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Old 04-27-2009, 02:22 PM   #5221
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Thanks ED! And thanks for all the help and your great resource site
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Old 04-28-2009, 02:07 AM   #5222
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I've had a look at Eds Roll Center Calculator thingy, but I dont really know what the values mean to me Can someone explain it a bit more? Please
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Old 04-28-2009, 05:01 AM   #5223
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I've had a look at Eds Roll Center Calculator thingy, but I dont really know what the values mean to me Can someone explain it a bit more? Please
What you are looking for is the amount of camber gain over the suspension travel. More camber gain generates more grip during cornering. Careful though, too much isn't good. But mind you , I couldn't get that thingy to work....
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Old 04-28-2009, 12:54 PM   #5224
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It's actually got diddly squat to do with camber change.

What it's showing is the static roll centre positon. This is the point around which the car starts to roll. A lower number (i.e. closer to 0), the higher the roll centre. A higher roll centre will give less roll, and so quicker reaction, better rotation and higher corner speed, at the expense of some outright grip. Much like stiffening the springs.

Now I say it's the static position because as the car rolls, the roll centre moves as well, because the links change position (the roll centre is calculated from the interaction of the steering links). To calculate that is well beyond the capabilities of what I can draw up, currently

Basically, the calculator is a guide, to give an indication a certain change will have on the roll centre of the car... it's quite useful to see how even changing the length of the arms alters it, for example.

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Old 04-28-2009, 01:51 PM   #5225
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Hi Ed, have you ever considered doing a similar program but for the steering of the car. Changing the spacers on the center to change the ackerman effect, as well as bump steer spacers and how they would effect the toe?

Just a crazy thought, but it would be interesting to be able to simulate this on screen to actually see it with a number reference.
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Old 04-28-2009, 07:46 PM   #5226
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It's actually got diddly squat to do with camber change.

What it's showing is the static roll centre positon. This is the point around which the car starts to roll. A lower number (i.e. closer to 0), the higher the roll centre. A higher roll centre will give less roll, and so quicker reaction, better rotation and higher corner speed, at the expense of some outright grip. Much like stiffening the springs.

Now I say it's the static position because as the car rolls, the roll centre moves as well, because the links change position (the roll centre is calculated from the interaction of the steering links). To calculate that is well beyond the capabilities of what I can draw up, currently

Basically, the calculator is a guide, to give an indication a certain change will have on the roll centre of the car... it's quite useful to see how even changing the length of the arms alters it, for example.

HiH
Ed
And any engineer will tell you that more camber makes cars turn....
Please don't try too hard to complicate the matter here.
If you like -1 camber but you need more in the corners you need more camber gain. Roll center is what you say it is yes but ... simple is better!
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Old 04-28-2009, 11:36 PM   #5227
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And any engineer will tell you that more camber makes cars turn....
Please don't try too hard to complicate the matter here.
If you like -1 camber but you need more in the corners you need more camber gain. Roll center is what you say it is yes but ... simple is better!
John, I'm not exactly sure what your getting at here... It's pretty simple really. Its a roll centre calculator, end of. Camber doesn't make any change to the program, as its been setup using 1deg.
Roll centre is as fundamental setting as camber... Get it wrong, and you'll be slow.

What the calculator does do, is help figure out what affect on the car changes will make... I'll take your camber change example, if you may.
So you want more camber change, you've got two options to increase the link angle, removing shims from the inside, or adding them to the outside.
If you look on the calc, you'll see that both changes raise the roll centre a little bit, but lowering the inner link has less of an effect on the roll centre.

Hopefully that explains it a bit more.
Remember, setups are (and always will be) a compromise, changing one swtting will alter a number of other things as well... You can try and simplfy it as much as poss, but it's still worth keeping that in the back of the mind.

Ed
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Old 04-29-2009, 01:41 AM   #5228
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Some cool new Tamiya related products I blogged about on my website:

www.rcracing2.com

Check the demon lipo tray, new ceramic diff balls, and more....
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Old 04-29-2009, 01:48 AM   #5229
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Sweet site man Where can I get that lipo tray? And the Mabuchi com cleaner?
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Old 04-29-2009, 01:50 AM   #5230
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Ed, noting the rcbearings.co.uk in your sig, do you use ceramic bearings or steel? I think after almost a year of solid use my 416 might be due for some new bearings - the ones on the centre shaft are sounding a bit worse for wear - I'm just wondering if the added cost for ceramics are worth it
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Old 04-29-2009, 02:48 AM   #5231
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And any engineer will tell you that more camber makes cars turn....
I am an engineer and unfortunately you are wrong. Ever tried -20 degrees camber? You will find you will have almost no grip during cornering since the contact patch on the tyre is reduced to almost nothing. Similarly if you run +20 degrees you will have no real grip although in all likelyhood you will roll the car immediatly if you enter a corner hard.

