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Old 05-31-2013, 09:13 AM   #18991
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Originally Posted by monkeyracing View Post
I get mixed up with bound and rebound as well. I'm never quite sure which is which. (I believe the proper terms are extension and compression.)

I generally build a damper the same way as Granpa. When installing the bladder and cap, I have the piston and rod all the way up inside the damper. I'm trying to make the damper as neutral as possible, so if I were to push the piston upwards, it would stay where I put it. To answer your question more specifically, some cars are set up to have more movement out (extension) of the damper than in (compression).
Thanks Jim,

that was exactly the thing I wanted to know. In fact, in my last German Tamiya Cup 2011 in the M-class, the top guy built the shocks of his M03 exactly like you and Granpa, and ripped everyone on an old, slippy carpet.
In fact, he had used an old setup sheet from Brad (Portelli).

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Rebound in a Tamiya-style shock is simply the spring effect of the bladder & air pocket. It affects both bound and rebound and whichever way you set it, all it does is affect the overall spring rate of the shock.
Youīre damn right with that,
but itīs not too far from real shocks when you compare it to the same effect which is the gas pressure. I even had one day some piggy back dampers, that had a rubber bulge inside you could air pressurize, which is not even far from the Tamiya design with the bladder.
The misleading term is, that the force, a real shock creates when extending, is called rebound (stage), and the opposite stage compression or bump.
In the modelcar the term rebound is used for the gas force...
But now itīs really enough (for me).

Thanks to everyone explaining his thoughts here in a nice and informative way!
Couldnīt think of any other forum here in Europe, where the discussions are that good and topdrivers sharing their secrets without the fear of giving too much knowledge to competitors.

Have a nice weekend,
Matthias
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Old 05-31-2013, 11:22 AM   #18992
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Matthis,
No punishment from me. Your explanation of shock rebound is excellent! I had to re-read your theory part a few times to really get your meaning (Sorry, my slow, not your words), and I like it - a lot.
Sosidge, you did good too until the last part, more complicated than just spring rate.
Yes, the way Grandpa and Jim use rebound is normal here. What you're calling rebound, I call "pull-back".
OK, Matthis, you address spring play at full droop, which most shock set-ups have (little to a lot), and how pull-back on the shaft will eliminate this play. Shocks with no (or little as possible) rebound do pull-back at full extension on that outside wheel, which should make the car corner a bit flatter. Brilliant!
OK, I can be easily impressed sometimes, and I am curious about some of those darn variables. But for now, should we all run down to the workshop and build the most rebound-less shocks we can?
Keep it up guys, this is great!
Bozo
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Old 06-01-2013, 07:15 AM   #18993
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Matthis,
No punishment from me. Your explanation of shock rebound is excellent! I had to re-read your theory part a few times to really get your meaning (Sorry, my slow, not your words), and I like it - a lot.
Sosidge, you did good too until the last part, more complicated than just spring rate.
Yes, the way Grandpa and Jim use rebound is normal here. What you're calling rebound, I call "pull-back".
OK, Matthis, you address spring play at full droop, which most shock set-ups have (little to a lot), and how pull-back on the shaft will eliminate this play. Shocks with no (or little as possible) rebound do pull-back at full extension on that outside wheel, which should make the car corner a bit flatter. Brilliant!
OK, I can be easily impressed sometimes, and I am curious about some of those darn variables. But for now, should we all run down to the workshop and build the most rebound-less shocks we can?
Keep it up guys, this is great!
Bozo
Thanks for your kind words, Bozo!
Itīs even quite complicated to tell In German, but I tried my best to say it in English...
Thanks also for your explanation on pull back! I always had the feeling that most of the guys out there describe rebound as the returning of the piston rod out of the shock body. I have to think more about basketball "rebound" when looking at this.

Now letīs try some shock builds, as you say!

BR,
Matthias
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Old 06-01-2013, 09:31 AM   #18994
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In German? Heck, I can hardly say "auf wiedersehen", and I live in Austria! Thankfully most of the younger folks here do English quite well, and don't mind mixing with old guys...
Let's do more shock thinking: While it sounds like this shock pull-back should help the Mini turn on smooth. grippy tracks, when would the opposite (rebound pressure all the way to full extension) help?
One of you guys said their (Australian?) buddy used kit manual shock assembly, meaning lots of rebound, and was a big winner. I'm sure he's a great driver, but what kind of track makes this work?
Bis Später,
Craig
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Old 06-01-2013, 01:41 PM   #18995
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Hey guys, just want to be sure we're all sprechen the same language here. I've read up on the subject of dampers on various manufacturer, technical and racing websites. The way we're using the terms bound and rebound is a bit confusing (and sometimes wrong). So, let's lay down a foundation for the topic. This is according to people who make real dampers and engineer/race real cars, not me:

Compression: (Sometimes called bound) is when a damper compresses.

