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Thread: Self-navigating rover, and how to ruin an AX-12A

  1. #1

    Self-navigating rover, and how to ruin an AX-12A

    Saturday, there's a race in Oakland, with a track made from yellow intermittent centerline and white solid sidelines.
    (You're allowed to go past the sidelines.)
    This is indoors, and the track is small enough that GPS is not that useful, so vision it is.

    I whacked at my Raspberry Pi code that previously knew how to detect orange cones, to make it detect yellow centerlines.
    You can see that I probably need to tune my steering gains here:

    https://goo.gl/photos/1cH5JVdPD78MssQ79

    Some example media:

    Raspberi pi camera input:

    Click image for larger version. 

Name:	sample.png 
Views:	26 
Size:	140.8 KB 
ID:	7075


    Processed to find "yellow lines":

    Click image for larger version. 

Name:	foo.png 
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ID:	7074

    Re-projected into a virtual "top down" coordinate system:

    Name:  square.png
Views: 85
Size:  600 Bytes


    So, what about the AX-12A?


    Well, when you see the bot slipping so much in the middle, you can kind-of catch the right rear wheel twisting, and then not twisting back.
    It turns out, this was the plastic gears in the AX-12A slipping!
    I don't know why this happens, because the friction from the wheels is not that big, and the wheels are only two inches wide, seven inches tall, with the center of rotation straight above the contact point -- so, at most an inch of torque. The rover weighs less than 12 kilos, but perhaps with enough dynamic force, and the wheel catching on something, and the other wheels slipping, it could push hard enough to slip the gears?

    Anyway, I may have to take some MX-64 from Onyx, or perhaps treat this as an opportunity to test out some XM-430...
    But not before Saturday! Wish me luck :-)

  2. #2

    Re: Self-navigating rover, and how to ruin an AX-12A

    Could it be an angular momentum thing? Does the slipping happen if you spin the wheels in the air with no surface contact?

  3. #3

    Re: Self-navigating rover, and how to ruin an AX-12A

    When the wheels spin/turn free, there's no problem with the gears. It needs significant torque to push the gears out of alignment.
    It didn't happen yesterday at the races; the surface there was a polished concrete floor, so quite slick, which probably helped prevent the wheels from being pulled sideways.
    Also, I had turned down the maximum allowed slew rate for steering; limiting it to 0.15 radians per 1/60th of a second; that might have helped, too!

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