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Color0's Micro RC Blog -- A technical brain dump from the mind of yours truly...
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Rehashing the Classic Single Side Damper

Posted 12-09-2012 at 07:49 AM by color0
It's been said before that there are never any new ideas, everything new is just a rehash of something old. That's not always true but for the new racing "season" I'm doing it, using one Kyosho Oil Shock as a single side damper (SSD) on the MR03. The idea has been around a long time -- they've faded in and out of fashion in 1/12 pan cars, the InZane (now Lajf) P28 carries one, and to be fair, we at Greyscale have been playing with SSD's for a long time already. It just never occurred to me till recently that the Kyosho shock might be the best candidate to actually implement the concept with. For shame.

And it's simple as heck too.

The philosophy behind this kind of a setup is that you have a narrow setup window in which you can use a tube damper for bump and a proper oil shock for roll -- the bump stiffness must be a fair bit higher than the roll stiffness, such that individual road bumps hitting a rear wheel will actuate the roll (oil) damper more than the bump (tube) damper. Fortunately, we deliver! since most MR-03 T-plates are cut to be softer in roll than bump stiffness. Should the outside rear wheel encounter a mid-corner disturbance, the Kyosho oil shock can handle it better than any existing side shock or disk damper setup, thanks to the "packing" effect.

Unfortunately, I couldn't find any good pictures to illustrate, but I'll explain: The "packing" effect is one inherent to oil shocks, whereby if you actuate the shock fast enough, you can cause it to lock up. In a nutshell, oil shocks' pistons directly push and pull on a volume of oil, whereas tube and disk dampers indirectly do so via something akin to friction between the surface and the layer of grease itself (FYI, the grease at the interface between grease and surface actually doesn't move relative to the surface. This is called the "boundary layer" for almost all fluid flows, gas or liquid). Because there's no direct force exerted on the grease by a tube or disk damper, you can wail as hard as you want on them, and they will simply move more the faster you actuate it. Do it too fast and the grease can even cease to remain attached to the surface (disks/plates or tubes/shafts). If you lose the bond, you no longer have damping for that split second, and that is a nice big problem to have mid-lap on the track isn't it.

Oil shocks work differently -- since they push directly on an oil volume, in both compression and extension directions, if you push sufficiently hard you will actually not give the oil time to gather itself and flow around the piston. Instead, the oil in the oil shock will resist your movement while it's still gathering itself, and the remaining volume of oil that can't move yet essentially is an incompressible fluid that your piston is trying to compress. The piston can't move then, and thus you get lockup, or "pack", of the oil shock. With this opposite effect from tube and disk dampers, you are (barring mechanical failure) guaranteed not to lose damping with an oil shock, the only question is how you control the transition between normal damping and "pack" damping, and the magnitude of pack once you hit the transition.

And I will be the first to admit that I haven't played with it much yet! The Kyosho oil shock is a tiny, tiny thing and it's going to take a lot of experimentation with different viscosity oil, as well as possibly developing different sized pistons, before one can master packing of this particular shock. Till we do (and it'll probably happen), I used Kyosho/R246's #400 oil as the normal, non-packing damping characteristics came out similar to my old PN Tri-shock with Kyosho 15k grease in the tubes.

The brackets may look familiar, I used them a long time ago to experiment with a SSSD setup (sprung! lol) using the PN Dual Spring Shock, but it did not turn out as nice as I needed it to, mostly due to the annoyance of readjusting the shock every time you wanted to do maintenance. But with the Kyosho shock you just build it one, build it right, and then forget about it till it starts feeling scratchy. I lament the loss of rear tweak adjustment, but the rear end of my car was found to be 100% square so long as you build the shock right -- figure out the ideal resting length that the Kyosho shock should be, and then when filling the shock, set it to that ideal length before installing the bladder and shock cap. The bladder provides a little spring force to keep your rear suspension centered, so do it right or regret it. You can probably use the bladder preload to adjust tweak, too! But that takes even more care, and likely redos, before you get the car properly tweak-adjusted.

With the new shock in replacing the tri-shock components, I believe you save a little bit of weight, but the setup lies higher so there may not be a CG benefit. But on the bench, the damping smoothness feels perfect and I'll make good of my next Kenon time to figure out the right fluid weights and T-plates to dial in the setup properly on track. Studying the packing effect will be particularly fun, thankfully Grant has a slow-motion enabled camera, maybe if we're slow enough you might be able to catch the pack differences between tri-shock, disk damper and our SSD concept! Till we do, this will be an exciting new development for me and I can't wait to pair it with something else I've also been working on since before the Worlds.
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