R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Electric On-Road

Reply
 
Thread Tools Search this Thread
Old 04-23-2004, 11:14 AM   #1
Tech Champion
 
rayhuang's Avatar
 
Join Date: Dec 2001
Location: Cleveland Heights, Ohio
Posts: 6,511
Trader Rating: 5 (100%+)
Send a message via AIM to rayhuang
Default RC Car Action article-Wrong???

Okay-I couldnt ask for better timing on the roll center article by Joel JOhnson in the latest RC car action.

It was very informative, but one box of type seems wrong to me. And this is not good as I would never say Joel is wrong and I am correct. The box states that a Low roll center is ideal for low traction surfaces and a high roll center is best suited for high grip like carpet/foam racing.

I am sorry-but that is flat out wrong. So either I am a block head, or RC Car action misquoted Joel Johnson.

Someone please help me out here. I have burned out millions of brain cells on roll centers-just to now hear I am 180º off on when to use low and when to use high roll centers.
rayhuang is offline   Reply With Quote
Old 04-23-2004, 11:15 AM   #2
Tech Elite
 
dr_hfuhuhurr's Avatar
 
Join Date: Aug 2003
Location: Westchester, NY
Posts: 4,502
Trader Rating: 75 (100%+)
Default Re: RC Car Action article-Wrong???

Quote:
Originally posted by rayhuang
I have burned out millions of brain cells on roll centers
I can think of better things to burn brain cells on Ray. I've always beleived the same though...
__________________
"There is a fine line between hobby and mental illness. Which side are you on?"

“Life is hard; it's harder if you're stupid.” - John Wayne
dr_hfuhuhurr is offline   Reply With Quote
Old 04-23-2004, 11:17 AM   #3
Tech Champion
 
rayhuang's Avatar
 
Join Date: Dec 2001
Location: Cleveland Heights, Ohio
Posts: 6,511
Trader Rating: 5 (100%+)
Send a message via AIM to rayhuang
Default Re: Re: RC Car Action article-Wrong???

Quote:
Originally posted by dr_hfuhuhurr
I can think of better things to burn brain cells on Ray. I've always beleived the same though...
Ummm-that was the early 80's!!!
rayhuang is offline   Reply With Quote
Old 04-23-2004, 11:21 AM   #4
Tech Elite
 
Jack Smash's Avatar
 
Join Date: Aug 2001
Location: Reno, NV
Posts: 2,897
Trader Rating: 29 (100%+)
Default

That is what I believe as well. If the chassis roll occurs at a lower point, it helps plant the outside tires and increase thier grip. A higher roll center helps keep more load on the inside tires and allows the car to make quicker transitional changes.
Jack Smash is offline   Reply With Quote
Old 04-23-2004, 11:23 AM   #5
Tech Elite
 
PitCrew's Avatar
 
Join Date: Sep 2003
Location: Seattle Indoor Raceway
Posts: 2,129
Default

I think Joel is right. Thats why guys who run TC3 on carpet are putting the shims under the shock tower, to rasie the roll center, for more efficient roll (reducing the mechancial ability for the car to grip because of the high grip of the tires) this aids in corner speed.
PitCrew is offline   Reply With Quote
Old 04-23-2004, 11:25 AM   #6
Tech Elite
 
BigDogRacing's Avatar
R/C Tech Charter Subscriber
 
Join Date: Aug 2001
Location: Memphis, TN
Posts: 2,955
Trader Rating: 12 (100%+)
Send a message via MSN to BigDogRacing
Default

Ray- you are probably just a little mixed up. Low roll centers means the roll moment (distance between the CG and roll center) is longer which gives the CG leverage over the RC and causes more roll with the same given amount of lateral force. Opposite for high roll center. Example- raising the inner hinge pin on the lower arm raises the roll center and lessens the roll moment thus causing a decrease in roll moment, decrease in roll and a decrease in traction.

Where I get confused (and probably you care confused as well) is that on very high traction like carpet with foam tires, often just the opposite of what we expect to happen... happens!! In talking with more educated racers like Barry, Fernando, PW etc, I have concluded that this is a result of the flat foam tires, camber gain (AKA camber rise) and other issues that affect high traction foam tire racing.

