Anyone knowledgeable about the subject?

Basically....I am not (but need to be)I know what it is, and that the roll axis should generally rise towards the rear of the car, but I am rather lost beyond that.

I know there is likely no magic formula, and that it will likely vary from car to car, and with intended use... But anyone have any good reading? Rules of thumb? Things you heard your friends say.... Anything?

Vehicle in question is a tube frame open wheel car with a ride high of approximately 2 inches, weight of ~1000lb with a 40/60 weight distribution (front/rear). Track width of 50in and wheel base of 60in. Total chassis length of 102in.

I personally have no idea, but here is some info that may or may not helphttp://zzyzxmotorsports.com/tech/papers

http://www.google.com/search?h...=f&oq=

I've done some googling for sure, and found some info.Found a real good thread on why it angles upwards towards the rear....

But every one LOVES to just say "put the rear roll center higher"

Which uhhh..... still leaves quite a bit of options on the design

I may look at the adjustable lower control arms SPL offers for the S13 and see if we can't do something similar so that we can just put it somewhere and play with it later... But I don't know if cost and complexity will reject that idea.

se...this is stuff that belongs in the "engineering section"

Not your fault OP, I just get sick and tired of seeing STUPID crap being posted in the "engineering section" that belongs in general car discussion, and GOOD legite engineering questions being asked in Unrelated forums *shrug*

Chukidori wrote:se...this is stuff that belongs in the "engineering section"

Not your fault OP, I just get sick and tired of seeing STUPID crap being posted in the "engineering section" that belongs in general car discussion, and GOOD legite engineering questions being asked in Unrelated forums *shrug*

yeah, I almost did put it there, but this section is Quote »A forum dedicated to Nissans involved in road racing, track days, and autocross.[/quote]And if your going road racing you probably know something about chassis set up... or have someone on your team that does...

I figured it fit well enough in either, and hoped for a little bit more traffic here.

Any engineer on here who works with this stuff is likely involved in road racing, so I figured I may catch them here too.

I know what you mean about stuff posted in the engineering section, but I wouldn't call this one unrelated.

Edit: though it isn't a nissan.... I'm still calling it good because I was looking for Nissan road racers with chassis/suspension set up experience.
Modified by Red coupe at 9:02 PM 8/28/2008

Have you checked over at corner carvers???

cracker wrote:Have you checked over at corner carvers???

Not familiar with them....

Hmmm, google doesn't seem to point to the actual forum.... just other forums talking about how mean they are (or I am blind)

Got a link?

Edit: found it. ****, cant use their search... it asks for me to type in the letters in the image... the image that seems to not be displayed....

I've seen those same post about how mean they are.

They are hard core and don't mess around, most of 240 gen wouldn't last a day, assuming they could even manage to registar.

Make sure to read every thing in the registration process. There is some info barried in the yet to be allowed full access area that requires you to email some one info, and if you don't they won't activate your acount.

But as "mean" as they are, they have some really good info, and some sharp people. As far as I could tell, as long as you play by their rules you should be fine. I had a hard time getting registerd as well, and I can't find my login info any more either. Good luck.

*sigh*I think I am gonna just put it an inch higher, lol....

or at least assume that then work through some calculations to see if that shows me anything...I think it would be better to be closer to level, then to an extreme angle as I can use the rest of the suspension to make it better if I am under where it should be, but if I am over the effects may be too extreme to fix.

While I still haven't found much good info, on larger cars I have read about 2in higher in the rear, since our car is a little less the wheel base, the same angle should be a little more then half the height... so I figure go half that to be safe...

Kinda the style in which we are designing the car But its our teams first year, we have almost nothing to build off of, and no one on the team has any previous experience (including me...)

Kinda just have to build something, see how it does, and how we can make it better next year.

To make things even better, our adviser who has been awol for almost a month just came back... and wants to scrap the chassis we already have to build one from scratch... Even though we have already completed the FEA and solidworks modeling of the current one, are behind schedule on design, and are having enough trouble figuring how to modify our current chassis (which was build by a team with years of experience, and has seen a few seasons of iterative progress).

FSAE????

