tom_chang79

iTrader: (13)

+1000%

I've always believed that choosing the right tires for any vehicle, off-road, on-road, accounts for 85 to 90% of the setup. You can do anything to a setup, but without the right tire, it won't matter...

Case in point, I've already worn down two full sets of tires on my B44. Each time it nears the end, no amount of maintenance, setup, shock change, can compensate my B44 sliding all over the place because there's no traction...


For me, I have trouble getting both pairs to be consistent with rebounds. So no rebounds, some rebounds, full rebounds, doesn't matter to me as much as getting it symmetrical...

If conditions were ideal, I usually don't like any rebound. I like the rebound to come from the springs, but things are not always ideal so I do get bout 1/4 to 1/2 travel of rebound most of the time after my rebuilds...

gameover

no, what i mean is shocks that have different damping for bump and rebound conditions like real racing shocks. eg. 3 holes for bump and 2 holes for rebound. So you can get different characteristics for on/off power steering etc.

I run Xray cars for now and use those adjustable clicker shocks a lot in testing to quickly try ballpark settings (instead of the messy alternative). Although for actual racing i usually use the fixed piston and change oils.

gameover

here's something i found in offroad from RPM. The checkvalve part could be done with a floating piston as they have done, balls, flexible plastic membrane or other. For onroad you would need something precise that operates with small shock movement. I think it would be a nice thing.

http://www.rpmrcproducts.com/faq/pistons.htm

A flexible membrane could be an easy addition to existing designs and you could install it above or below the piston depending on what you wanted to acheive. It would allow oil thru all the holes in one direction and block some holes in the other.

Kronos

I've read through the whole thread, but I don't understand the following :

- By adjusting the volume of oil you pour into the shock body when building the shock, and by altering the position of the piston relative to the threaded end (containing the o-rings) it seems you can adjust the rebound of the shock.

But how do these cause the shock to rebound? Is it related to a pressure difference either side of the piston?

Also, when a shock is assembled to have some "rebound" - the shaft self-extends, but the rebound damping is still equal to the bump damping right?

Any help would be appreciated!

- Kronos

MaxRain

iTrader: (2)

I suggest watching this video of Jilles Groskamp, it will help you..

http://www.youtube.com/watch?v=wRufP_X9K3g

Kronos

Hi MaxRain, thanks you for the link. The video is very good, but it doesn't explain why the position of the piston in the shock body (when assembling the shock) affects the rebound. What is the force causing the shock to "rebound"?

Also, since the damping depends only on the velocity of the piston through the oil and on the damping coefficient (C), could somebody confirm that "rebound" doesn't alter the damping force of the shock in rebound (i.e.extension) (compared to the damping force in compression).

Thanks!

- Kronos.

94eg!

iTrader: (17)

The original 1985 Tamiya Hotshot had this in it's front damper. It was a thin plastic washer that you could put on either side of the piston. It would restrict flow when oil pushed it against the piston, and it would allow flow when oil pushed it away from the piston. Works quite well, but I don't know what that translates to on the track...

InspGadgt

Except for where there is a hole at the top of the shock...Shocks are essentially pressurized in the way our shocks are built. Because the top of the shock is sealed and the bottom of the shock is not entirely sealed (due to the shaft moving through the bottom) this creates a higher pressure at the top of the shock than at the bottom which causes the shaft to rebound after compression when there is no spring attached. At least that is my understanding of it.

gameover

rebound is caused by the shock bladder wanting to return to its equilibrium position. For example, in compression, the shaft moving into the shock decreases the available volume for the oil and since oil doesn't compress, the bladder expands upwards. The more things you have helping the bladder return to equilibrium position (or resisting it expanding) the faster the shock will rebound. eg. bladder made of thicker rubber, sealed air gap above bladder, foam insert etc.

Jochim_18

iTrader: (10)

I found this article today online this will help us answer our question on how shocks really works on R/C Vehicle.

There is two components of shock damping, shock pistons and shock oil.

Like all other aspects of rc suspension tuning any changes to the shocks is going to have an affect on all other aspects of how your suspension works, it could have subtle or an extreme effect on handling and performance.

Do you have your rc vehicle handling good, but are you looking to get just a little more performance? Changing your shock damping, by either changing shock pistons or oil could give you that little edge.

To understand shock damping you first need to understand just how a shock works. The basic purpose of your shocks is to take the bounce out of your springs. This is accomplished by the size of holes in your shock pistons and the viscosity (weight) of your shock oil.

