- What information does PredSim use to describe the musculoskeletal dynamics?
- Limitations on the OpenSim model
- Using a very different model
- bodies, joints, coordinates
- inverse dynamics (via OpenSimAD)
- muscles: names, geometry, Hill-type parameters (FMo, lMo, alphao, vMmax, lTs)
- ligaments: names, geometry, parameters (resting length, pcsa force)
- coordinate actuators
- contact elements
- coordinate bounds
- bounds on coordinates and activations
- scale muscle params (extended)
- coordinate stiffness and damping
- coordinate limit torques
- ligament stress-strain model (see template model)
- muscle contraction and activation dynamics - F. De Groote, A. L. Kinney, A. V. Rao, and B. J. Fregly, “Evaluation of Direct Collocation Optimal Control Problem Formulations for Solving the Muscle Redundancy Problem,” Annals of biomedical engineering, vol. 44, no. 10, pp. 2922–2936, 2016.
- muscle activation and deactivation time constants - 0.015s and 0.060s resp.
- ratio of slow twitch fibres for each muscle - used for metabolic energy model
- specific tension of each muscle - used to calculate muscle mass for metabolic energy model
- Your model should not have locked joints. Locked joints would technically require having kinematic constraints, which are not supported. Replace them with weld joints instead.
- Constraints on coordinates will be ignored (eg, coupling constraints).
- Using SimmSplines to describe coordinates (e.g. Yamaguchi knee model) is not supported as the implementation in OpenSim is not really compatible with algorithmic differentiation. Change them to Polynomials instead. AdaptOpenSimModel.m takes care of changing SimmSplines present in joint definitions to polynomials. GeometryPaths can contain SimmSplines.
- Your model needs to have contact elements that interact with the ground. Only SmoothSphereHalfSpaceForce contact forces are supported. You can use AdaptOpenSimModel.m to add contact geometries and forces to your model. You can also scale the radius, stiffness and dissipation of the contact spheres.
- Your model can have any Hill-type muscle model, but it will be implemented as a DeGroote-Fregly muscle.
- Torque/force actuators of the class ActivationCoordinateActuator are supported. You can add actuators by running AdaptOpenSimModel.m. Actuators are not required.
- non-human
- with different joint definitions than the example models (e.g. knee flexion is positive)
Required changes w.r.t. default settings
- S.bounds.default_coordinate_bounds: create different table, or set to empty to use coordinate bounds from opensim model
- S.misc.default_msk_geom_bounds: create different table, or set to empty to use coordinate bounds from opensim model
- S.subject.default_coord_lim_torq_coeff: create different table
- S.bounds.distanceConstraints: prevent limbs from clipping through eachother/torso
- S.subject.base_joints_legs and S.subject.base_joints_arms: identify limbs
Changes in hardcoded parts might be required
- muscle activation and deactivation time constants - 0.015s and 0.060s resp.
- ratio of slow twitch fibres for each muscle - used for metabolic energy model
- specific tension of each muscle - used to calculate muscle mass for metabolic energy model