Attachement of suspension to chassis

[FloMo]

When searching the internet for information on F1 suspension I stumbled over this site and find it a highly informative source on the topic.

I am a member of a Formula Student team in Germany an responsible for the chassis/suspension of next years car.

Right now we are using a double wishbone system with ball joints at each end, whereas we exchanged the Ball joints on the hub side with milled parts, that we welded to the wishbones. this was done after the two ball joints at the front suspension simply broke during the brake test in Silverstone.

We intend a Formula 1 like solution for the next years car. Most pictures I can find here relate to the attachment at the Brakes.

More interesting for me would be to see how the front is attached to the body itself.

Furthermore would be interesting how the teams realize the adjustment. Most pictures of the rear chassis show screwed attachments. Are the teams using chims for adjusting camber, toe and so on?

Thanks in advance, I guess there will be more questions from my side.

Greetings

Flo

[timbo]

http://www.scarbsf1.com/
here's plenty of info!
Scarbs is also posting on this forum

[bazanaius]

Certainly scarbs page is great for F1 stuff.

For formula student student stuff, www.fsae.com has an excellent forum where members of FSAE teams from all over the globe discuss items just like this.

Also - when you say ball joints I take it you mean spherical or rod end bearings. I would certainly look into why they broke in the brake test at Silverstone, to understand and try not to make the same mistake again. Rod ends are used widely in FS, and hence I'd suspect it was a design flaw that could easily be changed and be a lot simpler than redesigning the application.

For example, were your bearings undersized? or did you have rod-ends mounted in bending? these are common mistakes in FSAE and certainly worth checking for.

Back to your original point tho, this is certainly an interesting discussion about F1 cars, and I'd be interested in any pictures or descriptions beyond scarbs that people have.

[DaveKillens]

Welcome to THE forum, FloMo. I recall watching a TV article, and they were adjusting the ride height with shims. But the differences were in millimeters.. which is mind-boggling in many ways.

[FloMo]

Thanks for your fast answers.

"bazanaius": We suppose that we had a production failure with the rod ends used. The suspension geometry was nearly the same as with our last years car where no problems occured. After replacing the rod ends with alloy steel rod ends everything worked fine.

Although the rod ends are used widely in FS they are only tolerated and in some events you get penalties in the Design event. Our aim for this year is to limit the use of rod ends to a minimum (lets say the steering links and the tie rods), which we started between Silverstone and Hockenheim by replacing the outer rod ends through milled parts without threads.

Because of this the solutions used in the Formula 1 seems very interesting for us, as the use of rod ends is limited, too.

Still I'm wondering how the attach the front suspension to the chassis and how they allow it to move vertically, as it mostly looks like laminated to the chassis.

"DaveKillens": We are using shims, too. But we use them to adjust the camber. In my opinion this is a not so exact option to change the suspension geometry and a continuous adjustment would be more interesting. as I didn't see any shims at the wishbone geometries in this forum I'm curious how they might realize the adjustment (or I'm just to blind to see them).

I already took a look at scarbs website, which is awesome and gave me the chance to understand more of that topic.

Maybe here are more people with a deep understanding and insight that will give that information to us.

[zac510]

On the front where the wishbones join the chassis all of the teams are using titanium 'flexures' that are solid metal but more like springs that can move a bit allowing them to go up and down without 'stiction' in the joint. Then they use shims to adjust the ride height. Not sure about camber, probably the same for the reason below:
The range they move in (maybe chosen by simulations and then aerodynamic limited) seems to be so small that they can get away with using shims. A FSAE car might need more range throughout its development and competition life?

On the rear last time I looked some still have ball joints especially on the forward mount points. Maybe the rear has a bit more wheel travel.

edit to clarify some stuff.

[riff_raff]

As zac510 notes, F1 suspension wishbone ends are titanium flex beams. Titanium is used for several reasons: It is light, has excellent flexural strength properties, it's corrosion resistant, and it can be bonded directly to a graphite/epoxy composite wishbone without any galvanic corrosion issues.

The reason flexures are preferred over spherical bearings is that they provide more predictable and consistent deflection characteristics, they are more durable, and the teams can analyze and manufacture them quickly and easily in-house to whatever configuration they need. The predictable and consistent nature of titanium flexures throughout their lifespan means one less variable to deal with when setting up the car's suspension. Unfortunately, titanium flexures are only practical for racing chassis A-arms with limited suspension travel, so they aren't suitable for road cars.

If you're breaking spherical rod ends on your FS project car, then you're probably loading the rod end axially or in bending, which you shouldn't do. Rod ends are really only designed to take radial loads at the spherical end. So double check your suspension geometry to make sure your unsprung suspension structures are only seeing tension/compression loads in the A-arm tubes, push rods, tie rods and toe links, and that your spherical rod ends are only seeing radial loads along the threaded body axis. Also check to make sure that available angular travel in the rod ends is adequate for your suspension travel. Most conventional rod ends can only tolerate about +/-6deg of rotation before they bind up. And once they bind up, they are easily over-stressed.

