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Old 01-30-2006, 10:38 PM   #16
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Quote:
Originally Posted by iblumberg

Will all cars adopt this approach?

Ira
It depends...

If saying that a car has variable stiffness will sell cars to people who demand more features...more features...and yes....more features, then you will see more companies offering cars with variable stiffness.

But as you pointed out, that will not stop these companies from selling these extra chassis to people who 'think' they need them.

So you have a guy buy a car because it "works on all surfaces"....

...only to turn around and buy the "super stiff chassis" for carpet and the "super flex" upper deck for outdoor asphalt.

Basically it supports the theory that there is a sucker born every minute.
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Old 01-30-2006, 10:43 PM   #17
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Quote:
Originally Posted by John Stranahan
Now using flex in the suspension arms is in vouge in Formula I. Here flexures are used instead of a lower arms and coil springs on the front of the car. The lower arm is solid graphite fibre piece that flexes. This reduces suspension friction immensely. Lowering suspension friction also seems to help our cars a lot. I wonder if flexures would be allowed by the rules.

F1 cars have been using flexures instead of spherical joints on the front suspension for quite a few years now, they still use springs(or torsion bars), the only reason they use flexures is to eliminate the stiction of the spherical joints which gives inconsistant wheel rate, especially with the tiny suspension travel they have.

I could be wrong, there might be a team that is trying just using flexures but the logistics and time to make setup changes would be mind boggling.
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Old 01-30-2006, 10:43 PM   #18
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I thought they milled out part of the center rib in the TC3 tub to move the batteries closer to the center!
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Old 01-30-2006, 10:48 PM   #19
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Originally Posted by AdrianM
Its 1997 and Masami discovers that their plastic Mr-4 is faster than their carbon Yr-4M2Pro. Masami and Barry win a ton of racers with that cheap plastic car. Yokomo comes out with the Mr-4 Pro Graphite. Its super cool and super slow....until...Masami starts cutting up the top deck to make the car flex. Barry won every race, every where with that car....except the Worlds...Hara won that! Yokomo Releases the World's Edition Mr-4 with the top deck milled out of the box.
I agree with you so much on this point.

As a TA05 owner, right now the TA05 is mirroring the lifespan of the MR4. And I keep trying to convince the people on that thread to take a look at what happened with the MR4. Yokomo took a really fast flexable car and "improved" it until it was a REALLY slow stiff "pro" car.

Yet people continue to call for a super stiff plate chassis, all graphite components, and an all around stiffer version of the TA05.

No matter how good a car is out of the box, the grass is always greener with hop ups. If it comes out of the box stiff, they want more flex, if it comes out of the box with flex, they want it stiffer.
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Old 01-30-2006, 10:57 PM   #20
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[QUOTE=John Stranahan]Tuning with chassis flex is a little puzzling to me. You never hear of a full size car designer wishing his chassis was more flexible, in fact every effort is made to make it stiff while still lightweight. When you make the chassis flexible it detunes the car. QUOTE]

Actually thats not true, I have been involved in building and racing full sized cars most of My life(a long time ) and controled chassis flex or twist is very important, and very often the difference between cars that drivers pick as a favorite car. Everything from drag cars, sprint cars, modifieds, late models, they all flex by design.......
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Old 01-30-2006, 11:18 PM   #21
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Mdoc-I stand corrected. I was thinking more of IRL cars and F1 cars Trans Am cars . I know that the big cars flex. The last Trans Am race I viewed, though, the pit boss was telling me about all the shear plates he had put in the car to reduce chassis flex. I got to crawl around and under his car. Performance wise on Asphalt The F1 cars are more similar to a touring RC car. They develop about 3.5 g's cornering. 2.8 g's is what I have measured for an RC touring car on asphalt without so much help from the aero downforce (about 3.5 g's on carpet).
Adrian-Well that is quite a bit better, backing it up with some data or observation or positve statement rather than just criticizing other people on this web site. Thanks for the information.

Last edited by John Stranahan; 02-02-2006 at 07:52 AM.
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Old 01-30-2006, 11:39 PM   #22
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cool john

do you think the additional down aero down force (quite considerable as Im sure you know) could be some of the reason they dont need much or any flex from the chassis to help them in the turns, as compared to a tc sedan on asphalt ?
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Old 01-31-2006, 12:01 AM   #23
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Mdoc-As far as I know in F1 they have always gone for a stiff tub even before the aerodynamic downforce was so well developed. On these cars with wide tires, camber control is very critical and I think that might be what influences their design. You can change the camber a full degree on my touring car and it is hardly noticable. You just wear the tire poorly. I plan to do the chassis flex experiment myself with the JRXS which is about 4 times stiffer (measured) than the XXXS after I get more cosistent lap times with it. I can remove 6 upper plate support posts and reduce its torsional stiffness by that factor of 4.

