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Thread: T11.2.1 and floating buttons/bobbins

  1. #1

    T11.2.1 and floating buttons/bobbins

    Hello guys.

    I'm planning on using floating rotors for the first time in my FSE team, but I stumbled across the interaction of rule T11.2.1 and the floating buttons. I know some teams design their own buttons and most pictures I saw shows the use of a screw to lock the buttons in place.

    But, all the commercial buttons I saw available only comes with an E-Clip type of locking. Does T11.2.1 restrict this kind of lock? Any team using this kind of setup? Any design judge around could clarify if this is possible?
    I know I could just design my own buttons, but for now the commercial ones are the most viable for the team (uni doesn't have the necessary machinery for it).

    Thanks in advance.

    T11.2.1 All critical bolt, nuts, and other fasteners on the steering, braking, driver’s harness, and suspension
    must be secured from unintentional loosening by the use of positive locking mechanisms. Positive
    locking mechanisms are defined as those that:

    a. The Technical Inspectors (and the team members) are able to see that the device/system is in
    place, i.e. it is visible.
    b. The “positive locking mechanism” does not rely on the clamping force to apply the “locking”
    or anti-vibration feature. In other words, if it loosens a bit, it still prevents the nut or bolt
    coming completely loose.

  2. #2
    Don't use e-type clips.


    EDIT: If you don't have the resources to make brake buttons, how are you building a car? Don't take this as a jab, I'm genuinely curious if you're managing to do this with 100% off-the-shelf components.
    Penn Electric Racing

  3. #3
    I said I couldn't make the buttons in-house. We have a sponsor that is able to do the machining of the most critical parts.

    The real problem for me, is having another thing to design...there is already so much (I'm kinda of overloaded with the amount of things I have to do. Rotors, hubs, uprights, transmission, etc)

    What would you sugest to use instead of the e-clips to hold the buttons and comply with the rules?

    Thanks in advance.

  4. #4
    Senior Member
    Join Date
    Oct 2007
    Bolton, CT
    What's wrong with e-clips? I think that most team's use e-clips on their rotor buttons. Technically they work in the same way as any other snap ring.
    "Old guy #1" at UCONN Racing

  5. #5
    E-clips are pretty standard as far as bobbins go. Size them correctly and they'll be fine.

  6. #6
    So, using E-clips is acceptable with T11.2.1? That's what I want to hear hahahah

  7. #7
    It used to be that a "critical fastener" as covered by that rule on steering, braking, harness, and suspension parts was that there were three or fewer fasteners retaining the "critical" ppart in question. So if you use 4 lug nuts / bolts to retain the wheel, they are not required to have a positive locking feature as defined above, but if you use a single center-lock nut, or three lug nuts for example, you are. Brake calipers with two bolts are required to have the approved locking mechanism, but brake rotor hats with 5 fasteners were not.

    HOWEVER. This may not still be true! As with all rules questions, ask the rules committee for a clarification, and search on here for the supplemental rules clarifications from the past check this out for yourself.

    I'd personally use snap rings over E-clips for this application, since you get more engagement of the clip, and being able to quickly remove them without a spacial tool is probably not a design requirement for your brake rotors.

    Northwestern Formula Racing Alum
    Head Engineer, Frame/Suspension 2006-2009

    My '73 Saab 99 Road Race Build

  8. #8
    I've sent an e-mail to my local rules committee, waiting for the answer. Thanks for the help, everyone. If someone still wishes to add more info, please feel free

  9. #9
    Traditional snap rings are cheap and can be installed with harbor freight snap ring pliers. They are much safer and less likely to disengage than E-type clips, which can come off with the tap of a screwdriver.
    Penn Electric Racing

  10. #10
    Yes, I'm leaning towards using traditional snap rings. Is anybody willing to share some tips regarding the clearance between the bobbin and the bell-rotor hole? I'll contact our sponsor and try to design the bobbins myself, but I'm somewhat in the dark regarding the
    clearance to define my tolerances. In my mind, the thermal expansion at the max working temperature should not be enough to bind the buttons, so is this the only parameter for radial clearance? And what you guys consider a reasonable axial play? By that last question, how much in the dark am I?

    Never really got my hands in a working system like this, and my searches on the internet don't return me any technical aspect of the system

    If I wrote any technical term wrong please feel free to correct me, I need to improve my english.

    Thanks in advance!

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