Rose jointed suspension system

[mach11]

what are the advantages of using a Rose jointed suspension system.

I am aware and have been advised by many that unless you do not know how to adjust the suspension system and also if you know what you are doing, then go ahead in using rose joints.

also if you have a big budget then you can afford to use rose joints for the suspension system.

The thing is, I am still looking for a convencing answer to use rose joints on a suspension system. (say an FSAE vehicle)

The play that is obtained by using a rose joint is advisable but are there other critical advanteges when compared to the arrangement used in normal road cars where an eye with a metallic bushing is bolted. ??

I hope I made myself clear...

Thanks in advance.

[marcush.]

I really don´t understand what you are looking for.
Design build and campaigning a car is a technical exercise .You have certain targets and a plan how to achieve them.
One of them is to provide grip to the racetrack through your tyres.the tyres will demand a certain characteristic from the chassis and the connection to the chassis ...finding the best compromise is what it´s all about.
Start with the rule book.You need tyre endurance ? or is it more important to quickly get the tyres to work only no matter who is driving the thing?
there is not just rosejoint and elastomermetallic bushing in this and certainly nobody could make these important decisions for you without knowing anything about your concepts.
You have not even shared your basic idea of the car apart from SAE...so it would be open four wheeler..but have you put any thoughts in how to suspend these 4 to the main structure?

[riff_raff]

mach11,

Based on your question, I'll assume you're a student. You probably could have answered your own question if you would have thought the situation through logically.

You need to think of a suspension in kinematic terms. What is the difference in the degrees of freedom (translational & rotational) between a bushing and a spherical bearing? And which type would have the proper DOF's for your particular suspension at each joint? And then take into consideration other factors such as stiffness, friction, strength, weight, etc.

The most important (and rewarding) part of a technical education is learning to think things through on your own.

Best of luck to you.
riff_raff

[DaveW]

mach11, your question has stimulated wise responses, although that fact might not be entirely obvious to you.

Engineering solutions are usually the result of compromises made between conflicting requirements, and understanding those compromises is key to understanding the solutions. For example, priorities for a road vehicle are usually cost, ride, durability & handling in that order. By way of contrast, the priorities for a race (or "performance") vehicle are usually handling, cost, durability & (at a very low priority) ride, & this implies that a solution that works adequately for a road vehicle might not be appropriate for a race vehicle.

Suspension bushes are an example. They are cheap, quiet (tend not to transmit "noise") and are durable, but they have "parasitic" compliances (they allow translation as well as rotation). They work well provided that the parasitic compliances are small (i.e. parasitic stiffnesses are high compared with suspension stiffnesses). That situation can change if suspension stiffnesses are increased & accurate suspension control is required at high loads. The trailing arm bushes used in a "twist beam" rear suspension, for example, usually cause increasingly poor hub control as the damper "strength" is increased, resulting in unpredictable handling. Control will be regained by replacing the trailing arm bushes by "proper" bearings. I leave you to work out why that is the case....

"Golden" rules for converting a road vehicle for racing (probably incomplete):

1. Install a roll-over cage, & make that the vehicle structure.
2. "bolt" the engine to the chassis.
3. Replace bushes with bearings.
4. Stiffen structure that transmits suspension loads.

[marcush.]

I would not even start to talk about parasitic losses here.In karting and RC cars suspension does not even exist /has not existed in the usual sense with dampers springs and wishbones in the sense of what we usually see on a race car.Still those things are blindgly quick.
I would start with basic needs and go from there.If you do not have a clue nor time to tackle the ins and outs of damping and spring configuartions it might be wiser to get rid of the problem ...and go for a completely different compromise.
so why narrowing your options at the start alreadfy? just a thought.
As the objective is not to replace parts but design the whole shebang it comes down to what you really need to be quick in the competition you are aiming at.Keeping things simple is always a good start ,especially for those who are at the beginning of their journey.

[mach11]

Hi all,

I appreciate your responses. I did not get time to post a more elaborate question the last time around as firstly I did not know how many actually knew what a rose joint was ( the reason being, i have had people refer to it in many different terms )...

Moving on, suspension is not my strong points but I would tell you this, during the engineering design of our FSAE car, we started off like all books suggested. Tyre - suspension - chassis.

The chassis was designed with a suspension system that incorporated rose joints on mounting points towards the uprights as well as on to the chassis as well. But it was expensive and so we had to drop that plan.

But by then, the chassis was fabricated and there was no option but to use conventional mounts like those used in some road cars where a pipe (hollow) was welded perpendicular to wishbone ends and use rubber bushings with metal inserts through which a bolt ( M10 to be specific) would be inserted parallel to chassis members.

This has worked for a long time on road cars which have been subjected to loads over a period of time and it is a cheap option.

now what has that caused :

1. A reduction in wheel base length.
2. Reduction in front and rear track width.
3. A longer fabrication process.

that led to me asking the above question.
Being a first year team, and being the capt. I would like to take a proper call before letting the guys do anything on the chassis.

I guess this would give you a better idea on why I posted this question.

let me know.

[RacingManiac]

Tires like certain condition to be presented to them in order for them to provide optimum grip. Rosejoints(in US we call rod ends) allows only the designed amount of movement(plus material deflection based compliance), allows for better control of the wheel end to present the tires with those set parameter(which you need to determine for yourself). So when you arrive at your set wheel/chassis kinematics, you will get(or closest to getting) what you've designed.

Remember in Formula SAE(and racing in general, really), ultimate performance is what you are after, you are doing everything you can control to go faster on track. On road car that is not your goal. You have performance that you care about, but you also need to consider NVH, ride quality, maintenance, cost...etc.