Zero Roll Stiffness

[Will98Cobra]

Has anyone ever messed with this type of suspesion setup on the Formula's.

William Austin
ODU Motorsports
Chassis/Suspension/Controls

[ben]

How would zero roll stiffness resist a lateral acceleration?

Do you mean zero warp stiffness? If so, I've thought about it and am sketching some conceptual ideas at the moment. A lot of potential in my opinion.

Ben

[Denny Trimble]

I read something about a rally car with front and rear ARB's connected with a hydraulic system, so they resist total vehicle roll but don't resist one-wheel bump. Is this what you mean by zero warp stiffness? Of course the springs still resist one-wheel bump / warp, but taking the ARB's out of the equation helps for very bumpy surfaces.

I don't think FSAE cars would benefit from this, but who knows. I hope someone tries it!

University of Washington Formula SAE ('98, '99, '03)

[Will98Cobra]

Well let me clarify myself, the basic idea is this, you have one shock and spring holding up one end of the car. So just imagine the shock and spring in between the left and right belcrank of the rear. This would creat zero roll stiffness, the body is free to roll. ALl body roll is controlled by a swapbar. Thus allowing the spring and shock to do to only what they are designed to do. So in the end you can change spring rates, shock settings and not effect the roll stiffness of the car. Does this help? I know this used to be used in the 70's on old formula V's and some dirt track cars. There are only a few draw backs that i can think of but the seem very minimal to our particular car.

William Austin
ODU Motorsports
Chassis/Suspension/Controls

[Denny Trimble]

I heard the judges criticized our '95 car for the design you mention. Somthing about undamped oscillation in roll...

better put a damper on your swaybar if that's your plan http://fsae.com/groupee_common/emoticons/icon_smile.gif

RIT had an interesting monoshock up front last year or the year before, with a bellcrank that slid laterally on a shaft. They eventually put rubber bumpers on the shaft to create some roll stiffness (with some damping).

If you're shooting for sub-400lbs (was that Illinois in '99?), I'd got his route. But otherwise, it's hard to deal with the damping in roll.

University of Washington Formula SAE ('98, '99, '03)

[woollymoof]

Will98Cobra, what you are talking about is "similar" to a Z-bar but without damping in roll as Denny says.

[Marc Jaxa-Rozen]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>RIT had an interesting monoshock up front last year or the year before, with a bellcrank that slid laterally on a shaft. They eventually put rubber bumpers on the shaft to create some roll stiffness (with some damping).<HR></BLOCKQUOTE>

Hmm, that's about exactly what we're planning for our car - I had no idea RIT had attempted it already.

I was thinking of using springs mounted laterally on the monoshock rocker shaft to create 100% of the front roll stiffness...which would be functionally similar to the Belleville washers found on F. Renault monoshocks, but more appropriate for the kind of roll stiffnesses we need. But the thought just occurred to me that we need some kind of damping in there http://fsae.com/groupee_common/emoticons/icon_eek.gif

I think that a properly executed monoshock could be very viable for FSAE. Of course the REAL reason we're doing it is that one shock is cheaper to buy than two http://fsae.com/groupee_common/emoticons/icon_wink.gif

Marc Jaxa-Rozen
École Nationale d'Aérotechnique

[Will98Cobra]

Well i forgot about the roll dampning, glad i asked. See im trying to come up with something to save weight, cost and a more compact design. When you look at these cars they are so small and it seems to me that at times they are over engineered. I guess i could go with the spring mounted in between the rocker arms and have an individual shock for each corner. I dont know i give up for the night.

Later

William Austin
ODU Motorsports
Chassis/Suspension/Controls

[gug]

well, if your looking for something different, check out this site: Drysdale open wheeler (http://home.mira.net/~iwd/openwheeler/index.html)
a very unique engineer with some serious credentials built this car:
http://home.mira.net/~iwd/openwheeler/dh-7.jpg

http://home.mira.net/~iwd/openwheeler/dh-2.jpg

just off the top of my head, wouldnt this thing have some pretty serious body roll, encouraged by this suspension setup? anyway, im not a suspension guru, so ill leave it up to you lot to debate.

the bloke who made this has also designed a motorbike with a 750cc v8 that goes to 17,000 rmp (19,000 in race engines!) and puts out 120kw! if only we were allowed to use 750cc http://fsae.com/groupee_common/emoticons/icon_frown.gif and didnt have the restrictor, god knows how much air that thing would suck

"I come from a land down under,
Where beer does flow and men chunder"

[A Reinke]

bet someone on here could figure out how much air a 600 engine at 19,000 rpm would take in unrestricted. http://fsae.com/groupee_common/emoticons/icon_eek.gif

[Marc Jaxa-Rozen]

Probably around 220 CFM...talk about choked flow in a 20mm restrictor http://fsae.com/groupee_common/emoticons/icon_eek.gif

Anyway, that's a pretty interesting setup...

