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Old 01-31-2014, 05:24 AM   #76
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Originally Posted by Rouge711 View Post
Hi all, i've a question for Martin.
Saing that i have fully understood weight transfer and RC theory, if you take a look at last setupsheets from several pro driver in high traction condition (carpet tracks) you can see the tendency in raising up RC putting almost 1mm under lower suspension blocks and shortening camber links which means raising again RC.
What is the goal i can't find? Why this choice?
In addition, sometimes we can read more droop in rear end like 4.8!!

Personally i have experienced in my last high carpet grip race that 1mm under suspension blocks, 0.5 antidive in front, shortening camber links and raising outer and inner camber link let the car more easy to drive.
Maybe i am wrong, in fact this seems a contraddiction to the theory which teach me to choose a lower RC in case of high grip in order to reduce lateral grip and prevent traction rolling...

Thanks Martin...
I dont mean to answer martins question but if they are running a mod motor like a 5.0 for example than they need more traction a good deal more traction than if they were running 17.5 blinky because the car gets pushed way harder and is expected go cope with it
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Old 01-31-2014, 04:33 PM   #77
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Quote:
Originally Posted by Rouge711 View Post
Hi all, i've a question for Martin.
Saing that i have fully understood weight transfer and RC theory, if you take a look at last setupsheets from several pro driver in high traction condition (carpet tracks) you can see the tendency in raising up RC putting almost 1mm under lower suspension blocks and shortening camber links which means raising again RC.
What is the goal i can't find? Why this choice?
In addition, sometimes we can read more droop in rear end like 4.8!!

Personally i have experienced in my last high carpet grip race that 1mm under suspension blocks, 0.5 antidive in front, shortening camber links and raising outer and inner camber link let the car more easy to drive.
Maybe i am wrong, in fact this seems a contraddiction to the theory which teach me to choose a lower RC in case of high grip in order to reduce lateral grip and prevent traction rolling...

Thanks Martin...
You general car setting may be very soft? If that's the case, maybe the car rolls too much with low RC. The chassis may hit the track at turns, or lateral weight transfer may be too much due to rolls.
When you up the RC, the car rolls less, the shocks outer side of the car don't bottom out as quickly, the car doesn't hit the ground so more stable and turns w/o traction roll.
Well this is what happened to me yesterday when I took mine to a high traction carpet track. Mine is set very soft 40w, 35wt oil with 3 piston holes and 14,15lbs spirngs. I ended up raising RC front and rear and lower droops from 2F,2.5R to 1.8 F/R. No more instability at mid turns(car was getting loose all of sudden at mid turns due to chassis hitting bottom) and no more traction rolls at beginning of turns.
Well what do I know? Just my thought based on what I learned from Martin's.
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Old 01-31-2014, 10:26 PM   #78
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What was the droop when the Roll Center was low??? If it was too high(above 1.5mm), then you would traction roll with too soft a spring set... You need to spring the Car until it barely scrubs the carpet, and clean the underside of the chassis after every run...
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Old 02-01-2014, 12:34 PM   #79
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Quote:
Originally Posted by Rouge711 View Post
Hi all, i've a question for Martin.
Saing that i have fully understood weight transfer and RC theory, if you take a look at last setupsheets from several pro driver in high traction condition (carpet tracks) you can see the tendency in raising up RC putting almost 1mm under lower suspension blocks and shortening camber links which means raising again RC.
What is the goal i can't find? Why this choice?
In addition, sometimes we can read more droop in rear end like 4.8!!

Personally i have experienced in my last high carpet grip race that 1mm under suspension blocks, 0.5 antidive in front, shortening camber links and raising outer and inner camber link let the car more easy to drive.
Maybe i am wrong, in fact this seems a contraddiction to the theory which teach me to choose a lower RC in case of high grip in order to reduce lateral grip and prevent traction rolling...

Thanks Martin...
If you read the Roll center section of my app again, it does go through and explain details about how droop affects roll center and how the length of the upper arm affects roll center.

For example when the droop screws hit the chassis the roll center sharply goes to the center point of the inside tire. This can make the car feel very edgy and have sudden changes in balance. This is why you don't want to run zero droop, as that would take away a lot of smoothness and consistency in the way your car feels.

If you put a 1mm spacer under the hinge pin blocks yes you are raising the RC, but if you also raise the upper links by adding an equal amount of spacers on the inboard and outboard this will lower the RC because the IC is further away from the car. So the static RC may actually end up being the same. But as the car rolls the RC may move around differently giving you a different feel.


Keep in mind that the RC changes as the car rolls. The shorter the upper links the less the RC drops as the car starts to lean. In contrast the longer the upper links the more the RC drops as the car starts to lean. So shorter upper links give you more lateral grip when the car is leaning.

Also keep in mind that shorter upper links also give you more camber gain, which will give you more later grip in addition to additional lateral grip added by keeping the roll center higher while the car leans.

In terms of why drivers would choose the kind of setups you describe on higher grip tracks...it comes down to two things. One is the feel the like...i.e. how edgy or lazy do the like the car to feel in the corners. Secondly trying to maximize lateral grip without traction rolling. In other words if they had gone with lower roll centers, they may have less chances of traction rolling, but maybe for that track they could get away with slightly higher roll centers to gain more lateral grip, but not actually experience traction rolling.
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Old 02-01-2014, 12:36 PM   #80
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I dont mean to answer martins question but if they are running a mod motor like a 5.0 for example than they need more traction a good deal more traction than if they were running 17.5 blinky because the car gets pushed way harder and is expected go cope with it
yep
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Old 02-01-2014, 01:50 PM   #81
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First off, this thread is awesome. Second, I wish I could fully understand all the information exchanged, lol.

