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Old 04-09-2004, 06:26 AM   #76
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Just wanted to say this is great reading!!!

Question that comes to hand for me is when xray created the short arm car alot of testing went into it. I can only come to a cobclusion that the short arm car will work better for most tracks as they released it as their new car. However this maybe just a way to make more money by putting out another version of the car. So to some this up is short better? or long?? or are we debating which is better for certian circumstances?

Thanks
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Old 04-09-2004, 07:59 AM   #77
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i too must say that i am very pleased with the contributions that everyone has made.

it is still too early to come to any conclusions that one is better than the other. not to mention, the fact that you have to state the task you are referring to when claiming that one is better. perhaps, more versatile? i don't think that anything brought about by changing arm length is purely additive. what i mean, is that while some things are improved, others are degraded. it is a matter of recognizing, and prioritizing the importance of each of these characteristics. and then deciding which alignment favors those which you deemed most important.

to use xray's latest design as a method of concluding that short arms are better is completely out of phase with the philosophy of the thread. all that has been offered here to date has deliberately taken hearsay and marketing out of the equation. instead, looking to science to validate the claims made for these shorter arms.

short arms may truly be more suitable for our application, but we still haven't yet a unanimous opinion for the answer(s) to why.

let's keep it up.
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Old 04-09-2004, 08:28 AM   #78
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Seaball, Well put. I think the first thing I learned in r/c tunning is exactly that.

quote: what i mean, is that while some things are improved, others are degraded.
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Old 04-09-2004, 09:00 AM   #79
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im glad someone knows what they are talking about

Quote:
Originally posted by Dragonfire
I belive seaball metioned rollcenter change eailer. Usually when a car rolls, the movement in the suspension arms resaults in the rollcenter dropping. As we all know, low rollcenters yield more grip and allow the car to corner faster. If you consider how the rollcenter changes, the shorter arms resault in more rollcenter change which should yield more grip mid turn than a car with the same setup but longer arms.

As for being faster around the track???? Well its up to the driver to exract the performance for that.. I have been trying a new car recently (atlas ym34si with "long arms") and have found that the biggest advantge is the speed it changes direction. I can make moves on the inside of ppl during s-turns that give me a huge advantage.

So whats better??? Alot of crap is said about this car has this and that car has that. A car is fast because of the driver and that fact will never change. As long as the car is adjustable (modern) you will always have the potential to be competative.
here is a bit about rollcenters.

Low rollcenters=more mid corner grip
High rollcenters=less mid corner grip

When a car with short arms goes around a corner, the rollcenter will drop more than what a car with long arms would.

The short arms change the motion ratio of the shock, making it stiffer (in a motion ratio way, not physicaly), making it look as if the car rolls less. The car will roll less when it goes through quick direction changes where it doesnt get a chance to roll alot.

THEORECTICALY short arms should be better for rubber tires and long arms should be better for foam tires.

But this is THEORECTICALY, so sometimes things work in ways they might not normally work.

and there is driver ability like Dragonfire said
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Old 04-09-2004, 09:02 AM   #80
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Team Orion used have an excellent "vehicle dynamics" guide, specifically aimed at rc cars. I will try and post it
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Old 04-09-2004, 09:04 AM   #81
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Dontfeelcold:

You just posted the first thing that made some sense to me or that I could truely understand thanks

quote:
here is a bit about rollcenters.

Low rollcenters=more mid corner grip
High rollcenters=less mid corner grip

When a car with short arms goes around a corner, the rollcenter will drop more than what a car with long arms would.

The short arms change the motion ratio of the shock, making it stiffer (in a motion ratio way, not physicaly), making it look as if the car rolls less. The car will roll less when it goes through quick direction changes where it doesnt get a chance to roll alot.
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Old 04-09-2004, 09:15 AM   #82
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if you want the Orion setup guide, PM me, and i will email it toyou as the file is to large to post on RC Tech
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Old 04-09-2004, 12:55 PM   #83
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dont' feel cold - how would a short arm setup with high static roll centers compare to a long arm setup with low static roll centers?
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Old 04-12-2004, 06:16 AM   #84
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thought I would bump this cause I have enjoyed reading thoughts on this subject
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Old 04-12-2004, 11:37 AM   #85
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Well, I was eagerly awaiting a concise answer to my last question, presumably from the person who is qualified enough to determine who actually “knows what they are talking about.”

