Emulsion??????

Cost.

That is certainly true and a term that I used which greatly simplified what effect is technically at the very extreme end of things which most will never see. I realized I shouldn't have used the term once the question arose about using bump stops instead of pack.

I can see how this logic gets used and when it comes from a well known and credible source can certainly be easy to agree with. To think that something is still done for a potentially good reason is a bit of a flawed way to think. At the very lease it should always be viewed with a bit of skepticism, regardless of the source. It is very easy to do something for a long time and then get set into a certain way and then building on it without looking at different ways to do things or reasons why things were done that way. I'm not saying that proponents of emulsion are necessarily wrong, but I will say that I absolutely disagree with them. As with everything else I'll explain my logic.

First off the only thing I ever see anyone say is an advantage about emulsion is that they land better from jumps. This is nearly verbatim off of a Losi shock building memo which makes me question whether people are blindly repeating it or actually agree with it. The parameters seem to be identical shocks but with the only change being one has a bladder and the other doesn't. This hardly makes anything equal though since one change almost always affects more than one thing. In this case it would be the pack characteristics. Oil moving through holes in a piston is going to behave differently than oil mixed with air moving through holes in a piston. Emulsion is the mixing of two things which don't mix. That seems like a contradiction so why do we do it? Because of a memo? Because it's easy? Because X driver does it? How can you guarantee the exact same amount of air entrained in the oil as it moves through those holes every single time? Can you guarantee it's consistency? If you said yet to any of those, I'd love to know how since building each shock the exact same guarantees none of that.

If we have no air in the oil, we know exactly how much oil is going to pass through the piston holes. We know it's going to stay the same and won't change. I know some are saying that we have an air pocket entrapped in the shock cap that is an unknown. Actually it's not. It's a very well known thing. As the shock compresses and the piston moves upwards, more and more shock shaft enters the shock body, displacing space. If you have no bladders and the shock body is completely full with no air, that shock shaft isn't going to move very far before it completely locks up. This is bad. This is essentially what happens when you build some rebound into an emulsion shock. It puts stress on the shock body, the piston rod, and the shock shaft and contrary to popular belief has nothing to do with actual chassis rebound from a bump. At least not in a manner in which we would want it to be.

Since the piston rod needs some displacement space, people just leave it in the form of air and then allow it to mix with the oil. As it sits there it will try to separate out. The action of the shock will allow it to mix again but even then it is tough to guarantee it is mixed evenly and nearly impossible to guarantee that it will stay consistent.

The other way is to still allow a small air pocket but separate it out with a bladder. Now only oil moves through the pistons and the air and oil never mix. There is no need to worry about consistency. I know some are saying that a soft rubber bladder will compress before oil travels through the pistons which would soften the dampening. This is a valid concern but the amount of pressure above the bladder is a useful tuning aid in this regards. On many real race car shocks, this area may have the air (nitrogen) pressure adjusted as a fine tuning measure. In rc some people run open bladder which leaves the bleed screw out of the shock cap. This way there is no pressure on the bladder. Personally I wouldn't do this but if you like it, go ahead. I install the bladder onto the full shock body and then screw on the shock cap above it. I leave the bleeder screw out until the cap is on. Then I reinstall the bleed screw.

Something that is overlooked with bladders though is that a front shock piston rod being shorter than a rear shock piston rod will displace less total area than the rear rod, yet everyone runs the exact same size bladder all around. How can this truly be equal? It can't! This is yet another example of only one change not being equal. You need to take up the difference in area between the longer shaft and shorter shaft in the front bladder. This can be done with bladder inserts. TSR Products is the only company that I've seen which seems to recognize this problem and they offer different foam inserts for bladder shocks.

I personally find a bladder shock much easier to adjust for pack this way and changes are consistent and predictable. I find no issues with landings being worse since I adjust from square one rather than trying to fix what is already there.

