Shock valving?

[hilslamer]

OK, so I already posted in the NOOB section, so I'm officially not a NOOB anymore.

I raced r/c cars back in the early 90's with my dad, and we raced anythign from dirt offroad to pavement and carpet oval too. In all cases suspension and weight distribution was paramount to handling.

I now come back from the 1:1 world of trucks and buggies and motorcycles, and it's no secret that suspension is the key to speed and control. At the full-scale level, great efforts are made to create dampers and suspension that works the best. Developments are coming out frequently, from shock designs to bumpstop setups to suspension designs that allow for more travel with less geometry change, etc.

It seems as though the R/c world has ben almost completely stagnant for 20+ years now in terms of shock design and suspension development.

Why am I posting this on a rockcrawler board?

Because some rebound control would really help all the crawlers I see in the videos! While I'm still screwing around with my el-cheapo NewBright, I can safely say that biased damping control(meaning more damping on the rebound stroke than on the compression stroke) would make a huge difference in the way a scale crawler works.

This is especially true for wheel-hop situations, and also for snapping hte rig up steps and ledges. Lareg body-roll movements, as when crossing a large gap, would be much more controlled too.

Has anyone experimented with this? It would be pretty easy to make aftermarket pistons for all these shocks you guys are all using that had some sort of valving...

 

[DaViolentOne]

It hasn't been that stagnant... X-Ray for their on-roaders have variable "valving" click spots on the shocks to add or open the holes more or less depending on which way you click... It may seem stagnant, but there has been some great changes in shocks and such over the last few years... Most ppl just get different pistons with varying # of holes and sizes.. Some even make new holes or bore the stock ones out... A lot of that stuff goes on unseen and unmentioned...

I, myself, run with no oil... Yea I get some squat and such, but, I also have some fast acting and silky smooth suspension for my truck... Wheels don't want to hang... They drop immediately and keep the rubber where it belongs... On the ground... I haven't even tried running with oil nor do I actually intend to on this rig... It works perfect for me and my driving style as it is... I like the fast acting suspension...

 

[Mad Scientist]

RPM offers two-stage shock pistons for Traxxas shocks. They allow a faster rebound rate than compression.

 

[JohnRobHolmes]

RPM offers two-stage shock pistons for Traxxas shocks. They allow a faster rebound rate than compression.

I run these. You can flip them for more "pack" as well.


A lot of the hop you see in vids isnt from the shocks, its from an improper link setup.

 

[Reflection]

OK, so I already posted in the NOOB section, so I'm officially not a NOOB anymore.

1 post in the noob section doesn't remove your noob status"thumbsup" :lol:

I agree with John. Allot of the bad wheel hop and bad characteristics you see in allot of the videos are due to bad link configuration. Different valving in your shocks can help things. I don't care what kinda super shock set up you have,it won't solve bad link configuration.

 

[hilslamer]

RPM offers two-stage shock pistons for Traxxas shocks. They allow a faster rebound rate than compression.

Hmm...I would suspect, based on my experience with the real world off-road stuff, that this piston is flippable by coincidence and the original intention was to allow a much faster(digressive) compression stroke and a slower rebound stroke. The prior sentance would describe the general behavior of most real-world shocks developed for off-road and competition...But perhaps in rockcrawling you want the opposite?

The RPM design is clever(and a very simple, effective solution), but I guess I'm just surprised that in the scale world there hasn't been anyone that has brought things like bypass shocks or truely digressive valving to market since it is such an advantage.

Does anyone remember Paragon racing's Jump Jets? they were as close as you could get to a modern bypass shock. They were actually a crude version of a shock that Curnutt sold to the VW bug owners using them offroad way back in the heyday of the Baja 1000 and the like...

 

[JohnRobHolmes]

It seems just recently(past ten years maybe?) has the bypass shock made it to mountain biking. I remember when nice suspension meant riding on foam or urethane cushion! I imagine the machining on such a 1:10 bypass shock would be a feat!

