Modeling badminton racket as an elastic rod using cable #1386
Replies: 3 comments 7 replies
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I was able to get the rod to behave in a similar way at 100 times larger timestep with the following attributes inside the joint definition of the composite body: <joint kind="main" damping="20" stiffness="2000" armature="0.01"/> If it's too wobbly, bump up the stiffness to 10000<. I'm not sure how specifying stiffness there interacts with the Also, the |
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Heya when you say absolutely rigid do you mean no bend at all? Because that is of course very easy. Decreasing the number of segments will also likely decrease the wobbliness and make it more stable. Also play a bit with the armature arguement, I added that to prevent exploding, but too much can add unneeded inertia to the rod, also making it wobbly. |
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Hey! thank you for your prompt reply, I'll give it a try. Yeap, I thought of having a scale from absolutely rigid one to a flexible stick.
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Yeah, it becomes unstable with lower armature.. |
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As for number of segments - probably I don't need 20. But I'm not clear about that - initially I thought that the more parts - the closer to real rod it will be. What I'm expecting from the flexibility model is that with increasing flexibility the rod is going to be bend more in a bow as a whole. I have some doubts - did I correctly choose cable, maybe I need a rope for such a lengthty object? |
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@quagla can you advise how the elasticity plugin could be used to achieve this kind of high stiffness bending? |
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Another idea - may be Mujoco is not the right emulation framework for my needs as I don't need any contacts or some other complicated niceties. |
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Discussed and solved in #1399. |
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Hi,
I'm an amateur researcher and I'm trying to use MuJoCo for modeling a badminton racket (later with an arm).
I'm not a physicist but I'm a programmer.
I'm aiming at modeling a racket rotating around a wrist for the beginning.
I want to compare speeds of a rigid stick and flexible rod ends and therefore measure the whipping effect.
Later I wanted to model shoulder-elbow-wrist system and find optimal swing using reinforcement learning.
I'm looking for some help with understanding how to simulate an elastic rod of approximate badminton racket characteristics.
I was successfull at rigging up a flexible stick on a hinge which can be rotated using an actuator.
But when I try to play with it, f.i. make it thinner it becomes unstable.
I have to use quite a small timestep to make it work.
Questions:
Can I have a general advice - am I doing right or my simulation can be made more robust?
I need it to be quite effective as I suppose to use it for RL later - so it should calculate quickly.
Can I have an advice on bringing my rod closer to real badminton racket on physical characteristics?
Here is a notebook I'm experimenting with (section Flexible rod based on cable) -
https://github.com/google-deepmind/mujoco#asking-questions
Here is a model from this notebook:
minimal XML
Here is a video of simple simulation of applying force for a second and opposite force later.
flexible.rod.on.a.hinge.mp4
All feedback is appreciated!
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