Fred,
Great posts thanks for sharing your knowledge with us! I've only got a few things I want to add to this thread first off (and it was discussed thoroughly at the beginning of the thread but why not kick a dead horse?) the shock collar doesn't change spring rate at all period, not even on progressive springs but rather it changes the location of the spring in regards to the shock body, thus raising the ride hight (after all a rate is a constant right? Example one might pay $.10 a text, the more you use it, it's not going to increase right?) now with springs we get spring rate, so we will use an example of a losi orange spring. The losi orange spring has a spring rate of 2.9 lbs, what this translates to is that to compress the spring one inch you have to add 2.9 lbs, to compress it 2 inches we need to put 5.8 pounds on it and so on and so forth.

Second is anti squat, I noticed that people have been shying away from anti squat, and from what I've seen it has to do with two things 1st is not really understanding what it does and 2nd is not knowing when to apply it. So to tackle the first problem lets quickly touch on tire loading characteristics. As earlier discussed in this thread we know that less weight on a tire equals more grip, and more weight on the same tire produces less grip. Now what anti squat does is it resists weight transfer under acceleration by pushing the driving wheels into the ground more (see http://youtu.be/5_JrPUFk6p8 ). In that video we can clearly see that under acceleration the suspension clearly rises and is resisting the weight being transferred to the rear under acceleration effectively increasing rear grip. Well we can also see that that's a drag car and we want our cars to do more than just go straight. So if I haven't lost you by now here's where it comes into play with cars that have to turn. When we tune the roll centers we cannot tune the car to corner perfectly throughout the entire corner, we have to make compromises somewhere, and the reason why is the weight being transferred as we brake into a corner (the weight moves forward under braking decreasing overall front traction) and when we pass the apex and begin to accelerate out of the corner (the weight then moves rearward decreasing overall rear traction). When we bring anti squat into the equation we can counter this and the way I use anti squat is as such, to minimize these compromise I start tuning with 0* anti squat and i focus on corner entry up to mid corner grip and once I've got a car that can do this I focus my efforts on weight transfer, past the apex is when you should be getting on the throttle changing the weight balance and thus unsettling the car, well to counter the over steer that is going to happen on exit due to this transfer you start adding anti squat to keep your car balanced throughout the exit of the turn pretty cool eh? Try it out and let me know how it goes! Unfortunately I can't claim this theory as my own, if you have time You should read chassis engineering by herb Adams. It's hands down the best chassis tuning book I've ever read and most of what has been talked about in this thread is discussed in that book. It's a VERY interesting book if you like suspension tuning. Thanks !

After thinking about it, I should have gone into tire traction more. In my last post I said that less weight on a tire equals more traction, well that's partially true. A better way to put it is it increases tire efficiency, for example (these are pulled from the chassis engineering book I talked about) if we have a tire with a 1000lbs load it will have 1000lbs traction available theoretically, so that tire can produce 1g of cornering force or it's 100% efficient. Now let's take the exact same tire and change the vertical load to 500lbs it will have 700lbs of traction available, well we can see that the lighter tire has less traction, 300lbs less, however we can see that the tire with the 500lbs vertical load will now produce 1.4g's or it is 140% efficient.


EDIT: here's a link to where this was pulled from, in the preview you can read pages 1-2 that covers tire traction vs load and will explain it a little better than I have

http://books.google.com/books?id=rY2...epage&q&f=true

You might not like them, but hopefully I can at least change your opinion a little bit.

There are benefits to emulsion shocks. Yes, they aren't technically as consistent as a shock with bladders, but it's a trade off that is usually worth it in 10th scale (read, lighter) cars under conditions common to a groomed track.

First, imagine you had a piston that perfectly sealed against the shock body and had no holes. Basically, no oil could get to the other side of the piston. Imagine you assembled the shock in such a way that oil was above and below the piston (with no air mixed in whatsoever and a bladder for good measure. If you tried to move the shock shaft, it wouldn't budge. The fluid below the piston won't expand no matter how hard you push even though there is air above the piston willing to be compressed.

A shock built for emulsion has air on both sides of the piston, allowing for some piston movement to happen without any fluid flow through the piston. This does help on jump landings and other sudden impacts (say, running over a hose) as the shock packs up, but has air on either side to expand and compress acting more like a regressive rate damping system over a small amount of travel while still being a rising rate system overall.