What are you building this for???

Is there any one else you have contact with that has built one before? Tried contacting any of the local racers to see if there are any good suspension / chassi guys in the area? Might Start with any regional NASA SCCA forums, or REAL race shops in the area. I imagine all you need is the right equation to work the math out?

Good luck. . .

cracker wrote:FSAE????

What are you building this for???

Is there any one else you have contact with that has built one before? Tried contacting any of the local racers to see if there are any good suspension / chassi guys in the area? Might Start with any regional NASA SCCA forums, or REAL race shops in the area. I imagine all you need is the right equation to work the math out?

Good luck. . .

FHSAE (Formula Hybrid), FSAE rulebook + 27 pages of modifications.... Pretty close to the same competition, the program is made to pretty much mirror the formula program with smaller IC engines and electric motors.(though your first year the car can be all electric, other wise limited to 250cc rather then 600cc but with no intake restrictions).The chassis we have to start with is our schools 2006 FSAE chassis, however the 600cc engine is used as a structural member so the whole rear is built around it. We will be lopping it off past the main roll hoop and redesigning the rear end.

No equations really... Some that involve roll axis to CG height that will tell you things about weight transfer, but suspension doesn't really have "set it up like this" formulas... Loading and stresses in suspension members OK, but nothing mathematical about what it should be, just equations to analyze what it is... We have spoken with our baja team, and our formula team... and they said what every one else says "trial and error, rear RCH higher"

Trouble is we don't have trials to go off of, and by the time we get to the error half we are pretty much done

Tube Chassis?

KU's FSAE car is all carbon fiber (**I Think** If it isn't all carbon, it is mostly carbon fiber.), and it is dry carbon fiber at that. I have seen it run a few times. Very cool car. Nose cone comes off a lot though.

Sounds like trial and error. I know the FSAE KU guys ran a lot of local autoX's with their car. I don't know if they where doing test and tuning or not. But they had several of the local hot shoe's run the car. I don't know if they where asking them about the car's set up afterward or not. Might be worth looking into.

Like I said. . . good luck. Oh, and do you have any pics or any more info? The project sounds really cool / interesting!

I am betting that the actual chassis isn't made out of carbon fiber... As I hear it doesn't take bending too well, and I would imagine there are rules against it considering how sharp fragmented CF can be...

our FSAE team is making carbon fiber wheels this season though. Not too many pics yet, as we are still designing and don't start building for a while yet...

But a couple of the chassis...[From the drivers seat, cosy little bastards...

Weighing the chassis to find its CG, the piece of wood is 1", the chassis was designed to have the front end 1" higher then the lowest point. Everything past the large hoop behind the drivers seat will get lopped off and redesigned...

When I was out at our local SCCA autocross the FSAE guys were out there... I am not sure if we will do that or not, hopefully so.

However as long as we do it late at night and notify security ahead of time we can use the parking lots at school for testing But unless we make it one of the control arm ball joints can be shimmed up or down roll centers are set at that point. Alignment, shocks and possibly springs are still up for adjustment at that point though...

In one of my classes we did a project for traffix devices, one of the larger suppliers of road cones and traffic control devices... We presented our designs to one of their engineers, and at the end I talked to him about supplying road cones... and about all he had to say was "How many do you want and what size?"

So we will be able to set up our own autocross/ random corners to test on in the school parking lots for free

I usually only pop into the engineering section so I didn't see this. I have an article posted in my tech section that goes over roll axis inclination.

http://pdv-motorsports.com/Mar...n.pdf

What is your question exactly? You are sticking with your suspension as is and therefore your front roll center height and you want to know how high you should make your rear roll center?

FYI, at Drexel, the Formula Hybrid team knows that they are a new team with no history to work off of and plan on just getting a running reliable car. They don't care about the details right now, they'll go over them and worry about better dynamic performance after a successful competition is under their belt already. If this is where your team is at I'd suggest the same, just shoot for the same suspension parameters that the FSAE team originally did and get to driving asap. The judges at the hybrid comp don't even care about this stuff, the entire competition is built around the hybrid teams taking the already built FSAE chassis. They don't expect you to know what goes into the original suspension design.

