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Post by otr on Mar 25, 2009 11:53:26 GMT
I notice the XXX Main book suggests having roll centres as equal front to rear as possible which to me makes perfect sense.
However from what I can see on set up sheets of some of the better racers, and from asking around it does seem that generally it is better to run a lower front roll centre than rear.
I have been told the lighter end of the car should always have a lower roll centre.
Now mine are equal front to back. The question is......
am I right or wrong? Should I be changing mine.
I also wonder if the roll centre is affected by the amount of flex in the chassis and where you have your weight distributed.
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Post by lesbaldry on Mar 25, 2009 12:38:07 GMT
Roll centers? are you refering to top camber links or wishbone hight from chassis.
Carpet racers normaly run different roll centers front to rear compared to tarmac ie higher wishbone position at the front?(Xray)
For me the Cyclone TC at our track likes the pivots flat to the chassis in low grip ,raised up 1mm in medium grip,2mm on high speed high grip tracks,the upper links I normaly leave at 2mm or may be drop the rears to 1mm depending apon "feel" on the day
1mm shims/washers under the wishbone pivots give the Cyclone a nice direct stable feel ,flat to the chassis gives the car roll and more grip but makes the drive "soft"...If you are having a "turn in "prob Its worth playing with Akaman spacers and front shock position...plus this time of year I would get away from kit shock oil (30wt)and perhaps use 45/40 front 35/40 rear,this will give a very different feel to the car (direction change)
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Post by otr on Mar 25, 2009 12:58:09 GMT
I suppose it is easier to talk about adjustments on the upper camber links as to changing roll centres.
If you check the difference between Andy Moores carpet and tarmac set ups the camber link positin is 1mm different front to rear for tarmac and 0.5mm different for carpet. However for carpet the link is overall 1mm higher.
What I am trying to ascertain is whether having a different roll centre/upper camber link height front to rear is correct or not and what is an acceptable difference and why should there need to be a difference.
What does changing the roll centre really do and what does having a large difference between front and rear do.
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Post by otr on Mar 25, 2009 13:01:39 GMT
Have I think solved my turn in problem and the unequal turning.
Was fine in practice on Sunday using my old Lipos. In the race I used new "flat" Lipos that are slightly thicker which reduced (to zero!) the gap between battery and motor mount so stopping any flex on one side of the car. I am fairly certain that is what was causing the poor turn in and uneven turning. Tried it the other night with the old Lipos and it was fine so have "adjusted" the clearance for the new packs.
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Post by lesbaldry on Mar 25, 2009 13:17:54 GMT
I suppose it is easier to talk about adjustments on the upper camber links as to changing roll centres. If you check the difference between Andy Moores carpet and tarmac set ups the camber link positin is 1mm different front to rear for tarmac and 0.5mm different for carpet. However for carpet the link is overall 1mm higher. What I am trying to ascertain is whether having a different roll centre/upper camber link height front to rear is correct or not and what is an acceptable difference and why should there need to be a difference. What does changing the roll centre really do and what does having a large difference between front and rear do. I could quote the theory from a book but to be honest I feel adjustments affect various chassis in different ways"to a degree" plus Im not worried about "why/what they do" and tend to work the feel/grip on the day..depending apon which end of the car is playing up  ...ie get to know your chassis and personal driving preference  what works for one may not work for another?? |
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Post by Simon Crabb on Mar 25, 2009 13:28:48 GMT
Have I think solved my turn in problem and the unequal turning. Was fine in practice on Sunday using my old Lipos. In the race I used new "flat" Lipos that are slightly thicker which reduced (to zero!) the gap between battery and motor mount so stopping any flex on one side of the car. I am fairly certain that is what was causing the poor turn in and uneven turning. Tried it the other night with the old Lipos and it was fine so have "adjusted" the clearance for the new packs. Also, note that lipos of differing types weigh different and amounts, and more importantly, have that weight distributted differently, I've found this makes a big difference, as well, as you say ensuring flex is maintained.