Yes, mixing air and oil isn't as consistent, but it is a very small consistency change that is worth the increased capabilities of having air on both sides of the piston. If you build the shock right, it is a very small quantity of air that gets mixed in. Take an emulsion shock, pump it a dozen times fairly quickly, take off the cap, and see how long it takes for the air to completely bubble out. It takes several minutes. Unless you are practicing by yourself and take your sweet time to marshal yourself, over a 5-10 minute race with marshals keeping you wheels down, the consistency is a non issue.

I used to run a unique setup on the old, 'small bore' associated shocks. I was too busy to maintain my cars to their full potential, so I used some tricks to increase the time between rebuilds. The goal was to obtain the damping benefits of a emulsion shock with the ease of maintenance of a bladder shock. I used to run the TC4/5 touring car caps and bladders in addition to using the old VCS2 system from the TC3 shocks. This put air on both sides of the piston with the bladder above and the VCS2 sponge below. Yes, it limited my shock travel more than I cared for, but I could go a lot longer between rebuilds with the benefits of emulsion. Could someone come out with a slim 'air donut' to place below the piston? Whoops. Guess I should apply for the patent for one of my current projects.

Added my thoughts in blue.

Not convinced in the slightest. I used to feel that way though. I'm never going back.

Sorry to disagree, but that's not so straight forward. I assume the example here was for a defined set of parameters and most likely not for off road?

The bigger issue in determining the coefficient of friction of rubber on a rough surface hinges highly on 2 things: the tires ability to maintain contact with the ground (the suspension) and the contact patch. The contact patch is very straight forward in on-road scenarios, but on a surface that isn't level means there needs to be enough force behind the tire to conform it to the surface of the track. Tires are designed to deform the right amount for a given weight. Any more and you run into the situation you presented where the mass of the car is increasing faster than the frictional force generated, but any lighter and the coefficient of friction starts falling off faster than the mass of the car. The result is a bell curve-esque graph with an ideal mass.

Now, keeping the tires in contact with the ground is the second part. There is a big reason why most people say a heavier car is better on a rougher track. It's because the suspension can act more efficiently with a heavier car. Let's say 'X' is the mass of the car (just the sprung mass) and look at what happens as X approaches 0 and as X approaches infinity:

As X approaches 0, you are eliminating the mass that the shocks 'push against' to keep the tires in contact with the ground. If you hit a bump and the tires move up the bump, there is nothing for the shocks to push against once the tire is over the bump. The tire will continue upwards in a state of free fall. Picture rolling a tire over a garden hose at a decent speed. The tire would bounce off the hose a couple feet in the air before returning to the ground.

Now, as X approaches infinity you are providing an immovable object for the shocks to push against in their effort to keep the tires on the ground. You could go for an infinitely stiff spring to match and the tires would follow the grounds imperfections perfectly. What it comes down to is the ratio of unsprung mass to sprung mass. The higher the ratio, the better the suspension will be able to keep the tires on the ground.

As an example, 8th scale buggy tires are designed with a 7 to 7.5 lb car in mind, as this is a typical weight for nitro buggies in this current crop of cars. When electric 8th scale first hit the scene, they were tipping the scales at 8 or more lbs. On rougher tracks, many people found their electric buggies to handle better as their suspensions worked more efficiently through naturally whooped out sections. However this extra mass is beyond what the tires were designed for, so losing some weight would benefit the handling of the car on smoother tracks. Some people took it to the extreme, getting their 8th scale buggies down to 6.5 lbs and have found their cars more skittish as the tires can't properly conform to the track surface. It's all a balancing act.

Disclaimer: I've left out the possibility of redesigning tires as the average consumer can't do such a thing. Plus, minimum weights on each class mean that most tires are designed to work their best close to that weight.

