DAX suspension on radio controlled car

[Peter-RC]

first of all, sry for posting in the F1 part of this forum...

anyway, to the point:
a Dutch radio controlled racing car manufacturer has build a DAX type rear suspension for their 1:10 scale car.
http://www.serpent.com/news/13127/USA:- ... ystem.html

to my understanding this is just a rude cover-up to keep your wheel camber upright when in roll... instead of designing a proper suspension lay-out.
With this the wheel stay upright, but it still has some huge roll moments.
And is it's rear RC not moving all over the place when something happens?

They also quote it works also as an anti rollbar... but i can't figure out how.
can some suspension guru tell me the finer details about this suspension design?

[Jersey Tom]

Eh. With regard to "proper suspension layouts," nothing is perfect. With an independent, SLA suspension you have the option of great camber control in roll but terrible in bump... great bump control but terrible in roll, or a blend of "decent in roll and bump but not perfect for either." With regard to kinematic curves it's not so much a question of "good" vs "bad" as much as how well suited it is for an application.

In any event, it's hard to see from just a couple small pictures what all this thing does... but to me it kinda just looks like a roll-stiffening mechanism.

[Peter-RC]

i know that with designing a suspension lay-out it is the most difficult compromise known to man to make ... sort of
with R/C cars having good camber control in bump is kinda useless, we run with ground clearance of about 5mm... and the tires are getting about 1cm smaller in diameter... so i would focus on having good camber control with roll.

If i got some time i'll make a flash animation to see what happens in bump/roll, that might help me (and maybe others too) to understand it a bit more.
(i'm not going into the RC location stuff.. for that is winGEO and others)

[DaveW]

Peter, This might be helpful: http://locost7.info/mirror/dax.php

[mep]

left wheel up (single wheel bump): right wheel gets positive chamber

bump: (both wheels up): both wheels gets positive chamber

roll: (outside wheel up/inside down) inside gets positive/ outside negative 0 tires stay parallel

They also quote it works also as an anti rollbar... but i can't figure out how.

My idea is they use cornering forces on the tire for that.
Imagine you drive through a corner then you get some force (pointing towards corner centre) on your outside tire trying to rotate the tire around the lower pivot point (towards positive chamber).
So the bar connection the inside tire pulls the inside tire up.
The inside tire does the same just vice versa means it pushes the outside tire down. The force on inside tire is lower due to weight shift to outside tire.


Roll: Imagine your car body fixed and you have some roll, your outside tire goes up relative to the car body and your inside down.
The forces counter this movement. They make the suspension a bit stiff, something like anti-roll geometry but different. The problem I see is that you can't adjust that very much. Due to all the angles and the force reduction on the leverage it might be even small effect but I can't tell for sure. When you have a high RC you will still get roll. Anyway I think roll is not the thing to worry about here because your tires stay parallel.

[Peter-RC]

these 1:10 scale cars have a quite high CoG... and a very low RC (4cm below the CoG, or more)... and with their 200mm width limit they are quite sensetive on high traction tracks, they often suffer from traction roll.
So trowing your concerns about roll out of the window is, in my opinion, not the way to go.

at least a normal anti rollbar can be swapped for one with a different diameter, with this .... you need to be creative

Is it ever tried in F1/indy/lemans?
(i believe it is banned in F1, suspension mounts must be rigid or something like that.. remember something vagely about that.. not sure)


still, if you are creative enough to implement this complex suspension type on a car, you can also be creative to make a suspension design with minimal camber rise in roll without going positive in bump.

[747heavy]

Hi Peter-RC

I don´t know if the DAX suspension was ever tested/used in F1 or LMP.
One of the more innovative suspension concepts used/tested in F1 was Michelins OCP (Optimized Contact Patch) suspension.

I´m not sure, if this is useful for your application, but you are maybe interested - have a look here. (sorry some parts are in German only)

http://scarbsf1.com/renault_opt/Renault_OPT.htm

http://www.tuev-sued.de/pub/akd/2008/pd ... eiss_d.pdf

http://www.google.com/patents?id=CK0QAA ... &q&f=false

[mep]

I made a simple CAD model today to see how the suspension actually behaves.
Seems like I made one mistake on my last post:

bump: (both wheels up): both wheels gets positive chamber

In fact they get negative chamber when both wheels go up and positive when they go down. Hm I would like them to change towards positive more.
I also noticed that during roll they don't stay 100% parallel but almost.

Also:
left wheel up (single wheel bump): right wheel gets positive chamber and left wheel gets towards negative chamber.

In fact when I write positive or negative chamber it doesn't mean that there actually is positive or negative chamber I just want to point out that it goes into this direction. It depends what chamber you had on neutral position. When you have zero on neutral you will see the above.

these 1:10 scale cars have a quite high CoG... and a very low RC (4cm below the CoG, or more)... and with their 200mm width limit they are quite sensetive on high traction tracks, they often suffer from traction roll.
So trowing your concerns about roll out of the window is, in my opinion, not the way to go.

Yea 4cm seems to be a lot for such a small car. What do you think actually is the problem with the cars rolling? Maybe the problem is just that your tires get into a bad chamber angle when your car body rolls and therefore they loose contact patch. This problem should be fixed with this design because tires almost stay parallel. On the other hand I think it helps when your inside tire gets slightly positive during roll. Why not just rise your RC on your normal suspension to get some anti-geometry.

(hmm 747 understands german, I am kinda surprised by this)

[747heavy]

(hmm 747 understands german, I am kinda surprised by this)

How come ??

[mep]

I just didn't expected it.

[747heavy]

Fair enough - no problems

Ich hoffe Du hast ein schönes und erholsames Wochenende

mit freundlichen Grüssen
747heavy

[Peter-RC]

I´m not sure, if this is useful for your application, but you are maybe interested - have a look here. (sorry some parts are in German only)

http://scarbsf1.com/renault_opt/Renault_OPT.htm

god, i totally forgot about michelin's OCP.
somewhere i have read it isn't used because it became to heavy, but i can't remember where i read it... maybe in racecar engineering... or maybe Wright's book F1 Technology.

It is something i will look into for my 1:8 scale racecar.

[747heavy]

AFAIK finally it was banned by the FIA, so that is the reason, that it is not used anymore.
Another interesting comment about it comes from Pascal Vasselon (ex Michelin)

courtesy Race Car Engineering:

>>>>>>>

Vasselon continues by citing a couple of examples from his days with Michelin. ‘In 2002 there was the omega tyre concept. It was a breakthrough, but the tyre was totally different and didn’t work because it had such an aero influence it was destroying the balance and the flow structure around the car. Even if the Michelin partners developed the car to get around that, they never recovered from this massive change of concept. So whilst the tyre in isolation was probably worth a second a lap, the car was in fact slower. A similar thing happened with the OCP [optimum contact patch] suspension concept. It is exactly what the tyre needs and, in itself, was worth roughly a second a lap, but when it was tested on a car the base line was down by two seconds, simply because you had to totally re-think the rear cooling and the interferences with the end plates from the moving tyres destroyed the flow.’

<<<<<<<

[wrcsti]

Let me guess, it was movable aero?

[Peter-RC]

courtesy Race Car Engineering:

ah, that's where i read it!

since touring cars/lmp have slighty less dominant aero around the wheels it could work there.

And with these little R/C cars they have almost zero aero development [so they can't upset it any more then it already is ]
I might work it out and give it a go.