On the subject of roll centres, after listing to local Tamiya drivers bang on about them so much, I now regularly change mine in the pits, they are a great adjustment.
I just deleted a whole explanation of how I think they work, but they're so complicated I thought it might be wrong, so will leave it to an expert to fill in the details! |
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Post by lesbaldry on Mar 25, 2009 13:47:20 GMT
None of us are Experts Simon and I would imagine you do the on the day feel bit like me ;D Ok for what its worth, no doubt someone will debate my roll center findings  ..so what I dont care it works for me ;D Should I want to get rid of wicked steering I would raise the front wishbone roll centers and perhaps the camber links too,but to me this can somtimes unsettle the rear and a further adjustment may be needed here,springing,shock position or just rear camber link hight?...this is why I tend to stick to equal lower front /rear roll centers for Tarmac and just play with different front to rear camber link hights. |
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Post by otr on Mar 25, 2009 14:01:02 GMT
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Post by Reuben on Mar 25, 2009 14:03:35 GMT
Sunday I ran my camber links at 1 on front and 1.5 at rear. I found this perfect for the day, whereas running 1 and 1 caused the back end to loose it very slightly under braking pushing me off line. The extra .5 on the rear settled the car on braking.. :S make sense of that  |
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Post by otr on Mar 25, 2009 14:24:12 GMT
I suppose as with all these things if what you do suits you then it is correct.
However I do like to know the theory behind these things although having read a bit about roll centres it seems to be far mire complex than I thought. I guess the answer is to try different settings, maybe go to extremes so you can feel what happens and then take your judgment from there.
If you know increasing rear camber link height does "such" and reducing it does "other such" then you have a good chance of being able to use those adjustments if needed.
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Post by lesbaldry on Mar 25, 2009 14:24:21 GMT
basicaly I use roll centers to dial out/in grip or to keep the car flat on high speed high grip tracks or to make the chassis roll (low centers) in low grip.
All this is also linked to springs,roll bars,shock oil/pack/rebound,droop,diff hight...bugger!mind numbing stuff ;D
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Post by Martin Young on Mar 25, 2009 16:37:22 GMT
Sunday I ran my camber links at 1 on front and 1.5 at rear. I found this perfect for the day, whereas running 1 and 1 caused the back end to loose it very slightly under braking pushing me off line. The extra .5 on the rear settled the car on braking.. :S make sense of that With 1 and 1.5 on the camber links what did you run under the pivot blocks? |
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Post by Reuben on Mar 25, 2009 17:14:50 GMT
nothing.
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Post by lesbaldry on Mar 25, 2009 23:02:42 GMT
Ian I took note of your comment regarding "lower roll centers to the lighter end of the car" it makes some sort of sense ie the lighter end will need to roll more due to lack of weight?..so I got curious,my balance point is dead central to the wheel base,this is something I always thought was correct and tried to achieve(equal wieght transfer front to rear??)...should I/we be balancing our cars to a rearward or forward bias...somthing I have never thought about  . is it worth playing with? perhaps this why I find my prefered equal front/ rear roll centers give a better balanced feel to the drive to my make of chassis/set up/ balance?...Id love to hear an experts opinion The old Losi xxx alowed the cells to be moved via the 7th cell slot to adjust steering /grip "I think" should roll centers be adjusted to compensate for weight bias?....slot car racing is starting to look more atractive,at least you wont have to worry about turn in ;D ;D ;D |
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Post by otr on Mar 26, 2009 8:34:44 GMT
Les maybe we should go back to Nimhs and brushed motors. At least then we would not have as much time to worry about all these set up things! LOL
My understanding is that there should be a slight rear bias for weight distribution but there is divided opinion about that.
As long as you fully understand the effects of weight transfer I guess you could set the car up accordingly whatever the weight bias is. Most of the stuff I have found regarding this is based on either rear wheel drive or off road and I am not sure how relevant it is.
At least if your weight centre is in the middle of the car you should (in theory) be able to set the car up better I would have thought. However I am happy to be proved wrong if someone out there is more up with this.
