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

William Austin
ODU Motorsports
Chassis/Suspension/Controls

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

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)

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

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

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)

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

quote:

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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).

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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

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

Marc Jaxa-Rozen
École Nationale d'Aérotechnique

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

well, if your looking for something different, check out this site: Drysdale open wheeler
a very unique engineer with some serious credentials built this car:




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 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"

bet someone on here could figure out how much air a 600 engine at 19,000 rpm would take in unrestricted.

Probably around 220 CFM...talk about choked flow in a 20mm restrictor

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

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

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

Eric Wort
UIUC Formula SAE

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.

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>

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...

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

quote:

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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

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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

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

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

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?