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Old 01-31-2006, 12:14 AM   #24
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the short arms, and center battery and motor placment could change how much flex affects the jrxs in comparison to cars with a more common layout, Iv noticed that the long frt camber link as a major change on that car.....
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Old 01-31-2006, 05:49 AM   #25
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Mdoc- It will have to do.

We did run the milled rib experiment on the TC3 with a good driver at Reflex. We had proper side to side balance with both setups. Lap times were indistinguishable full rib or milled rib.
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Old 01-31-2006, 06:39 AM   #26
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John,
Just wanted to add, I'm pretty sure no F1 teams use just flexures for suspension. Most of the A-arms are solid stiff carbon tubing (aerodynamically shaped), with a blade connecting into the tub. Instead of using a rose-joint, they use the blade's instead. Fathead has commented on this already.
Springing is controled by Torsion bars, and the damping now seems to be either by rotary damper (ferrari), or a longitudinal through-damper (toyota). Don't forget most teams also incorperate a third spring/damper unit to control pitch.

I'm in agreement with adrian, that given the difference in the suspension systems on and F1 and our RC cars, it is very difficult to compare them. The only car that I can recall that used a push-rod suspension system was the Tenth-Technology T1, in about '98 - '99.

I do find a more felxable chassis better in certain situations. For example, last year I tried a back to back test on my old 415. It was a std car, with a 3mm thick chassis. I firstly ran the car with the 4 chassis posts in the car, and then removed them for the next run, without changing anything else on the car.
The car handled much better without the posts, more than anything it coped much better with the bumps at my local track, whilst also generating more traction. Car was faster by a couple of tenths a lap because of it. I was more consistent too, as the car wasn't being thrown off line due to bumps.

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Old 01-31-2006, 09:16 AM   #27
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Talking to a couple guys on the team that race more asphalt than myself, I get the impression more flex in the chassis tends to make the car easier to drive in really high temperature conditions. Corally offers 2.4, 2.9 and 3.9mm main chassis plates. Most people tend to stick with the 2.9mm since it's a happy medium, but in florida where the conditions are extremely warm in the summer, the added flex of the 2.4mm makes the car stable and way easier to drive.

Honestly.... I see a lot of cars that tend to work very well on asphalt with somewhat flexible chassis. A lot of the cars made in japan are never super rigid, and a majority of their racing is on asphalt. They are still pretty stiff, but not rock hard like my 3.5mm upper deck and 3.9mm main chassis setup I use when running on super high traction carpet with foam tires.

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Old 01-31-2006, 09:42 AM   #28
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Ed and Fathead-Thanks for the additional detail on the F1 cars. I don't think the pushrod suspension would negate a comparison. This is done for aerodyamic streamlining rather than a change in characteristic. I realize that there are additional springs now, but the flexure carries the majority of the load and that is the improvement. Less Stiction or suspension friction.


Now the experiment needs to go like this. First you have to have a car with the side to side weights and corner weights in good order. If not then milling the chassis may have a benefit, but it is not neccesarily due to more flex. Maybe its just an improvement in side to side balance. Adrian tells me none of the big dogs use scales.

Next the car has to be in good tune with full chassis stiffness. The stiffness changed and then the car retuned. Other wise your improvement may only be due to a better state of tune.

Finally if you change from a double deck car to a molded chassis, you change a billion factors all at once. How do you decide which is the one that caused the improvement. We did a good thorought test on indoor asphalt with the TC3 molded chassis. I personally don't like double deck cars as there are way too many pieces that can move slightly and tweak the car causing poor performance, but that is what Losi is offering at the moment.

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Old 01-31-2006, 09:54 AM   #29
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I too was involved if full sized racing at top level for some years. It took me some time to actually give in and start playing with chassis flex as in most formula that I worked you generally wanted the stiffest tub/chassis you could come up with whilst always keeping the CofG and weight as low as possible.

I think that there is one critical difference however that separates models cars from full sized cars and that is you are not sitting in it driving! When driving a full sized racecar on the limit you are constantly reacting to what you are feeling through the seat and the wheel. When driving a model car you are reacting to what you SEE which is a much slower process and of course the given condition has then already happened (understeer/oversteer rtc..). Some element of chassis flex makes the car much more forgiving and driveable. Seting it up theoretically as you would a full sized car makes it too unforgiving and responsive for our tired old eyes then brains to keep up...then we crash!
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Old 01-31-2006, 11:58 AM   #30
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The way I see chassis flex is that it greatly depends on the car itself, suspension geometry, and track conditions. A more flexible chassis will create more grip most of the time. Sometimes too much. It can make the car feel like you're driving a Caddy. A stiffer chassis can, in some cases, take away some grip and let the car flow through the corners better and react more quickly. Personally, I like a car that kind of middle of the road. Not a super flexible car, but not a stiff as most carpet cars either. Right now, I'm currently running the Mi2EC Foam spec car with the stiffer chassis and I've modified the top deck to give more flex. It's not as flexible as the rubber spec car, but it's not too stiff either. So far, it's yielded some good results and I'll be trying different top decks that will give different amounts of flex to see where I like it the most.
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