Far too much time on our hands these days. Too many questions and too few answers. The ANSMAN class looks ever more appealing!
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Post by lesbaldry on Mar 26, 2009 9:34:37 GMT
Ian I took a look at that set up site and as you say its "off road"..what confuses me hence my dissregard of the whys and hows is that some expert set up scribes contradict each other..Ill stick to set up by "brail" |
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Post by otr on Mar 26, 2009 9:45:01 GMT
It may be that REAL car racing "experts" know more although again how relevant to our application is debatable. I found this on a car racing site in answer to a question regarding roll centres. Is it relevant?
"Forget front and rear roll couples and the 'mass centroid axis'. Unless your chassis is made out of boiled spaghetti, they are irrelevant - the front and rear of the car can't roll independently of each other!
Also, be aware that contrary to what many textbooks either state or imply, a car does not roll around its roll centres or roll axis.
Effectively, the only thing you are interested in is the centre of gravity of the sprung mass. Imagine attaching a string to this point and pulling - sideways to simulate a cornering load, fore or aft to simulate acceleration or braking, diagonally to simulate a combination. The attitude a car adopts when subject to these forces is dependent upon how stiff the springs and anti roll bars are, and of course these will be different front and rear. Due to differing roll resistances front and rear, and the fact that weight is transferred diagonally, the car will almost always be operating in what Allan Staniforth refers to as 'skewed roll' - ie. a combination of roll and dive/squat.
The main implication of the roll centre locations are that they are used to calculate diagonal weight transfer, which in turn can be used to derive suspension deflection and individual tyre loads (which in turn influence understeer/oversteer balance).
The traditional rule of thumb was that that the roll centre is lower at lighter end of the car, but many other factors have to be taken into account - spring/roll bar stiffness, tyre sizes, front and rear track, CG location etc., so this rule is by no means hard-and-fast.
Probably more important to make sure that your roll centres don't move about much in relation to the sprung mass, as movement changes the diagonal weight transfer and can lead to very uncertain handling characteristics. "
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Post by lesbaldry on Mar 26, 2009 13:20:40 GMT
Is it relevent..who knows Ian,some physics must be but we are racing a centrally weighted 4 wdr rocket with drag car acceleration and cornering ability of a bob slay,it may be 1/10th in size but certainly not in weight and speed,but we do run very very flexi chassis...interesting stuff though Over the years I have given up trying to fully understand set up,its mind blowing and can lead you astray from the basics and lets face it if we do have a handling prob 99% of the time its something very basic!..to get the best out our chassis is another story. Ill stick to my trial, error and learn method thanks ,I must be doing something right Sam disappeared of in the distance (6 secs off my fastest time) after he ended up with my identical set up and was extremely happy with the balanced handling too...I do wish he hadn't re joined  ... |
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Post by otr on Mar 26, 2009 15:01:04 GMT
I agree with what you say Les without question. However, I do think we need a basic understanding of what happens when you move this or what happens if I raise that. The only way is indeed to try it and see. Hopefully as far as roll centres go I am going to do some testing one evening with extreme changes to roll centres to see what happens and then work from there. The theory is way too complex to understand and how it actually affects MY car and the way I drive it can I think only be understood by trying it and seeing what happens. I reckon a Saturday soon spent trying all these things would be good, not by changing small amounts but by changing large amounts so you can really get an effect. That way you should know what small amounts of change will do. If you get what I mean.
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Post by lesbaldry on Mar 26, 2009 15:30:56 GMT
Thats how I work too,I expect top teams/drivers started this way too...but they can afford to wear things out too day in day out:'( Its a fact that some things dont perform as well when scaled down,might be the same with full size race car set up theory too? |
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Post by mattsedgley on Mar 26, 2009 15:48:29 GMT
Can i see the beginings of a testing day? or maybe even some kind of group sessions to try and figure these things out??
