How to scale the model? #2476

Huzz2022 · 2025-03-07T08:55:28Z

Huzz2022
Mar 7, 2025

Intro

Hi!

I am a researcher in the field of biomechanics and use Mujoco for related studies.

My setup

3.1.6

My question

How to scale the skeletal muscle model of Mujoco? I scaled the mesh under one Body separately, but the joints did not change accordingly, and the positions of the sub-bodies did not change either. How should I directly scale the Body so that the joints between the sub-bodies also change, just like the scaling system of Opensim?

Minimal model and/or code that explain my question

                              <body name="metacarpal3_l" pos="-0.00423 -0.00765 0.0045" quat="0.994135 -0.0472114 -0.085078 0.0472114">
                                <inertial pos="0 0 0" mass="0.01" diaginertia="0.02 0.02 0.01" />
                                <geom name="metacarpal3_l_geom_0" type="mesh" rgba="1 1 1 1" mesh="metacarpal3_l_geom_0_metacarp3_l" />
                                <site name="ECRB_l_ECRB_l_P5" pos="-0.01136 -0.00455 -0.00679" />
                                <site name="FDSM_l_FDSM_l_P8" pos="0.01296 -0.01469 -0.00907" />
                                <site name="FDSM_l_FDSM_l_P9" pos="0.00386 -0.07211 -0.01436" />
                                <site name="FDSR_l_FDSR_l_P7" pos="0.01296 -0.02268 0.00091" />
                                <site name="FDPM_l_FDPM_l_P6" pos="0.01451 0.00527 -0.00679" />
                                <site name="FDPM_l_FDPM_l_P7" pos="0.01015 -0.01287 -0.00727" />
                                <site name="FDPM_l_FDPM_l_P8" pos="0.00688 -0.06838 -0.01159" />
                                <site name="FDPR_l_FDPR_l_P7" pos="0.01137 -0.01777 0.00011" />
                                <site name="EDCI_l_EDCI_l_P7" pos="-0.01279 -0.01697 -0.0166" />
                                <site name="EDCM_l_EDCM_l_P7" pos="-0.01453 -0.06926 -0.00997" />
                                <site name="EDCR_l_EDCR_l_P6" pos="-0.00813 0.00753 0.00667" />
                                <site name="EDCL_l_EDCL_l_P7" pos="-0.00986 -0.02225 0.01731" />
                                <site name="PL_l_PL_l_P4" pos="0.00839 -0.02139 -0.00883" />
                                <body name="middle_1_l" pos="-0.00243 -0.06867 -0.01458">
                                  <inertial pos="0 0 0" mass="0.01" diaginertia="0.02 0.02 0.01" />
                                  <joint name="MCP3_lateral_l" pos="0 0 0" axis="-1 0 0" range="-0.3491 0.3491" />
                                  <joint name="MCP3_flex_l" pos="0 0 0" axis="0 0 1" range="-0.1745 1.571" />
                                  <geom name="middle_1_l_geom_0" type="mesh" rgba="1 1 1 1" mesh="middle_1_l_geom_0_middle1_l" />
                                  <site name="FDSM_l_FDSM_l_P10" pos="-0.00412 -0.04695 -0.0024" />
                                  <site name="FDPM_l_FDPM_l_P9" pos="0.00349 -0.04808 -0.00217" />
                                  <site name="EDCM_l_EDCM_l_P8" pos="-0.0098 -0.01023 0.00325" />
                                  <site name="EDCM_l_EDCM_l_P9" pos="-0.00962 -0.05132 -0.00255" />
                                  <site name="EDCM_l_EDCM_l_P10" pos="-0.00933 -0.05524 -0.00271" />
                                  <site name="LPPH3_marker" pos="-0.01904 0.004881 0.003926" size="0.01" group="4" rgba="1 0.1 0.5 0.5" />
                                  <body name="middle_2_l" pos="-0.00315 -0.04892 -0.002781">
                                    <inertial pos="0 0 0" mass="0.01" diaginertia="0.02 0.02 0.01" />
                                    <joint name="PIP3_flex_l" pos="0 0 0" axis="0 0 1" range="-0.08727 1.571" />
                                    <geom name="middle_2_l_geom_0" type="mesh" rgba="1 1 1 1" mesh="middle_2_l_geom_0_middle2_l" />
                                    <site name="EDCM_l_EDCM_l_P11" pos="-0.00592 -0.00985 -8e-05" />
                                    <site name="EDCM_l_EDCM_l_P12" pos="-0.0033 -0.03477 -0.00022" />
                                    <site name="LMPH3_marker" pos="-0.01247 0.001269 0.004702" size="0.01" group="4" rgba="1 0.1 0.5 0.5" />
                                    <body name="middle_3_l" pos="0.000837 -0.03165 -0.001368">
                                      <inertial pos="0 0 0" mass="0.01" diaginertia="0.02 0.02 0.01" />
                                      <joint name="DIP3_flex_l" pos="0 0 0" axis="0 0 1" range="-0.08727 1.571" />
                                      <geom name="middle_3_l_geom_0" type="mesh" rgba="1 1 1 1" mesh="middle_3_l_geom_0_middle3_l" />
                                      <site name="FDSM_l_FDSM_l_P11" pos="0.00349 -0.00706 -0.00072" />
                                      <site name="FDPM_l_FDPM_l_P10" pos="0.00389 -0.00346 -0.0001" />
                                      <site name="EDCM_l_EDCM_l_P13" pos="-0.00445 -0.00996 -4e-05" />
                                      <site name="LDPH3_marker" pos="-0.01183 -0.01381 0.00136" size="0.01" group="4" rgba="1 0.1 0.5 0.5" />
                                    </body>
                                  </body>
                                </body>

Confirmations

I searched the latest documentation thoroughly before posting.
I searched previous Issues and Discussions, I am certain this has not been raised before.

yuvaltassa · 2025-03-07T11:29:46Z

yuvaltassa
Mar 7, 2025
Maintainer

This is now possible using the mjSpec API, we will add a section to the tutorial showing how to do that soon.
cc @powertj

2 replies

Huzz2022 Mar 17, 2025
Author

Thank you. May I ask where the tutorials related to mjSpec scaling will be published? I saw similar questions in other discussion areas, and the solutions they replied below are to use mjcf. Is this still a relatively good solution?

yuvaltassa Mar 17, 2025
Maintainer

It'll be easier to do it with mjSpec. We will publish this in the model editing tutorial, which should probably now be advertised a bit better 🙂

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How to scale the model? #2476

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Huzz2022 Mar 7, 2025

Intro

My setup

My question

Minimal model and/or code that explain my question

Confirmations

Replies: 1 comment · 2 replies

Uh oh!

yuvaltassa Mar 7, 2025 Maintainer

Uh oh!

Huzz2022 Mar 17, 2025 Author

Uh oh!

yuvaltassa Mar 17, 2025 Maintainer

Huzz2022
Mar 7, 2025

Replies: 1 comment 2 replies

yuvaltassa
Mar 7, 2025
Maintainer

Huzz2022 Mar 17, 2025
Author

yuvaltassa Mar 17, 2025
Maintainer