What the 'Fric' is it?

[DaveW]

I would assume that for a heave, roll and pitch movement, the body is fixed.

Tim, the body is never fixed, although it is true that inertia sometimes makes it appear to be so. In the case of roll inertia of an open wheeler, the sprung mass contribution is small compared with those of the unsprung masses. The true roll mode (there are two when the vehicle is rolled about the ground plane) usually coincides pretty much with the unsprung modes, and the body roll freedom becomes significant (it would be less so in a tin-top, for example).

What do you mean by wheel pan and CPL?

Wheel pans are the devices that support the vehicle on the input actuators. In our case they house load cells (from which Contact Patch Loads are derived) and vertical accelerometers (these provide the measure of wheel pan displacements).

Is your rig a 4 post or 7 post? (its not clear from the company's website)

It is actually a "six post" rig. There are two clones, one located in Thetford (UK) and the other in Markham, Toronto. In both cases, four hydraulic actuators support the vehicle via its tyres and two pneumatic actuators are (can be) attached to the sprung mass to control down-force, notionally on the centreline of the vehicle at the front & rear axles, respectively. Central to both facities is analysis software that is used to analyse rig test measurements, to supply parameters for mathematical models from rig test measurements, and also to validate models created by other software, incuding ADAMS.

EDIT: the down-force actuators were intended to minimise energy dissipation. Static stiffness is small, but they do have damping. Typically total energy dissipation would be <3 % of input at the heave mode. I don't wish to be critical, but my experience would suggest that similar figures for a 7 post would be around five times that figure.

[Tim.Wright]

I would assume that for a heave, roll and pitch movement, the body is fixed.

Tim, the body is never fixed, although it is true that inertia sometimes makes it appear to be so. In the case of roll inertia of an open wheeler, the sprung mass contribution is small compared with those of the unsprung masses. The true roll mode (there are two when the vehicle is rolled about the ground plane) usually coincides pretty much with the unsprung modes, and the body roll freedom becomes significant (it would be less so in a tin-top, for example).

Interesting info, but I was actually meaning on the rig, when you find the heave pitch and roll stiffness. Do you fix the body or do you leave it free? I'm guessing if you only have 2 body actuaors it must be left free. I'm asking because I'm used to KnC measurements where the body is fixed and the wheels are moved. You see different contact patch loads in that case.

[DaveW]

Do you fix the body or do you leave it free?

We try hard to leave it free (see the edit above). You might be surprised just how revealing that can be. I don't wish to belittle K&C tests (where would we be without them), but the limitations (both of rig tests & mathematical modelling) should be understood.

[Tim.Wright]

Ok, I'm understanding the test better now. The fact that a KnC test fixes the chassis means that the body mass and inertia are cut out of the equation. But thats fine if you only want to know your camber curves, or your braking toe compliance (which I imagine you can't measure on a post rig)

Different tools for different jobs...

I've revised my warp calculations now so they are with a free body. Im getting warp to roll ratios of about 4 for a GT car (which I believe has been on your rig). Sound about right?

[marcush.]

i was actually trying to make it a bit basic that interlinking suspension axles are not all positives but you seem to prey on anything. by the way, when an inner front lifts you dont lose half of frontal grip as proven by the delta shaped race car as center of pressure will determine its physics

That´s not what I wrote,mate.
When you lift one wheel you lose half of your front load capacity simply because one tyre is out of the equation.This could be 1N ,10N ,100 or 1000N ...of actual force -therefore I was referring to capacity (or potential).but i stop preying now..

[DaveW]

... if you only want to know your camber curves, or your braking toe compliance (which I imagine you can't measure on a post rig)

You are right. I might be able to do something, given the displacement measurements you have (a Lotus rig, perhaps?), but why re-invent the wheel.

I've revised my warp calculations now so they are with a free body. Im getting warp to roll ratios of about 4 for a GT car (which I believe has been on your rig). Sound about right?

warp to roll, are you sure?

[Tim.Wright]

warp to roll, are you sure?

Yep definitely sure its warp to roll. Whether is calculated correctly or not is another thing!

[GSpeedR]

Tim, assuming that we are ignoring unsprung DoFs (or just combining them with the suspension), a fixed chassis with actuated wheel-pans has only kinematically controlled degrees of freedom. The fixed chassis reacts loads/moments and couples modal rates together (ie roll & warp, heave & pitch, heave & roll), for anything except a perfectly symmetric vehicle. So asymmetric geometry or springing front/rear or left/right will give you incorrect modal rates with such a setup.

I agree with Dave, that a warp/roll stiffness ratio should be less than 1 for any 'traditional' suspension.

