Structural Stability After Position Control #1961

hea467 · 2024-08-01T21:08:53Z

hea467
Aug 1, 2024

Hi,

I'm a student and I'm trying to use MuJoCo to simulate origami / deformable structures.

I'm looking for some help with positional control of my structure. After assigning a value to the positional actuator at a joint, the other vertices/joints fail to reach an equilibrium and will slowly fall down due to gravity. My goal is to establish an instantaneous equilibrium at all vertices after applying a positional control. What is the best way to do this? So far I have experimented with damping and stiffness, neither of which gave satisfactory results.

Here is a model which explains my question:

<mujoco model="cubes_arm">
	<extension>
		<plugin plugin="mujoco.elasticity.membrane" />
	</extension>
	<include file="scene.xml" />
	<worldbody>
		<body name="v1" pos="0.05 0 0.10500000000000001">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
		</body>
		<body name="v2" pos="0.05 0.05 0.10500000000000001">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
		</body>
		<body name="v3" pos="0.05 0 0.13">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v3_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.45 0.05"  damping = "20" />
			<joint name="v3_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.45 0.05"  damping = "20" />
		</body>
		<body name="v4" pos="0.05 0.05 0.13">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v4_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.45 0.05" damping = "20"  />
			<joint name="v4_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.45 0.05" damping = "20"  />
		</body>
		<body name="v5" pos="0.05 0 0.155">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v5_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.1 0.1" damping = "20" />
			<joint name="v5_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.1 0.1" damping = "20" />
		</body>
		<body name="v6" pos="0.05 0.05 0.155">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v6_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.1 0.1" damping = "20" />
			<joint name="v6_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.1 0.1" damping = "20" />
		</body>
		<body name="v7" pos="0.05 0 0.18">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v7_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.45 0.05"  damping = "20" />
			<joint name="v7_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.45 0.05"  damping = "20" />
		</body>
		<body name="v8" pos="0.05 0.05 0.18">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v8_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.45 0.05"  damping = "20" />
			<joint name="v8_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.45 0.05"  damping = "20" />
		</body>
		<body name="v9" pos="0.05 0 0.205">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v9_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.1 0.1" damping = "20" />
			<joint name="v9_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.1 0.1" damping = "20" />
		</body>
		<body name="v10" pos="0.05 0.05 0.205">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v10_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.1 0.1" damping = "20" />
			<joint name="v10_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.1 0.1" damping = "20" />
		</body>
		<body name="v11" pos="0 0 0.10500000000000001">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
		</body>
		<body name="v12" pos="0 0.05 0.10500000000000001">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
		</body>
		<body name="v13" pos="0 0 0.13">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v13_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.05 0.45" damping = "20"  />
			<joint name="v13_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.05 0.45" damping = "20"  />
		</body>
		<body name="v14" pos="0 0.05 0.13">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v14_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.05 0.45" damping = "20"  />
			<joint name="v14_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.05 0.45" damping = "20"  />
		</body>
		<body name="v15" pos="0 0 0.155">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v15_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.1 0.1" damping = "20" />
			<joint name="v15_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.1 0.1" damping = "20" />
		</body>
		<body name="v16" pos="0 0.05 0.155">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v16_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.1 0.1" damping = "20" />
			<joint name="v16_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.1 0.1" damping = "20" />
		</body>
		<body name="v17" pos="0 0 0.18">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v17_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.05 0.45" />