On rubber tires, nitro (somewhat) and off road, the roll centers seem to work the way they are SUPPOSED to work!!

BTW- all of my information is based on what I have learned AND poven to myself in racing conditions. I won't waste yours or my time with theoretical notions.
BigDogRacing is offline   Reply With Quote
Old 04-23-2004, 11:28 AM   #7
Tech Elite
 
mtveten's Avatar
 
Join Date: Jan 2003
Posts: 2,668
Trader Rating: 27 (100%+)
Default

Ray the article is correct. To clarify by lowering the roll center your car will produce more chassis roll and thus provide more grip in the corners. In simplest terms a low roll center has more chassis roll and a high roll center will result in less chassis roll.
mtveten is offline   Reply With Quote
Old 04-23-2004, 11:31 AM   #8
Registered User
 
OB42TC3's Avatar
 
Join Date: Nov 2001
Location: Columbus, OH
Posts: 417
Default Re: RC Car Action article-Wrong???

Quote:
Originally posted by rayhuang
Okay-I couldnt ask for better timing on the roll center article by Joel JOhnson in the latest RC car action.

It was very informative, but one box of type seems wrong to me. And this is not good as I would never say Joel is wrong and I am correct. The box states that a Low roll center is ideal for low traction surfaces and a high roll center is best suited for high grip like carpet/foam racing.

I am sorry-but that is flat out wrong. So either I am a block head, or RC Car action misquoted Joel Johnson.

Someone please help me out here. I have burned out millions of brain cells on roll centers-just to now hear I am 180º off on when to use low and when to use high roll centers.
..depends on the slip angles of the tires in question. foam on carpet, foam on vht treated ashalt, rubber on asphalt, etc. The statement (as with most) in Car Action was too general. I have noticed most of the revisions of electric and ntiro tourers deal primaerily with RC changes (NTC3 V2, S710, MTX3, R40). I agree with you Ray, that the low RC upper link is right for carpet touring, but I think the small diameter tires, play a big role in where the RC starting point is, and just b/c the upper link says lower RC, the lower arms are at the point where they are almost angled down which would mean a higher RC. Now if you put 62 mm rubber tires on and adjust to 4mm Ride height it'll probably be under the ground plane.
OB42TC3 is offline   Reply With Quote
Old 04-23-2004, 11:31 AM   #9
R/C Tech Founder
R/C Tech Charter Subscriber
 
Join Date: Aug 2001
Location: Del Mar, CA, USA
Posts: 7,063
Default

I recently wrote a similar, as-yet-unpublished article. I have not read Joel's. But based on what you say, I think Joel is both right and wrong depending on how you look at it.

I think he's using "low traction" to mean "in need of rear traction." When you run a lower rear roll center relative to the front, you will transfer more weight to the outside rear tire during a corner and gain some traction. However, running a low (or lower) front roll center under the same conditions could actually work against you, since you'll be transferring more to the outside or to the outside front, and the rear end will be more likely to break loose.

High grip situations are basically the reverse. You rarely want to run a low front roll center in, say, foam carpet racing, since you want less weight transfer up front. More weight transfer would make the car "dig in" entering corners and probably lead to traction rolls or other poor results. The rear roll center in this case could be either, depending on the rest of the car's setup. The same principle applies, though: the lower the roll center relative to the center of gravity, the more weight you'll be transferring under cornering forces.

I think the real benefit in tuning roll center comes from the front-rear stagger, though it doesn't sound like Joel referenced that in his article -- at least not that bit of it. A car with identical front-to-rear roll center (which probably never occurs since the weight distributions are different) should be more neutral feeling than one with a staggered roll center. Generally you don't want to run the lowest possible roll center at both the front and the rear of a car, since you'll end up being sluggish all around the track as the chassis rolls from side to side.

Hope this makes some sense...
__________________
Visit my store: www.ampdraw.com
futureal is offline   Reply With Quote
Old 04-23-2004, 11:34 AM   #10
Tech Champion
 
rayhuang's Avatar
 
Join Date: Dec 2001
Location: Cleveland Heights, Ohio
Posts: 6,511
Trader Rating: 5 (100%+)
Send a message via AIM to rayhuang
Default

BigDog-what up?

