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#21
31-01-2011
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From Ronny who makes the Ghea Tapered Pistons
Hi Guys, When we first started making pistons I was not sure how they really worked,so I figured that I had to measure them to fully understand what happens. With some help from a friend we started to build this machine for measuring low to high speed damping forces and we can also simulate different pack situations. When you measure for example a 16mm big bore piston from low to high speed you will find them to be quite linear up to the high speed area where the damping force gets more progressive. With our pistons we make the damping force more linear than standard pistons and that's what make the cars calm down. Today we are testing what we call "pack control" that means you just change oil with outside temperature to get the right low speed damping and choose the piston depending on what high speed damping you need. Thanks/Ronny Guta GHEA 
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#22
31-01-2011
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It's all to do with discharge coefficients and edge effects .... but nobody asked me yet so won't bore with the details .. other than they should and indeed do give the effects stated, basically changing the balance between bump and rebound but more significantly changing the pack ratio.
As for not being able to compress a fluid I can assure you that if you speak to people working in diesel fuel systems (for example) they will tell you that it is very much the case you can. Most operating conditions thrown at a modern common rail diesel fuel system the fuel is not only compressed but actually has higher stiffeness than the the metal around it, some pretty impressive bore dilations and profile changes for the designers to deal with.
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#24
31-01-2011
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Quote:
so you havent even tried them but your neighbours says they cant work, are shock piston unlike full sized dont seal to the damper side so oil leaks around the edge, the tape allows the oil to flow faster aorund that, what hard to under stand about that, more than one person on here have tried them are using them and know they work,
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Mattys the driver,my names carl
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#25
31-01-2011
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I am not just speaking for the sake of it Roger as I qualified in diesel tec and compressed air brakes tec
The fuel is pressurised perfectly not compressed as you say If it was it is yes stronger than the metal of the pump and incorrect adjusted will destroy the pump we are talking 1600 bar 23206.04psi do you think our Ali shocks with little just fitting o rings pushed by a plastic wishbone will take that,  This isn't meant negatively . Just a good bit of debate for those who do need stuff to think about. Cheers for your input Roger We together will get the truth lol I am working today on a large scaffold and a lorry has just crashed into it and driven off. Pants change required
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#26
31-01-2011
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Carl don't go all nasty nick cotton on me
I have used them . And just wanted to gain peoples ideas to why they work! that oil passing over the taper and around the piston that you talk about , then where does it go? I will tell you smack into more oil so that counsels that idea out Cheers anyway Carl
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#27
31-01-2011
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I think my thoughts on this topic differ from others.....
The problem with RC cars is that as much as they are scaled down, it is not possible to scale down the laws of physics. if we where to scale up everything about our cars, we would have a massively soft and bouncy car. It would almost be funny how bouncy it would be... think beach buggy. Now i dont know about you, but i dont fancy the thought of going flat out on a super grippy surface, with velcro tyres in said beach buggy, but we do when controlling our RC cars (mind you i would never want to be in one)... comparing super grippy surface and velcro tyres in the real world would be tarmac and soft rubber tyres. Try pushing a real race car down and you will struggle... super hard suspension, but of course they dont go over bumps or jumps. The thing missing in the RC world is downforce and load.. again scale our cars up, and your have a super lightweight car. Add suspension that does not move on a super grippy track with velcro tyres, and it would fall over all the time due to massive ride height..... I could go on and on. but point is, you cant always compare real life with RC... certain things you can, but only with a RC head on. Taking that into consideration, my thinking is that a shock does not work as a shock on a car... more close to that of a motocross bike. Add into that our shock goes up and down at a million miles an hour with a stoke length that is again un-comparable. Soooo to the taper shaped piston.... with the taper on the lower face of the piston, the shape allows the oil under it to be forced to the outside of the piston where it flows through the one hole that does not exist.... ie the gap between barrel and piston. Now if we had an o-ring around the piston edge which sealed the piston to the barrel, chances are the taper would have no effect, but we dont because the friction would mess up our long stroke, multi thrusting shocker. This free floating piston, which is being moved from one side of the barrel to the other, appreciates the oil being directed to the path of least resistance, the gap between piston and barrel, wheres when the piston moves upwards, the oil hits a deadhead of the flat faced piston. Maybe this could be better proved with a piston that is shaped like a contact lens. hmmmm, or maybe that would just develop a whole host of other things... must copy right that.