Let first take a look at the shock pistons and exactly what they do. The shock piston is attached to the end of your shock shaft inside your shock body. The shock piston is a flat round disk with holes in it.

The entire outer edge of the shock piston comes in contact with the inside edge of the shock body. The piston is a restrictor or dam that only lets the shock oil to past through it at a certain rate depending on the size of the holes or the viscosity of the oil.



The smaller the holes the more restriction and like wise the larger the holes the less restriction. This restriction happens on both compression and decompression of your rc suspension.

Compression being when your rc vehicle hits a dump or landing after a jump. Decompression is when your springs want to return your rc vehicle to ride height after the bump or jump.

Shock damping is the speed at which this happens, small piston holes will be slower and large piston holes will be faster.







As the shock piston moves inside your shock body oil passes through the piston. When the shock piston reaches a certain speed oil will start to backup behind the piston, this is called "packing up". As the shock packs up it acts like it is locked up. This is what keeps you from bottoming out after the big jump.
If your track has a lot of jumps or a big jump with a small landing area try using smaller holed pistons. This will keep your rc vehicle from bottoming out after the jump. Also it will keep your suspension working will over the small stuff, but your shocks will pack up on the big stuff. Using smaller holed pistons is also helpful on low-bite tracks, it is going to be helpful through the rough stuff, helping to maintain maximum traction.

If you are running on a high-bite track you may want to use a bigger holed piston. This will allow your rc vehicle to bottom out after that big jump to scrub off some speed to get into that corner that is directly ahead.



One last thing to keep in mind about shock pistons is the type of hole. There are two different types of holes in shock pistons, straight and tapered.
A straight holed piston is going to allow for the same damping on both compression and decompression or rebound.

A piston with a tapered hole is going to compress and rebound differently. With the taper up your shock is going to have less damping on compression, with more damping on rebound. Just the opposite is going to take place with the taper pointing down, more damping on compression and less damping on rebound.

How a tapered shock piston performs or when and where to use them is up to your driving style. This is one area of rc suspension tuning that depends on your driving style and the performance you want out of your rc vehicle.

For an example, if you want your shocks to pack up quickly, so you will not bottom out after that big jump, but return to ride height a fast as possible. You may want a tapered piston, with the large part of the taper pointing down. This will make your shock act like it has heavier oil on compression and lighter oil on rebound.

Using shock pistons to control when your shock packs up. You can use shock oil to control just how fast your shock is going to move.

A lighter viscosity oil is going to let your shock move faster, while a heavier viscosity oil is going to slow down your shock movement.

If your track is smooth, with lots of traction, big sweeping corners, with no or one big jump you may want to consider shocks with big holed pistons and heavy oil. This will allow you to blast into the corners letting your rc vehicle just take a set. Your shocks will react slowly transferring weight slowly through the corner.

On the other hand if your track is bumpy, with little or no traction, tight corners and a load of jumps and dumps. You may consider a smaller holed piston with lighter oil. This allows your shocks to react quickly, to transfer weight when needed and maximize traction.

Finding the right combination of shock damping can be tricky and it depends a lot on your driving style. So, finding the combination of shock piston and oil weight to achieve the shock damping you want takes patience and practice.

Keep notes and or setup sheets so you will know how each combination works for you.

tom_chang79

iTrader: (13)

+1. In the old days, 0 rebound was the way to tell whether you have the right amount of fluid in your shocks. For some reason, lately, most instruction manuals states a rebound rate...

I've always thought that rebound was a bad thing...

MaxRain

iTrader: (2)

Building shocks with equal rebound is easier than you think it is.
The trick is to watch the youtube video. When you hear Jilles talk about 4mm of rebound, the way to get this is to make yourself some c-clips. Put them on the outside shaft, put oil into the body, compress the shaft into the body while holding the bladder down with an exacto knife. The purpose is to bleed the shock gently and do not lift the bladder before you put the cap on. Do this to other shocks and then check the rebound. If you do it correctly, they will be evenly matched. To check your results, you can use the losi shock tool. I have one, and my shocks have never been matched that closely using this method.

One other tip, is to make sure the top of the shaft and piston do not touch the bladder when fully compressed. adjust this again perfectly with the losi shock tool.

Lugnutz1

Anybody know where to find the shock pumps that remove air?