RCCrawler Forums

solomon7 · 01-06-2009, 10:15 PM

I've read all the AS tech threads and am still not sure about some details.
Ideally, where would you want the Roll Center to be in ralation to the Center of Gravity. Above or below?
Also, regarding Instant Center , in a droop setup would it be benificial to have the IC be in the negatives, i.e. behind the axle and below the 'ground'?
I guess I'm asking for some clarification of the related effects of these values in a droop setup.
Right now I'm getting 46% AS, CG is 3", Roll Center is 3.4" , IC is 43" out and 4" from ground if i understand.
I could change the uppers and bring AS to -4% as well as bring the IC down to .4" above ground but the IC will be behind the axle..
Thoughts?
I could also bring the uppers out on the axle(lateral) and lower the roll center below the CG.
Any input is appreciated.
pics help sometimes

Edit: the rear uppers are on bent rod ends, so they are a bit lower on the axle end.

EeePee · 01-06-2009, 10:17 PM

Sure, but let's see a picture at least.

Duuuuuuuude · 01-06-2009, 10:39 PM

I hate numbers and I have a really hard time wrapping my head around suspension tech. Thats why my old chassis had so many holes in it...

I prefer the test and tune method...

solomon7 · 01-06-2009, 11:04 PM

pics added to first post

Greatscott · 01-07-2009, 10:16 PM

I gotta be honest here solomon7, I'm a geek, and good at math... your post gave me a headache.

I tried doing the same thing, figuring out the details, the geometry for the links and what-not, after the migrane subsided I just threw the truck on the rocks and had fun.

solomon7 · 01-07-2009, 11:11 PM

Been there, man. took off the decimals

I've been driving this thing 6 hours a week for months at least and done a ton of small changes noting the results. It was handling fine, but it can always be better. A dif of a few mm's can make a wheel hopping turd plant itself firm, so I ask those who have been doing this longer than me in RC and the 1:1 world.
The numbers are relative. Formulas save countless hours of experimentation once a control scenario is established. I'm just trying to give a very concise explanation of the effects these changes would have. The percentages are a bit 'rigid' but they do establish values of change.
With a few more or less % of AS the entire rig's characteristics can change.... that, and droop is a very complicated can of worms regarding AS, and it seems IC has a more direct effect as well.
I'm REALLY just wondering about roll center vs CG and where the ideal placement of the RC should be in relation to CG. Also, how IC relates to the RC, and what is ideal in their relationto each other.
Hope I didn't convalute things more!

solomon7 · 01-08-2009, 02:09 PM

anyone? Do i want the RC under, above or with the CG? Does the ideal placement change with a sprung setup?

EeePee · 01-08-2009, 02:14 PM

I wouldn't think too hard about RC with these things. There might be some worth in trying, but weight transfer is going to happen anyways. And the bulk of the weight is on the axles, not the chassis.

solomon7 · 01-08-2009, 02:48 PM

That's true. I like to tinker, and there's always ways to improve. Crawler OCD

and an unexpected 'vacation' from work are a wacky combo!
Really if someone could give a simple explanation of how roll center relates to center of gravity in general, it'd tie everything together for me.
I get what all the terms mean and their effects, but roll center's relation to CG, if any(?), and vice versa eludes me for some reason

.
It's like the last chapter in suspension tech in my head lol!

EeePee · 01-08-2009, 03:11 PM

Try this: http://www.jalopyjournal.com/forum/s...d.php?t=220819

solomon7 · 01-08-2009, 05:51 PM

Fog is slowly clearing. Thanks EeePee! Seems the lower the roll center the better....

I think

that would kinda explain why the triangulated lower, parralel upper setup
works well. Good dual triangulation + low RC.

moabax · 01-10-2009, 04:46 AM

Quote:

Originally Posted by solomon7

Good dual triangulation + low RC.

That is correct.

