A Mono Shock rotary damper system...

[P-2 Mark]

Brian,

Thanks for the response. I really enjoy these discussions and information learned from the posts
you, Mike and others have provided. I would think that any surface irregularities that you might
encounter in the middle of a corner when you're near full load jacking / resistance could artificially
cause the resistance to increase for a short period of time, and cause loss of traction and a spin?
I can't imagine the amount of time and effort that Mike has put into the rear supsension to make it
work etc.....

Thanks!

Mark

[hardingfv32-1]

Of coarse in the center of the turn at a max cornering force levels any degradation of traction will mean the rear suspension UN-JACKS and camber increase to UNFAVORABLE levels. The jacking force is directly proportional to the traction level of the rear tires. No traction, no jacking... no favorable camber levels.

Brian

[jpetillo]

Brian, well said and right on the money. Thanks for starting the new thread -I think!
John

[remmers]

that rear suspension on the redbull car is actually not a 3-spring system so much as a 3-dampener system. something i've been interested in the concept of on a formula vee for a few years now, as the problem with roll resistance on a formula vee is weight jacking, and the Z-bar was what appeared to be a band-aid for the problem, and geometry redesign in the form of zero roll was the fix, however there may be some use for a dampened roll resistance on a formula vee, as i've noticed my protoform has a tenancy to have a good balance if not a tick loose in high speed corners, but pushes pretty badly in very low speed situations. this kinda goes against chris' "do no harm" a little bit, but my thoughts are since dampeners are speed sensitive, not position sensitive like ARB's are, you wind up having higher roll resistance the harder you throw the car into the turn. so your corner entry characteristics would be dependent on how forceful your turn-in is. steady state mid-corner would behave as a normal zero-roll system and corner entry and exit would behave as a z-bar. best of both worlds? where can i locate a rotary shock that is tunable to try this?

veefan's picture of the front suspension is in fact a three-spring system with very stiff roll characteristics. RPI's FSAE car of yore had one of these, the idea was all the more roll resistance you were allowed was for the minute amount of travel along that sprung bar. this picture seems as though there's all of maybe 1/8" of roll travel allowable, if that. they can get away with using a linear system to produce predictable angular resistance because the amount of roll the car experiences is so small that it's effectively the sin of a small angle.

[hardingfv32-1]

1) The RB rear suspension is three springs: 2 vertical torsion bars and one heave coil over spring. A very normal F1 suspension for the last 10 or so years.

2) What does jacking have to do with roll resistance? No band aid about a z-bar system, it is just not a zero roll resistance. Provided the correct tires it would be fine.

3) Sachs makes a rotary shock for Ferrari F1. It's benefits are strictly for packaging issues. You can design anything you need using standard shocks, if you have the space.

4) The rear suspension of a FV is generally steady state through 50% of a turn assuming a smooth track. With the shock thus not moving in the low speed range, it can have NO effect on roll during the center 50% of the turn.

5) It is a very common characteristic of ANY road race car to be perfect in sweepers and tight/understeer in slow turns. This is a steering issue and a function of the different slip angle that the tires find themselves in with both types of turns. It is not possible to make both type of turn situations perfect with a non-aero or non active suspension car.

Brian

[remmers]

i would imagine though, if it's speed-sensitive suspension, then it is in effect active. just outside-force controlled rather than computer or manual control... the idea would be to make the rear slip a bit more to in effect get the car more neutral, and i'm sure it's mathematically possible to change the suspension geometry of a car to optimize it for both... it may not be pretty or ultimately competitive, but i do believe it would be possible. i would imagine it would just require more extreme angles on the front tie-rods that would cause toe-out under larger inputs from the steering wheel. the trick would be getting those angles and the arcs created by the tie-rods to be just right.

[FV80]

...i would imagine it would just require more extreme angles on the front tie-rods that would cause toe-out under larger inputs from the steering wheel....

It's called Akerman - and VW designed it right into that wonderful link pin front end . It IS adjustable - just not dynamically on the track.
Steve, FV80

[brian]

Ackerman is depenent on wheel base and the offset stock steering arms are based on a longer wb than vees have. Ackerman is adjustable from no ackerman (parallel steering) to excess ackerment. Neutral or zero ackerman is when all four wheels have a common center point.

[hardingfv32-1]

Can Ackermann be described as positive or negative with zero being the typical traditional drawn configuration?

It is not obvious how the Ackermann should be setup on a race car. Assuming a starting point of a standard Ackermann configuration, do you want the outside wheel turned more than the inside wheel because it requires more slip angle to handle the extra load it is seeing? Or do we want the inside wheel turned in excessively to kind of drag the inside wheel causing a turning torque?

Brian

[CitationFV21]

[quote="hardingfv32-1"]Can Ackermann be described as positive or negative with zero being the typical traditional drawn configuration?

