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how to get flexible body position and velocity #1674

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Pablo-M-V-99 opened this issue May 17, 2024 · 1 comment
Closed

how to get flexible body position and velocity #1674

Pablo-M-V-99 opened this issue May 17, 2024 · 1 comment
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@quagla
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@Pablo-M-V-99
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Hi,
I'm a student and I'm trying to use MuJoCo for simulating a moving flag.
Here is the model I'm using for the flag:

	<body name="pin" pos="0 0 1.5">
  		<flexcomp name="flag" type="grid" count="9 19 1" spacing="0.05 0.05 0.05" mass="10" radius="0.001">
	    	<edge equality="true" damping="0.001"/>
			<plugin plugin="mujoco.elasticity.shell">
			  	<config key="thickness" value="1e-2"/>
			 	<!--Units are in Pa (SI)-->					
			  	<config key="poisson" value="0"/>
			  	<config key="young" value="3e6"/>
	    	        </plugin>
	  	</flexcomp>
	</body>

At the moment two hems of the flag are locked in place, while the other two are connected to a mocap body that I use to simulate a desired movement for the flag. For the movement I wrote a 5th degree polynomial trajectory, which, in theory, guarantees the movement ends with zero speed and zero acceleration.
However, I would like to implement a test on the velocity of all the elements that make up the flag to be sure the flag is completely still before starting a new movement.
Something like:

for all the elements that make up the flag
if element_speed > threshold_speed
wait until element_speed <= threshold_speed

I have started using Mujoco only recently, so I don't know how I can access this information. Can you help me?
@Pablo-M-V-99 Pablo-M-V-99 added the question Request for help or information label May 17, 2024
@quagla
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quagla commented May 28, 2024 •
edited

Hi @Pablo-M-V-99

These are the arrays you want to look at https://github.com/google-deepmind/mujoco/blob/main/include/mujoco/mjmodel.h#L840

For an usage example, please have a look at e.g.

mujoco/src/engine/engine_setconst.c

Line 216 in 7ca8a62

int b1 = m->flex_vertbodyid[m->flex_vertadr[f] + m->flex_edge[2*i]];

Let me know if it doesn't help!

@quagla quagla closed this as completed May 28, 2024
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