Matt
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Post by lesbaldry on Mar 26, 2009 16:09:34 GMT
Can i see the beginings of a testing day? or maybe even some kind of group sessions to try and figure these things out?? Matt May work with the same chassis's?? Here's an example why it may not..as you know I have ran a Cyclone and 008 side by side..the Cyclone is easy to drive and very stable with the lowest roll center setting the 008 was an absolute pig and needed the equivalent too 1.5mm on the Cyclone for the same "feel"even though the rest of the geometry was very similar..and yes it was all measured correctly to copy the known stable Cyclone set up for our track! |
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Post by gwesty on Mar 26, 2009 16:12:10 GMT
hi , u guys are getting way too deep with this !lol
roll centers as uv stated are pivitol points around the axis of the car , raising or lowering will control when the car transfers weight from side to side . coupled with spring weights to control the pressure of roll ! generally the front camber links are flatter due to the weight mass being tranfered under braking . i could go on all day here as there is loads of reasons why this does this and that !!! hth glenn , just go drive ur cars its far easier
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Post by yellowshark on Mar 26, 2009 21:26:50 GMT
,but we do run very very flexi chassis...interesting stuff though That is the one point that has always stumped me Les. When I started this, I set our car up influenced by real life, ie STIFF. It took me a fair while to realise that this was not what everyone else was doing and that there seemed to be a mantra that soft was good cos it improved grip and cornering with the exception that setup books admitted that hard was better for naigating chicanes. Soft aint good in real life |
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Post by lesbaldry on Mar 26, 2009 21:55:45 GMT
,but we do run very very flexi chassis...interesting stuff though That is the one point that has always stumped me Les. When I started this, I set our car up influenced by real life, ie STIFF. It took me a fair while to realise that this was not what everyone else was doing and that there seemed to be a mantra that soft was good cos it improved grip and cornering with the exception that setup books admitted that hard was better for naigating chicanes. Soft aint good in real life Years ago Pete it always was "stiffer the better" those who remember the TC3 and Losi will know what I mean,but they were not easy to set up,very narrow window of decent handling,the cars nowadays have a few more adjustments including flex settings..thats progress for you and track lap time prove it works A brave man took a Dremel to theses chassis's to make them flex and went faster..perhaps manufactures took notice and thats how we ended up with chassis that look like Skeletor ;D....My thoughts were the same regarding stiffness,it worked in 1/8th circuit and I think still does?? I would imagine that the stock classes lap times are probably as fast as a mod was 5 or so years ago,even at our little track 4 years ago 19 laps was a hard target in 19t,now we are pushing well into the 20's in 17.5 and 22 in pro stock |
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Post by lesbaldry on Mar 26, 2009 22:02:43 GMT
hi , u guys are getting way too deep with this !lol roll centers as uv stated are pivitol points around the axis of the car , raising or lowering will control when the car transfers weight from side to side . coupled with spring weights to control the pressure of roll ! generally the front camber links are flatter due to the weight mass being tranfered under braking . i could go on all day here as there is loads of reasons why this does this and that !!! hth glenn , just go drive ur cars its far easier Dont blame me  ;D...it's Lloydie's fault,he loves going deep!!..he's always "up to his axels" in something or other....lucky chap Nice to see you're still keeping an eye on what the competition are up too Glen.....all this roll centre bo****ks is team tactics in code  Roll on Aldershot and the SLCC,then we can all put this bo****ks into practice...then throw our toys out of the pram and moan when the theory dont work ;D |
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Post by gwesty on Mar 27, 2009 13:39:08 GMT
schumacher chassis is ultra flexi , the 2.5mm is faster tho !
yeah les , keeping an eye on you lot !!!lol
see you soon
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...ie get to know your chassis and personal driving preference 
what works for one may not work for another??
..so what I dont care it works for me ;D
. is it worth playing with? perhaps this why I find my prefered equal front/ rear roll centers give a better balanced feel to the drive to my make of chassis/set up/ balance?...Id love to hear an experts opinion
... 
;D...it's Lloydie's fault,he loves going deep!!..he's always "up to his axels" in something or other....lucky chap 