 

[DaViolentOne]

Aren't Integy piggybacks bypass? As well as the CEN Genesis shocks? Piggyback and bypass all seem the same to me... Some even look ientical...

 

[Reflection]

My brother and I both run the CEN Genesis shocks on our Twin Force crawlers. I've yet to take them apart to try any adjustments inside the shock. I need to though,a couple of them are leaking and need new seals.

I'd like to read up more on the "droop" set up. Run internal springs in my CEN shocks and set it up for all droop,no up travel.

 

[rockmike]

i run the rpm dual pistons on my tlt the right side has more dampning on extension than compresion.Left side has more dampning on compresion than extension,seems to help torque twist.Soon ill be changing it back because ive got alot better grasp on the t.t. thanx to ee pee dezfans conversations i listned in on.but these dual stage pistons are cool theres more potentual here.

 

[hilslamer]

It seems just recently(past ten years maybe?) has the bypass shock made it to mountain biking. I remember when nice suspension meant riding on foam or urethane cushion! I imagine the machining on such a 1:10 bypass shock would be a feat!

Aren't Integy piggybacks bypass? As well as the CEN Genesis shocks? Piggyback and bypass all seem the same to me... Some even look ientical...

Piggyback shocks are NOT bypass-style shock absorbers. They are straight rate and the reservior(piggyback) is there to accomodate the volume of oil displaced by the shaft as the shock is compressed. The reservior, in real-world shocks, allows the overall length of the shock to be shorter while remaining a "charged" shock. High pressure gas pushes on a floating piston or bladder to keep the oil itself at high pressure...this prevents cavitation and foaming in the oil, the primary contributor to shock "fade". Since the Integy shocks are not actually putting significant pressure on the oil in any way despite the reserviors, they are more or less a gimmick from a functional standpoint.

A bypass shock is position-sensitive, by means of some sort of mechanism that allows oil around the piston (instead of through it). Monroe uses slots in the cylinder wall of the shock to allow oil around and create less damping for as long as the slots are, King and Fox and Bilstien use tubes and check valves.

This of course rmoves the coil-over option, but they are usually in a dual shock arrangement with another shock providing "base" damping and the bypass providing position sensitivity.

Old Curnutt shocks used long, tapered needles that went through the piston, allowing less bypass as the shock was compressed. Paragon Racing's 'Jump Jets' did the same thing for R/C cars.

 

[hilslamer]

i run the rpm dual pistons on my tlt the right side has more dampning on extension than compresion.Left side has more dampning on compresion than extension,seems to help torque twist.Soon ill be changing it back because ive got alot better grasp on the t.t. thanx to ee pee dezfans conversations i listned in on.but these dual stage pistons are cool theres more potentual here.

This is what all the trophy truck teams do - they run more rebound valving on one side of the straight axle in the back to compensate for driveline torque. They reall only do that so when the axle loses traction(as when airborn, or between whoops) it does not drop one wheel while the driver is still on the throttle. With 800 hp, 100 mph of wheelspin, a spool and that much weight, the tire that touches next will literally spin the truck = bad news.

There IS more potential there, as in a LOT. I can see this as being a major development phase in the R/C world - small precision parts aren;t nearly as hard to manufacture as they once were.

 

[JohnRobHolmes]

My marz downhill shock has 11 stage valving

 

[racerx]

The shocks I had on my old T-maxx from pro-line were a bypass shock I believe and they worked very good. I don't see them on there website any more, knowing pro-line they are disco'ed!

 

[DaViolentOne]

Hey yea... Those ones... One was sprung, the other was a by-pass shock... That's right...

 

[racerx]

Yeah, thats them. I traded those for two full sets of new big bore maxx shocks when I first started building crawlers. DUMBASS! I should have kept them and at least tried them first.:roll:





I just found them on pro-lines website, $60 pr.!! Yikes.

