FBD)

You're right about numbers not lie-ing , but "sense" or "feel" has it's place too. I'm sure you've heard of the "right hand rule" when it comes to forces.

Either way, let's try to keep this engineering dialog civil. It will all come out in the math for everyone.

This thread has been very informative thus far. Good info for a personal project.

Erich

 

the math is simple. fix one end of the shock to the axle which isnt moving vertically. the other to the body which is.

shock force is damping coefficient C*velocity
C is constant for a given shock, so velocity is the ONLY thing that can change the shocks force at an instant.

so shock force is then C*V*sin(theta) for any angle.
vertical will be C*V, horizontal will be C*0

45degrees is C*V*(.707)

this isnt complicated.

and if you really think youre right. then how come ive found two sources that say EXACTLY " shock damping effectiveness at 45* is 70%" lol.
and, youve only sited two textbooks which i know dont have the material anywhere near the scope of dampers in them?

ill draw something in paint, and send it to the guy who wants it, then he can post if he likes.

is everyone lying to you. no. you just need to accept youre wrong.

 

right, that means plus or minus a few percent, due to pitch, heave,lateral location/mounting, and roll. not "yeah we know we're off by 20% so we'll just say rule of thumb and be ok".

 

yeah man, try reading the article again under "how shocks work" they know that, theyre not stupid. but you need to come to grips with the fact that youre just seeing this whole problem incorrectly. im not trying to be rude, but its a good quality when someone can accept their mistakes and learn from them.

 

If you want to see the slower angled shock velocity relative to the vertical suspension deflections, try this page:
- http://www.saltire.com/applets/triangles/tri2sia.htm

If you set the sides of the triangle to 10.0 units each and the angle BAC to 90 degrees, this will represent the length of the shock (on the diagonal) at 45 degrees (it'll be upside down as shown). Then "nudge" the AB distance by setting it to 10.1 units (a 0,10 unit change in length) and notice the "shock" length changes from 14.142 to 14.213 units, or a change of 0.071 units or 0.71 times the rate of change of the vertical dimension (which was 0.10 units).

A shock that compresses or extends slower generates less damping force, per the C*xdot formula, or in this case xdot' where xdot' is the dx/dt of the shock's length and C is the damping coefficient of the shock and xdot' = 0.71 * xdot (where xdot is the rate of change of the suspension's vertical axis).

And note I am talking about the effectiveness of the shock absorber in damping vertical motions of the suspension, not just the effectiveness of the shock on it's own. So you have two factors at work, the fact that the shock compresses/extends slower when mounted at an angle. That reduces the forces in the shock. Then you have the fact that the shock is applying a force in the suspension system at an angle. Only the vertical component of that force is applicable and that vertical component is less as the shock's angle moves away from 90 degrees. If I push with 100 pounds at a 45 degree angle, 70.7 lbs. is applied upward and 70.7 lbs. is applied horizontallly.

But this lesser force is also applied at an angle, and thus only the vertical component is useful in terms of damping the suspension's up-down motion, so that force in line with the shock must be multipled by the sin of the shock's angle, to find the vertical component of the force. So the 0.71 factor shows up twice (squared) in determining the effectiveness of the shock at an angle.

 

yeah i see your flaw now.
you really cant count the angle twice like you are. thats a mistake.
counting it once accounts for it being at an angle. saying that the resulting force is then again applied at the angle is wrong since its alreay been accounted for. but at least now i know where youre coming from.

cant fight the math.

 

im reading my SAE published "The Shock Absorber Handbook" and what i believe youre thinking of is the motion ratio of the shock. this applies to a more complex problem.
I suggest you pick up this book if youd like to look into it further, as i wont describe it here because theres too many formulae youd need to see.
its around page 146-162, then solid axle discussion is on 182 though.
a great picture is also included on page 185 which is a solid axle representation and a position/velocity diagram

the book is great, and itll explain everything better than i can.

cliff notes:
in bump travel the shock(purely the shock) is 71% effective on a 45degree angle.

 

Regardless of the content of this thread, you realize Roger is a PE, right? He's worked for NASA too.

 

This is amazing.

You are attempting to quantify, to an irrelevant and potentially fallacious degree, something pretty irrelevant.

The shock works at least 30% worse, and for Roger and I, it works 50% worse. Either way, that is terrible, you have excess bodyroll or you over shock it.

Not really sure getting an exact value here is necessary.

Should I quote Pirate? Certified experts there have used the 50% figure over and over again. They may even be SAWengr or KINGengr.

