DIY robot arm, integration with moveit

Course Support ROSManipulationIn5Days
#1

Hello ,

I recently bought a 6 dof DIY robot arm, 7 servos (with gripper) no feedback

I tried to make an accurate simple urdf, and then with moveit setup assistant i created a moveit package,
since i dont want to use ros control (i am not good on that, and i dont need it), moveit seems to want a FollowJointTrajectory action server that ros control typically handles, however i found an executable that does that for me, I was able then to make another node to listen to the arm_controller/follow_joint_trajectory/goal topic and extract the trajectory points, which i plan with some transformation to send to my rosserial node for execution on the real robot.

Is there a simpler way to do that? i think i will also need to publish a sensor_msgs/JointState topic to publish the new joint_state values (assuming perfect execution) for arm TF.

Also moveit_simple_controller_manager/MoveItSimpleControllerManager plugin seems to not work for me,

so in essence what i should do to easily control a arm without feedback and preferably without ros control?
they way i am currently headed i think the robot should be able to execute the trajectory but it will not respond to action cancel for example etc.

I hope i make sense!!

Thanks

#2

You might want to check out this video series that we did on creating your own robot arm, you might find usefull indications and code to help you there:
VideoRobotArmTutorials

#3

Hello, very helpfull content!!

I managed to use ros control (follow_joint_trajectory) with moveit and gazebo, then i created a node that subscribe to joint_states (from gazebo) and with some transformation (e.g -1.57 - 1.57 to 0-450 plus offset, reverse on some joints) send the position arguments to rosserial for execution on the real robot (quite hacky) Note: i should publish only when joint_states change value as not to overload the arduino due with 50hz

question1: can i use gazebo in headless mode just for the arm on the jetson nano, on a mobile base and kinect that dont live inside gazebo? or should i build a hardware interface so not to use gazebo? I think the example of hardware interface on the documentation is not working and you should use async spinner or RRT loop?? quite confusing not many simple examples??

question2: my arm seems to have depedent the joints 1 and 2 with a pulley, (e.g if joint1 moves down while joint2 stays put the orientation of link2 stays the same) in the urdf i assume indepedent joints, for the arm to work in the same way i have to move joint1 and joint2 together with the command of joint1, plus joint2 with command of joint2, anyway i can handle that with some clever transformations but is there a better way to descibe depedent joints in moveit or urdf? plus i need mechanical reduction for joint2 because of the pulley :slight_smile:

Thanks!!!