Manticore

copied from a web site before it was removed about roll centre



Can be defined as an imaginary point that a car rolls around when it corners. Imagine you are looking at the back of a car as it enters a corner, as the car starts to lean, you can imagine a point the car is 'twisting' around.

The front and rear roll centers will usually be at different heights, you can use this as another tuning aid.

Firstly we need to determine the roll center height. This is usually easier to draw than to measure. Look at the back of the car, imagine a line traced along the upper and lower suspension links, unless these links are parallel, these lines will intersect somewhere.

Now imagine a line going from this intersection point to the center of the opposite tires contact patch with the ground. Where this line intersects with the center of the car is your roll center.

Keeping up so far, OK now things get complicated, as the car moves on it's suspension, the roll center will move, it even moves as the car rolls! So unless you want to calculate it for each possible combination of suspension positions, you will have to make some estimations.

OK now we have a pretty good idea of where the roll center is, how does it affect handling? There is one important relationship to consider, the distance between the roll center and the cars center of gravity (C of G). Under lateral forces (turning) the car will try to keep going straight, (Newton explained all this stuff) while the tires will try to turn; the sideways force acting on the car can be said to be acting at one point, the C of G. The forces resisting the car can be said to be acting at one point, the RC. The further these two points are apart, the greater effect the lateral forces will have on the suspension, or the more the car will roll. Theoretically, if the C of G was below the RC, the car would lean into corners like a motorbike! (Don't try this, it will be a bad thing)

So how do you adjust RC? It's actually fairly easy, if you look at it, if you lower the car 1mm, the roll center will actually move further. You may have heard people say that if you lower the front, it will put more weight on the wheels and the front will grip more. What actually happens, is that when you lower the front, the roll center drops further than the rest of the car, and this effectively softens the front suspension in roll, much the same as fitting softer springs. You can also adjust RC by moving the upper camber links around, which brings us to camber change.

This is actually fairly simple, if you look at the camber on the car, then compress the suspension all the way, you will see that you now have more camber. If you look at the way the upper link moves through the suspension travel, you can see that the shorter the link or the closer the link is to vertical, the more camber change you will get. Camber change is a very useful tuning aid, you will need to have some to counter the fact that the car rolls while cornering. If you have more, it enables you to have a small amount of camber when you're going in a straight line, and then have the car automatically dial in more when you're cornering. Problem, what happens when the car hits a bump? The car instantly develops heaps of negative camber, or when the rear drops into a hole it develops positive camber. Neither of which are good for traction. Basically running large amounts of camber change is OK if you're running on a smooth surface, with stiff springs.

black-knight

Ackermann in relation to RC cars is discussed on the pages at this link http://home.tiscali.be/be067749/58/c3/index.htm

Corse-R

Well,

I've just ended of assembling my MTX3 and taking some time to 'massaging' the brake disk with the indications given by the people on this thread (48 pages long thread) lightly sanding the upper bracket, brake pads and center core of the disk. Only left to install the throttle/brake linkage - I don't have a servo suitable to drive throttle/brake correctly).

I have taken note to do several things to the car, Tuesday if the weather permits I'll go to run for the virgin run of the car.

Some throughs:

1. Car quality is thumbs up, but the manual stinks a lot I needed to assemble the car guiding for the drawings who are pretty good but lacks of comments (anyone on Mugen factory has seen an Xray manual?).

2. Seems that the front axle is underdriven rather than being overdriven is this true?

3. My car leaks oil from the diff. I've found a gasket on the box along with the manuals. Is normal to leak oil from the diff or I need to install the gasket?

Motorman

iTrader: (1)

you need the gasket to clearance the gearset properly. coat it with a little shoe go or silicone.

Cartman

for shipping what kind sir

fuse01

Need advise on a huge 1/8 track (gearing)

running a JP S5 on stock gearinging... way too short,

please advise.. need more speed.

sparksy

iTrader: (14)

Without seeing the car on your track, its hard to give you a ratio....

If your running out of revs too early on the straight, gear up...

The best gearing will be found with a little trial and error.... or ask what the other drivers are running

nova racer

does the mtx3 come with gear diffs front and rear because i am now very smooth with a 1 way and i was thinking of picking 1 up to use as a foam car and my v1flex for rubber

Motorman

iTrader: (1)

comes with a gear in the rear and a one way in the front. they also give you cases for a front gear diff to fit it but no gears to go inside.

sparksy

iTrader: (14)

I went through Dennis' thread and found thid for you Fuse... Dennis had put it in words easily understandable and I wouldnt have been able to explain it as easy.

Hope it helps

"unless the car is a total handfull handling wise.
This is the first thing I do when I get to a new track.(other than set the top end fuel mixture by sound) I see if I run out of top end on the straight. if i do I gear up if I dont I gear down untill the engine runs out of steam before I lift on the back straight. at that point I gear up 1 tooth. 2nd is found.
I then do the same for first looking for the midrange punch in the infield.(after adjusting low speed fuel mixture). 1st gear is now picked. Once that is found then set the clutch for as much off the corner punch as you can drive. set it higher and higher untill you cant take it anymore then back it off a touch.

Now its time to tune the chassis. Once that is done you may need to readjust the clutch again. and also adjust it during the day some as traction goes up and down."

nova racer

kool thanks

Manticore

the number of screws on top of the chassis is far more then that at the main chassis. i.e. overall CG wont be affected that much in the bad side but at the good side (lower now).

Just got some Ti pivot balls for my MTX3.

the pack said: standard balls 3.53gm and Ti balls 2.04gm

David

Just a question for you guys regarding the front oneway.

i was sitting here looking over my car just now and noticed that i can move the oneway little sideways using my fingers between the the bearing blocks is this ok?

black-knight

should not be an issue, a small amount of play is ok. no play at all is bad.

David

Thanks BK

i just needed reassuring it was ok