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Why chassis flex? (Sorry noob ?)

Why chassis flex? (Sorry noob ?)

Old 08-21-2014, 10:04 AM
  #16  
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Originally Posted by d16dcoe45 View Post
Seems logical, but I don't think it plays out like that in the real world. Each bump or asphalt pebble on an rc track is HUGE compared to what a full size car sees and the cars are so much lighter that any little thing can upset them.
Please read again what I said.

Here is the OP statement:

Originally Posted by Glowplug007 View Post
I understand the physics are somewhat different between 1/1 and 1/10 but chassis flex in 1:1 is the spawn of satan.
to which I replied:

Originally Posted by howardcano View Post
It's no different.
Many conditions are different as the scale is varied; your example of the asphalt is a good one, since the asphalt is not scaled (and would look more like fine sandpaper if it were). But there is no difference in the physics. Quantities such as dimensions, masses, and velocities can vary, but they are only inputs to the same equations. The same physics apply. The same concepts apply.
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Old 08-21-2014, 10:53 AM
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Originally Posted by howardcano View Post
I would stick with the basics (only one of which has to do with this thread):

1) Increase the torsional rigidity of the chassis.

2) Lower the CG by laying the dampers down, or using rotary (or other) dampers.

3) Make the bump spring rates, roll spring rates, and damping infinitely adjustable.

4) Make the bump springing and roll springing mechanisms independent from each other.

(Items 2 and 3 are already being done in the Awesomatix design.)

Then I would consider other, more esoteric items. For instance:

Active differential, so coupling can be varied in real-time depending on torque, velocity, or some other selectable parameters.

I'll stop here, since these items are best discussed (and have been discussed) in a different thread.
Good see some insight on issues that TC has.
First off about the CG, the current TC has this thing called "sedan" bodies which has regulations on how high it needs to be etc. The body is a good 80-100g of weight on top of the car. But unless we get away from these sedan bodies, we will never get that. The idea on the awesomatix is great and all, but its effects cannot be fully felt with the bodies in its current state.
The dampers designs are ancient, and never really changed all these years. Some companies tried variable valve pistons, but it never caught on. But it is something that needs to be revised.
Differentials could be changed to LSD style ones, and again, it did come out for 1/8 off-road, but also never caught on. Not to mention expensive.

1/10 TC is in it's own science when it comes to handling. Spools will never work on 1:1 cars, and a lack of a center diff also mandates special setups.
Unless someone can break the current mold of regulations, we probably won't see any significant changes. Hence we have to make things work with unconventional means.
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Old 08-21-2014, 11:26 AM
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Originally Posted by inpuressa View Post
Spools will never work on 1:1 cars, and a lack of a center diff also mandates special setups.
Spools can and do work on some 1:1 cars, but the ones I can think of are 2WD. Many years ago I drove an H production Sprite that had a locked rear diff. Even though it was on the opposite end of the car from a TC, it was used for the same reason (to prevent spinning the inside driven wheel coming out of a corner) and worked pretty well.

I think we should definitely start another thread called something like "RC versus Full-Scale: What's the Same, What's Different?" It's fun and addictive to share ideas on the subject.
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Old 08-21-2014, 11:26 AM
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Originally Posted by inpuressa View Post

1/10 TC is in it's own science when it comes to handling. Spools will never work on 1:1 cars, and a lack of a center diff also mandates special setups.
Unless someone can break the current mold of regulations, we probably won't see any significant changes. Hence we have to make things work with unconventional means.
To start off, spools are very common in 1:1 race cars (and not just at the drag strip). They are very often used in lower-HP production-based cars to help the car rotate, because road cars are designed to understeer. Go to a local SCCA track event or autocross, and you will find cars with spools all over. We have one in our race car and believe me, its way to go with a low-HP production car.

I read this thread with great interest because I have often wondered the same thing about chassis flex, and there have been some great comments. First and foremost, the physics apply EXACTLY the same way between 1:1 and 1:10. Gravity is a constant, and the tires cannot give more grip than than the physics will allow.

