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Old 09-22-2009, 07:33 AM   #1
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Arrow Chassis Flex

The main aim of this thread will be to clarify why we need the chassis to Flex.

Considering real cars, there is no explanation to use this criteria, so please, if you want leave your opinions.

Here we developed the following structure and we try it with good results in our track.
Because of the design we are using, the total weight, believe it or not, is lighter than the original chasis, but it is around 60% stiffer than it.




The bottom of the chassis is flat.
Consider that our track is bumpy, and the surface after a season is very rough and we have big jumps on it.

All the people who saw it said it is very rigid, but... why do you need it to flex ? My opinion is that that work must be done by the suspension, shocks, bars, etc.

Please leave your opinions.

Thanks !
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Old 09-22-2009, 07:49 AM   #2
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Most real car chassis flex also. I know this because I can see them twist when I set them on the lift. Put a convertible on a lift and open the door and try and shut it again. Put a pickup on a lift and watch the bed seperate from the cab. Ever see a big rig when they accelerate hard? Those chassis are intentionally made to twist because otherwise they would break apart just because we cant see or feel it doesnt mean it isnt there.

However when it comes to the pan chassis of our RC cars Ive never really believed that the flexing was all that beneficial. When I picture the chassis flexing in my head it looks like a leaf spring (for a lack of a better analogy) so if it bends its gonna spring back. Its been my experience that a car with aluminum braces feels better to me on the track than one with plastic ones.

But all that being said there is always a point at which something good turns into something bad and its up to trail and error to find that point and stay within the limits. Some flex is probably good but too much is certainly not and I dont think zero flex would work all that well either.
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Old 09-22-2009, 07:50 AM   #3
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The reason for chassis flex is to account for the fact that RC shocks do not account for high speed dampening. Granted the tires do to a point, but if you look at full size CORR, Motocross, even street car shocks, they have high speed and low speed dampening.

So... until there is a breaktrhough in RC Car shock design, the chassis needs to flex longitudinally. Lateral rigidity is a very good idea though. You could achieve this by machining splines from side to side (or diagonally) in certain spots. Also, you could achieve this having less reinforcement between the chassis braces and the center diff brace, on the corresponding side.
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Old 09-22-2009, 08:25 AM   #4
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Default please.. can explain clear...

Hi...

if the chasis have to flex..

can anyone tell me how much??!!.. this is the real KEY!!!....
it is not correct..

If the factories donīt made chasis more stiff is be cause these result in more expensive prices..
That the chasis have to flex is a great lies around the Buggys RC 1/8....

You have to the chasis have to be rigid to suport the other elements speceally designeds to absorv deformation from the road..


If you have to absorve deformation from the track or road.. you have 4 elements especealy designed to this critical responsabllity..
The Tires.. the Springs.. The Shocks Absorvers.. the Bars...

Diego.
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Old 09-22-2009, 08:43 AM   #5
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Stiff chassis' are more suited to high bite surfaces.

In off road we don't have enough grip (even on blue groove tracks) to support a chassis like the one pictured above.

We have to use long shocks and suspension travel to get over the bumps and jumps. The normal engineering benefit of a stiff chassis goes out the window. The chassis needs to twist/ articulate to help absorb what the suspension cannot to keep our "300MPH" cars controlable.


Some of the best handling buggies are ones with a decent amount of longitudal flex (or twist)

Remember the Thunder Tiger with the monocoque chassis? Not so good.
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Old 09-22-2009, 08:50 AM   #6
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Well I think that your chassis looks like a work of art and am interested to see how it works. The only issue that I see is the thickness, the chassis will in effect sit much lower due to the suspention pieces being mounted on top of it (looks to be what, 6-7mm thick?) so you would have less clearance, but it looks like a neat experament. Maybe a bit expensive to replace as well, but with a project like that who cares.
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Old 09-22-2009, 08:55 AM   #7
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Racecrafter...

may be you know a Rally car that have to chasis flex??!!.. or Paris Dakar,, or Formula One.. or Indy Car.. or Traxxas Series...

Please... explain me how much to flex??!!!...
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Old 09-22-2009, 10:20 AM   #8
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the amount of chassis flex is going to vary with the length of the chassis, weight distribution, and desired effect. It'll also depend on the thickness and overall rigidity of the material used.

Take a look at what losi did w/ their tuned flex chassis on the 8ight-T 2.0, as well as the buggy. They both are lengthened, vs their predecessors. Additionally, there are spots in the chassis that flex more than others.

One other thing is that they're experimenting with using a dampener in place of the rear chassis brace. This will effectively allow you to tune the flex of the chassis.
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Old 09-22-2009, 10:21 AM   #9
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The only way to find what the optimum amount of flex is would be by trail and error. There is never going to be one set amount that is optimum either. It would vary from car to car, set-up to set-up, driver to driver, and track to track.

I would think that all race cars except for those made with carbon fiber uni-bodies have some sort of flex to them.
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Old 09-22-2009, 10:26 AM   #10
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My matrix chassis's flexed at least double what the stockers did and Sure as Shi* they felt A Whack load more planted in the rough.....chassis flex is 10000% needed in RC or the car's would be OVERLY twitchy and not handle nearly as well as they do.
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Old 09-22-2009, 10:31 AM   #11
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I would have thought the Matrix carbon fiber chassis would have had less flex than the stocker. Interesting.

You might wanna check the thread about the BCE 3mm chassis for the 8ight. Lots of people seem to think there is an advantage to the extra flex.
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Old 09-22-2009, 10:39 AM   #12
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dont you think if chassis flex was bad the manufacturers of these products would have addressed it? and went with stiffer chassis instead of flexible ones.
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Old 09-22-2009, 10:41 AM   #13
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Quote:
Originally Posted by PTP Racing View Post
I would have thought the Matrix carbon fiber chassis would have had less flex than the stocker. Interesting.
assuming we're talking about the moosracing CF chassis for the Cen Matrix
it is... I spoke with Neils Vansoe last night, and he specifically asked me about that. I'm hoping to have a CF extended matrix truggy chassis made soon
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Old 09-22-2009, 10:41 AM   #14
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Hi Diego, you probably will not find the level of engineering expertise you're looking for here. Suffice it to say, there is a point when a 1/8 buggy chassis is too stiff. Thunder Tiger released the at the time revolutionary EB4 S3 with a box section chassis. Within a year they were doing a conventional plate style chassis that helped the car to run decently. RC suspension just isn't sophisticated enough to handle everything itself.
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Old 09-22-2009, 10:44 AM   #15
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I was speaking about the brand name Matrix carbon chassis for the 8ight. I assumed Integra was also.

I just yesterday for the first time saw a carbon chassis for the CEN Matrix which I think they said they are just now beginning to test.
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