[Tim.Wright]

Tim, assuming that we are ignoring unsprung DoFs (or just combining them with the suspension), a fixed chassis with actuated wheel-pans has only kinematically controlled degrees of freedom. The fixed chassis reacts loads/moments and couples modal rates together (ie roll & warp, heave & pitch, heave & roll), for anything except a perfectly symmetric vehicle. So asymmetric geometry or springing front/rear or left/right will give you incorrect modal rates with such a setup.

I agree with Dave, that a warp/roll stiffness ratio should be less than 1 for any 'traditional' suspension.

Ah sht, no I meant roll/warp sorry. So the roll stiffness I see is about 4 times the warp stiffness.

I see what you mean about the coupling of the modes. I wanted to explain this but couldn't put it into wards as well as you did.

[Powerslide]

[quote="marcush."][quote="Powerslide"]i was actually trying to make it a bit basic that interlinking suspension axles are not all positives but you seem to prey on anything. by the way, when an inner front lifts you dont lose half of frontal grip as proven by the delta shaped race car as center of pressure will determine its physics[/quote]

That´s not what I wrote,mate.
When you lift one wheel you lose half of your front load capacity simply because one tyre is out of the equation.This could be 1N ,10N ,100 or 1000N ...of actual force -therefore I was referring to capacity (or potential).but i stop preying now..[/quote]

first of all, the post on this forum is now about chassis rigidity and how it behaves to interconnect the two axles hence what the fric is it? hehe. so i think we are not talking about fric arent we? maybe originally i read the topic wrongly and to think, not grip, but as you said, load, is halved at the front when the rear brings up the opposite end is complete rubbish actually.

[marcush.]

load bearing capacity and applied load is not the same .that was the point .Having one tyre less is surely reducing your load bearing capacity there is no way around it.
If that is significant or not is another matter . But on second thought a fully unloaded tyre will always play havoc with your dynamics be it reducing braking capacity or unsteadyiness in your grip levels when contact to the ground is regained.

[ringo]

How this system would be activated between qualifying and the race?
It looks pretty unreliable though, which may explain Mercedes problems

It's not unreliable, The spool would be similarly to that use on hydraulic equipment controls. I have a simplified it in the diagram but it is by no means finicky. It is activated like a heave spring, it's only after a certain vertical loading does the spool let out the fluid.
Keep in mind that the pushrod length only has to be fixed for qualifying. This means we don't want fluid motion in that case.
In qualifying the fuel loads are light, so the car wont be pressed into the ground too much and give the same rocker discplacement. So you wont have much if any fluid bleed.
When you put in race fuel now, then you'll have your pushrod lenght reduction activation. As the fuel goes down so does the rocker displacement, hence the frequency of bleed.

[ringo]

....In this case my control valve is a spool that is connect like a heave spring. It only works under high aero loading, like the end of a back straight....So this will happen at the end of every straight, or at whatever speed the team desires. Fluid will prediodically bleed into this tank at measured amounts, reducing the ride height as the race progresses.
...

How does your system distinguish aero loads from braking loads and from running-over-curbs loads?

I thought somebody tied something like this years ago but with a mechanical ratchet system.

You take into accound braking loads. You have to brake at the end of a long straight. The driver doesn't have a choice.
The beauty of this solution as well is that in the event of a safety car, the "clock is stopped" and you don't have an uncontrolled reduction in ride height.

This system is not ratecheted. It's more flexible than that. It's also less likely to fail. Guess i woundt have thought of this without the Fric discussion. But it's quite viable, i'm not really seeing an issue so far.

[ringo]

Basically you are putting this on a front heave element.


We will only have one outlet port per corner. For both corners we will simply have two of these spools.
Here you are:

Just without the levers, and obvious less chunky, as we aren't dealing with high pressure.
With Proper sealing of the pushrods, it should be very reliable.
Push rod cylinders may be of a similar nauture to the cylinders in this video.
[youtube]http://www.youtube.com/watch?v=7AME4v3qZkc[/youtube]
In fact i think i can simplify the design further and make it more compact. remove the corner springs from the bellcrank, place the push-rod cylinders within the body after the bellcrank, the corner springs would be within the body acting on the cylinder.
So we would have an aerodynamically clean pushrod.
The bleeding system would obviously be quite small, as we can see how small the hydraulic hoses are in the williams video.

If this is part of FRIC i guess i'd be satisfied with figuring out a ride height solution to some degree of certainty.
If it's not in use currently i guess a team can experiment with the principle for 2014.

[ringo]

A nice background to the Williams active suspension:
http://scarbsf1.com/williams_active/Wil ... YSTEMS.htm
Nice piece of work by Scarbs here , he did well to find this; guess this is before the fame and glamour

I see similarities. I may open another thread for this ride height control solution. But i feel this article can set the basis for some of the FRIC.