[Eric Wort]

Looks like the front swaybay on that setup takes care of roll control, and the damper there should be able to handle damping roll and bump. It seems like that car would do strange things when it hit a bump. I'm just the engines guy though http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Our '99 2nd year car 'Cheetah' was originally redesigned with a front monoshock, but I've heard that nobody could get it to handle correctly, so a normal twin shock system was installed right before competition. I think 398lbs was achieved with a bit of stretching, including the turbo and four coilovers. It was a great car, until it fell apart about a year after the 99 competition http://fsae.com/groupee_common/emoticons/icon_frown.gif

Eric Wort
UIUC Formula SAE (http://dilbert.cen.uiuc.edu/soc/sae/formula/)

[woollymoof]

The first car our uni built was a ridged monoshock front and rear, that isif one wheel went up, the other went up just as far. Handled like a dog, the judges liked it though. It wouldn't be that bad in bump, but cornering power would rise significantly.

[Moeye]

Along with random things breaking, when you're driving Cheetah, don't hit anything head on! You won't have any legs left. It has be the most dangerous car out of the bunch.

the cranky dood
UIUC <a href="http://dilbert.cen.uiuc.edu/soc/sae/formula/">Racing Illini</a>

[David Money]

Our university tried that in a 96 car with results that were not so good. They did exactly what you guys are talking about by running a single shock in between the 2 bellcranks. They had absolutely NO roll resistance. As a result, they tried to outfit the car with an ARB with little success. As soon as I drove that car in that condition, we decided to change it to a dual shock setup and man what a difference!!! Just my opinion.

PS: a "monoshock" setup can be done effectively, you just have to have some ingeneious roll control built into the system (i.e. bellville washers...

[Will98Cobra]

Well the whole point of that particular suspension setup is to have No roll stiffness (zero-roll stiffness). All roll is to be controlled by swaybars. My understaning is that it can work if you can keep the spring rate down, whatever spring the car need for two corners, it has to be doubled which make for a rough ride and doesnt allow the suspension to work. Well it was just a thought, guess that idea is out the window, back to the drawing board

Later on

William Austin
ODU Motorsports
Chassis/Suspension/Controls

[ben]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Will98Cobra:
Well the whole point of that particular suspension setup is to have No roll stiffness (zero-roll stiffness). All roll is to be controlled by swaybars. My understaning is that it can work if you can keep the spring rate down, whatever spring the car need for two corners, it has to be doubled which make for a rough ride and doesnt allow the suspension to work. Well it was just a thought, guess that idea is out the window, back to the drawing board

Later on

William Austin
ODU Motorsports
Chassis/Suspension/Controls
<HR></BLOCKQUOTE>

If roll is controlled by sway-bars then you don't have zero roll resistance. I think your whole discription is confusing.

I don't think it would be much good anyway, roll-rock from a stiff (undamped) antiroll bar is bad enough without it being the only roll control.

Ben

[Will98Cobra]

Well Ben im not actually going for Zero roll stiffness, that is just a name that was put on this type of suspension. The reason for my use of it is that it is light and compact and just happens to have a byproduct of zero roll stiffness. Ever who designed it wanted zero roll but i dont that is why there is the use of a sway bar. one good thing about having it setup like this is that it allows your damper and shock to do it actual job and it doesnt have any effect on the roll stiffness. So in other words you can change your spring or shock settings and it will not effect you roll stiffness. Does this help any.

William Austin
ODU Motorsports
Chassis/Suspension/Controls

[ben]

We're not currently running an anti-roll bar on the new car. We may at some point, but I've been discussing suspension engineering with a vehicle dynamicist that consults at our uni, and am starting to realise that undamped roll spinging (i.e. an antiroll bar) is a really bad idea and if you can avoid it that might be better.

Ben

[clausen]

I have a few points to add.

Formula V's run this no roll stiffness setup on the rear (no swaybar either), but they have a rear roll centre at the top of the gearbox somewhere (swing axle), terrible things.

I think the undamped roll thing sounds absolutrely terrible. An australian formula ford chassis builder made a car with the front end that Denny mentioned RIT used. It uses small coil sprigns to provide the roll stiffness. The company i work for part time has made a lot of money converting these back to twin shock. They have also heard of the roll oscillating being a problem.

I have heard of a formula 3 or something similar that was designed so that it could be swapped between single and twin shock. Apparently one setup suited faster tracks and vica versa.

Did i mention that no damping in roll is a horrible idea. Isnt damper tuning an important part of turnin etc?

