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Thread: Carbon Fiber Wheels

  1. #1

    Carbon Fiber Wheels

    Hello FS Community

    My name is Stefanos Stamoulis, im from TEIWM Racing Team from Western Macedonia University of Applied Sciences located in Kozani city, Northern Greece. Our team
    participated in our first ever Formula SAE event in Italy with our first race car called "Daedalus" [Greek Mythology] and we had pretty good results for a first year team.
    Now we want to improve our racecar and we are planning to utilize Carbon Fiber in every piece that we can improve in order to minimize the weight. We are thinking also the prospect of CF Wheels.

    Now my question is mostly in the manufacturing section, and it is about how to create the mold and if people use lamination (skin + honeycomb core + skin) to create the wheels.

    Any answer would be greatly appreciated.
    TEIWM Racing Formula SAE Team
    Team Lead Designer/Chassis Designer

  2. #2

    Wheels?

    Stefanos,

    Did pretty well for a first year at FS Italy? Can you be a bit more specific? There are teams (from India most often) who get back home telling their network that they "compete" in a international FS competition but in fact did not even pass technical inspection. Can you describe what results / point / position / lap time you got in both static and dynamic events?

    A bolt is the assembly of a screw and a nut. Similarly a wheel is the assembly of a rim and a tire. At a pit stop a team does not change tires; they change wheels. Students and some engineers and of course journalists too often do such mistake.

    I guess you speak bout rim, correct?

    I leave the specialists of composite material and manufacturing answering you but I suggest you not only look at weight and inertia and manufacturing cost and time but also at compliance. Some of the 13 " rim on the FS market have a camber compliance of 0.7 deg / G.
    If your car sustains 2.5 G in a corner (which today is a very FS minimum) your camber is already 1.75 deg. different from your calculations, just because of the rim (and believe me they are many other sources of compliance)

    Want a story? In 2002 a F1 team designed a front suspension with the brake caliper at the bottom instead of the back of the upright (too long to explain why, lets just say mainly aerodynamics - higher lower wishbone and outboard pick up points / less underwing disturbance and lower non suspended mass CG)
    They kept the same exact gap between the rim and the caliper than the previous year. They made just one lap at Silverstone and went home; both the caliper and the rim were machined. The deflection of the rim at the bottom of it is not the one 90 deg. before or after.
    Better have good FEA WITH FREQUENCY, not only static and VALIDATION with lab measurements.
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

  3. #3
    Senior Member
    Join Date
    Aug 2011
    Location
    Lawrence, KS
    Posts
    150
    You are falling into the same trap that many teams fall into.

    You get to your first competition, struggle to get through tech, miss most of the dynamic events, get on the track for endurance, and fail to finish. You missed out on 662 of the possible 675 dynamic points.

    After going through all of those struggles, you come back and think "We need to make ___ out of carbon fiber!"

    No!

    For a first year team, you did better than some other first year teams do. But if you got the same results next year you would be very disappointed, right? Well the best way to improve is to identify your biggest problem areas and fix them.

    Clearly your biggest problem was completing the car too late, lack of testing, lack of preparation. Ask yourself, do you think that increasing your workload (designing and manufacturing carbon fiber wheels) is going to help fix your biggest problem, or make it worse?

    The path that you are starting down is a very bad one. Instead of identifying the biggest areas you need to improve, you have simply blamed your problems on sponsors being late and the event scheduling being too tight. And now you want to start making everything out of carbon fiber, which will require more time to design, more time to figure out manufacturing methods, more time to make mistakes & re-make parts, more dependence on sponsors to make molds, provide autoclave time, etc. This is the exact opposite of what your team needs to improve.

    Another very important lesson you should learn:
    Carbon fiber does not cover up bad engineering. It magnifies it.

