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Forces acting on motorcycle swingarm

  1. Apr 12, 2017 #1
    Hi all,

    For my final project at university, I am required to design a new swing arm for a Gs500 Motorcycle. I have come up with a C sectional concept when regarding the side beams and will insert X shaped reinforcement throughout the areas of less strength.

    My main problem is inputting the model to FEA analysis. I am abit confused about what forces exactly are acting on the swingarm and where exactly they are applied. So far:

    ,
    1. I have calculated the rear shock force and it's vertical/horizontal components. Would I be correct in assuming they act directly on the middle of the rear shock pivot?

    2. I have calculated maximum acceleration as 9.54m/s^2 and the resultant force this acceleration generates. I am confused again on where exactly this load is acting on the swingarm?

    3. I have calculated the forces from cornering at high lean angle and assume they would be acting somewhere around the midpoint where the two arms join but not sure where exactly?

    Furthermore, I have heard about a lateral load and moment that acts upon the swingarm but have found no literature on how to calculate the values and again where exactly they are acting?

    I was wondering if anyone could help me out; mainly with the positioning of everything perhaps on a FBD? Statics has always been one of my weak points and I cannot seem picture it all in my head.
     
  2. jcsd
  3. Apr 12, 2017 #2

    Nidum

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    Please post a picture of the complete Gs500 with standard swing arm and a drawing of your proposed modifications to the swing arm .
     
  4. Apr 12, 2017 #3
    Hi again,

    I have attached below 1picture of my gs500 with the stock swingarm in place. The other picture shows a rough draft of my concept . As you can see, the two arms are made into C sectional beams where a titanium plate with an axle insert will clamp against the end of the arm to hold the axle. I imagine the design as it is will not work in FEA software and thus I will have to add some reinforcement in the c sectional area so I am not sure what the exact design will come out as after.

    I just want to get these calculations out the way first so that I can actually see how my model responds to the loads and change it with some sort of solid feedback.
     

    Attached Files:

  5. Apr 12, 2017 #4

    berkeman

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    Can you show a mechanical drawing view of the swingarm and rear suspension? You might be able to find one with Google Images, or from an on-line Service Manual.

    Where did you get the exact dimensions of the tie points for the swingarm that you are using in your new design?
     
  6. Apr 12, 2017 #5
    I attached
    I reattached the photos in my last post to clearly show my design and swingarm.

    I've had a good look around for a mechanical drawing of my swing arm to no luck unfortunately. One thing I have found is another similar swing arm analysis in which the user, similar to me, has calculated the corresponding x and y forces from the rear shock acting on the pivot point. Attached are the photos of his force calculations.

    Then I'm assuming the pressure hes drawn in there on the axle insert is related to the maximum braking/accelerating forces which I have calculated? If that was the case, he must have used an area on which the maximum braking/accelerating force acts upon but I do not know which area to use. Also in the second image, I have dome something similar in calculating the x and y forces of the loads during cornering but this is where I get very confused on how I would input this on to the model in terms of location. Would it be an x and y force acting on the part which joins the two arms or on each arm itself? I'm assuming there would be some sort of lateral imbalance and moment acting somewhere as well?

    Going back to his paper, he calculates the horizontal components of the cornering loads as lateral imbalance and the vertical components as torsional imbalance but does not indicate where they are acting exactly. http://inpressco.com/wp-content/uploads/2016/10/Paper61270-274.pdf Here is the paper if anyone can understand what they have done exactly?
     

    Attached Files:

  7. Apr 12, 2017 #6

    Nidum

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    Google and Google Images searches on 'motorcycle frame design' bring up large amounts of technical information and some good illustrations .
     
  8. Apr 13, 2017 #7

    berkeman

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    Staff: Mentor

    This tutorial video should help you visualize some of the forces acting on the swingarm. Pay close attention to the forces involved in the riders recovering from high-speed instabilities, and the unique force vectors on the swingarms after the 2 riders cross the finish line together...

    :smile:
     
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