• April 18, 2014 at 15:42 #5962

    I’m looking for tips from engineers to improve the stiffness of the robot arm. Right now the arms are shaped like I-beams because I don’t know any better.

    Ideas?

    May 7, 2014 at 01:10 #6466

    Out of curiosity, what are you trying to acheive here? Is the acrylic bending a noticeable amount?
    If you’re looking for “stability”, then you need to
    – reduce the strain on the servos (or use bigger servos) by adding counter-balance springs
    – increase the mass (use thicker plates, or aluminum, or sandwich the material

    May 7, 2014 at 01:51 #6467

    What do you mean when you say stability? I get a lot of overshoot/undershoot when I move the machine. I suspect a large part due to constant velocity /infinite acceleration.

    May 8, 2014 at 15:32 #6468

    yes the constant velocity is definately a problem. The use of steppers probably dosen’t help either.

    But I think the biggest improvement you can get is move to larger diameter bearings. Large enough that you don’t run a shaft through them, something like a 3″ inner diameter and a thin-ish wall. right now the bending of the bearing and support thereof are the weakest link.

    Probably the arm is stiffer than any other part of your assembly.

    The increase in mass is to make sure small vibrations get damped out.

    May 8, 2014 at 20:13 #6469

    3″? Wow! That would be a big elbow.

    Does the stiffness scale linearly or is it a power function?

    Something like this slew bearing, perhaps?

    https://www.marginallyclever.com/wordpress/wp-content/uploads/2014/05/Capture2.png

    May 13, 2014 at 17:14 #6470

    It’s a power function (well, square function). Stiffness goes up with Radius^2.
    The slew bearing is the right idea but not the right bearing type for the other joints (other than the base joint). For the base joint the slew bearing is correct since usually you preload it so that it’s always in compression (which is where slew bearings are strong). You cannot apply any tension or radial load to a slew bearing since it is not designed for it.
    For the elbow, wrist, etc, you can use thin section needle bearings combined with a pair of standard rolling ball bearings, or just use ball or thrust bearings.

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