ROS Answers: Open Source Q&A Forum - RSS feedhttps://answers.ros.org/questions/Open source question and answer forum written in Python and DjangoenROS Answers is licensed under Creative Commons Attribution 3.0Tue, 12 Nov 2019 14:30:38 -0600linear actuator with freely rotating joints at each endhttps://answers.ros.org/question/178974/linear-actuator-with-freely-rotating-joints-at-each-end/Hi All,
I am wanting to create a URDF model that models a linear actuator (a hydraulic ram) that is free to rotate at each end (i.e. the only aspect you control is ram length). The closest match appears to be a prismatic joint, but this joint requires an `axis` parameter as well as a length. The scenario I have only requires a length as the axis is constrained by the kinematics of the joint and changes continually with linear actuator length.
I can already get an angle measurement by other means, but I would also like to be able to calculate the angle from linear actuator length alone, and conversely calculate the required actuator length from angle targets using the standard transform libraries in ROS (or MoveIt!).
Thanks,
BartSun, 29 Jun 2014 18:33:07 -0500https://answers.ros.org/question/178974/linear-actuator-with-freely-rotating-joints-at-each-end/Answer by mlautman for <p>Hi All,</p>
<p>I am wanting to create a URDF model that models a linear actuator (a hydraulic ram) that is free to rotate at each end (i.e. the only aspect you control is ram length). The closest match appears to be a prismatic joint, but this joint requires an <code>axis</code> parameter as well as a length. The scenario I have only requires a length as the axis is constrained by the kinematics of the joint and changes continually with linear actuator length.</p>
<p>I can already get an angle measurement by other means, but I would also like to be able to calculate the angle from linear actuator length alone, and conversely calculate the required actuator length from angle targets using the standard transform libraries in ROS (or MoveIt!).</p>
<p>Thanks,
Bart</p>
https://answers.ros.org/question/178974/linear-actuator-with-freely-rotating-joints-at-each-end/?answer=337496#post-id-337496You could model your setup as two or three co-located passive rotational joints at each end of the linear joint. That said, i'm not sure how you would use MoveIt or ROS to get the angle of such an under constrained robot.
Tue, 12 Nov 2019 14:30:38 -0600https://answers.ros.org/question/178974/linear-actuator-with-freely-rotating-joints-at-each-end/?answer=337496#post-id-337496