[Schumi_Jr]

The Dallara F3 cars have been running a front monoshock for a while now. They achieve roll stiffness by using a couple of bellville washers. I'm not sure how successful the design is but Dallara totally dominates F3.

If you don't have any damping in roll then a) your car will oscillate undamped in roll
and b) you lose a significant element of transient u/s o/s tuning.

Aaron Johnston
University of Waterloo FSAE

www.eng.uwaterloo.ca/~fsae (http://www.eng.uwaterloo.ca/~fsae)

[Engelbert]

A steering damper from a motorbike could be used (in conjunction with some sort of linkage for adjustability) to do the job for the roll damping...they still use pressurised nitrogen to reduce oil cavitation etc, but since the shaft is a 'through' type, they dont have the preload normally associated with regular shockys.

Then both the roll and bump systems would be fully independent of each other, yet still fulfill their roles completely..

just a thought.

Sam.

[Fomula Freaky]

Dammit! Stop wasting time thinking outside the box, and just do a conventional setup like everyone else ! ! http://fsae.com/groupee_common/emoticons/icon_eek.gif ! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

I don't see enough people using Gas-Struts - as in the thing holding up your bonnet or boot/tailgate. Cheap and readily available, it's a spring AND a damper in one ! ! I don't quite understand why you'd chase a lower roll resistance: I'd be chasing Zero roll with maximum wheel independance - like the de-coupling Anti-Roll bars mentioned before. I've seen these done with hydraulic rotary coupling IN the A.R.B, and hydraulic A.R.B. MOUNTS - coupled to another hydraulic mount on the car's opposite corner.

BMW also do Active de-coupling of roll bars in their "Dynamic pack" for the 5/6 series Luxo-barges.

Hell - just blow the entire S.A.E. Budget on doing fully active suspension ! ! !

[Garlic]

OK... but you can't design a suspension with a half dozen random thoughts. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[jdstuff]

Will,

Just a little more background info, if you would like to know. As both you and Clausen mentioned, FVee's utilized "zero-roll" rear suspension...which means that almost no roll stiffness is provided by the rear suspension. The reasoning behind this is most likely a solution to an altogether different problem: the differential.

FVee's are open differential cars, which as you know can exhibit noticeable inner wheelspin during corner exit on slow/med speed corners. By allowing the front suspension to provide nearly all of the roll resistance, the rear inner wheel will always remain loaded by at least the unsprung weight at that corner. This might not be much weight, but it may be enough for an underpowered car (like a FVee) to prevent open differentail wheelspin.

Anyway, just my $.02......but I'm just a drivetrain guy, so don't take my word as gospel! Hope that provides some more insight.

[Erich Ohlde]

We ran a front monoshock on our '05 car. Works great, don't have roll dampening yet but the car has incredible turn-in and handles slaloms extremely well. I'm currently working on a way to include roll dampening. Hopefully the car will handle even better.

[Fomula Freaky]

Originally posted by jayhawk_electrical:
We ran a front monoshock on our '05 car. Works great, don't have roll dampening yet but the car has incredible turn-in and handles slaloms extremely well. I'm currently working on a way to include roll dampening. Hopefully the car will handle even better.

Think about running the front A.R.B. damping similar to that supplied by the regular dampers in the rear end. Otherwise you'll get a massive imbalance in effective roll resistance under dynamic loads between front and rear ends. i.e. when you turn-in. Has anyone ever tried running a monoshock, with active roll control? Think Williams FW14B, which can be seen here LEANING IN to a corner!
http://www.sportnetwork.net/mainadmin/img/1071021876913.jpg

I personally would run a conventional twin-shock/spring system, with no A.R.B. to interfere with wheel independance. To negate body roll, I'd mount the inboard ends of the springs&shocks on a common shaft, which can be moved via worm drive or a threaded shaft.

Mmmmm.. . . Anchovies . . .

[Z]

Jason,

Re: Formula Vee. These have, as a result of using the Beetle suspension, a ground level "roll-centre" at the front, and an ~axle-height RC at the rear (approx at the centre of the diff). If they had conventional springing at both ends then they would have way too much lateral-load-transfer at the rear, and hence be prone to oversteer in corners. This is because LLT = elastic-anti-roll (from the springs & ARBs) + viscous-anti-roll (from the dampers) + kinematic-anti-roll (from the slope of the line from wheelprint to RC). With the "zero-roll-stiffness" arrangement at the rear, their front/rear LLT's are about equal - all front LLT comes from the springs & dampers, all rear LLT comes from the high RC - hence reasonable handling.


Erich,

The monoshock Dallaras don't have front roll damping because it works better that way! I posted on this in "Anyone else run a Monoshock?" thread.

Z