The relative benefits of a pull rod suspension

[ringo]

Right about the motion ratio. That's a problem
I was thinking about a rotary damper for the rocker arm, maybe there might be some developement for those in the future.
Those damp for torque and angular velocity. I haven't seen one on a car suspension.
@747 i didn't get the time, but i haven't forgotten it.

edit: about rotary dampers, searched around and found out that BMW and ferrari tried using them before.

some more on F1t on rotary dampers:
viewtopic.php?f=6&t=6413


suzuki adjustable damper:

[DaveW]

I was thinking about a rotary damper for the rocker arm, maybe there might be some developement for those in the future.

Rotary dampers of the type you illustrated "package well", but performance is rather similar to that expected from a linear damper working with a motion ratio of around 3.5.

[747heavy]

while not F1, it may illustrates the motion ratio aspect of the rocker arm option well.
And I agree with DaveW, I don´t really think, you would want to go back there.

[ringo]

I was considering getting rid of the other half of the rocker; the half pinning the damper.
The rotary damper will be placed concentrically with the torsion bar.
in a sense it can't be called a rocker arm, more like a torque arm.
The arm will be the lower arm, not the upper arm.

I was hoping the rotary damper concentric with the torsion bar could negate the motion issue, since it will be working purely of angular velocity, however the angular displacements will be too small.

A planetary gear set would have to be concentric to the rocker to increase the angular displacement of the damper. I guess that would be too heavy but it solves the problem.
Too much of a compromise, but it's kind of compact.

[DaveW]

A planetary gear set would have to be concentric to the rocker to increase the angular displacement of the damper. I guess that would be too heavy but it solves the problem.
Too much of a compromise, but it's kind of compact.

The one vehicle I have seen fitted with rotary (corner) dampers had an installation stiffness for those elements rather lower than tyre stiffness. The saving grace was that a linear heave/pitch damper was also fitted which, in practice, did most of the work. I'm sure it would be possible to design effective rotary dampers by gearing &/or increasing paddle area, but I suspect that any packaging advantage would be lost.

What I find odd is that a respected damper manufacturer should have produced the dampers, & a respected team should have tested & fitted them without, apparently, anybody concluding that the concept was a nonsense.

[marcush.]

Dave.. =D>

with hindsight I always think I was very lucky with what I did in Racing but still I rarely found people asking more questions and being prepared to question themselves....it seems most of them involved may carry a degree and have experience galore but still have no idea what´s going on. It´s of course very refreshing to now and again have the pleasure to get into contact with people of the right attitude.

[Sayshina]

Dave W.: We can assume the damper mfg. was being compensated, and we can probably assume the team was searching for some other benefit, in this age that almost always means aero. I'm far too lazy to look it up, but weren't they using rotary dampers at right about the same time as that duct through the nose?

Ringo: If you look up old photos and vids of pullrod cars, you'll see the rods bending a great deal in rebound. The loads they're being subjected to are clearly not insignificant. Since you seem to think they are, I'm a bit confused by your next paragraph.

What goes on during a suspension cycle is not completely dissimilar to what goes on during a handgun cycle. In both cases the force that starts the whole thing off is very high impulse and mostly over before we see much movement. That's what I meant by violent. The rebound force is from the spring, which is to say it's energy we siphoned off from the compression event, and we have control over it's impulse.

[ringo]

I did not say they were insignificant.
I said i don't know and maybe dave could give some input on rebound dynamics.
I am clueless about suspension setup, i've repeated that many times. I don't know the typical damper characteristics or weight of an F1 corner.
So i cannot say if the forces are insignificant or not.

What is evident is that one rod is substantially smaller, so it can be assumed that on rebound the damper is taking most of the spring force.

AC cos phi yz = rod force * cos theta xz * cos theta yz
AC = 9825 * cos 19 * cos 50
= 5971.3 / cos 45
wishbone AC = 8444.7 N tension

wishbone AB = rodforce * cos theta xz * sin theta yz
AB = 9825 * cos 19 * sin 50
AB = 7116.3 N tension

the same values for the pull rod only in compression.