			<joint name="v17_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.05 0.45" />
		</body>
		<body name="v18" pos="0 0.05 0.18">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v18_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.05 0.45" />
			<joint name="v18_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.05 0.45" />
		</body>
		<body name="v19" pos="0 0 0.205">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v19_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.1 0.1" damping = "20" />
			<joint name="v19_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.1 0.1" damping = "20" />
		</body>
		<body name="v20" pos="0 0.05 0.205">
			<inertial pos="0 0 0" mass="0.001" diaginertia="1.66667e-07 1.66667e-07 1.66667e-07" />
			<joint name="v20_j1" pos="0 0 0" axis="1 0 0" type="slide" range="-0.1 0.1" springdamper="0.1 5" />
			<joint name="v20_j3" pos="0 0 0" axis="0 0 1" type="slide" range="-0.1 0.1" springdamper="0.1 5" />
		</body>
	</worldbody>
	<deformable>
		<flex name="body1" dim="2" body="v1 v2 v3 v4" vertex="0 0 0 0 0 0 0 0 0 0 0 0" element="0 2 1 1 2 3" rgba="0 0 1 0.9" radius="0.001">
			<edge damping="1" />
		</flex>
		<flex name="body2" dim="2" body="v3 v4 v5 v6" vertex="0 0 0 0 0 0 0 0 0 0 0 0" element="0 2 1 1 2 3" rgba="0 0 1 0.9" radius="0.001">
			<edge damping="1" />
		</flex>
		<flex name="body3" dim="2" body="v5 v6 v7 v8" vertex="0 0 0 0 0 0 0 0 0 0 0 0" element="0 2 1 1 2 3" rgba="0 0 1 0.9" radius="0.001">
			<edge damping="1" />
		</flex>
		<flex name="body4" dim="2" body="v7 v8 v9 v10" vertex="0 0 0 0 0 0 0 0 0 0 0 0" element="0 2 1 1 2 3" rgba="0 0 1 0.9" radius="0.001">
			<edge damping="1" />
		</flex>
		<flex name="body5" dim="2" body="v11 v12 v13 v14" vertex="0 0 0 0 0 0 0 0 0 0 0 0" element="0 2 1 1 2 3" rgba="0 0 1 0.9" radius="0.001">
			<edge damping="1" />
		</flex>
		<flex name="body6" dim="2" body="v13 v14 v15 v16" vertex="0 0 0 0 0 0 0 0 0 0 0 0" element="0 2 1 1 2 3" rgba="0 0 1 0.9" radius="0.001">
			<edge damping="1" />
		</flex>
		<flex name="body7" dim="2" body="v15 v16 v17 v18" vertex="0 0 0 0 0 0 0 0 0 0 0 0" element="0 2 1 1 2 3" rgba="0 0 1 0.9" radius="0.001">
			<edge damping="1" />
		</flex>
		<flex name="body8" dim="2" body="v17 v18 v19 v20" vertex="0 0 0 0 0 0 0 0 0 0 0 0" element="0 2 1 1 2 3" rgba="0 0 1 0.9" radius="0.001">
			<edge damping="1" />
		</flex>
		<flex name="body9" dim="2" body="v1 v2 v11 v12" vertex="0 0 0 0 0 0 0 0 0 0 0 0" element="0 1 3 3 2 0" rgba="0 0 1 0.9" radius="0.001">
			<edge damping="1" />
		</flex>
		<flex name="body10" dim="2" body="v5 v6 v15 v16" vertex="0 0 0 0 0 0 0 0 0 0 0 0" element="0 1 3 3 2 0" rgba="0 0 1 0.9" radius="0.001">
			<edge damping="1" />
		</flex>
		<flex name="body11" dim="2" body="v9 v10 v19 v20" vertex="0 0 0 0 0 0 0 0 0 0 0 0" element="0 1 3 3 2 0" rgba="0 0 1 0.9" radius="0.001">
			<edge damping="1" />
		</flex>
	</deformable>
	<equality>
		<flex flex="body1" />
		<flex flex="body2" />
		<flex flex="body3" />
		<flex flex="body4" />
		<flex flex="body5" />
		<flex flex="body6" />
		<flex flex="body7" />
		<flex flex="body8" />
		<flex flex="body9" />
		<flex flex="body10" />
		<flex flex="body11" />
		<joint joint1="v3_j1" joint2="v4_j1" polycoef="0 1 0 0 0" />
		<joint joint1="v3_j3" joint2="v4_j3" polycoef="0 1 0 0 0" />
		<joint joint1="v13_j1" joint2="v14_j1" polycoef="0 1 0 0 0" />
		<joint joint1="v13_j3" joint2="v14_j3" polycoef="0 1 0 0 0" />
		<joint joint1="v3_j3" joint2="v13_j3" polycoef="0 1 0 0 0" />
		<joint joint1="v4_j3" joint2="v14_j3" polycoef="0 1 0 0 0" />
		<joint joint1="v7_j1" joint2="v8_j1" polycoef="0 1 0 0 0" />
		<joint joint1="v7_j3" joint2="v8_j3" polycoef="0 1 0 0 0" />
		<joint joint1="v17_j1" joint2="v18_j1" polycoef="0 1 0 0 0" />
		<joint joint1="v17_j3" joint2="v18_j3" polycoef="0 1 0 0 0" />
		<joint joint1="v7_j3" joint2="v17_j3" polycoef="0 1 0 0 0" />
		<joint joint1="v8_j3" joint2="v18_j3" polycoef="0 1 0 0 0" />
	</equality>
	<actuator>
		<position name="x_act1" joint="v3_j1" kp="200" dampratio="1" ctrlrange="-0.045 0.005" />
		<position name="x_act2" joint="v7_j1" kp="200" dampratio="1" ctrlrange="-0.045 0.005" />
		<position name="x_act3" joint="v13_j1" kp="200" dampratio="1" ctrlrange="-0.005 0.045" />
		<position name="x_act4" joint="v17_j1" kp="200" dampratio="1" ctrlrange="-0.005 0.045" />
	</actuator>
</mujoco>

Here is a screenshot / video, illustrating my question:

Screen.Recording.2024-08-01.at.4.53.28.PM.mov

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Structural Stability After Position Control #1961

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Structural Stability After Position Control #1961

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hea467 Aug 1, 2024

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hea467
Aug 1, 2024