OK.... don't know much about flex joints, but isn't one of the main points of this competition to have a maximum mechanical grip? Therefore if you have a component that adds to stiction/friction of the movement of your "optimised" suspension system, wouldn't it be a disadvantage. Why would we want to risk the tyre compliance with the road?

ie. We have a rodend - that is placed correctly so it doesnt deal with bending and allows excellent motion, or we have a joint that relies on stiffness for its integrity.

I think in this case we cant really compare to F1. An F1 car has what sort of crazy stiffness springs? Add that little bit extra from flex joints cos they try to get as stiff as possible - makes no difference.
Now we have a 200kg car with damn soft springs, if we add just a little bit of stiffness to this through a joint aren't we just adding another uncertainty to an already "hard enough to work out" system????

Wont these joints add to the damping and stiffness of the car?

F1 use flexures to reduce stiction, because rod-ends bind up under load, they are plain bearings after all.

They also allow higher installation stiffness.

I think all those advantages would also be realised in an FSAE application of flexures but as has been mentioned the larger suspension movements with shorter wishbones presents a great challenge. Hence my original post that I almost choose it as a major area to explore in my final year.

Ben

oops... didn't realize this was from 2004!

Doesn't matter if its old or not.. did you have a specific question?

Since '04 there's been at least one team (Lehigh) that ran flexures, carbon ones at that, on their suspension.

Given the very high amount of friction / mechanical hysteresis in some of these cars suspensions it might not be a terrible idea to look into. You'd be surprised how little even a ChampCar steel flexure, such as the one I have handy, adds to the system. Feels stiff as hell at the joint, but if you clamp that in a vice and try moving the wheel-side point around it moves A LOT with little force.

I was just gonna say I could take a pic of our 89 car, its hanging on our wall.

TU Graz and TU Darmstadt are using flex joints this year. Graz is using steel and Darmstadt carbon fiber in one piece with the a-arms.

RBbugBITme: can you please post that picture?

Lehigh's arms from 2006:



http://evilengineering.com/gallery/v/SAE/FSAE/2006/

anvit, check out the picture gallery section of this forum and you'll find a topic called ERAU formula hybrid 2008. It should have a close up on its suspension.

Hi All,

I am the designer of the above Lehigh Univ. composite suspension parts. Below are some better pictures. The a-arms represented a significant amount of design and testing back in 2005-2006. The car you have pictured was completed the night before competition back in 2006, so it didn't fair very well. However, our 2007 car featured a similar suspension. Both cars have had extensive run-time now and I feel confident saying that the flexture a-arms are a good viable option for FSAE. They can take a good hit with a rock, wrench or cone, which is suprising to most people. These arms are vacuum infused unidirectional carbon fiber with an H80 Divinycell foam core. They are designed to flex only for a region of about half an inch on the inboard end of the arm. In this flexing region of the arm there is no foam core. Please note that these cars also feature a novel glass-fiber antiroll which is light as a feather.

I hope to write a paper (when I finally get some time) on these arms, giving the design process, and cross-sections cut-aways of the flexture portion of the arm.

Feel free to ask questions.

Many thanks to Tal (Lehigh FSAE Alum from the beginning of this thread) for his early work showing that flexing carbon was a possibility.

All right ERAU... nice job with the carbon flextures! Can we see some better pictures of perhaps an a-arm off of the car?

quote:

Originally posted by Composites Guy:

Feel free to ask questions.

Since you offered, I'm curious what your testing revealed was a safe range of motion (in degrees) from horizontal with this type of flexure, so as to not fatigue the joint?????

composites guy, what type of adhesive do you use for your metal to carbon bonding?
are they all unis? how many layers of uni?
how come i dont see the foam in the hole where the pushrod goes thru?
was it cure in an autoclave?
do you have pictures of your feather light ARB?

Here are some pictures of our flexijoints made of carbon fibre from Tu Darmstadt





They were tested statically and dynamically and our know used in our gamma2008

Dart: Thanks for posting the pictures... the carbon is beautiful. We do so many structural tests here that carbon's asthetics are often overlooked (but I know asthetics will count in the commercial world.) I'm curious as to how the inboard metal joint is designed. Those little metal tabs look quite small. What is hidden under the paint??? Have you embeded some trick piece in the body?

vreihen: I considered 1" bump and 1" droop measured from ride height at the wheel(to comply with FSAE minimum supsension travel.) The range of motion was tested accordingly. I made up a sample a-arm which was put through this travel 10^6 times.

RiNaZ: I used Henkel (formerly soverign chemical) epoxy E2119, which is some lovely stuff to work with. It has the look and consitency of tar, and it stays where you put it, and looks good with carbon. You can't see the foam in the hole because I inserted a small G10 phenolic block into the core prior to infusion. This makes for a finished and durable piece once the hole is cut. I have never seen an autoclave in person:-) Lehigh's specialty is vacuum infusion without needing an autoclave. Sometimes post cure is done in a light-bulb oven, though a black trashbag in the sunlight would do the trick too. The a-arms are completely uni, but I won't tell you the layering scheme (perhaps in a future paper.)

Below are two pictures pertaining to the lighweight anti-roll device that I mentioned. The basic idea is that bellcranks, shocks, push-rod, etc. are in the same plane. Two seperate wavy fiberglass springs are attached in an x-shaped pattern to the bellcranks. As the car rolls, one spring goes into tension, the other goes slack (and does nothing). As the car bumps (without roll) both strips stay (nearly) the same length (and do nothing). Thus these wavy strips provide the typical characteristics of an anti-roll device whilst being VERY lightweight. The strip's layup scheme and wavy shape determines the spring rate.

impressive, i dont think ive seen the ARB back in 06'. Are those seatbelt parts? I cant really see if you're just bonding the glass to one side of the ends or it's clamped with the metal (im asking about the ARB).

do you know how much the henkel epoxy is?
And do you still have the old A-arms from the first time you did it? Im curious to know how long can u use the A-arms before it starts to delam or sag just from the weight of car.

What are the design benefits of this type of joint, over say a plain spherical? Lower cost/weight? How about compared to a simple poly bushing? I'd think the flex section would make a Z shape pretty easily, changing the effective arm length and goofing with all of the suspension geometry values.

For the guys that have used them, what do you feel are the weaknesses of your design?

I remember doing a double take at the Lehigh paddock back in 2006 at those ARB's, followed by a fairly big "doh" moment wondering how I had never seen something like that. They were insanely light as well if I remember correctly.

Did you guys measure how linear or not the effect of the fiberglass ARB's were on your roll stiffness? Also were they used in the front and rear? Thanks

what kind of glass do you use for the ARB? it looks like 6oz surfboard glass and it looks really thin, how thick is it?

DART-CG, is the arm a one piece? i dont see the seam line in the close up. What do you guys use for core?