So if we understand that the two members for the pull rod is compression they should be thicker.

in short using same formulas:

tension member diameter AC= 3.6 mm , AB = 3.3mm

DE has a lenght of 500, DG length of 594mm

using same buckling equation, I = 4FL^2/pi^2xE
:

I= 4 x 8444.7 x 594^2 / 9.8596 x 1.1 x 10^5
= 10989.17

I= pi x d^4/64 ,
d = 21.75

pull rod compression members DE = 21.75mm, DG = 19.12 mm

so pull rod has bigger members at the part of the upright where it connects.

pull rod: 36.69, DE 993g DG 646g , total: 1675.9g

push rod: 1332.6g, AC 27.2g AB 19.2g total: 1379 g

so the push rod is lighter for these 3 members in isolation.

Whoever think i'm cooking numbers can rest easy, see the push rod is lighter.

but only if all other things are being ignored.

Now I guess the reason why we don't really see a pull rod with substantially thicker upper wishbones is because of the other forces taken up by the wishbones.
Both solutions have to provide for forces outside of the spring and damper force.
I'm too lazy to do them, and i lack knowledge on the size of these forces.

Forces such as braking, lateral forces, moment on the upright by the wheel force relating to the offset of the force and ant hub face, then you have the toe link etc. you name it, i don't know it.

[ringo]

A planetary gear set would have to be concentric to the rocker to increase the angular displacement of the damper. I guess that would be too heavy but it solves the problem.
Too much of a compromise, but it's kind of compact.

The one vehicle I have seen fitted with rotary (corner) dampers had an installation stiffness for those elements rather lower than tyre stiffness. The saving grace was that a linear heave/pitch damper was also fitted which, in practice, did most of the work. I'm sure it would be possible to design effective rotary dampers by gearing &/or increasing paddle area, but I suspect that any packaging advantage would be lost.

What I find odd is that a respected damper manufacturer should have produced the dampers, & a respected team should have tested & fitted them without, apparently, anybody concluding that the concept was a nonsense.

Any reasons behind the varying instalation stiffness between designs?
Any rule of thumb or are these settings experimental?

[DaveW]

....we can probably assume the team was searching for some other benefit, in this age that almost always means aero....

You are probably correct. However, it is just such decisions that lend credibility to the notion that "mechanical set-up has no effect on performance". Also to the observation that some teams are less able to "manage" tyre life/performance.

[Belatti]

I continue this small off topic here, but I recall that when I had hairless balls I attended to a GP (the last good Williams years) and the said went on more or less like this: "The Williams cars has so much mechanical grip that they can run with arround 15% less downforce and hence much less drag than the other cars."

Could you adopt this design philosophy nowadays? I dont know...

[PlatinumZealot]

I think if the teams had different tyres. With the same tyres and less downforce It's hard to see it happening.

[Sayshina]

I continue this small off topic here, but I recall that when I had hairless balls I attended to a GP (the last good Williams years) and the said went on more or less like this: "The Williams cars has so much mechanical grip that they can run with arround 15% less downforce and hence much less drag than the other cars."

Could you adopt this design philosophy nowadays? I dont know...

I don't remember it being aplicable then. And to be honest I find it very hard to believe. The balance between how much of a F1 cars grip comes from aero vs. mechanical has steadily gone in favor of aero, but that started long before the time you're talking about.

I remember in the late '80's there were lots of dark rumblings about "Sure the McClaren corners well, you'd corner well too if you had that Honda and could carry around a barn door of a rear wing.".

In fact, now that I'm thinking about the good old days, it was fairly common practice for people to estimate how much power various teams had by comparing rear wings. It was considered reasonably accurate, given the assumption that you'd always want as much downforce as you could get, or as much as you're available power would allow you to have.

All of the teams that carried low downforce would be very fast on the straights and slow in the corners.

[raymondu999]

Would an increase in mechanical grip also help you in high speed corners though?

[myurr]

Would an increase in mechanical grip also help you in high speed corners though?

It's more a case of relativity. More mechanical grip will help you in any corner, fast or slow, but may carry an aero or weight penalty for certain layouts and setups. Aero helps relatively more in fast corners than slow and carries the disadvantage of drag. The teams will be chasing the perfect balance between the mechanical and aero side of things.