Flex can never be eliminated. All things flex when loads are applied to them. Even the plastic keys under my fingers are flexing as I type, but it is an extremly small amount that would require extraordinary effort to measure, but it still flexes.

Ross Brawn (engineer for Michael Schumacher at Ferarri and Benetton in F1) was famously quoted as saying (paraphrasing here) "everything flexes. The trick is controlling how just much a component flexes." I can PROMISE you that Brawn did not engineer the chassis of any of his cars to flex more intentionally.

If the chassis is more rigid, the suspension will work more effectively and in a more precise manner that can be fine tuned. Whats the point of changing spring rates if the chassis itself is acting like a spring and flexing by itself? It becomes counterintuitive.

I will say, a more flexible chassis is a more forgiving chassis, requiring less precise control to drive. Of course, tuning the amount of flex a chassis has can have a dramatic effect on car handling.

Simply put, if the chassis is more rigid, the suspension needs to be set up accordingly. Consequently, if the chassis flexes like a playing card supporting two bricks, the suspension needs to be set up according. Its all a matter of finding the comprimise between the two, which is what all aspects of chassis tuning are---comprimise.

I will say, RC on road goes through more engineering fads than just about anything I've ever experienced. Super flexible chassis are a fad that is en vogue at the moment, in 5 years time, super stiff chassis' will be all the rage.

Last edited by fox88gt; 08-21-2014 at 11:29 AM. Reason: typo
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Old 08-21-2014, 11:29 AM
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I think that the trend of wet-noodle touring cars is starting to reverse. When you have to start thinking of how the placement of the double-stick tape on your battery will tweak your chassis, your car is too soft.
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Old 08-21-2014, 11:41 AM
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Originally Posted by fox88gt View Post
I will say, RC on road goes through more engineering fads than just about anything I've ever experienced. Super flexible chassis are a fad that is en vogue at the moment, in 5 years time, super stiff chassis' will be all the rage.
It's (almost) all about selling more product. Come up with something (anything!) different, put it in the hands of a driver who can win driving almost anything, then release it as the new version of car.

And again I offer my apologies, since my comments don't really answer the OP.
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Old 08-21-2014, 11:43 AM
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Originally Posted by howardcano View Post
It's all about selling more product. Come up with something (anything!) different, put it in the hands of a driver who can win driving almost anything, then release it as the new version of car.
Is that why my old touring car is faster than my new touring car?
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Old 08-21-2014, 11:53 AM
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This is starting to become an interesting thread. With the introduction of aluminum chassis, perhaps we may see new development in suspension components.

Another part is that since we are not sitting in the car and getting all the feedback through our bodies, we can't react properly. Not to mention if we really sat in a car with the cornering capabilities of today's TC, we would most likely pass out
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Old 08-21-2014, 12:30 PM
  #24  
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One of these days I will write up a detailed article on this subject but for now I will just give a basic way of thinking about it.

The more resistant to torsional flex a chassis is, the better the car can be theoretically but the window gets smaller making it harder to get it good. Also the stiffer it is, the more responsive to set-up changes the car will be and it will be more affected by track changes.

More torsional flex widens the window making the car easier to get good. It will be less responsive to set-up changes and less affected by track changes. It will not be possible to get it as good as a perfect stiff car but a slightly off set-up will still be good.

Think of it like this:

Stiff car has a theoretical max performance index of 100.

Flexible car has a max performance index of 90.

An average set-up guy can get 90% of the car's potential from the flexible car for an actual performance of 80.

The best engineer on Earth only gets 75% of the stiff car's potential for an actual performance of 75. In this case, flexible car wins by 5.

Now if we had a few hundred sensors on the car, telemetry and data logging, shaker rigs and simulators, sophisticated shocks with near infinite adjustment potential, a team of engineers to sort through all the data and a real pro race driver sitting in the car, we could probably get 90% or better out of the stiff car and win easily.