Rebound: Is when a damper extends.

By this logic "pull back" or the damper contracting would be under the heading of compression or bound.
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Old 06-01-2013, 05:09 PM   #18996
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Yeah, I figured we'd run into some definitional problems, and we do need to get everyone on the same page here.
Lets start with Rebound = Extension. That sounds easy. Push the shock together to its shortest length, let go, and how much if any, the shaft pops back out without any help is "rebound" (or you say "extension").
Now pull the shock out to its longest length, let go, and how much if any the shaft pulls back in without any help is what I've been calling "pull back" (but you like "compression").
The problem I see is that real shocks don't actually do any of this, only our RC shocks can. Gas shocks always return to full extension, so how can they talk about "pull back"? Old fashioned friction shocks stay where you put them. No compression or extension, until an outside force acts on them. Maybe some new technology shocks can do some of this stuff, but I've never seen them.
RC shocks have several variables so we can tune rebound/pull back. Those pink foam widgets, in or out. Holes in shock cap, or not. Bladders, soft or hard. How much oil, meaning like the manual, or something less. All these can be used to adjust that "sweet spot" between rebound and pull back.
Your turn...
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Old 06-01-2013, 05:42 PM   #18997
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@laguna bozo

Ok I take full responsibility for dragging monkeyracing back in.
I discussed the apparent wording confusion (I had) with him offline. Your sentence to Matthias had me perplexed. You said, "What you're calling rebound, I call "pullback".". Sorry for stirring things up.
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Old 06-01-2013, 06:18 PM   #18998
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Funny, there seems to be a history, both on and offline, of people apologizing when I show up. I must be one hell of a charming guy.

Just clarifying terms, Will. Want to be sure we all come to the same conclusion.
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Old 06-02-2013, 05:46 AM   #18999
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Hey Jim and Craig,
fully agree on your terms of definitions.
As explained, I was always little confused what different drivers were meaning when talking of "2mm rebound".
Could be 2mm pullback or 2mm extension...

Just some notes on Craigs comparisons to real shocks, as itīs my daily work:
Quote:
The problem I see is that real shocks don't actually do any of this, only our RC shocks can. Gas shocks always return to full extension, so how can they talk about "pull back"? Old fashioned friction shocks stay where you put them. No compression or extension, until an outside force acts on them. Maybe some new technology shocks can do some of this stuff, but I've never seen them.
Pull back in a real shock is possible with internal rebound springs (IRS) which is a small steel spring inside the shock under the piston on the piston rod. In fact itīs like the T-Shox do it with their new design and these small rebound springs. Without these springs, the T-shox have zero rebound / pull back, as they have a through rod design. This inspiration comes also from real shocks (Race cars). Thatīs why I was quite impressed when first seeing these new shocks, as they put a lot of thinking into them.
But I havenīt seen them in reality or tested some of them yet.
On a through rod design, the challenge is that you have 2 rod guides and sealings, that have to aline very well with the piston to get not too much friction, which is not wanted, because it "binds" the suspension.


Quote:
Let's do more shock thinking: While it sounds like this shock pull-back should help the Mini turn on smooth. grippy tracks, when would the opposite (rebound pressure all the way to full extension) help?
One of you guys said their (Australian?) buddy used kit manual shock assembly, meaning lots of rebound, and was a big winner. I'm sure he's a great driver, but what kind of track makes this work?
This is also something I never really tested out or found anyone, who could explain to me. Interesting question also for me.
Maybe some advice by buggy drivers? It seems that newer Tamiya buggy shocks have no bladder anymore and are bleed shocks, as the ones in the 417V5. At the time of my last Buggy (Top force evo), we built them according manual. Maybe the change in the buggy thinking can give us any hints on when we want rebound or when not for onroad?

Br,
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Old 06-02-2013, 10:09 AM   #19000
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Originally Posted by ruebiracer View Post

This is also something I never really tested out or found anyone, who could explain to me. Interesting question also for me.
Maybe some advice by buggy drivers? It seems that newer Tamiya buggy shocks have no bladder anymore and are bleed shocks, as the ones in the 417V5. At the time of my last Buggy (Top force evo), we built them according manual. Maybe the change in the buggy thinking can give us any hints on when we want rebound or when not for onroad?

Br,
Matthias
This post in no way means I'm jumping into this discussion. It's just to, perhaps, give Matthias some insight into his question, but not to give any particular answers. Unless your experiments are conducted on a track that has a lap timer, you'll never have any data that is meaningful. For the most part, in the trials I've conducted, the changes in lap times have been very small. Occasionally there is a difference in how the car "feels" for lack of a better descriptive term. However, sometimes even though the car may "feel" faster, it may actually be slower in lap times, thus the necessity for a lap timer.

