How this antiroll bar system works?

[romkasponka]

http://www.race-cars.com/carsales/lola/1100458739/1100458739le.htm

[romkasponka]

http://www.race-cars.com/carsales/lola/1100458739/1100458739le.htm

[K. Werkley]

The vertical bar is twisted in roll, adjustable by the small blades at the bottom of the bar. Free to move in bump.

[romkasponka]

Is this system usable in rear and front suspension to keep wheels parallel to the ground to improve traction when one wheel bump accur?

[Marshall Grice]

yes you can use it in front and rear, but it won't improve one wheel bump traction. quite the opposite really.

[romkasponka]

It's not antiroll bar only as i see, but what it improves when?

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by romkasponka:
It's not antiroll bar only as i see, but what it improves when? </div></BLOCKQUOTE>

It _is_ an antiroll bar, in as much as it only deflects when the left wheel and right wheel heave travels are different.

Generally, antiroll bars are fitted to reduce chassis roll and / or to re-distribute the lateral load transfer characteristics from one axle to the other. Whether that is an improvement or not depends on many other factors.

Ian

[fsae_alum]

It IS an antiroll bar. During roll, the vertical link in front of the center wing mount is twisted (very similar to a conventional arb on a passenger vehicle). Bump can be accomodated in the system by placing a spring/damper combo or a bumpstop type material on the center upright bar to displace during bump. I have seen this design taken one step further by incorporating a device into the top of the T bar (where the rod-ends attach from the links to the bellcranks) that is driver adjustable and allows the length of the top of the T to be increased or decreased to change the moment arm of the T thus changing the twist of the upright portion of the T. In actuality, this adjustability could be done using something very similar to a brake balance bar.

[K. Werkley]

The adjustment blades are on the bottom of that particular one.

[romkasponka]

You are right. I thought what it's working like Z bar http://fsae.com/groupee_common/emoticons/icon_smile.gif

Is it posible to make it without blades (why they are not used instead top lever)? I think what ajustable top levers lenght could work. Is it right calculation what if levers will be rigid the bar torsional stifnes will be like bar with two rigid levers?

[fsae_alum]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by K. Werkley:
The adjustment blades are on the bottom of that particular one. </div></BLOCKQUOTE>

Yep, got that....just offering up another way to get to the same destination without using blades. Have heard that blades can sometimes resonate and cause problems and thus was proposing an alternative.

Cheers!

[K. Werkley]

Never heard that, definitely something to consider. I like the bias bar adjustment idea.

[fsae_alum]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by K. Werkley:
Never heard that, definitely something to consider. I like the bias bar adjustment idea. </div></BLOCKQUOTE>

In one of Carroll Smiths books he talks about how with blades the rate is not at all linear as the blades are turned and is rather troublesome to calculate too. Just something to keep in mind for the future.

[Frank]

EDITED

The CS book does not have a good explaination

all "springs" are linear in response if the deflection is small, regardless of shape

what you DO get is: as the blade is rotated (stiff-soft), the angle is not proportional to the roll resistance. BUT, an EFFECTIVE blade does NOT have a strongly sinusoidal resistance VS angle

http://www.uq.edu.au/fsae/blades.jpg

Frank

[CMURacing - Prometheus]

shouldn't the increase from rotating the blades be something like sinusoidal in nature? it seems like a quick mental proof would put a trig term in your MOI, which would then correspond to the increase in bending stiffness of the blade as you rotate it...

[murpia]

I searched and decided to dig up this thread rather than start a new one... The picture is useful.

Does anyone have a reference for the mathematical treatment of a T-bar anti-roll bar as opposed to the more common U-bar? RCVD for example does not.

I have done my own analysis and it would seem the installed stiffness and therefore roll rate of a T-bar is exactly half that of a U-bar of the same diameter and moment arm length. This is due to the torque reaction between the base of the T-bar and the chassis.

Of course as a good engineer I'd like to check my analysis against a published source...

Regards, Ian

[Brian Evans]

Intuitively the rate would see the length of the bar twice, so your idea of half the rate of a typical U bar seems correct, assuming near infinite stiffness of the mount at the base. If it wasn't stiff in relation to the bar, you'd have to add any stiffness designed in at that end to the equation. Someone said above that there may be blade type adjustable mounts at the bottom that we couldn't see.

Often, the "bar" is so stiff it becomes part of the mount, and the actual rate comes just from the blades or the actuation arms.

[HenningO]

A bit OT:
Note the pullrods going from the rocker arm to the undertray. Neat! Single shear mounting though, not so neat! (Where is Pat Clarke when you need him!)

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Brian Evans:
Intuitively the rate would see the length of the bar twice, so your idea of half the rate of a typical U bar seems correct, assuming near infinite stiffness of the mount at the base. If it wasn't stiff in relation to the bar, you'd have to add any stiffness designed in at that end to the equation. Someone said above that there may be blade type adjustable mounts at the bottom that we couldn't see.

Often, the "bar" is so stiff it becomes part of the mount, and the actual rate comes just from the blades or the actuation arms. </div></BLOCKQUOTE>
In our case, there are no blades, but stiff reaction arms and a bar designed to operate in torsion. The chassis mount is designed to be stiff also.

Regards, Ian

[SuperSport2]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> have done my own analysis and it would seem the installed stiffness and therefore roll rate of a T-bar is exactly half that of a U-bar of the same diameter and moment arm length. This is due to the torque reaction between the base of the T-bar and the chassis. </div></BLOCKQUOTE>

If i use a 225 lb shock spring, my required roll stiffness for the front is 89 lbs/deg. A 7/16" OD tube with a 0.095 wall results in a 88lb/deg U-type ARB stiffness.

Because i want to use a T type arb, does this mean i should spec a tube that provide 164 lb/deg instead of the 88 lb/deg?

Our team has no ARB design experience, i am sorry if this is a novice question. I am looking for some clarification and help.

Brett Lucas
Washington State FSAE

[PatClarke]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Note the pullrods going from the rocker arm to the undertray. Neat! Single shear mounting though, not so neat! (Where is Pat Clarke when you need him!) </div></BLOCKQUOTE> =] =]

Pat is right here, watching! =]

Actually, the undertray support rod goes to the rocker pivot structure rather than the rocker (Otherwise it would be 'illegal' live aero).
As long as the structure is correctly sized, I would not have a problem with that. After all a failure wouldn't result in a catastrophic collapse of the suspension,

I am not really a 'Double Shear Nazi' =] After all, wheels, critical components, are always mounted in single shear.

Good to see you are paying attention though.
Cheers
Pat

PS Edit...spelling =]

[Fyhr]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by PatClarke:
(Otherwise it wopuld be 'illegal' live aero).
</div></BLOCKQUOTE>

Not FSAE illegal though right? http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Brian Evans]

Actually, the blade adjusters for the ARB are right there for all to see, right above the lower wishbone mounts. Hefty...set for full stiff I think.

Brian