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Note: This example is compatible with OpenSim version 4.1. |
Overview
In this exercise you will use the OpenSim software to design and simulate a dynamic walker. As a starting point, you will be given a Passive Dynamic Walker Model and an arena with obstacles. The goal of the exercise is to maximize the distance the walker can travel on increasingly challenging terrain by adjusting the model's parameters and adding new model components. You will use the OpenSim graphical user interface (GUI) and Matlab scripting commands to add model components, adjust component properties, visualize dynamic simulations, and make plots of your simulation results.
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Below are some useful (and necessary) resources that you should read before you begin and keep handy while you build your model;
Read the Introduction to the OpenSim API section
- Setup your Matlab environment using instructions from the Scripting with Matlab page.
- Bookmark the Common Scripting Commands page for helpful tips and code snippets
- Read the Guide to Using Doxygen pages and bookmark the OpenSim Doxygen documentation
- Bookmark the API Guide on Doxygen.
- Setup a working folder where you will save and test your model.
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- In the OpenSim GUI, select File>Open Model... to open the WalkerModelTerrain.osim.
- The View panel is used to control the model's visual display. You can move the view camera around the model using a combination of mouse and trackpad gestures.
- In the Navigator panel on the left side of the screen, use the + icon to expand the list of model components. Explore the individual components in the model by clicking on them in the Navigator Panel.
- As you click on each component, scroll through the component's properties in the Property Editor panel underneath the Navigator panel.
- Observe each of the following:
- Bodies: A platform, pelvis, thigh, ans and shank bodies with mass, inertia, and visual geometry.
- Joints: A Planar joint connecting the model with the Platform and Pin joints between all the segmentspin segments' pin joints.
- Contact Geometry: Contact spheres and a contact half space (plane), which are used to generate contact forces.
- Contact forces: Forces that are computed and applied due to the interaction between contact geometries.
- Other Forces: Coordinate limit forces, which enforce the desired range of motion of the joints. Springs and general other forces.
- The Coordinates panel lists the current values of the model's generalized coordinates.
- The values of the coordinates (in meters or degrees) can be changed with the sliders or by entering a value in the left text box.
- The initial coordinate speeds (in meters/second or radians/second) are used as the initial conditions forward simulations. These can be set in the speed text box on the right hand side of each row.
- The value of a coordinate can be locked by toggling the lock icon.
- To reset the model to the default pose, select Poses>Default. You can also uses the Poses menu to change the default pose and add custom poses.
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OpenSim comes with a large library of geometry files for visualizing elements of the human skeletal system, as well as simple generic shapes such as, spheres, cylinders, and boxes. If the base library is not sufficient for your model, it is easy to add additional geometry files. OpenSim can use Geometry types with the following file extensions: .vtp, .stl and .obj. By default, OpenSim looks for Geometry files in the Model's local directory and in the OpenSim Geometry folder. You can add additional locations to look for Geometry..
V. Design and Simulate your own Walker Model
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