Steering Wheel related

Hi everyone,

I know that this topic has been fully treated (http://www.fsae.com/forums/showthrea...-or-elliptical)and there is no doubt about the "almost" unique rule about steering wheels, but I come today to ask your opinion about the next case.

Of course, the problematic rule is the T6.5.6 The steering wheel must have a continuous perimeter that is near circular or near oval, i.e. the outer perimeter profile can have some straight sections, but no concave sections. “H”, “Figure 8”, or cutout wheels are not allowed.

I attach below some pics of the steering wheel concept. So, now it is time to give your opinion, does it meet the rule?

PPAL FRONT
Attachment 507

PPAL BACK
Attachment 508

BACK
Attachment 509

Ander,

Your wheel will be okay.

Pat Clarke

Ander,

As Pat said the wheel will be legal. However you may want to think about where the driver's hands and fingers will go on the wheel. The little spokes on the side might might be an annoyance.

Kev

Hello my name is Craig Kellermann. I am the project manager and member of the University of Texas-San Antonio.

I would like to state that people on this forum are not the rules committee although Pat maybe a member on that committee I would seek your answer from this of people.

Other than that looks cool and what Keven said is very true.

Somewhat related, but I'm absolutely not a fan of these wheels which are made from a single monolithic carbon sheet (typically 2-3mm thick) and then bulked up with foam or similar for the grips.

In a front offset crash they are almost certain to fail right along the spokes, leaving a razor sharp edge pointed directly at the driver's radial artery.

Its not only dangerous but it's also shit design. They might satisfy the static stiffness constraints in the rules but carbon is the worst material to use in an impact because its fragile. These designs need to be either bulked up as a sandwich structure or extremely thick monolithic structure to withstand the impact loads of a driver's weight x 20g. Even better would be to use a "tougher" material such as kevlar in the area of the spokes.

I saw quite a lot of these wheels at FSAE Italy last year.

I think a simple test should be: if a technical inspector can break your steering wheel from a seated position in the cockpit it's not strong enough...

Have you ever seen one fail Tim? I don't think that they are necessarily "Shit" design, they may meet other team targets of manufacturing ease, cost, stiffness etc, 2-3 mm thick is still quite strong and in a crash the bulk of the drivers weight will/should be going through the belts. Granted the dangerous edges from a failure will still exist, if the plate of carbon is sufficient for the loads it is to be placed under in a crash then there isn't really a problem.
Ander, your wheel does look like it could be tweaked to be better, especially considering it looks like you will already be using molds to create that part.

I havent one fail because I haven't seen one involved in a crash yet. That doesn't make them ok. Cost and manufacturing aspects are irrelevent as the main issue here is safety. A steering wheel, helmet or seatbelt that fails dangerously in a crash is shit design end of story.

2-3mm monolithic is not enough in my opinion. You can bend these wheels significantly with your hand just stitting in the car and this is often accompanied by cracking popping noises of the carbon. I was semi serious about the tech inspeczion test too. If a tech inspector can break a wheel with his bare hands, then the car shouldn't be allowed on the track.

I made a carbon wheel some years ago. The centre section was 2-3mm monolithic prepreg carbon. First time it was bolted to the car I noticed this flex And was immediately worried about its impact resistence. So I hurriedly added a foam core and wet layup second skin so the total thickness was approx 10mm and was now extremely stiff.

Our driver promptly stuffed it into a wall in the first endurance with enough force that it destroyed the rest of the steering system although the wheel remained intact. I'm positive that the original design would have snapped off in that impact.

Cost and manufacturing are very relevant, if designed to meet the loads the part will experience/crash loads... the dangerous edges from a failure are not an issue. That's like saying that side impact tubes may bend and trap the driver if he is hit by a truck, entirely possible, yet not in the scope of design.

2-3mm not being enough in your opinion is fine, but by good design, you should be designing by numbers not opinion. On top of that, what was the fibre orientation for you part you bent? It is likely fibres were not aligned for the bending loads. I have seen 2-3 mm of carbon form some damn strong structure, our longitudinal beams were only ~10mm across the length of the car, they take entire car loads!

For sure if the tech inspector can break it by loading it in that way then sure, ban the part, I agree completely with that.

FYI our carbon steering wheels are 3-4 plies, no core, though they are not "flat" they are immensely stiff.

Quote:

---

Originally Posted by NickFavazzo

2-3mm not being enough in your opinion is fine, but by good design, you should be designing by numbers not opinion.

---

You shouldn't really need to run the numbers to know that putting a 20g bending load into a flat, thin carbon spoke is going to snap it. Ply orientation and other manufacturing red herrings are also irrelevant in the impact case.

If you insist then I have calculated a stress of 5500MPa on a 2mm thick carbon spoke which takes 25% of the drivers weight force in a 20g impact. I'm interested to know how this can be considered acceptable in any way.

Does anyone have a picture of one of these wheels made of 2-3mm thick carbon? Perhaps this is just argument over an anomaly?

I'm interested in how the load case is chosen by a responsible designer. 20g I have no quarrel over, but what percentage of the driver's inertia SHOULD the wheel be designed to resist? Tim I see you've chosen 25%, I appreciate it was likely pulled out of a hat to make a point (which it does).

I appreciate the belts should be taking some proportion of this load in a crash event, but how do we quantify how much? In my mind it does not seem unreasonable for at least half of the driver's weight to go through the wheel when his arms are tensed, even with tight belts. We can all agree that some load will go through the wheel, the belts won't do it all.

If you are trying to responsibly optimise a custom steering wheel, you must have some kind of idea of this number in your head. If you've optimised for 25% and the actual proportion seen at an instant is 75%, you've got triple the stress levels. Does the responsible designer "play it safe" and design for 100% driver's weight?

I don't have any pictures. I saw 2-3 bad ones while I was tech inspecting/judging in FSAE Italy last year. There were also other wheels made in the same way but with a thicker laminate which seemed ok.

Yes, its a difficult thing to define a load case. I chose 25% on the assumption that 50% of the driver weight is reacted by the belts and each side of the wheel evenly reacts the remaining 50%. Its almost impossible to define properly but I don't think this is critical. The stress values that have calculated are so high that even with a +/-100% error in the loadcase, the stresses are still going to be too high for any composite.

The simplest way forward would be to ban brittle materials in the primary structure of the wheel. Perhaps with an exception if you can prove your wheel will survive some defined impact load.