You're building a 1000lb car?!?!?!? Our hybrid is around 750lbs w/driver.

RBbugBITme wrote:I usually only pop into the engineering section so I didn't see this. I have an article posted in my tech section that goes over roll axis inclination.

http://pdv-motorsports.com/Mar...n.pdf

What is your question exactly? You are sticking with your suspension as is and therefore your front roll center height and you want to know how high you should make your rear roll center?

FYI, at Drexel, the Formula Hybrid team knows that they are a new team with no history to work off of and plan on just getting a running reliable car. They don't care about the details right now, they'll go over them and worry about better dynamic performance after a successful competition is under their belt already. If this is where your team is at I'd suggest the same, just shoot for the same suspension parameters that the FSAE team originally did and get to driving asap. The judges at the hybrid comp don't even care about this stuff, the entire competition is built around the hybrid teams taking the already built FSAE chassis. They don't expect you to know what goes into the original suspension design.

You're building a 1000lb car?!?!?!? Our hybrid is around 750lbs w/driver.

Kinda what we are doing, however the rear end is designed around the 600cc engine, and uses it as a stressed member so we need to redesign it and while doing so we are trying to do the best we can to make a good car, and trying to do as much as we can to gain some experience.

Yeah you pretty much got my question rightThanks for the newsletter, is there a place I can sign up for that?But in all honesty, I have already read and gone over info pretty much the same as that, only real difference being that he states that the overall weight transfer changes where I saw it more as changing back and forth between rolling and non rolling moments.

However, as much as I was looking for an explanation I was making this thread with pretty close to that one in mind, and really looking for a suggestion on HOW MUCH it should be inclined. (or even ballpark)

While we can (and have) gone and measured the other FSAE chassis, and talk to them a bit... with some stuff they have been less then willing to share, though I guess the main thing we got shut down on was tire info that they had to pay for.... But there still seems to be a very much a "figure it out on our own & learn from our mistakes" mentality projected by team, captain, ect...

750lbs eh? The research the team has done says thats a fairly light car, and that with driver they are closer to 1000lbs. We are planning to build it as light as possible, but have been using it as a projected weight for early calculations. Then again I have also heard closer to an 850lbs weight used by members for some stuff (yeah, we are a model of efficiency, communication, and organizations )

We have some what of the same mentality of just get a working car and get driving... but until we get money that isn't happening too soon anyways, so we might as well do the best we can on design. Besides, in all honesty I could give a **** about hybrids... I am just here to learn about suspension design. And Im afford a much better opportunity to do so on a forming team then in our FSAE team which is pretty much set, and the most I could do is struggle to watch over the group of shoulders in front of me.

As far as for signing up for the news letter, if what he says in the intro doesn't work anymore then there are no more news letters to sign up for anyways.

As far as for the roll axis inclination, you really have to guess at this point I think. If you're 60% rear weight bias you may end up with a higher roll center in the front than in the rear. As an engineer working to compete in an enigeering competition, I'd say design an upright and suspension arms that bolt onto the same inner pick up points that adjust the RC height in the rear for the same ride height and work from there if you're really serious about fine tuning the suspension (which I don't agree with in your situation).

Personally, I don't agree with your attitude about the differences between FSAE and Hybrid. I put together a new slideshow for freshman with the running theme that "It is what you make of it." Essentially if you can prove that your idea will increase dynamic performance and follow through with a thorough report on its design factors, any team member will allow you to work on your project which you presumably will enjoy working on yourself and you'll learn a hell of a lot about engineering in the process. I would think a situation like that would be better than spending 6-9 months trying to figure out the basics fo chassis design and building a "newb" evolution of current technology rather than spending 6-9 months perfecting the FSAE LLTD based on the tire data the team paid for or any number of other specific topics the FSAE team could use work on.

If you don't follow what I'm trying to say, just say so and I'll clarify cause I've had a few brews with my brohem tonight.

Bump for formula hybrid.

I guess we'll be meeting at the competition in may? I'm with Texas A&M. What school do you go to?

crzycav86 wrote:Bump for formula hybrid.