As with most settings the truth is somewhere in the middle and depends on a lot of factors.

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Please don't try too hard to complicate the matter here.
Agreed, but that is the point. When talking roll center it is easiest to stick to that (a very common engineering practice) effect first. It is quite possible to change roll center without affecting camber gain (the opposite is a bit harder). Moreover the effects are different too although, as you rightly point out, both have an effect on grip and on cornering speed.
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Old 04-29-2009, 05:43 AM   #5232
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Originally Posted by TryHard View Post
John, I'm not exactly sure what your getting at here... It's pretty simple really. Its a roll centre calculator, end of. Camber doesn't make any change to the program, as its been setup using 1deg.
Roll centre is as fundamental setting as camber... Get it wrong, and you'll be slow.

What the calculator does do, is help figure out what affect on the car changes will make... I'll take your camber change example, if you may.
So you want more camber change, you've got two options to increase the link angle, removing shims from the inside, or adding them to the outside.
If you look on the calc, you'll see that both changes raise the roll centre a little bit, but lowering the inner link has less of an effect on the roll centre.

Hopefully that explains it a bit more.
Remember, setups are (and always will be) a compromise, changing one swtting will alter a number of other things as well... You can try and simplfy it as much as poss, but it's still worth keeping that in the back of the mind.

Ed
Quote:
Originally Posted by tonyv View Post
I am an engineer and unfortunately you are wrong. Ever tried -20 degrees camber? You will find you will have almost no grip during cornering since the contact patch on the tyre is reduced to almost nothing. Similarly if you run +20 degrees you will have no real grip although in all likelyhood you will roll the car immediatly if you enter a corner hard.

As with most settings the truth is somewhere in the middle and depends on a lot of factors.



Agreed, but that is the point. When talking roll center it is easiest to stick to that (a very common engineering practice) effect first. It is quite possible to change roll center without affecting camber gain (the opposite is a bit harder). Moreover the effects are different too although, as you rightly point out, both have an effect on grip and on cornering speed.

Whoa whoa man... -20? Are you insane? No one would EVER need more than -4 or -5 maximum, EVER!!! Lets not get carried away here okay. I'm merely stating the fact that for general purposes there is an all wheel drive car (real world here) Audi, Talon, Subaru WRX. (real cars) We would add camber , mostly to the front end and the cars turned so much harder that if you were at the stock settings you were getting left in the dust! And yes Ed you are 100% correct about what you are saying there. Changing the pivot points in certain ways gives the wheel more leverage to the chassis and can limit chassis roll. The tool you provided is very cool and I've played with it too. Very cool!! More over sway bars and springs. But think about what the chassis is doing mid corner and how if your wheel rolls over positive that grip will go out the window. You can run an initial setting of 0 deg camber if you have more camber gain. Or if theres no grip at all and the car is spinning out then perhaps no camber gain is required. But also the tool does not provide the actual angle of chassis deflection during load conditions (i.e. mid corner). If there were a tool that showed the geometry of all the parts with relation to the chassis (left & right) so that you can watch the full effect of roll center on the chassis and not just the wheel. Or did I miss something?
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Old 04-29-2009, 05:56 AM   #5233
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To think all I asked was what the numbers mean
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Old 04-29-2009, 07:08 AM   #5234
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Sweet site man And the Mabuchi com cleaner?
Just make your own, man. I have made mine a long time ago and I didn't even know these existed. All you need is a bent piece of steel and a "normal" comm cleaner you cut to a little square shape and superglue it on the bent end of the steel bar.
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Old 04-29-2009, 08:02 AM   #5235
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Whoa whoa man... -20? Are you insane? No one would EVER need more than -4 or -5 maximum, EVER!!! Lets not get carried away here okay.
I am not getting carried away, I am doing what any engineer would do to show that something is not linear, go to the extremes. With RC cars -4 or -5 will still in almost all situations result in less, not more grip. So stating that to get more grip you would allways need to add camber (change) is quite simply incorrect.

There is a reason the standard (rubber tyre) setups usually have -1.5 degrees of static camber. This works best in general. In general meaning that in some cases less static camber works better and in some cases more static camber works better assuming no change is made to camber change.

I am all for keeping things simple. But if a "rule of thumb" is just as likely to have the wrong result as it is to give the right result I don't consider that simple at all. It means that relative newbies get frustrated because they cannot get things to work and cannot understand why they get less grip where they think they should be getting more.
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