That is, apparently, not going to happen. So, when I do get a chance to do some minor math, It is likely that I will again have more questions to present.

Oh, and props for the bump.
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Old 04-13-2004, 04:10 AM   #86
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ROTFLMAO!

*Everything* in engineering comes down to solving a differntial equation! :-)


Quote:
Originally posted by seaball
this discussion is heading more and more toward a ridiculous differential equation. oh god no.

the crazy part is that all of this is, and has been, done by many people in full scale racing. this information should be plentiful. or is this all under wraps for all of the various teams out there?

nah, we aren't even discussing anything close to what these guys would consider secretive

and what am i doing in sales??

i guess, just being jealous.
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Old 04-13-2004, 04:14 AM   #87
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and BTW the setup guide on the team orion site is the same as on http://users.pandora.be/elvo , only a slightly older version.
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Old 04-13-2004, 06:36 AM   #88
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Just a point I'd like to clear, lateral displacement of the roll centre does not affect the rolling moment applied on the chassis, but only how the car will roll.

More horizontal displacement means that the suspension travel will increase on the outer wheel, and decrease on the inner wheel, this makes me think that the effect of downtravel in the middle of the corner will be lessened.
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Old 04-13-2004, 11:34 AM   #89
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Quote:
Well, I was eagerly awaiting a concise answer to my last question, presumably from the person who is qualified enough to determine who actually “knows what they are talking about.”
sorry, but threads move through so fast that i end up missing them.

I dont know everything about rollcenters, car setup etc, but from what i have learnt from the setup guide and put into practice at the track i have been able to get my car to go very quick.


Quote:
how would a short arm setup with high static roll centers compare to a long arm setup with low static roll centers?
the one with the short arms will sit lower than the long arms. The only time the rollcenters will be static is when you are on the grid ready to start a race, and when the car is on your pit table. even mid corner the car will never be static as the track will never be 100% smooth.

I would be paying attention to what Josh Cyrul has said, he knows what he is doing. ive taken the liberty of taking a copy of what he wrote in this forum and adding it to my setup stuff.

hope that helps
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Old 04-13-2004, 12:50 PM   #90
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certainly, no one is arguing that the things that you or josh are doing aren't working. the questions are directed more toward why they are working, and whether or not other alignments can produce similar results.

at big races, when track conditions change from heat to heat, or from practice to main, you don't always have the luxury to try a bunch things that won't help to alleviate a particular problem your car is having. unless you run the same car that everyone else has, their solution may not be applicable to your chassis. so where then can you turn?

additionally, if one were to design a car, with the intention to make it superior to everything before it, without knowing what is primarily responsible for certain characteristics, it would be nearly impossible to do. even with that knowledge, it is a tall order.

despite the fact that the car is only static while it is sitting on the line, that state was used as a state of reference for defining the geometry for the comparison.

roll center locations are a direct result of the upper and lower arm angles which are created by the mounting locations for the inner and outer arm pivots. it is quite conceivable on a modern chassis to have a setup where the roll center of a long arm car is lower for all stages of dive or roll than that of a short arm car.

if the low roll center produced is the desired effect of the short arms, i am wondering why very few people are lowering the roll center to its maximum. people are lowering the inner hingepins on the chassis, but why haven't i seen anyone using other manufacturers' hubs and carriers to further raise the outer hingepin? is there a point of diminishing return? high roll centers can quicken the response of a car, but with that comes the jacking effect that outside arm can elicit. someone, i believe it was robk, eluded to the idea that the short arms quicken response, without the ill tendecies to traction roll.

so how low can we go? is there a point of diminishing returns? and what are the symptoms?

lata

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.

lata
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