I guess we'll be meeting at the competition in may? I'm with Texas A&M. What school do you go to?

Your on your schools Formula Hybrid? Guess I will have to watch what I say around here

What are you doing for the team?

I am from Cal Poly Pomona

Our school does SAE a little differently. We only let seniors do design as part of their senior design curriculum. We let everyone else help build/maintain the cars. So I'll be on the design team starting next fall semester, which means I won't have any responsibilities until next semester when we start building the car. I'll probably end up doing suspension.

LOL boy was i drunk when I wrote my last response.

Do you think thats how it should be done crzycav? I'm (unfortunately - 20 credits for the fall and winter ) the sole chassis and suspension designer for 09. As a senior now, if the entire car was designed solely by seniors I'd hate this team because you're cutting out years of learning experience. We have 4 week old freshman already designing and making carbon parts which means by the time they're juniors or seniors we'll probably be talking about a carbon monocoque.

RBbugBITme wrote:LOL boy was i drunk when I wrote my last response.

Do you think thats how it should be done crzycav? I'm (unfortunately - 20 credits for the fall and winter ) the sole chassis and suspension designer for 09. As a senior now, if the entire car was designed solely by seniors I'd hate this team because you're cutting out years of learning experience. We have 4 week old freshman already designing and making carbon parts which means by the time they're juniors or seniors we'll probably be talking about a carbon monocoque.

What good is being on an SAE racing team if you can't hold it over people and be elite

RBbugBITme wrote:LOL boy was i drunk when I wrote my last response.

Do you think thats how it should be done crzycav? I'm (unfortunately - 20 credits for the fall and winter ) the sole chassis and suspension designer for 09. As a senior now, if the entire car was designed solely by seniors I'd hate this team because you're cutting out years of learning experience. We have 4 week old freshman already designing and making carbon parts which means by the time they're juniors or seniors we'll probably be talking about a carbon monocoque.

if you want to win, that's how it should be done. we have freshman and underclassmen do plenty of work on the cars to get experience with the equipment and fabrication, we just don't let them do design. as i mentioned in another thread, it puts a lot of pressure on the seniors to get a car done when it's for a grade.

what actual design do these freshman undertake? as i recall, freshman are still taking physics 1. i didn't see a solid mechanics until my 2nd spring semester. so i would be highly suspect of the justifications for their "design".

i'm not saying underclassmen aren't encouraged to get involved and share ideas, but if they can't justify [usually quantitatively] why something should be done a certain way, their idea won't be considered.

Upperclassmen on our team are just as much teachers as anything else. Typically I'll ask them to design a solution to whatever problem there may be and then analyze their solution with them. Hopefully the kids below me will be far ahead of their classwork like I was due to those before me. By the time I was in Dynamics, I was solving early chapter problems with techniques taught in the latter half of the book. This is what I think makes the whole FSAE process so great. Hell I've got sophmores that know ProEngineer better than some seniors!

"if you want to win, that's how it should be done." Totally disagree, if a 3rd year engineer (coming from a 5 year school here) can't design and fabricate a pedal box or a bell crank, he's a little behind imo.
Modified by RBbugBITme at 2:42 PM 10/8/2008

That sounds pretty remarkable. I don't think students here would be too willing to do that, so props to you for that.

We do get a lot of seniors who have never been involved with SAE before joining the design team, but they seem to pick things up pretty fast. I do agree that SAE members need to be mentored to get the most out of them, but I still think you get a better car(or at least A car, an accomplishment in itself) when your grade depends on it.

I can see you guys getting a lot of flakers, stopping halfway through a project because the semester gets rough. We have plenty of flaky volunteers at our school, but the seniors cannot afford to give up lest they fail the class.

crzycav86 wrote:That sounds pretty remarkable. I don't think students here would be too willing to do that, so props to you for that.

We do get a lot of seniors who have never been involved with SAE before joining the design team, but they seem to pick things up pretty fast. I do agree that SAE members need to be mentored to get the most out of them, but I still think you get a better car(or at least A car, an accomplishment in itself) when your grade depends on it.

