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Thread: Drive Sprocket FOS

  1. #1
    I was wondering if anyone knew what an appropriate Factor of Safety would be for a 48 tooth drive sprocket made of 7075 aluminum (running a CBR 600 engine). I'm just not sure how low you can go and still be comfortably safe with the design. I appreciate any feedback.

  2. #2
    I was wondering if anyone knew what an appropriate Factor of Safety would be for a 48 tooth drive sprocket made of 7075 aluminum (running a CBR 600 engine). I'm just not sure how low you can go and still be comfortably safe with the design. I appreciate any feedback.

  3. #3
    Yeah, pretty much anything above 1 should work just fine.
    Billy Wight
    University of California, San Diego - Formula SAE 2004-2006

  4. #4
    It obviously depends on your loading model, and how you define comfortable. Without knowing that, its pointless to answer the question. If you haven't built/tested or run the part on a previous car I would go very conservative considering its not something you can afford to have fail. Remmember that no loading model is ever going to be perfect because its a model of reality based on assumptions.

    FEA And destructive testing are your friend.

  5. #5
    Yes, FEA is your friend.

    And remember when you're doing your load case, take your worst case as the max grip you can get from your tires, not the max output torque, as you will break traction before all that force can be applied to your drivetrain.

  6. #6
    Fatigue.. keep that one in mind. Also be pretty careful of alignment when you set your car up. Or else it'll eat up those aluminum teeth.

    I'd reccomend a hard anodize on top. MIL-A-8625E, Type III, Class 1 or 2, at least .0020" thick.
    Colorado FSAE | '05 - '07
    Goodyear Tire & Rubber | '07 - '11
    NASCAR Engineer | '11 - ??

  7. #7
    Thanx for your replies guys. I have a few designs already in Solidworks and did some COSMOS on it. I applied our worst case output torque at the tires (not torque from the engine); is that the same as what Welfares is saying? I noticed that many motorcycle drive sprockets are made from 7075 aluminum; is it still recommended to anodize this alloy even though it was designed for such applications? Does anyone know if or how you can apply cyclic fatigues in COSMOS? Thanx for the help.

  8. #8
    Well first you have to know what fatigue loading the sprocket will see.

    Motorcycle drive sprockets might be made from 7075 but I bet you anything they have some surface treatment. I would HIGHLY reccomend the hard anodize for wear resistance.

    But yea, you can do fatigue analysis in Cosmosworks.
    Colorado FSAE | '05 - '07
    Goodyear Tire & Rubber | '07 - '11
    NASCAR Engineer | '11 - ??

  9. #9
    Go through the COSMOS tutorial using a steel fatigue curve since it has a "knee" on the curve, most aluminum alloys don't have that "knee." About the safety factor, since it is a drivetrain component, every time there's a shift in the transmission there will be a shock loading scenario that will break any low safetyfactor just above 1 with time. As far as fatigue safety factor, just aim for a value of 1!
    Ricardo Valdez
    Matador Motorsports
    Formula SAE
    2005 Drivetrain Engineer
    2006 Project Manager
    2007 Powertrain Engineer

  10. #10
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Welfares:
    And remember when you're doing your load case, take your worst case as the max grip you can get from your tires, not the max output torque, as you will break traction before all that force can be applied to your drivetrain. </div></BLOCKQUOTE>
    No, you need to use max output torque. Your drivetrain and rear wheels have inertia, so they can accept more torque than the grip limit by accelerating.
    Regards, Ian

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