As for physics, as Howard said, they don't change. There is no such thing as scale speeds. The math for an RC car doing 40mph are the exact same as the math for a real car doing 40. There is no conversion factor, there is no fundamental difference. So why do we prefer more flexible cars? Well mainly for the reasons I listed above but then there is this:

Yes, F1 and other major road racing cars are designed to be as stiff as possible but contrary to common thought, there are full size race cars designed to have a bit more flex intentionally. They are dirt oval cars. The reason being that they run in circumstances much more similar to what we find in RC. Bumpy, traction limited and sometimes rapidly changing grip levels. In these sorts of conditions, a bit more flexible car can be helpful since it will be less affected by the changing grip levels and easier to find a set-up that the driver is comfortable with, even if it never does really get perfect.

Also, did you ever notice that often Jimmy Johnson would be terrible at the start of a NASCAR race only to dominate at the end while others seemed to never be that bad, yet couldn't quite keep up when Jimmy was good? I have heard from several different sources that this is mainly because Hendrick was running a much stiffer chassis than say Harvick at RCR who always seemed to be good but never really dominant. New rules have made all the cars much more similar but if you look back at some of those pre-COT races, you can kind of see it. Difficult, rapidly changing conditions saw the Harvicks and Stewarts up front but once Knauss found the right adjustment, Jimmy went to the front.
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Old 08-21-2014, 12:34 PM
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Look at USVTA, some of the best performing chassis are the old carbon tub chassis. Those are about as stiff as you can get. For this class, on carpet anyway, I think the stiff chassis help to counter the massive amount of grip the tires develope. I just went with a aluminum chassis on my VBC and it already does better.
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Old 08-21-2014, 12:57 PM
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Originally Posted by wingracer View Post
One of these days I will write up a detailed article on this subject but for now I will just give a basic way of thinking about it.

The more resistant to torsional flex a chassis is, the better the car can be theoretically but the window gets smaller making it harder to get it good. Also the stiffer it is, the more responsive to set-up changes the car will be and it will be more affected by track changes.

More torsional flex widens the window making the car easier to get good. It will be less responsive to set-up changes and less affected by track changes. It will not be possible to get it as good as a perfect stiff car but a slightly off set-up will still be good.

Think of it like this:

Stiff car has a theoretical max performance index of 100.

Flexible car has a max performance index of 90.

An average set-up guy can get 90% of the car's potential from the flexible car for an actual performance of 80.

The best engineer on Earth only gets 75% of the stiff car's potential for an actual performance of 75. In this case, flexible car wins by 5.

Now if we had a few hundred sensors on the car, telemetry and data logging, shaker rigs and simulators, sophisticated shocks with near infinite adjustment potential, a team of engineers to sort through all the data and a real pro race driver sitting in the car, we could probably get 90% or better out of the stiff car and win easily.

As for physics, as Howard said, they don't change. There is no such thing as scale speeds. The math for an RC car doing 40mph are the exact same as the math for a real car doing 40. There is no conversion factor, there is no fundamental difference. So why do we prefer more flexible cars? Well mainly for the reasons I listed above but then there is this:

Yes, F1 and other major road racing cars are designed to be as stiff as possible but contrary to common thought, there are full size race cars designed to have a bit more flex intentionally. They are dirt oval cars. The reason being that they run in circumstances much more similar to what we find in RC. Bumpy, traction limited and sometimes rapidly changing grip levels. In these sorts of conditions, a bit more flexible car can be helpful since it will be less affected by the changing grip levels and easier to find a set-up that the driver is comfortable with, even if it never does really get perfect.

