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Topic: how do you model a flexible/elastic revolute joint in simmechanics (urgent please)
Replies: 1   Last Post: Aug 27, 2014 6:30 PM

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jphoton

Posts: 4
Registered: 8/22/14
how do you model a flexible/elastic revolute joint in simmechanics (urgent please)
Posted: Aug 22, 2014 11:45 PM
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I have a rigid body model of a robot and I have successfully implemented a trajectory using motions (position, velocity and acceleration). It runs fine in forward and inverse dynamics mode. (see figure below)
Then I added joint flexibilities like so; ONE joint is modeled using a rigid revolute joint connected to a dummy part (of negligible mass and inertia) connected to another revolute joint with spring & mass damper input. I have put reasonable values for K. (see figure below)
Now problems; 1. when I run the simulation with a damping coefficient (b) of 0, the joints simply oscillate all over the place and hence don't follow my trajectory at all! (its almost like letting it fall under gravity). 2. If I put a high damping coefficient, it runs VERY slowly and it kind of follows the trajectory but the error still seems too large and I'm sure the real robot wouldn't have this kind of error. 3. Finally, it doesn't run in inverse dynamics mode. It gives an error saying all the joints need to be kinematically actuated. I presume this is because of the joint with the spring and damper but that cannot be actuated or the model won't make sense.
Where am I going wrong?? :-(

Figures can be found in the post at this link:
http://www.mathworks.co.uk/matlabcentral/answers/147754-how-do-you-model-a-flexible-elastic-revolute-joint-in-simmechanics-urgent-please

Thanks.





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