 

check a book then

 

yeah electrical engineer. so no he hasnt had the experience in a classroom with dampers.

 

Here's my synopsis of both sides of the the discussion. Correct me if I'm wrong...

Both dfoxenger and Roger agree that sin(45)=.707. So a shock at 45deg will experience 71% the force it would at vertical.

Now here's where the disagreement is: dfoxenger says that the shocks he's using (can't say ALL shocks are like this) do not react with less resistance the slower they are cycled.

This to me is the major disagreement. Roger is saying that a shock's damping rate is dynamic in that if you push faster, it reacts with more resistance.

This is where the second sin(45)=.707 comes into play.

I think in this discussion it now falls on dfoxenger to prove that the shocks we use on our rigs (Rancho, Bilstein, etc) do NOT show this dynamic damping rate, so to speak.

Carry on

Erich

 

my information isn't irrelevant.

I'm going off of EXACTLY what you posted...You are right, you can't argue math.

I wasn't claiming to know anything about shocks or engineering. I know math. If someone posts an equation, which you did, i can figure it out.

This is the way your post made me think about it

.707=.707[(c)(xdot)] cannot be valid unless [(c)(xdot)]=1 I did not understand why you dispute this.

What you left out was that you are defining .707[(c)(xdot)] as the total damping effect of the shock at an angle of 45deg. That was where the confusion is.

However, for a constant damped shock, this is fine.

I believe what everyone else is talking about is a dynamicly damped shock, that will have c as a variable, becasue of more shock resistance at higher rates of compression.

 

Class room experience?

The only experience that makes a difference is real world...Classroom stuff is all idealized to teach the concepts. No one takes classroom experience seriously.

 

Here is a simple explanation:
http://www.enidine.com/ShockTheory.html

(linked photo did not display well on a black background - see it on the page above)

And in my case I am assuming a simple automotive type hydraulic shock absorber that has a force proportional to it's speed of compression or extension. I admit I am ignoring linear friction from things like seals and so forth as well as any spring constant effects from an internal high pressure gas charge as well as shocks with progressive valving that changes damping rates with different velocities and with different sections of the shock's stroke.

And for sure, if you have a shock that does something different or want to model the shock in some other more complex model, by all means, go for it. The Rancho 9000s that I have on my truck are a pretty basic shock, aside from the manual adjuster. You can for sure feel the change in force required to compress or extend them. Push slowly and it is fairly easy to move, try to push faster and the force required goes up as well.

 

".707=.707[(c)(xdot)] cannot be valid unless [(c)(xdot)]=1 I did not understand why you dispute this."

no thats not what i said.
i said C*xdot = F.
.707 is not the force, so C*xdot definitely does not have to equal 1.
what we're doing is relating the same shock but at different angles.
with the sin function in there, all else being the same, you get a percentage, since theres no way we can calculate the force since we dont know anything else.
what the math is saying is that 45 degrees is 70% effective as 90 degrees.

your comment about education is ridiculous. thats where the basics come from. so unless you learn something by a qualified person, you might not be teaching yourself correctly. which is why im saying a self taught EE could be incorrect.

i think im done with this thread, because i really dont need to prove anything to anyone, and i know im right, and ive sited now 4 or 5 sources that agree, so you all being so closed minded are missing out. ill check with my vibes teacher tuesday, but i probably wont reply back since you wouldnt believe me anyways, lol.
good luck with your misinformation.

 

The education comment was simply to point out that taking two people, one who's still in college, and another who has been through college and has x number of years in the field, i'll believe the guy who's been in the field. You are still in school, he is certified. You have to take a test to be certified, so he obviously knows enough.

No one here is close minded, we just dissagree with you. You have posted links, and Roger has posted links. I don't think that makes him closed minded. I was only trying to understand your math, and you ridiculed me. I wouldn't bother asking your prof, I think everyone is past caring. You are convinced you are right, Roger has convinced us you are wrong, and I think that if your prof told you you were wrong, you wouldn't come back to admit it anyway, so why bother?

Back to the original topic of this thread: Regardless of who is right and wrong, this will remain a stupid idea, becasue even at 70%, you will still have crappy handling. However, it is your truck, and while the Roger's shock information in this thread was interesting, i think exactly zero people here actually care what you do with the vehicle.

Thankfully you have chosen to stop posting. We will not miss you. We will hope you get employed in another aspect of ME that does not have to do with shock absorbers.