Also, did you ever notice that often Jimmy Johnson would be terrible at the start of a NASCAR race only to dominate at the end while others seemed to never be that bad, yet couldn't quite keep up when Jimmy was good? I have heard from several different sources that this is mainly because Hendrick was running a much stiffer chassis than say Harvick at RCR who always seemed to be good but never really dominant. New rules have made all the cars much more similar but if you look back at some of those pre-COT races, you can kind of see it. Difficult, rapidly changing conditions saw the Harvicks and Stewarts up front but once Knauss found the right adjustment, Jimmy went to the front.
Years ago I did some professional go karting, these things had tons of flex. In fact I remember specifically a rear brace that was just hanging lose on my new go kart. The nuts holding the brace onto the studs had that thread locking material on them and were not tight. I was specifically told to not tighten it, as the flex was important.
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Old 08-21-2014, 01:21 PM
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Originally Posted by napoleon1981 View Post
Years ago I did some professional go karting, these things had tons of flex. In fact I remember specifically a rear brace that was just hanging lose on my new go kart. The nuts holding the brace onto the studs had that thread locking material on them and were not tight. I was specifically told to not tighten it, as the flex was important.
That makes a lot of sense for a pro-level kart, because most (if not all karts) have no suspension other than the sidewall of the tire.
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Old 08-21-2014, 02:16 PM
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Originally Posted by wingracer View Post
As for physics, as Howard said, they don't change. There is no such thing as scale speeds. The math for an RC car doing 40mph are the exact same as the math for a real car doing 40. There is no conversion factor, there is no fundamental difference. So why do we prefer more flexible cars? Well mainly for the reasons I listed above but then there is this:
I have an observation on this, which has always intrigued me. While the laws of Physics remain the same, I think the application might change a bit. I think where things get tricky is that Surface area increases ^2 and volume increases ^3.

I will try to find an article I read in a racing magazine that my dad gave me where the real car set-up guru goes into a little bit of detail (it is still fairly general) of how we have to look at things differently because of how the total volume vs. surface area relationship is different due to the exponential factors it is subject to.

One example that stuck in my brain was the effect of down force at the slower speeds affected our cars. Since down force is the same at 40mph for both a full sized car than a small sized car, the reason why our wings were so effective (aside from the obvious size) is because the volume of our cars (which is related to the overall weight) in relationship to the surface area of the wings made a lower amount of down force way more effective. In other words, a little bit went a long way.

I would think that chassis stiffness would apply in similar ways. A near- zero flex chassis in 10th scale would be relatively "stiffer" than a near zero flex chassis on a full sized car. I am no expert in physics, so I can't really do the math that would be needed to calculate this.

What I can tell you is from the 5 years that we have been designing chassis, we have learned quite a bit about flex. Flex can be very different car to car and is influenced by so many different factors.

The gist of it is this: The older cars had stiff bulkheads and motor mounts so the cars required flex to be cut out around the bulkheads (think scallops behind the droop screws on a 417 and Yokomo BD5) This allowed the car to generate a little better road compliance which translated into a little bit better traction in and out of the corners. The cars benefited from isolated flex points, one in front of the rear bulkheads and one behind.

The newer cars have a lot of flex around the bulkheads, and the chassis stiffness trend has been going the opposite direction. The cars are now getting smoother chassis designs where the flex is lessened and moved around to a more central point at the center of the car. With the less structurally sound bulkheads, making the cars flex around the bulkheads make the cars twist too much under power and therefore make it unstable and lose grip (an example of more flex being bad) The Yokomo BD7, which is probably the benchmark in the industry right now is not a very flexible car. The set-up has been refined a lot on it though, so the window has been set for it. Almost everyone runs the same set-up most everywhere, with maybe a spring change and a shim here or there from asphalt to carpet. This would go along with wingracer's theory about maximizing a stiff car set-up and being faster with it. From all the testing I have done, there has not been a car that is more responsive to set-up changes and fine tuned out of the box than a BD7.
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Old 08-21-2014, 02:49 PM
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@ Cristian.

Yep, that was a David Ortiz article. The guy knows his stuff. Basically he showed that our cars are more affected by downforce than a full size TC would be. We are in the same ballpark as heavily modded TC's with big rear wings and front splitters or maybe even 70s CanAm cars. Still not formula car downforce figures though.
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Old 08-21-2014, 03:05 PM
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Thank you Christian


(...for making me want a Yokomo)





http://www.eviltwinmotorsports.com/?page_id=204&page=3
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