cyclone

Hello Erhard,
I believe that Robert will of be using that post to replace the lipo c/f piece and allow a raised rollcentre by also raising the centre pivot ball up to achieve a fully raised rollcentre (see std roll centre adjustment on the E1 kit).

What you are talking about is different. I dont believe the adjustment to be roll centre, as the centre of roll for the rear suspension is pinned down by the height of the centre pivot ball, relative to the chassis plate.

Raising the front of the side links does have an effect. I mapped it on cad. If you raise the front of the side link by 5mm, the rear axle will steer away from the corner in full roll by 0.5°. (truck like rear steering that would increase slow speed steering. This can not really be achieved though, as the side link length change would be too much with such a big angle change. You could try it for yourself by raising the front ball by using a shorter post on the E2, and using normal turnbuckles and sockets to set the length correctly.

Making the side links have an angle inward (toe-in like), has no effect on rear steer.

patorz31

Does anyone have a weight out of the box for this thing?

TrevCoult

I mentioned it earlier, but my son's was 745g out of the box with XR10 pro, Futaba 9650 and Ketter Ultra. Now underweight with replacement Ti screws etc.

Erhard

Hello Andy,
things are easy to clarify. Rollcenter is the center of movement that the tires rotate around. This cannot be the pivot ball, as it is not located between the tyres. The only exception is parallel links (parallel to the ground). Then roll center and pivot ball height coincide.

With a center of gravity beeing the same height as the roll centre, the chassis would not lean(roll) to the outside/inside of a turn
With a center of gravity beeing higher than the roll centre, the chassis would lean(roll) to the outside of a turn. This is the normal situation. It is controlled by side springs, side tubes or a roll bar in other cars. It is also controlled by a weight transfer to the outside tyre of the other (front) axle.

What is interesting is the fact, that normally the axle with the lower roll centre produces more grip. Lowering the roll center brings grip to the rear axle at expense of the front. This means, roll center adjustment does adjust between oversteer/understeer mid corner. (remark: The full balance is also a result of front springs and side springs stiffnesses, eventual roll bars, tyres etc.)
This means balance adjustment is possible by simply tilting the side bars! Try it as an alternative to raising/lowering pivot ball and side bars together, which is just more work. There is no disadvantage in tilting the bars to adjust roll centre. As you noticed, the possible steering effect is negligible.

BR Erhard

DavidNERODease

The plastic ride height adjusters fit perfectly... the bulkheads are machined so that any left over sprue does not interfere with the fit. Very nice. The axle bearing does fit a little loose in the adjuster however. Do the team guys score the inside with a hobby knife to tighten the fit of the bearing?

Erhard

Finally I am allowed to upload.
This is what I wanted to share from the beginning about the connection between pivot ball, angle of side bars and the resulting position of roll center at the rear axle.
I know quality of this sketch is low, but hopefully it is possible to understand.
BR Erhard

DavidNERODease

Raising the forward pivot point of the side links will only affect roll steer not the roll axis. Your diagram is not correct. That is not how the roll centre is calculated. Sorry to be blunt but that just isn't how it works.

Erhard

Hello David,
no Problem,
Just tell me the correct way.
Maybe there might be a misunderstanding. This is not the Roll Axis. It is only the construction of the Roll center of the rear. which is a point. not an axis.
Connecting line of front and rear roll center points is the Roll axis of a car.
BR Erhard

DavidNERODease

The rear suspension of this type on a pan car is just a trailing arm from the centre pivot to the tire contact patch. The side links just keep rear axle squared up to the chassis.

Erhard

No, they do a little different.
They (and the pivot joint) restrict the axle carrier in motion as it could also be done with two axis rotation.
One axis we already discuss. The direction is the line/direction of the side links plus it goes through the pivot. (which is no roll center)
The other is allowing up and down for the trailing arm. This goes also through the pivot.
Here pivot height will result in squat effects under acceleration and braking.
BR Erhard

DavidNERODease

The side links are just tierods and don't affect anything except rear axle alignment. Remove them and play with the suspension. The rear wheels still follow the same path during suspension compression. It's like saying that if you change steering tierod angle on your TC that the roll centre changes. It doesn't, but bump or roll steer will.

XCELL

iTrader: (10)

Erhard

Hmmh. No thats not the same.

I did not say the rear wheel doesn´t follow the same path under suspension movement (without roll movement), what can we learn here regarding roll centre?

In other words, how do you think, a roll center is defined, and how do you derive it for this type or any other suspension. There is clear literature about it. Do you know the definition of roll center? What literature do you refer to?

BR Erhard

DavidNERODease

View the suspension from the back of the car, draw a line through the aft side link ball joints and the centre pivot. That's it. Done. The only way to lower the RC with this design is to lower the those ball joints which is what Schumacher did. The only way to lower the RC more than what the Eclipse has (while still using a center pivot) is to use a Mumford linkage. A Panhard can't and Watt's link can't and neither can raising the forward side link pivot balls. I don't know what else to tell you but remember that a lot of really knowledgeable people have been trying to improve this suspension for decades. If the RC could be lowered by your method, then it would have happened a long time ago.

DavidNERODease

Actually, even with a Mumford linkage (instead of side links) the RC might not behave as expected as it would still be in conflict with the centre pivot (for sideways axle location).