I am currently trying to get my trusty TA05 back in the VTA circuit. The problem I have, and have always had, is that the Ta05 loves to lean. The battery and motor are very far from the center of the chassis. If I wanted to reduce the lean, would I shorten the camber links? Would this also help with the lazy feel it has in chicanes?

MANY THANKS!

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Old 02-01-2014, 03:29 PM   #82
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Originally Posted by rc car guy View Post
I dont mean to answer martins question but if they are running a mod motor like a 5.0 for example than they need more traction a good deal more traction than if they were running 17.5 blinky because the car gets pushed way harder and is expected go cope with it
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Originally Posted by big al View Post
First off, this thread is awesome. Second, I wish I could fully understand all the information exchanged, lol.

I am currently trying to get my trusty TA05 back in the VTA circuit. The problem I have, and have always had, is that the Ta05 loves to lean. The battery and motor are very far from the center of the chassis. If I wanted to reduce the lean, would I shorten the camber links? Would this also help with the lazy feel it has in chicanes?

MANY THANKS!

--Al
Glad you like the thread. It has been fun for me to get back involved in RC, even if it is only through this forum

I loved my TA05. One of the easiest cars to drive.

You could try shortening the links...that might help. It will give you more lateral grip because the RC stays higher, and the camber gain is greater when leaning. Having said that for me personally I have rarely preferred shorter upper links. I always found a longer link made the car feel smoother.

You might want to try raising the static roll center by raising the lower a arm inboard hinge pin height (if you can do that on the ta05...can't remember). Otherwise you could remove spacers from the inboard upper link or add spacers to the outboard upper link. If I recall there is not a lot of space to add spacers outboard on the upper links.

You could also go a little stiffer on the swaybars to help with the chicanes and that lazy feeling.

Cheers.
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Old 02-01-2014, 04:48 PM   #83
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Hi Martin, for those that want to dive deeper do you have any recommended books for learning about the dynamic roll center behavior and the geometry behind it?
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Old 02-01-2014, 06:14 PM   #84
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You could try shortening the links...that might help. It will give you more lateral grip because the RC stays higher, and the camber gain is greater when leaning. Having said that for me personally I have rarely preferred shorter upper links. I always found a longer link made the car feel smoother.

Cheers.

I too have found longer upper links to be smoother and less on edge but if you can drive well with shorter links they are typically faster.
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Old 02-01-2014, 09:06 PM   #85
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You can counter the lazy feel with stiffer springs or swaybars, and still not traction roll... I also don't like lengthening and shortening the links too often, since they tend to wear out fast...
Also you need to have the correct chassis flex characteristics for the Car to work...

Last edited by bertrandsv87; 02-01-2014 at 09:33 PM.
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Old 02-02-2014, 06:40 AM   #86
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Originally Posted by Martin Crisp View Post
If you read the Roll center section of my app again, it does go through and explain details about how droop affects roll center and how the length of the upper arm affects roll center.

For example when the droop screws hit the chassis the roll center sharply goes to the center point of the inside tire. This can make the car feel very edgy and have sudden changes in balance. This is why you don't want to run zero droop, as that would take away a lot of smoothness and consistency in the way your car feels.

If you put a 1mm spacer under the hinge pin blocks yes you are raising the RC, but if you also raise the upper links by adding an equal amount of spacers on the inboard and outboard this will lower the RC because the IC is further away from the car. So the static RC may actually end up being the same. But as the car rolls the RC may move around differently giving you a different feel.


Keep in mind that the RC changes as the car rolls. The shorter the upper links the less the RC drops as the car starts to lean. In contrast the longer the upper links the more the RC drops as the car starts to lean. So shorter upper links give you more lateral grip when the car is leaning.

Also keep in mind that shorter upper links also give you more camber gain, which will give you more later grip in addition to additional lateral grip added by keeping the roll center higher while the car leans.

In terms of why drivers would choose the kind of setups you describe on higher grip tracks...it comes down to two things. One is the feel the like...i.e. how edgy or lazy do the like the car to feel in the corners. Secondly trying to maximize lateral grip without traction rolling. In other words if they had gone with lower roll centers, they may have less chances of traction rolling, but maybe for that track they could get away with slightly higher roll centers to gain more lateral grip, but not actually experience traction rolling.
Well, this is a superb answer, thank you! Now i must experience it with some testings...!
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Old 02-02-2014, 10:11 PM   #87
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Hi Martin, for those that want to dive deeper do you have any recommended books for learning about the dynamic roll center behavior and the geometry behind it?

here is the book I bought I think about 12 years ago...still a great book.


http://www.millikenresearch.com/rcvd.html
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Old 02-02-2014, 10:13 PM   #88
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Well, this is a superb answer, thank you! Now i must experience it with some testings...!
Excellent!

Many people always asked me why I do so much practice...its to figure out what works for a given car on a given track. You must experiment to optimize your setups.

Cheers.
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Old 02-02-2014, 11:01 PM   #89
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martin, i read into slip angles a bit on the rear (just a blurp on here somewhere). my car felt like a slug in the corners. (bought a slighlty used 6.1) then looked at the rear and it had tons of toe, almost 5 degrees. they previous owner had 2 extra 1mm shims in the back mounts. i removed those and wow, so much more corner speed. im back too the stock 2.5 that the kit is assembled with. im planning on purchasing your app for my phone so i have it at the track. great info so far and i look foreward to getting the app so i can use it to the best of my ability. thanks, doug.
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Old 02-02-2014, 11:04 PM   #90
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The roll happens when the Center of Gravity goes over the point that is supporting the weight.
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