    You said that your car was 268kg in your other topic. The only way an FS car can end up at 268kg is through many many examples of poor engineering all over the car. For a car with a 4 cylinder engine and 13" diameter wheels you should be at about 195kg to be competitive.
    -Do you have bad load paths putting things in bending?
    -Do you have parts with a bad shape for the type of load they carry? Features with big stress concentrations, etc?
    -Did you make errors or over-estimate load cases on parts?
    -Did you design for excessively high factors of safety?
    -Did you use some parts without any stress calculation or FEA at all?
    -Do you have excessively thick material on non-structural parts (bodywork, intake plenum, etc)
    -Did you make something that broke right before competition, then fixed it in a hurry with something twice as heavy?
    -Did you have to add a heavy muffler to pass sound?
    -Do you have flaws in your cooling design that required you to compensate with a huge radiator & fan (bad ducting, restrictive plumbing, etc)
    -Did you use off-the-shelf parts that were made for a much heavier application than a formula student car?
    -Do you have extra crap on the car that doesn't need to be there at all?
    If your car is 268kg I would bet money the answer is "yes" to most or all of those questions. Changing the material to carbon fiber won't fix those problems, only better engineering will.

    If you carry on those engineering flaws, but start making everything you can make out of carbon fiber, you might save 10% weight. And then you'd still be severely overweight at~240kg. And you will have more part failures, much higher expenses, more manufacturing delays, and less testing time.

    If you fix those engineering flaws, you could be at 195kg without using any carbon fiber at all. And no loss in reliability.

    Then if you get a lot of testing time, determine the minimum factor of safety you need for each part, validate your load cases with data aquisition, validate your FEA simulations with physical tests, and establish confidence in your team's engineering methods, then you can take what you've learned and use it for carbon fiber part designs with success. And that will get you down to 175-180kg. Knock that down to 150kg if you switch to a 1 cylinder and 10" diameter wheels.
    Last edited by JT A.; 08-23-2017 at 01:25 PM.

  4. #4
    Fun Fact:
    Zurich tried to do CF wheels in 2008 for their second car.
    And in every subsequent year thereafter. The first functional wheels were ready for 2011...

    So. Nope. Don't do it.
    -------------------------------------------
    Alumnus
    AMZ Racing
    ETH Zürich

    2010-2011: Suspension
    2012: Aerodynamics
    2013: Technical Lead

    2014: FSA Engineering Design Judge

  5. #5
    Quote Originally Posted by JT A. View Post

    You missed out on 662 of the possible 675 dynamic points.

    "We need to make ___ out of carbon fiber!"

    Knock that down to 150kg if you switch to a 1 cylinder and 10" diameter wheels.
    To finish first, first you must finish.

    Adding composites does not fix problems, only creates more. Only well established engineering and manufacturing techniques can tame those problems to turn them into benefits.

    In terms of light weighting without composites: can confirm. Our 2014 car was designed as a beefy, simple car to allow us to move to the 10" tire concept without (hopefully) running into issues to allow us lots of time to test. This was completed successfully with only failures in very few parts occurring post-competition.
    This car weighed 370lbs, surprising ourselves at what we had accomplished already. After the concept proved successful, we very aggressively stripped weight further leading to some competition failures in 2015.

    The Kettering University 2015 car that I spearheaded had 1 composite part on it, the nosecone, because it needed to be completed at the last second, it was originally plastic like the 2014 car. It was 342lbs with wet tires, full fluids, as verified on the scales at MIS.
    With LC0 tires with some wear on them it was about 330lbs. It can be done. But it took some serious development for us to evolve from an established, successful package that we had run for a good 5 years already.
    This car also included pneumatic shifting and a large turbocharger (Both very heavy subsystems). It. can. be. done.

    Start with simple designs, use large safety factors, get the car 100% complete and running at least 3 months before the competition.
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

  6. #6
    Well, as many others have said, "carbon everything" is not the way to go for your team, but will leave this here anyways. You don't have to make your own rims, there are other alternatives out there.

    http://blackwave.de/en/formula-student-carbon-rim/
    Johan Sahlström

    Lund University 2010-2015

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