 

[Mad Scientist]

...and the original intention was to allow a much faster(digressive) compression stroke and a slower rebound stroke. The prior sentance would describe the general behavior of most real-world shocks developed for off-road and competition...

I'm not so sure about that. :?

A faster, or regressive (not digressive) compression stroke would simply bottom the truck out during big jumps, and a slow rebound wouldn't allow the suspension to cycle fast enough to keep the wheels planted.

Most setups I have seen use progressive compression to soak up the impact, while allowing a quick enough rebound to get the suspension back to full extension and ready to cycle again.

 

[hilslamer]

I'm not so sure about that. :?

A faster, or regressive (not digressive) compression stroke would simply bottom the truck out during big jumps, and a slow rebound wouldn't allow the suspension to cycle fast enough to keep the wheels planted.

Most setups I have seen use progressive compression to soak up the impact, while allowing a quick enough rebound to get the suspension back to full extension and ready to cycle again.

This is a common misconception - that you want more resistance on impact to an obstacle that the suspension could have simply cycle over without distrubing the path fo the suspended mass of the vehicle. In fact, and this is confirmed by nearly every patent and SAE study on the subject, you want less or nearly no resistance to movement until it becames imperative that whatever was struck by the vehicle will change it's course inevitably. Damping should fall out of the equation, and the only thing absorbing energy should be the spring.

On the rebound stroke, a surprising amount of damping is needed to absorb all that energy that the spring just stored - the blackmagic of rebound is to allow the tire to get back to the terrain in such a manner that it happens as fast as possible without the tire itself "bouncing". This is what the go-fast guys call wheelhop, and what the raockcrawler guys call bouncing or bucking. It usually happens for the same reasons, but at different frequencies mostly die to tire sidewall differences and tire stiffness differences due to tire pressure settings. Rebound movements are surprisingly slow and controlled because of this, and need to be even slower in the case of rock crawlers because of the soft tires with large sidewalls they typically run....

A "progressive compression" damping curve in modern bypass shocks used in desert and offroad racing(and some rockcrawlers) is actually offset by digressive valving on the piston itself. As each stage of bypass becomes active, more and more oil is routed through the digressive valving on the piston instead of around it through the metered bypass circuit. This means that while the resistance is greater overall, it can still "blow off" and digress in the case that whateverr the vehicle hit still needs the wheel to move further out of the way...


*********************

Now in the case of crawling, you normally have a very different set of circumstances and desireable outcomes. Body roll control, and cyclic axlehop/tire rebound is really all you're interested in controlling. In cases of models like the Stick, the shocks are ONLY about roll control and axle articulation control. In many ways, and in this case, you DO actually want damping to increase at a certain shaft velocity.

It would be interesting to put a very light spring between the two pieces of the RPM pistons, so that they were held apart enough that during slower cycling on both rebound and compression valving and allowed for smooth movement, but during a faster rabound movements - such as those encountered when snapping the crawler up a ledge that is taller than the radius of the tire, or across a gap, rebound stiffened and bounce was controlled.

When I get a more serious crawler I'll do some experimenting and post up videos and results.

 

[hilslamer]

1 post in the noob section doesn't remove your noob status"thumbsup" :lol:

I agree with John. Allot of the bad wheel hop and bad characteristics you see in allot of the videos are due to bad link configuration. Different valving in your shocks can help things. I don't care what kinda super shock set up you have,it won't solve bad link configuration.

So to further emphasize hwo important rebound control is - would you agree that the "bad" link configurations created too much anti-squat or too little? in the case of too much, this could be controlled with rebound...too little, with more low-speed compression valving. A shock can be a very powerful tuning tool, as has been proven in 1:1 offroad racing and competition for decades.

 

[hilslamer]

The shocks I had on my old T-maxx from pro-line were a bypass shock I believe and they worked very good. I don't see them on there website any more, knowing pro-line they are disco'ed!

How did the oil bypass the piston? and where along the travel of the shock?