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Thread: Steering Subassembly Sanity Check

  1. #1
    Associate Engineer
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    Steering Subassembly Sanity Check

    Hello!

    I am designing a steering sub assembly for a roving robot. I am doing most of this from scratch and I wanted to make sure I am on the right track.

    Basically I am fastening a 12mm shaft to an aluminum extrusion with shaft supports. The front fork and a steering gear slide onto the shaft and rotate freely. The steering gear is sitting on an aluminum spacers with thrust washers on either side. Does this seem feasible/appropriate for the application? Designing to bear the weight of a human (~200lbs).

    Thanks in advance for any feedback!!!

    CAD Below:
    steering_screenshot_6_27.JPG

  2. #2
    Technical Fellow jboggs's Avatar
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    The shaft supports you're using are not designed for a thrust load. In fact I don't think their surfaces supporting your thrust bearing are even truly perpendicular to the shaft. Plus they are gripping a very thin area of the extrusion which under load will just deform outward. You say this thing is supposed to support 200 lbs but your picture is unclear, or incomplete. Either way a more thorough understanding is required.

  3. #3
    Associate Engineer
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    jboggs- thanks for your response! Sorry if I did not provide enough information, this project is still in early stages and while I have experience in physics and hobby robotics I am no engineer!

    So you are saying the main issues are #1 the shaft supports I am using are not designed to support thrust loads at all and #2 the contact with the extrusion is not sufficient to transfer the load.

    Does this mean that a better way of mounting the shaft would be directly underneath the aluminum extrusion rather than side-mounted like I have it? Or is there something other than these shaft supports I should be looking for? I am wondering about mounting directly to a plate underneath the t slot with something like this: https://www.mcmaster.com/11445T1

    I am working on modelling what I am talking about and will post a diagram later on.

    Thanks again for your feedback!

  4. #4
    Technical Fellow jboggs's Avatar
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    My comments are based on assumptions I'm making on from the very limited view of your design that you have provided.

    Your shaft support should be rigid enough to absorb the side or bending loads that will undoubtedly occur as the device moves and steers with a 200 lb load above.

    The thrust load should be absorbed by a thrust bearing or washer between two horizontal and exactly parallel surfaces, one stationary and one rotating.

    The McMaster plate you referenced is designed for hanging or tension loads. I doubt if it would handle the bending load. The center hole is threaded, intended for an all-thread rod commonly used as a pipe hanger. Did you intend to thread your shaft to fit it? Also the attachment holes are probably too big for the slots on your extrusion. Check the drawing on the McM website.

    I would suggest you search the extrusion manufacturer's website for accessories designed to fit that extrusion.

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