I can see you guys getting a lot of flakers, stopping halfway through a project because the semester gets rough. We have plenty of flaky volunteers at our school, but the seniors cannot afford to give up lest they fail the class.

YOUR DOING IT WRONG!

As I see it, no need to place restrictions on who can design... Like you said the typical freshman is still learning what a vector is, he will be excluded from any actual design work by the sheer fact that he cannot do it. But if by chance one can pick it up, or has done enough outside reading why have rules in place to exclude him?

we dont have freshman like that... must be that texas inbreeding i kid i kid

but really, the way our freshman learn is by fixing the previous years cars. we used to have 4 cars sitting in our engine lab, usually none of them are running. while we're fixing cars, freshmen will ask why things are done certain ways. then, when its their turn to design, they have an idea of what they're up against.

LOL my senior design team is forcing the FSAE team to ramp up development, we're registered for FSAE West which is 8 months away and I'm still playing with the suspension design. This should be an interesting year full of design compromises.

RBbugBITme wrote:LOL my senior design team is forcing the FSAE team to ramp up development, we're registered for FSAE West which is 8 months away and I'm still playing with the suspension design. This should be an interesting year full of design compromises.

Pffft, I'll have our suspension design completed by December...

You wanna talk comprise... we are starting from ground zero. Our FSAE team seems too busy laughing at the hybrid guys to want to help, and I think they even confronted our president for going on their FTP server for 1 or 2 very basic specs on the chassis we are using from them.

Plus with various other discussions going on, I still don't have info on CG location or even a solid guess at the weight of the car....

So camber curves/instant center locations/roll axis/ect... "This seems good.....?"

I am supposed to design the side view front suspension geometry today, and I don't really have any brake info, any kind of performance projection, and most of all no CG info...

Its a whole lot of guessing with out a previous car to test. God damn I hope this thing doesn't suck

Really just aiming for it to come out competent, and be able to tune it up to the decent level so that its drivable at the limit then we can pick up more sponsors, and have a base with some testing to REALLY build off of for next year.

Starting from scratch is fun

I laugh at our hybrid team too but at least I answer any and all questions they have.

zero anti's correct?

I'm also starting from zero for the front due to the new template rules. I've unfortunately been forced to widen our track width, we were one of the narrowist FSAE cars in the world due to our extremely low CG so I'm not happy.

80-90" is what I've been told as average IC lengths for FSAE cars. We've had 50.3% rear weight bias with driver and a roll axis that I think was too inclined for that setup. I'm shooting for closer to 55% now and trying to keep the roll axis where its been. Now my only issues is roll center migration in the front which I should find out by the end of the day.

Theres more but gotta run...

RBbugBITme wrote:I laugh at our hybrid team too but at least I answer any and all questions they have.

zero anti's correct?

I'm also starting from zero for the front due to the new template rules. I've unfortunately been forced to widen our track width, we were one of the narrowist FSAE cars in the world due to our extremely low CG so I'm not happy.

80-90" is what I've been told as average IC lengths for FSAE cars. We've had 50.3% rear weight bias with driver and a roll axis that I think was too inclined for that setup. I'm shooting for closer to 55% now and trying to keep the roll axis where its been. Now my only issues is roll center migration in the front which I should find out by the end of the day.

Theres more but gotta run...

Our roll center moves only like an inch , I know for sure under two... The front view instant centers do drop below the ground a bit, but still only a few inches, I suppose better then it going above the ground.

We just had a race car design seminar on campus, and the speaker brought up a good point. While you would normally shoot for no lateral scrub its not necessarily a bad thing... You loose some grip due to the tires being worked back and forth, but you gain much more by actually getting the tires up into their operating temps, since they are such light cars that are only doing autocross using race rubber some scrub to generate heat in the tires may be better then no scrub (and no heat )

as far as our "antis" with out CG and brake distribution information we can't really plan it (well all the antis RCVD refers to are side view stuff)... So uh....Like i said our chassis mounting points are pre-existing anyways so to some degree our influence is limited anyways.

Our front view IC lengths are a bit shorter then that, but it still only gives us 1deg of camber under full compression.

Hopefully we will have more info when designing the rear.