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Old 04-13-2004, 01:09 PM   #91
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i think the main reason people arent using other manufacturers hubs to raise the hingepin is because they might not always fit(i know some brands are interchangeable) so it is easier to lower the inner hingepin.

theoretically higher rollcenters to make the car react quickly, works well with foams, not so well with rubber. i can make my car on rubbers change direction really fast with static low rollcentres that stay very low during the corner. its all in the other parts of the suspension.

the theoretical lowest static rollcentre is when the bottom and top arms are parallel. if you want to make the rollcntre to stay as low as possible while cornering, make both the top and bottom arm exactly the same length.



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food for thought - the tc3's roll center, both front and rear, is moderately high. yet, when the setup is good, it works so well indoors. how would this car change if we could change nothing but the relative height of the hinge pins (inner and outter) in order that the static roll center be drastically lowered? assume the angles of the other links (camber and tie rods) to change accordingly so that bump steer and camber curves remain virtually unchanged.
instead of changing the bottom arm, raising and lowering the top arm will have the same effect. providing your chassis lets you do that. if you cant space the lower arm holders and make new hub carriers. then again not all cars let you do this. That is what you pay for when you buy an rc car. the R&D that the company does to fing the optimum hinge points so that you dont have to fry your brain worrying about these things
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Old 04-13-2004, 01:23 PM   #92
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As ccm39 or seaball said-if we had to actually drive our RC cars sitting in the cockpit, they very well might be completely undriveable to us. Or so aggressive and scary that we'd need a diaper on.
put a tiny camera (ones that send a live feed to a tv) in a 1/8th nitro car. that would be so cool
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Old 04-13-2004, 01:28 PM   #93
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I think one of the challenges facing someone who wants to design the ultimate RC racing sedan-is to find a design that has a HUGE sweet spot for set-ups that is generally recognized as fast and relatively easy to drive (Tc3, XXXS-G+ come to mind) in all situations.
BUT-also to have the flexibility to be incredibly dialed in any situation-given the time to dial it in. And also to perform exactly as intended by the designer.

I must admit-I am almost more lost now than before I started reading this thread-but given time and more exposure to new concepts and reflecting back to these pages-I hope to gain more knowledge that I can apply during race weekends to solve handling problems or just plain old go faster.
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Old 04-13-2004, 01:36 PM   #94
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Let me restate the final paragraph-What I mean is-I hope from this thread that at some point during practice or a heat-a little light will come on in my head. I will see or feel something the car is doing and with this new knowledge-be able to turn it into positive results on the track. Like an epipheny?!?!?

An example mght be like this: Cars handlign well-but as the run goes on-it feels like its getting slower, building traction in rear and starting to push. If you hadnt read this thread-you mght be inclined to live with it or use less tire dope or just throw a stiffer spring in back. But as your now more knowledgeable-you might try lowering the rear roll center slightly to allow the car to run freer the entire run.

And in so doing-not disrupt the balance of the car as much.
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Old 04-13-2004, 01:36 PM   #95
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it took a while for it all to soak in, now i am afraid that i will forget more important things.

like i said, all the R&D has been done, choose a car you like the look of, then just experiment to see what different changes have on the feel of the car and most importantly the laptimes
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Old 04-13-2004, 10:52 PM   #96
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i guess i disagree with the idea that all the r&d has been done. we are what??? 6 years into touring cars, and still making new discoveries about something as fundamental as arm length. we have aftermarket c/f chassis manufacturers re-doing the entire chassis because there is a huge design/quality flaw with the factory ones.

progression will never stop in any industry so long as the market doesn't vanish. i'd rather help set the pace, than sit back and watch others do it.

who knows, at some point i may just have that opportunity.

and as for the confusion factor. that is a result of questions unanswered. with only a partial understanding of any subject, the added complexity of new information is bound to confuse. this thread never started as a tuning thread, but as a thread asking for insight and some dynamics expertise.

we have exposed enough, and i am certainly of the opinion that there is some merit to the performance changes brought about by the short arms. and that really was all i was looking for. i'm pretty hooked on the lateral shift of roll center more than the vertical at this point.

i am not 100% sure that the short arms are not a band aid solution for an alignment this is difficult to achieve with the lengthy counterparts. so consider me among the confused.
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Old 04-14-2004, 10:45 AM   #97
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IMO :

A car with short arms, high static RC but a lot of RC drop during cornering will have smoother response entering and exiting corners (as the general grip will be lower when the chassis rolls less), but will have a lot of MID corner grip.

A car with long arms, a low RC and few RC drop will be more responsive entering and exiting corners, and in gereral for small direction changes, but the grip will be constent during the corner.

Thus, I think the car with shorter arms will feel smoother than the car with long arms, and being smoother maybe will be easier to drive, not necessarly faster.

A big advantage with longer arms is on a bumpy track. This is true for touring cars as much as for Off Road cars. When I moved from the 414M to the SD I saw a huge difference on bumpy tracks. The SD was much better from the very start, whereas I never had the 414 very good on such surfaces.

Last edited by Cobra81li200; 04-14-2004 at 10:53 AM.
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Old 04-14-2004, 11:03 AM   #98
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Cobra-That is what I felt when running the long-arm Xray-it was hard to tune it to feel consistent all the way through the corner. I know I bugged all the Pros and amateurs alike about how to solve it squaring up too hard on exit-or more grip in middle of corner-or an on power push....

It was like youd tune out one thing-and cause another problem that was different-but just as debilitating to ultimate performance.





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Originally posted by Cobra81li200
IMO :

A car with short arms, high static RC but a lot of RC drop during cornering will have smoother response entering and exiting corners (as the general grip will be lower when the chassis rolls less), but will have a lot of MID corner grip.

A car with long arms, a low RC and few RC drop will be more responsive entering and exiting corners, and in gereral for small direction changes, but the grip will be constent during the corner.

Thus, I think the car with shorter arms will feel smoother than the car with long arms, and being smoother maybe will be easier to drive, not necessarly faster.

A big advantage with longer arms is on a bumpy track. This is true for touring cars as much as for Off Road cars. When I moved from the 414M to the SD I saw a huge difference on bumpy tracks. The SD was much better from the very start, whereas I never had the 414 very good on such surfaces.
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Old 08-01-2005, 11:18 PM   #99
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It's obvious that Losi's newest car (JRXS) needs to be dicussed in this thread. Please have at it, oh big-brained enginerds!
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Old 08-01-2005, 11:57 PM   #100
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I agree Rayhaung, the XXX-S was so easy to drive. If Losi would only fix a few minor things I hated about the car, I would get another one. Or a cf version of it. The LVDs were a nice concept for the XXX-S.
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Old 08-02-2005, 12:49 AM   #101
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Quote:
Originally Posted by rayhuang
It was like youd tune out one thing-and cause another problem that was different-but just as debilitating to ultimate performance.
I feel that way about the short arm XRay

Here is a post I made about it earlier:

In my case, When I converted my XRay to short arm it turned my car into absolute rubbish. I tried everything to get the car good but even after four and a half months I still couldn't turn anywhere near the quality of laps with the short arm car (which I only used for a few weeks) as I could with the long-arm car

My opinion on the XRay FK04 on carpet (with rubber tires) is very low. The long arm car on the other hand is an absolute beast on rubber!

AM I SERIOUSLY THE ONLY ONE WHO HATES THEIR FK04 ON RUBBER TIRES?
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