Let's dissect what's happening here. I still stand by my statement about less weight increases tire efficiency. The problem with tires is they are never consist and and are always changing. From surface to contact patch to weight transfer humidity, ambient air pressure, tire air pressure, sidewall flex, ect. And will change with each tire, so the constant we have to tune for is how grip is effected by weight, and I still stand by the fact that a tire with less weight will be more efficient than a tire with more vertical load. Now let's not confuse grip with driveability. A light car with too much grip will change directions quickly, so now let's look into the heavier buggy in your example was easier to drive and thus quicker. For now let's assume I'm wrong and that tire grip vs weight is linear (the function might be t=w or maybe t=w/2 or possibly t=w*2 where t=traction and w=vertical load or weight. Or better yet let's just ignore traction for a minute). Now what we want to focus on is the variables that have changed and how they have effected the buggy. Let's take three identical buggies and name them A, B, and C. Buggy a is a buggy that was built with now weight added and has a perfect l/r and f/r balance and weighs 7lbs. Buggy B is one that is identical to buggy A except for one thing, buggy B added 1lb of weight directly on the center balance point of the chassis. Now buggy C is the same as buggy B except for the .25lbs was added to each corner for a total of 1lbs. Now let's apply newtons law of motion to these buggies and compare how they act in a turn. Newtons law of motion summarized is that an object in motion stays in motion and an object at rest stays at rest unless acted upon by an outside source. So from the we can see that buggy A is the lightest buggy and will be the twitchiest of the 3 buggies, well buggy B and C weigh the same so they should act the same right? Actually no, now if we look at how the car rotates buggy C will have more body roll in the corners regardless of the weight, and it will also be the numbest car of the 3. The reason being is that the further out the weight is from the center balance point, the further the weight has to travel and more speed is required to make it change angles (think of swinging a bat with a ten pound bag on the tip of it vs a ten pound bag on the handle of the bat) what's going on in your example (more so than how tire traction is effected by the extra vertical weight) is the effects of weight transfer on these buggies, buggy C is going to push on entry more than buggy B and buggy B will do the opposite in comparison. When you change one aspect if the suspension many things are effected and that's where people get lost. Now when I said more traction does not make a car easier to drive, the best example I can think of is with onroad touring cars. If you are running a rubber tire and change to a rubber based foam tire without changing anything else, the car will be many times harder to drive with the higher traction of the foam vs the rubber. This is my take on things I'll leave it up to you to take it or leave it.


Edit: the reason suspension wasn't added into the tire grip equation is that no suspension is perfect and varies from car to car (including chassis from the same manufacturer, the traction numbers listed above should NEVER be used to tune you suspension rather they are there to show the relationship of grip to weight and that's what we use to tune our suspension. If you have a 4000lbs car it will never pull 1g of mechanical grip. At best you might be able to reach .75g's but again that will vary from car to car)

Krio, Here's a link to better explain it, it's a google preview and the very first thing covered is tire traction vs load. I tried to summarize it and this will explain it better.

http://books.google.com/books?id=rY2...epage&q&f=true

I'm also going to edit the original post to include this

I used to have that book. It's a great read. I leant it to someone several years ago and haven't seen it since. I don't even remember who has it. I need to get it again.

Fred, I was thinking about weight bias and weight transfer on mid motor cars vs rear motor cars and I realized that the rear motor car will have less weight upfront and thus more front end grip. Well with a mid motor car it's going to be closer to a 50/50 weight balance and that means that the front end will have less grip, so what if you run a 4wd front tire on it to increase grip at the front end? I don't own a mid motor buggy so if you feel like being generous would you mind seeing if there's a difference on your mid motor car, or anyone else out there? I do think that the car will need to be retuned but I don't think that you will have to rebalance your springs but the car will have to be tuned for the extra front end grip. Just curious

fyi - here is an interesting chart with damping coefficient numbers of various RC pistons....
http://www.petitrc.com/setup/ShockPistonComparison.pdf
Fred you know better than to dump a good book ! that nerd stuff is awesome.
I remember when I got my hands on Kyosho gold shocks with bladders. Wow were they a great shock. Of course there were aftermarket bladders for RC10 shocks so we used those too. They were butter smooth and seemed to hold there tune a little longer. Funny how times change.

you might think about reading the Xfactory cubed thread, you would find it interesting.