What's with tapered pistons?

[DaveG28]

Errr, right, anyway, so real world time:

My car is awesome over single bumps/jump landings, but goes all to s**t when faced with a ripple section. Will tapered pistons help? (with taper on the underside)

[bigred5765]

they will defo make it better then it is now,

[ghea]

Originally Posted by Rebelrc

Thanks Ron for contributing
How does the high speed damping get more progressive?
And how does your machine work, it sounds interesting
Is anyone getting where I am coming from?

Hi!
The damping force will increase in relation to the piston speed in a quite
linear curve as long as the fluid is laminar but when the piston reach the
high speed area the fluid gets turbulent and create what we call pack.
Hope thats what you were asking for?

This thread do hide somewere here on Oople with the pics and all but dont know were so i will attache them again.

With the Dyno machine i can measure damping force with different speed and stroke.
I have to make some of you disappointed with this info:
I dont see any differens in damping forces wether the piston is moving in or out
The only difference i can measure is that the taper pistons is more linear.
I have my idea Why but hey..I need to have some secrets to my self
What happens in the car is much more complex than i ever is capable to measure so there might be some other effect to.
In the diagram you can see the most straigt curve as the taper piston compared to more progressive pistons.
Lets see who will crack this nut first
/Ronny
GHEA

[Rebelrc]

looks like my theory was out the window and proved completley wrong but one thing i was correct about is they are more complicated than first thought
Thanks Ghea, i best be ordering some then as i am running homemade ones (tapers) and they are not accurate enough
Machine looks cool
Cheers
love techy threads

[Rebelrc]

I missed that you say there was no difference in damping force in or out!
That was the point I was trying to make as you can see
But there is also a definate benefit from fitting them
Everybody's happy
Thanks

[RogerM]

Geah, just out of interest what range of piston accelerations and displacement speeds were tested?

[ghea]

Originally Posted by RogerM

Geah, just out of interest what range of piston accelerations and displacement speeds were tested?

In this specifik test we reach 1.2m/sek at 50hz (if i remember corectly)
As you can see of the test we are just in the beginning of the pack area.
/Ronny

[SHY]

I'm sure RogerM's post is the most accurate, but it's too complex for me to understand

I'm impressed by Lowe's observations, very good point! And for sure yes, the oil doesn't just flow through the holes!

So the whole idea with tapered pistons are a quicker rebound = still pack after jumps, but quicker reaction on bumps?

I've also got those RPM dual-stage shock pistons lying around, but never tested them. They supposedly do the same, they divide on rebound catering for a quicker piston return.

Myself I didn't feel a difference with Ghea pistons, but then again I didn't do back-to-back tests.

Agreed that comparing RC to full scale very seldom is fruitful, RC racing is a basket case!

Why don't the RPM pistons work? (in layman's terms please!)

And when will we see more "through dampers"? I've only seen that on 1:12 so far... With shocks without bladders for compensating the changed volume when the shaft goes in/out, I'm thinking this must be the ideal solution?

Btw have anyone else discovered that some AE shock cylinders are not perfectly true inside? Put on a Losi piston (which are slightly larger) and you'll feel it pinch at certain places... not ideal!

[ghea]

Maybe someone would like to do a simple test?

Take the rear shocks and flip one of the taper pistons over.
Make sure the shocks have the same rebound after filling them.
Also be sure that the preload of the spring are the same on both shocks.

Put them on the car and compress and lift the car without letting the wheels touch the surface.
If you repeat this a couple of time you should see if one of the shocks rebound quicker or not.

Please share what you find out.
/Ronny

[Richard Lowe]

How about if someone has one of the SLR camera's that can shoot high framerate video filmed a car landing from being dropped?

Or just put the two shocks with opposed pistons on one of those losi shock balancing tools and see if they can notice a difference?

[SHY]

Originally Posted by Richard Lowe

Or just put the two shocks with opposed pistons on one of those losi shock balancing tools and see if they can notice a difference?

Blast! You beat me to it!

Cool tool! And I was surprised to see how equal the shocks actually are!!!

[SHY]

Originally Posted by ghea

Maybe someone would like to do a simple test?

Take the rear shocks and flip one of the taper pistons over.
Make sure the shocks have the same rebound after filling them.
Also be sure that the preload of the spring are the same on both shocks.

Put them on the car and compress and lift the car without letting the wheels touch the surface.
If you repeat this a couple of time you should see if one of the shocks rebound quicker or not.

Please share what you find out.
/Ronny

You guys could make a cool advertising movie here:

-two identical & setup cars
-one with std. pistons, one with Ghea
-exact same drop time & height (make a simple tool)
-test, film, and try again with swapped shocks on the two cars

>> show in slow motion...

[reg]

or just put them on and go racing

[ianjoyner]

Originally Posted by ghea

I have to make some of you disappointed with this info:
I dont see any differens in damping forces wether the piston is moving in or out
The only difference i can measure is that the taper pistons is more linear.
I have my idea Why but hey..I need to have some secrets to my self

So are you saying it doesn't matter which way up we run the pistons, the only effect is more linearity (less pack effect), or do you want to share some more info?

[SHY]

Why not taper on both sides?

[AmiSMB]

Or like Xray for 1/8th rallycross cars where they made the hole tapered. Has made great reading in this thread but at the end of the day if people like the change then always do what works for you. That is one of the fun things in this miniaturized world we play in.
The truth is out there

[SHY]

Btw I've heard some say that the shocks will (and "should") have air inside (bubbles). Anyone got more on this?

I've for years been using vacuum pumps to get them free of air when overhauling - is this a vaste of time???

[ghea]

Originally Posted by ianjoyner

So are you saying it doesn't matter which way up we run the pistons, the only effect is more linearity (less pack effect), or do you want to share some more info?

So far as i can see it makes no difference wich way you put the pistons.

The linearity makes the high speed damping softer and thats what make the car feel more calm over the rough parts

For you guys i really have no problems with sharing what i have learned after building the Dyno but i like to believe i am one step ahead of my competitors though

@SHY
When building shocks with wery little rebound you will create under pressure when pulling out the piston rod.The under pressure makes the air suck in.At least i have not yet achieved to keep the air out.
If you dont want air in your shock yo need to build them with almost maximum rebound but it seams that the majority like them with less.
/Ronny

[Rebelrc]

Many thanks Ronny
Taper up or down ,doesn't matter
That's all I need to here
Wooohoooo!
I win! For all those that said I was wrong
Many thanks Ronny for your honesty and test findings
Good luck with ghea
I have some fitted now in my vega and durango they are ace!:
Thanks everyone for your input and opinions
Good thread