It is not obvious how the Ackermann should be setup on a race car. Assuming a starting point of a standard Ackermann configuration, do you want the outside wheel turned more than the inside wheel because it requires more slip angle to handle the extra load it is seeing? Or do we want the inside wheel turned in excessively to kind of drag the inside wheel causing a turning torque?

Brian[/quote]

For a good discussion on Ackerman (one "n") see "Engineer to Win" pgs 214 to 218.

Using standard spindles you normally have Ackerman steering. If you are using modified spindles, you are close to parallel steering and depending how your steering is set up you might have reverse Ackerman.

One theory is that the inside tire, being lighter in loading, needs more steering angle in order to generate the maximum cornering force. That is why some people find toe out make the car handle better in slower turns and not too bad in high speed. But that comes with the disadvantage of drag on the straights.

NOTE -no toe out in the rear unless you are running autocross or wish to see where you have been more that where you are going....

Since most of us don't have the time or the ability to modify our steering, we pretty much take what the car was designed with. If you have degree plates, you can check the steering angles from L to R and see what you have. Of course it should be the comparable turning left and turning right or your steering is way off!

With cars with steering rockers, like the Citation and Predator, you can probably affect the Ackerman with the angle of the rockers. For other cars you have to play at the steering arms. With racks (on FST) you can move them front and back to adjust. I will have to draw out and see if the front box (like on the VDF) is different than a beam mounted box.

And again, it makes more difference wider the tires.

ChrisZ

[DanRemmers]

NOTE -no toe out in the rear unless you are running autocross or wish to see where you have been more that where you are going....

I can vouch for that.

I adjust the amount of throttle oversteer on my solo vee by changing the rear toe. Some toe in almost prevents oversteer, toe out allows me to rotate the car quickly but not easily, so I settle for zero.

[brian]

The increasing turning radius of the inside tire is to provide a common radius for all 4 tires and reduce scrub and tire wear for street cars. We use ackerman on race cars to provide "lead" on turn in. On Sprint cars the inside tire has a ton of ackerman and leads the car into rotation for opposite lock style of driving. On my vee, the ackerman will provide a more responsive turn in on tight turns. Ackerman is toe out so it is not preferred on sweeping turns or ovals since the toe setting will tend to scrub off speed. At RA, if your toe is off, you will loose time in the carousel. How much ackerman is a function of the tracks you run, thats why mine is adjustable.

After I'm finished with my Thanksgiving bird I will post a procedure for establishing ackerman that can be done at home.

[jpetillo]

Brian, excellent - I can't wait!

John

[brian]

Plotting ackermann requires either stretching lines out from the four tires to almost infinity and almost impossible to do in a garage. But the do it yourself method is a bit easier, a bit subjective and doesn't really produce an objective number. We can measure the toe difference at a predescribed steering angle but that takes a bit longer.

Tie a string around the center of the king pin on the spindle. Stretch the string out over the center line of the outside connecting point of the tie rod and extend the string until it dissects the center line of the chassis. If the string parallels the car then you have parallel steering or no ackermann. How far forward of the rear end the intersection takes place demonstrates how much ackermann there is. Most modern vees will have intersection somewhere in the engine compartment. For tighter courses I have mine set at about where the front pulley is, likewise, for a longer course, where there may be a sweeper I move the intersection back closer to the bell housing.

You can either use multiple holes or bolt on plates with varying locations. You can speed up the steering without changing the ackermann by moving up the imaginary line your string created towards the kingpin.

[problemchild]

How are you allowing for steering box location, pitman arm design, and steering rod angle to the spindle? Without factoring these items in, are your pulley and bell-housing observations merely reference points on a single car and irrelevant to any other car without identical steering configuration?

[hardingfv32-1]

I would say the tradition plotting method depends on perfectly placed Steering Rack. The length and arc that our steering arm travels through is a complication.

I think you are better severed to just measure the tow changes at deferent steering angles. You need to setup a reference plane on the outside of each front wheel.

Brian

[brian]

Brian, I think you make a valid point about steering box location and pitman arms. Like I said, the approach is not scientific but a good approximation. When you think of all the cars with boxes mounted on the h beam with typical pitman arms, this approach will be fairly accurate in showing how much ackermann you have. I'm not sure I really want to ever be severed, but if I want more detail, I put a degree wheel on steering wheel. It's the same one I use for timing cams. Then I place two jack stands parallel to the wheel with a string between them. Then I measure the toe out at a couple of steering angles. Once again, you get a number but knowing what it means can be a challenge. Back in the day when we were modifying limo steering arms to correct tire wear, we shot for a common radius on all four tires at fairly high turning angles. You can imagine what happens when you stretch out the wheelbase and not change the steering.