Good luck and remember to stand on the gas!

[RacingManiac]

were you using a rodend on the outboard side? the problem, regardless whether it worked in previous years or now, it is fundementally a flawed design. Since you are putting a rodend in bending. And regardless how carefully or tolerance a rod end has to meet, the threads are stress concentration spots. On our a-arms(from Toronto), we use machined spherical bearing housing, welded in a jig than post machined to the the spec of the bearing(the original housing during welding were undersized to leave meat for post machining). We've never had problem with them breaking, and we are using 10-32 sized fasteners on the inboard and 1/4" on UBJ and 5/16" on LBJ. We bend a-arms one year because of the amount of anti-dive we had that year on the kinematic, and it puts one of the lower a-arm member in funny loading condition and not allowing to rodend to misalign properly. We changed that design the year after and we've had no issues since. In THAT season we just made oversized a-arms(and spares) to deal with the issues. If you just changed your rodend to flexture and tell the judges that you changed them because "F1 uses them" and "our rodend broke so we switched", design judges will still crucify you...

Issues with flexture itself, while mechanically it can probably be done, it is a fundementally different joint compare to a spherical bearing. The "pivot" is not fixed, as it relies on a piece of metal bending. How they affects your kinematic is what I find most intriguing about. You can't just assume the pivot stays where it is, and as it move it changes the kinematic of the suspension as well. One of my friend who is doing a thesis with Honda F1 is studying the effect of flexture on suspension kinematic and such. So it is a real concern. On the fsae.com thread someone also raised the same question but to no real answer....Flexture also reduces the suspension hysterisis as it has no friction contact like a spherical bearing, but how much hysterisis in your system to start with to quantify your gain from switching is a question, and I am sure design judges will ask you that too...

[alexbarwell]

As an example, I think the titanium 'flex'plates are visible in the pic for the twin/zero keel article in these pages - you can see them attaching the lower front arms as inserts with angles into the nose section with the suspension push rods with more traditional unions formed into the ends. BTW, an issue that ran around F1 regs a while back was degree of flexure of certain components - any idea how much the arms currently flex compared to the titanium plates themselves, a limiting factor being stress failures from repeated flexing of composites, but then suspension travel is not a big number.

[Jersey Tom]

Only reason you'd get knocked down in Design for using rod-ends is if they're wheel-side. Nothing wrong with using them chassis-side.

Using spherical bearings all around is a solution and is pretty easy. It can be kind of a pain to get mechanical friction down. Using flexures is certainly worth looking at, but they don't need to be Ti. Could just as easily be hardened, tempered steel.

[Conceptual]

What about NiTi?

It is like spring steel, so it sounds like it would be a great "flexture" metal.

But, I am not a metal guy, so who knows?

Chris

[mep]

Does anybode have some mechanical attributes of a TiNi alloy or a typical spring stell. Values for e-modul, tensile strengh and so on.
You (FloMo) will need this values anyway if you want to take the solution of a flexi spring into account.

[RacingManiac]

have you tried www.matweb.com?

[flynfrog]

Only reason you'd get knocked down in Design for using rod-ends is if they're wheel-side. Nothing wrong with using them chassis-side.

Using spherical bearings all around is a solution and is pretty easy. It can be kind of a pain to get mechanical friction down. Using flexures is certainly worth looking at, but they don't need to be Ti. Could just as easily be hardened, tempered steel.

from my secret folder of spy photos

[FloMo]

Thanks to all of you for your answers. Right now we are still in finding the concept. The picture 'flynfrog' attatched is very interesting. The team is using no additional flextures but the carbon itself.

Still I have to evalutate which is better. Either taking a flexture from a second material like Ti and have further bonding areas which will make the calculation and manufacturing a lot more complex, or like in the picture posted above, calculate the A-Arms in that way, that the carbon itself is the flexture.

I found a figure in the web, that the wheel travel of a Formula One or Champcar lies between 1/4 - 1/2 an inch whereas we have to realize a wheel travel of 1 inch up and 1 inch down. So there is the question whether the solution is still suitable for us.

Yet other formula student teams that are running CFRP-A-Arms tend to use either flextures from steel, Ti or the Carbon itself like in the picture above.

A question that is coming up, when looking especially at the last picture and keeping in mind that the formula 1 is using extra flextures is, why they are doing that. My idea would be, that they take the disadvantages for another part, that needs to be manufactured and to be bonded to the suspension because of the better known and less critical material characteristics.

'mep': regarding the material characteristics, we are working closely with a Carbon manufacturer, so getting material data from them, or material to do tests with will surely be no problem. still like every new solution it should be tested under real circumstances.