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Mugen Seiki, Beat, Proline, LMR
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#28
31-01-2011
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Quote:
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Mugen Seiki, Beat, Proline, LMR
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#29
31-01-2011
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Quote:
Different subject and interested in your thoughts, do you have any thoughts on why 6 holes of 1.0mm feels harder than 3 holes of 2.0mm?
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Mugen Seiki, Beat, Proline, LMR
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#30
31-01-2011
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There are two other variables that haven't been mentioned yet.
A tapered piston has less surface area around it's circumference to interact with the shock body as it gets thinner at the outside. Also on the tapered side the angle between that face and the edge of the piston is less than the 90 degrees of the flat side. Would the lesser angle change pack differently in each direction? Or would the reduced area make the way the shock pack's more progressive (is the oil flow turbulent all the way round the side of the piston when it packs  )?
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#31
31-01-2011
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Cheers Richard
Thats what i am trying to get at obviously i know that oil can go around the sides of the piston as i mentioned at the start the same tolerances now i am confused  imagine having two identical water tanks with equal ammounts of water one has a taper in an outlet pipe leading to a 15mm hole and the other a straight step then a 15mm hole they will drain the same.i think
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#32
31-01-2011
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I think I have cracked it!
Why the ghea pistons work so well When the piston is driven in fast its hydrostatic pressure ( pack )deflects it sideways ( especialy on our angle driven shocks )where friction plays a small part but less on the taper But when returning the hydrostatic pressure on the taper centralises the piston aiding it's return smoothly But to get a large difference lots of pack with a quick return you need a valve. Is that right? Thanks to everyone who has commented
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#34
31-01-2011
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lol no nasty nick mate,
just lots of people saying it works,to be honest don't think most know exactly why it works tbh i don't care just know it works thats all that matter lol its not a massive difference theres no need for a massive difference just enough to help keep the wheels on the deck lots of things we do in racing and use make no real sense, but on he track if it helps hell who cares,
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Mattys the driver,my names carl
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#35
31-01-2011
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If anyone wants to play with the RPM dual stage ones I have a HUGE bag full here in front of me!
 G
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Graham North http://www.atomic-carbon.co.uk https://www.facebook.com/atomiccarbon https://www.facebook.com/nortechracing 
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#36
31-01-2011
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ill play with some from ur bag gee
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Mattys the driver,my names carl
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#37
01-02-2011
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Ok, here goes.
