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+# MyoLeg
+
+## General:
+
+The myoLeg mujoco musculoskeletal (MSK) models are generated with taking [Rajagopal's full body gait model](https://github.com/opensim-org/opensim-models/tree/master/Models/RajagopalModel) as close
+reference.
+
+These generated mujoco MSK models have almost identical kinematics, and very similar muscle kinematics (moment arms) and kinetic (forces) properties.
+
+
+## Conversion process:
+
+The myoLeg models were generated using our developed automatic conversion pipeline (will release at June 2023).
+
+Three Conversion steps were taken to generate the myoLeg models from the reference Osim model:
+
+1. Basic element conversion [bone meshes, joint definitions, muscle paths, wrapping objects]
+2. Moment arm optimization [matching the moment arm of each muscle by optimizing how muscles wrap over wrapping objects]
+3. Muscle force optimizaiton [matching the muscle force-length relationship by optimizing muscle parameters]
+
+After the conversion, a manual adjusting process is done to correct the abnormal results.
+
+## Maunal adjustment:
+
+1. Removed wrapping objects for glmax1_l, glmax2_l, glmax1_r, glmax2_r, psoas_l, and psoas_r muscles to avoid the wrapping path jumping. These wrapping objects are:
+	- Gmax1_at_pelvis_l_wrap
+	- Gmax2_at_pelvis_l_wrap
+	- Gmax1_at_pelvis_r_wrap
+	- Gmax2_at_pelvis_r_wrap
+	- PS_at_brim_l_wrap
+	- PS_at_brim_r_wrap
+
+2. Changed the wrapping objects from 'cylinder' to 'sphere' for iliacus_l and iliacus_r muscles to avoid the wrapping path jumping. These wrapping objects are:
+	- IL_at_brim_l_wrap
+	- IL_at_brim_r_wrap
+
+3. Adjusted the 'lmin' of gaslat_l, gaslat_r, semimem_l, and semimem_r muscles to avoid negative muscle forces.
+	- changed from 0.1 to 0.05
+
+4. Adjustments post conversion to optimize for kitnematic and dynamic behaviors
+5. Inertial properties
+6. Dynamics properties of the joints
+
+
+## Contact Geometries:
+
+The contact geometries take the well defined [Yeadon measurement method](https://yeadon.readthedocs.io/en/latest/measurements.html#measurements) as reference. Geometries are very close to the reference but slightly adjusted to fit our MKS mode. Contact properties were optimized for contact rich behaviors.
+
+
+## Issues:
+
+1. Endpoints (markers) below the knee joints have around 1 cm differences between the converted Mujoco and Osim model.
+	- This may due to the constraints defined at the knee translation DoF. In Mujoco model, a polynomial function is used to approximate the Osim lookup table. Differences may generated.
+	- Will look into this approximation to improve the accuracy.
+
+2. Muscle moment arms inside the reference Osim model contains sudden changes (muscle wrapping path jumping), which need to be corrected.
+	- This is why the manual adjustment is needed
+
+3. Vastus muscle moment arms at the knee joint has relatively large differences (same sign, a few cm).
+	- Need to check whether this is caused by the dependend joint constraints at knee.
+	- This moment arm difference also affected the knee extenser muscle force, will look into in future.
+
+4. Muscle forces are not identical between the converted MuJoCo and Osim models, due to the difference in muscle model definitions (stiff vs elastic tendons).
+	- Will investage to implement elastic tendon inside mujoco.
+
+## ChangeLog
+
+**myoleg_v0.51(mj120).mjb**
+- new keyposes added to mark convenient poses.
+
+**myoleg_v0.52(mj120).mjb**
+- Removing the extra body that made the torso twice as heavy. The body now is ~80 kgs.
+
+**myoleg_v0.53(mj120).mjb**
+- Improved collisions. Adding a height field.
+
+**myoleg_v0.56(mj237).mjb**
+- height field adjusted
+- moved to mujoco 2.3.7
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