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Thread: MX/AX servo arm - trouble connecting via ArbotiX

  1. #11

    Re: MX/AX servo arm - trouble connecting via ArbotiX

    Well...about that picture: As I was testing the servos, and did not really expect them to move in unpredictable ways, one of the link brackets broke. And then I took apart the arm to test each servo with DynaManager, so it is not really in a presentable state right now... Bu here are the two parts of it; link 2 is missing atm, bcz broken.



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  2. #12

    Re: MX/AX servo arm - trouble connecting via ArbotiX

    Quote Originally Posted by a_saf View Post
    I will take a look into arbotix_python. That it the first time I hear about it and I had no idea it is used.
    I looked at the arm.launch file and it showed:
    Code:
    <launch>
    
      <node name="arbotix" pkg="arbotix_python" type="arbotix_driver" output="screen">
          <rosparam file="$(find turtlebot_arm_bringup)/config/arm.yaml" command="load" />
      </node>
    
      <node name="gripper_controller" pkg="arbotix_controllers" type="gripper_controller">
          <param name="model" value="singlesided"/>
          <param name="invert" value="true"/>
          <param name="pad_width" value="0.0254"/>
      </node>
    
    </launch>
    Also the package.xml file has a run time dependency.
    Code:
    <package>
      <name>turtlebot_arm_bringup</name>
      <version>0.3.3</version>
      <description>
       turtlebot_arm_bringup provides launch files for starting the drivers for the TurtleBot arm.
      </description>
      <author>Michael Ferguson</author>
      <author>Helen Oleynikova</author>
      <author>Melonee Wise</author>
      <maintainer email="[email protected]">Jorge Santos</maintainer>
      <license>BSD</license>
      
      <url>http://ros.org/wiki/turtlebot_arm_bringup</url>
    
      <buildtool_depend>catkin</buildtool_depend>
    
      <run_depend>arbotix_python</run_depend>
      <run_depend>arbotix_controllers</run_depend>
    </package>

  3. #13

    Re: MX/AX servo arm - trouble connecting via ArbotiX

    Oh, I accidentally deleted my reply to this. So once again, here is my yaml file:

    port: /dev/ttyUSB0
    read_rate: 15
    write_rate: 25
    joints: {
    arm_shoulder_rotation_joint: {id: 1, neutral: 150, max_angle: 300, min_angle: 0, max_speed: 15},
    arm_shoulder_lift_joint: {id: 2, max_angle: 180, min_angle: 0, max_speed: 15},
    arm_elbow_flex_joint: {id: 3, max_angle: 150, min_angle: -150, max_speed: 25},
    arm_elbow_rotation_joint: {id: 4, neutral: 150, max_angle: 300, min_angle: 0, max_speed: 15},
    arm_wrist_flex_joint: {id: 5, max_angle: 150, min_angle: -150, max_speed: 15},
    arm_wrist_rotation_joint: {id: 6, neutral: 0, max_angle: 150, min_angle: -150, max_speed: 15},
    gripper_joint: {id: 7, max_speed: 5},
    }
    controllers: {
    arm_controller: {type: follow_controller, joints: [arm_shoulder_lift_joint, arm_elbow_flex_joint, arm_elbow_rotation_joint, arm_wrist_flex_joint, arm_wrist_rotation_joint], action_name: arm_controller/follow_joint_trajectory, onboard: False }
    }

    And I didn't realize it was running the arbotix_python package. Looking into it now, to see if I can change the ranges a bit to fix this issue. But one thing I am worried, is that if I change the range to be compatible with MX, then the package will not be compatible with AX servos of the arm.

  4. #14

    Re: MX/AX servo arm - trouble connecting via ArbotiX

    Yes, I'm realizing this now, that the information is right there. But I did not really know that I can get it from these files, or what the run-time dependency meant. I think I'm on board now. Thank you.

  5. #15
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    Re: MX/AX servo arm - trouble connecting via ArbotiX

    Interesting little custom arm. Is that carbon fiber?

    Looks like you will be having a fun summer.

  6. #16

    Re: MX/AX servo arm - trouble connecting via ArbotiX

    _ADAM_,

    Yep, carbon fiber brackets. The arm can be improved in a few ways in terms of mechanics, but before I get to mechanics, I am hoping to get everything software fixed more or less

    Thanks!

  7. #17
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    Re: MX/AX servo arm - trouble connecting via ArbotiX

    FWIW, the MX-64 in the shoulder can handle lifting that arm without the gearing. Unnecessary mechanical complexity creates additional points of failure.

    You have probably seen this, but check out the WidowX arm, which use a MX-64 in the shoulder:
    http://www.trossenrobotics.com/widowxrobotarm

  8. #18

    Re: MX/AX servo arm - trouble connecting via ArbotiX

    No, I haven't actually seen this, thanks.

  9. #19
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    Re: MX/AX servo arm - trouble connecting via ArbotiX

    Quote Originally Posted by _ADAM_ View Post
    FWIW, the MX-64 in the shoulder can handle lifting that arm without the gearing..
    I'll go a step further and say I suspect it could rip the teeth right off those plastic gears!

    Quote Originally Posted by _ADAM_ View Post
    Unnecessary mechanical complexity creates additional points of failure.
    That should be carved over the doorway of all engineering schools! Hardware and software!
    Last edited by Brooks; 06-16-2016 at 04:08 PM.

  10. #20
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    Re: MX/AX servo arm - trouble connecting via ArbotiX

    The external gearing with multi-turn mode means you get higher resolution position control and lower running torque requirements/loading, which are both very good for longer arms that need to be extended for any length of time. Metal herringbone gears, or timing belt with metal sprockets, would better than plastic gears by having greater strength and lower backlash, but would also a bit more expensive.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    [git][mech][hack]
    gives free advice only on public threads

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