As Mr Lowe correctly states there are benefits from having the smaller interacting area at the outside edge, they don't touch so it's not friction that matters but the way in which the fluid passes the two edges (one perpendicular to the vector of travel and the other at some angle slightly less than that) and also the length it has to flow past. The length is important as the flow (yes even at the rates of movement and displacements we see in an RC shock) will transition between laminar and turbulent flow at some point along that surface depending on the fluid properties, gap between surfaces and the specifics of the motion of the piston. The interaction between this and the edge conditions will have an effect on the level of resistance of the piston to the displacement it is subjected to. So now we have only considered the piston as a disc with no holes in and a certain amount of bypass flow around it's edge and already we see a slight (and it is slight to be honest) but still potentially important difference in resistance depending on the direction of the displacement, this difference will be more marked the faster the piston tries to accelerate and / or the heavier the damper oil weight by the way. Now the more interesting bit, the holes in the damper piston. Hole edge conditions first; The simplest way to think of this, and this is a little simplified, is to just consider the outlet areas at either end of the hole when measured perpendicular to the hole itself. Again this is one of those things where a picture is worth a 1000 words! Draw one up yourself to help with understanding (I can't upload pictures from here saddly). If the hole in the piston is drilled perpendicular to the non tappered side the surface area will be simply the area associated with the diameter of the hole. Now where the same hole breaks out on the tappered side of the piston the area will be LARGER because on the surface it breaks out through it's form will be eliptical not round. Does that make sense so far? This larger area gives a higher potential flow through the piston but only for a very short distance as it soon gets throttled down to the flow associated with the normal drilling size. This is again a slight difference but not the most significant one. The magic (or plain old orifice theory to those of us cursed with a life of fluid dynamics); Now as we have said the hole entry flow area isn't the major factor so what is? Well it is the effect caused by the fluid flowing around the edge of the hole to enter / leave. The larger entry caused by the elipse causes, again very simplified, an effect similar to a bell mouth (often called a velocity stack in carb' / fuel injection / air filter catalogues) accelerating the fluid into the hole and stalling it on the exit in the opposite direction. This cuases the eddies in the flow path to converge in a slightly different place in the flow path than they normally would changing the position in the hole where the turbulent flow starts to recombine to become laminar (boundry conditions ignored to reduce complication). The proportion of the flow through a short orifice that is laminar relative to that which is turbulent will dictate the flow characteristics through that hole. The difference between the sharp edge (flat side) and the edge with the effective lead in (tappered side) is more marked than you might imagine and it only takes a small angle difference, especially if one face it perfectly perpendicular to the vector of displacement, to make a significant bias in one direction of motion! Now there are many, many other things to consider such as the effects of the subtrate fluid (in our case silicone based oil), the pressure in the system, wether the system is pure (only contains fluid like bladdered shocks) or areated (like all RC shocks without bladders), the range of displacement speeds and crucially acceleratins in both directions .... you could go on and on and on (thankfully I won't on this occasion) I hope that explaination made some sense to you all. The "angled hole breaking out in to a realatively large volume" trick is often used in fluid transfer systems where flow needs to be non-symetrical, say when you want to drain something slowly but be able to refill it faster in the other. I wish I could have uploaded pictures to help explain it and I am more than happy to talk to any of you I meet at race meetings if you want further explainations, just ask  For those interested in fluid dynamics the best place to start is understanding REynolds Number http://en.wikipedia.org/wiki/Reynolds_number and work form there. Will help if I can. *** Not a dig @ you Rebel but more for information mate. Diesel IS compressed in modern fuel systems [i.e. it's bulk modulus changes], yes the system is pressurised which is different, in fact it's around 1400 bar this states to take place in ernest. Here is about the best link I could find quickly http://www.hydraulicspneumatics.com/...se/70094/Issue ... hope it helps with the understanding. I am a senior development engineer [Dr. of conceptual fuild dynamics according to my tacky business cards, typical US compnay things] for THE world technology leader in diesel fuel systems, currently working on common rail fuel systems for Euro 6 & US13 emmision regulations up to around 3000 bar and also something that will turn compression ignition fuel systems on it's head ... circa 2015 for that one though and obviously I can't talk about it on a public forum. Sad as it is to say this sort of shizzle is my bag baby ***
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#38
01-02-2011
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Nice post Roger
but every thing you have said is completly wrong!  only kidding Thats got to be one of the best on oople hats off to ya! i am glad that you explained that in leymans terms lol you have lost me but it reads beautifully this post originally was a bit of a wind up but now has become very legitimate and informative, many thanks so i was wrong on all counts i think? dont know anymore.  sorry if i upset people when fishing for a bite....it just a bit of fun....today i caught a big correct great white shark!!!!!!!!!!!!!!! My mates think its better than eastenders Thanks for posting Scott
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#39
01-02-2011
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Scott, I can try and clarify a bit when I get more time .... let me know where it gets confussing and I'll do my best.
The more people who understand what works and how it works the better as far as I am concerned ... there needs to be at least one person in each and every club who can help others and is willing to do so. RC was instrumental in my choice to become an engineer (think I made that choice about age 11 or so).
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Linear Mode