01-06-2009, 10:15 PM	#1
solomon7 Rock Crawler Join Date: Jul 2007 Location: Portland,OR Posts: 888	link geometry I've read all the AS tech threads and am still not sure about some details. Ideally, where would you want the Roll Center to be in ralation to the Center of Gravity. Above or below? Also, regarding Instant Center , in a droop setup would it be benificial to have the IC be in the negatives, i.e. behind the axle and below the 'ground'? I guess I'm asking for some clarification of the related effects of these values in a droop setup. Right now I'm getting 46% AS, CG is 3", Roll Center is 3.4" , IC is 43" out and 4" from ground if i understand. I could change the uppers and bring AS to -4% as well as bring the IC down to .4" above ground but the IC will be behind the axle.. Thoughts? I could also bring the uppers out on the axle(lateral) and lower the roll center below the CG. Any input is appreciated. pics help sometimes Edit: the rear uppers are on bent rod ends, so they are a bit lower on the axle end. Last edited by solomon7; 01-07-2009 at 11:13 PM.

01-07-2009, 11:11 PM	#6
solomon7 Rock Crawler Join Date: Jul 2007 Location: Portland,OR Posts: 888	Been there, man. took off the decimals I've been driving this thing 6 hours a week for months at least and done a ton of small changes noting the results. It was handling fine, but it can always be better. A dif of a few mm's can make a wheel hopping turd plant itself firm, so I ask those who have been doing this longer than me in RC and the 1:1 world. The numbers are relative. Formulas save countless hours of experimentation once a control scenario is established. I'm just trying to give a very concise explanation of the effects these changes would have. The percentages are a bit 'rigid' but they do establish values of change. With a few more or less % of AS the entire rig's characteristics can change.... that, and droop is a very complicated can of worms regarding AS, and it seems IC has a more direct effect as well. I'm REALLY just wondering about roll center vs CG and where the ideal placement of the RC should be in relation to CG. Also, how IC relates to the RC, and what is ideal in their relationto each other. Hope I didn't convalute things more! Last edited by solomon7; 01-07-2009 at 11:18 PM.

01-08-2009, 02:48 PM	#9
solomon7 Rock Crawler Join Date: Jul 2007 Location: Portland,OR Posts: 888	That's true. I like to tinker, and there's always ways to improve. Crawler OCD and an unexpected 'vacation' from work are a wacky combo! Really if someone could give a simple explanation of how roll center relates to center of gravity in general, it'd tie everything together for me. I get what all the terms mean and their effects, but roll center's relation to CG, if any(?), and vice versa eludes me for some reason. It's like the last chapter in suspension tech in my head lol! Last edited by solomon7; 01-08-2009 at 02:52 PM.

01-06-2009, 10:17 PM	#2
EeePee MODERATOR™ Join Date: Jul 2004 Location: Ohio Posts: 18,928	Sure, but let's see a picture at least.

01-06-2009, 10:39 PM	#3
Duuuuuuuude Suck it up! Join Date: Mar 2008 Location: Arkansas Posts: 11,652	I hate numbers and I have a really hard time wrapping my head around suspension tech. Thats why my old chassis had so many holes in it... I prefer the test and tune method...

01-06-2009, 11:04 PM	#4
solomon7 Rock Crawler Join Date: Jul 2007 Location: Portland,OR Posts: 888	pics added to first post

01-07-2009, 10:16 PM	#5
Greatscott I wanna be Dave Join Date: Jul 2005 Location: North Idaho Posts: 3,648	I gotta be honest here solomon7, I'm a geek, and good at math... your post gave me a headache. I tried doing the same thing, figuring out the details, the geometry for the links and what-not, after the migrane subsided I just threw the truck on the rocks and had fun.

01-08-2009, 02:09 PM	#7
solomon7 Rock Crawler Join Date: Jul 2007 Location: Portland,OR Posts: 888	anyone? Do i want the RC under, above or with the CG? Does the ideal placement change with a sprung setup?

01-08-2009, 02:14 PM	#8
EeePee MODERATOR™ Join Date: Jul 2004 Location: Ohio Posts: 18,928	I wouldn't think too hard about RC with these things. There might be some worth in trying, but weight transfer is going to happen anyways. And the bulk of the weight is on the axles, not the chassis.

01-08-2009, 03:11 PM	#10
EeePee MODERATOR™ Join Date: Jul 2004 Location: Ohio Posts: 18,928	Try this: http://www.jalopyjournal.com/forum/s...d.php?t=220819

01-08-2009, 05:51 PM	#11
solomon7 Rock Crawler Join Date: Jul 2007 Location: Portland,OR Posts: 888	Fog is slowly clearing. Thanks EeePee! Seems the lower the roll center the better.... I think that would kinda explain why the triangulated lower, parralel upper setup works well. Good dual triangulation + low RC.

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