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Closed Kinematic control of Excavator Boom

asked 2018-04-20 16:41:15 -0500

pchidamb gravatar image

updated 2018-05-09 08:09:42 -0500

Attached is a gazebo model of an excavator .C:\fakepath\BoomJoint.png I am trying to control the boom angle by setting displacement position or velocity for the 2 cylinder-rods sitting on either side of the boom. The 3 revolute joints must then adjust ( boom to upper-house ) and cylinder to upper house ( 2 joints) according to the rod displacement/velocity to move the boom . I am not able to control this with position or velocity control from the joint GUI. With force control the joint move but break at a certain point. What is the optimal way to model this and control this? Should I eliminate the cylinder rod mechanism and just control the revolute joints and use a look up table for the displacement? Or should I reduce the joint stiffness on the 3 revolute joints. Would programmatic control work better than the GUI as it appears that in the GUI 2 commands are fighting each other? (No real improvement with programmatic control !)

I am now trying to adjust the damping and other parameters on the 3 revolute joints to be able to get some compliance on the joints. This appears to be a slow and cumbersome process . Has anyone looked into an automated process of parallel joint tuning ?

I have tried programmatic control with extra damping on the hinge joints. This either seems to be not possible or too difficult to tune !!

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answered 2018-05-29 12:36:12 -0500

pchidamb gravatar image

updated 2018-05-31 10:09:02 -0500

Gazebo supports closed loop kinematic chains. The issue is in the precise placement of the joint axeses to ensure that the joint constraint can be maintained and no collisions occur.

I do wish there was some sort of warning or error message on the command prompt when a constraint is about to "break" and render the model unusable. If some of the experts can throw some light on this I will try to create a new question / development request with an example.

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Asked: 2018-04-20 16:41:15 -0500

Seen: 152 times

Last updated: May 31