I am so glad you threw in the bit about theoretical vs. reality as I too have played with roll centers at every practice and race and I seem to be able to use it to my advantage in tuning-but cannot effectively explain it to anyone. I feel somethng cars doing-then I change it based on part theory, part what others have told me or have on there cars and my own experience.

It is my belief that on foam tires on carpet that you lower the roll center in an attempt to put less traction in the tires and absorb more of the forces as body roll.

And conversely-you raise the roll center if you want the car to corner flatter and have more side bite.

IS that correct?
rayhuang is offline   Reply With Quote
Old 04-23-2004, 11:37 AM   #11
R/C Tech Founder
R/C Tech Charter Subscriber
 
Join Date: Aug 2001
Location: Del Mar, CA, USA
Posts: 7,063
Default

BigDog: One of the biggest differences in carpet foam racing is the strong spring rate that we use. The car's chassis will only roll until the cornering force is overcome by the opposing force from the compressed spring, before it rebounds and rolls back. With very stiff springs, the chassis will have a very limited range of movement, and may even "bounce back" in the other direction under a quick/hard corner.
__________________
Visit my store: www.ampdraw.com
futureal is offline   Reply With Quote
Old 04-23-2004, 11:40 AM   #12
R/C Tech Founder
R/C Tech Charter Subscriber
 
Join Date: Aug 2001
Location: Del Mar, CA, USA
Posts: 7,063
Default

Ray: Most everybody runs high front, low rear roll center, or same front-to-back in foam racing that I've seen. The camber links, however, are typically placed as close to parallel with the chassis as possible. This is not so much to play with the roll center but more to reduce the camber gain when cornering.
__________________
Visit my store: www.ampdraw.com
futureal is offline   Reply With Quote
Old 04-23-2004, 11:41 AM   #13
Tech Champion
 
rayhuang's Avatar
 
Join Date: Dec 2001
Location: Cleveland Heights, Ohio
Posts: 6,511
Trader Rating: 5 (100%+)
Send a message via AIM to rayhuang
Default

Quote:
Originally posted by PitCrew
I think Joel is right. Thats why guys who run TC3 on carpet are putting the shims under the shock tower, to rasie the roll center, for more efficient roll (reducing the mechancial ability for the car to grip because of the high grip of the tires) this aids in corner speed.
I think raising the shock towers is raising the inner camber link position-which leads to a lower roll center.
rayhuang is offline   Reply With Quote
Old 04-23-2004, 11:43 AM   #14
Tech Champion
 
rayhuang's Avatar
 
Join Date: Dec 2001
Location: Cleveland Heights, Ohio
Posts: 6,511
Trader Rating: 5 (100%+)
Send a message via AIM to rayhuang
Default

Quote:
Originally posted by futureal
Ray: Most everybody runs high front, low rear roll center, or same front-to-back in foam racing that I've seen. The camber links, however, are typically placed as close to parallel with the chassis as possible. This is not so much to play with the roll center but more to reduce the camber gain when cornering.
I would agree-but that again goes against the RC Car action artcle in my mind. As your running a low rear roll center to free up the back of the car by tacking away side bite. The article makes it sound like yu run low roll to increase traction.
rayhuang is offline   Reply With Quote
Old 04-23-2004, 11:49 AM   #15
Tech Champion
 
rayhuang's Avatar
 
Join Date: Dec 2001
Location: Cleveland Heights, Ohio
Posts: 6,511
Trader Rating: 5 (100%+)
Send a message via AIM to rayhuang
Default

And just to nip the inevitable post in the bud-Yes-I do practice and race often as I can, but thats just not enough for me. I am purty dumb-really-but I still need to know why my car does what it does.
rayhuang is offline   Reply With Quote
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
Newspaper Article rcdougie Florida Racing 0 04-27-2005 02:37 PM
Looking for an article online Coney Electric On-Road 2 07-28-2004 07:29 AM
B4 vs. XXX-KE article in new RCCA TurnNBurn Electric Off-Road 31 10-21-2003 11:18 PM
Painting Article - Need Help HauntedMyst Painting, Designs, Graphics and Photography 35 04-15-2003 09:48 PM
Article in Radio Control Car Action sixandeightstri Electric On-Road 6 01-02-2002 09:00 PM



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 11:09 PM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net