The many variables preclude giving any definitive answers. Type of track layout, track surface and temperature, driving style, motor or car speed, etc. What may be good in one situation, may not be desirable in another. I generally use a low rebound(2mm or less) shock cause it's much easier to build consistently, not necessarily cause it's the best.

There may be far more productive areas of experimentation. As many of you may know, I prefer the M03 over the M05 for reasons I won't go into now. I do, however, play with the M05 on occasion. This past Saturday, a one hole change in the front shock mounting position on the M05 netted a 0.5 sec improvement in lap times.This was with a very aggressive driver, new S-grip tires, open type track layout, low to mid grip, newly resurfaced track, in moderate temp with a track temp of 126 degrees F, stock Silvercan motor.

Last edited by Granpa; 06-02-2013 at 10:11 AM. Reason: Addition
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Old 06-02-2013, 12:20 PM   #19001
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Hooray Grandpa,
I was hoping we could suck you in here, even if just for a chat. I always enjoy you and your "bottomless bag of tricks".
As Matthis can attest, the weather here in Europe has been rainy for over a week, so we have plenty of computer time to amuse ourselves. This has been a fun topic, very interesting comments being swapped, but maybe so technical that it will never be as useful as a one-hole front shock mount change?
For today I'm contemplating if the emulsion shocks that Jim and Matthis mentioned could help a Mini. Can't wait to cut a hole in a bladder and experiment with bleeding...
Jump in, Bozo
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Old 06-02-2013, 12:42 PM   #19002
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I give up on this thread.....
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Old 06-02-2013, 03:57 PM   #19003
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I give up on this thread.....
Quote:
Originally Posted by Laguna Bozo View Post
Hooray Grandpa,
I was hoping we could suck you in here, even if just for a chat. I always enjoy you and your "bottomless bag of tricks".
As Matthis can attest, the weather here in Europe has been rainy for over a week, so we have plenty of computer time to amuse ourselves. This has been a fun topic, very interesting comments being swapped, but maybe so technical that it will never be as useful as a one-hole front shock mount change?
For today I'm contemplating if the emulsion shocks that Jim and Matthis mentioned could help a Mini. Can't wait to cut a hole in a bladder and experiment with bleeding...
Jump in, Bozo
Sorry to hear that Sydewynder. Hope my last post wasn't the cause.

Craig, in your absence, many of us have trying to figure out how to get the new S-Grip tires to work. You name it, we've been trying it. You're familiar with the car mentioned in the previous post. It's the one I commonly refer to as "that piece of crap". Right now it's actually gotten pretty decent, after a making a serious effort to sort it out. The car is very "smooth" and incredibly easy to drive.

For those who may be interested, this is the basic set up as it is now. The car is a MWB M05 with a Suzuki Swift body. Shocks are low rebound with 3 hole pistons, 40wt Losi oil. Springs are soft red fronts, soft blue rears and the small diameter roll bar in the rear. 4mm ride height F/R. Front shock is in the second hole on the option stick tower. 2 degree rear blocks with the camber link in the upper hole and 2 degrees camber. Battery is offset 6mm to the right, no added weights anywhere. There are a couple of other things ----- oh yeah, 6mm hexes F/R and the "tweak" was adjusted.

Off subject, but threw that in for the less technical minded.
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Old 06-02-2013, 04:20 PM   #19004
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Sorry to hear that Sydewynder. Hope my last post wasn't the cause.

Craig, in your absence, many of us have trying to figure out how to get the new S-Grip tires to work. You name it, we've been trying it. You're familiar with the car mentioned in the previous post. It's the one I commonly refer to as "that piece of crap". Right now it's actually gotten pretty decent, after a making a serious effort to sort it out. The car is very "smooth" and incredibly easy to drive.

For those who may be interested, this is the basic set up as it is now. The car is a MWB M05 with a Suzuki Swift body. Shocks are low rebound with 3 hole pistons, 40wt Losi oil. Springs are soft red fronts, soft blue rears and the small diameter roll bar in the rear. 4mm ride height F/R. Front shock is in the second hole on the option stick tower. 2 degree rear blocks with the camber link in the upper hole and 2 degrees camber. Battery is offset 6mm to the right, no added weights anywhere. There are a couple of other things ----- oh yeah, 6mm hexes F/R and the "tweak" was adjusted.

Off subject, but threw that in for the less technical minded.
Thanks for the set up information. I think anyone who's getting started in minis could use that as a great starting point.
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Old 06-02-2013, 04:35 PM   #19005
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Grandpa,
Wow, I hope the guys reading this appreciate what you just gave them. That is the state-of-the-art medium-grip asphalt track set-up!

Yeah, Sydewynder, was it something we said?
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