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Use the Inverse Dynamics Tool to find a set of generalized forces.
Read the page on How Inverse Dynamics Works to understand how the forces are calculated.
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Read the pages describing the Residual Reduction Algorithm.
Use the RRA Tool to calculate the size of the residuals.
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- In the input pane, set the desired kinematics as the IK motion file (e.g., leg69_IK_stance.mot).
- Check the box to filter kinematics at 6 Hz.
- In the input pane, specify the tracking tasks for RRA (use Stance\leg69_Tracking_Tasks.xml). This file specifies the coordinates to be tracked and the corresponding weights. Use the GUI File Editor or an XML editor (e.g., Notepad++) to view the tasks.
Check "Adjust model". Click on the folder icon, make sure you are in the Stance folder, specify a new model name (e.g., leg6dof9musc_RRA_adjusted.osim), and click Save.
- Make the pelvis the "Body COM to adjust". The center of mass of this body will be adjusted to reduce residuals. Typically, the segment that includes the torso is chosen.
- Specify the time range using your analysis from part A (see Questions: Leg Muscle Force Estimation, Part II, Question A.5).
- Specify an output directory (e.g., <YourWorkingDirectory>\Stance\RRA).
- Go to the Actuators and External Loads tab and choose "Replace model's force set" to replace the model's muscles with residual and joint motor actuators, since we are creating a torque-driven simulation.
- Click the "Edit..." button next to the "Additional force set files" textbox, then click "Add". Click the folder button next to the red textbox and select leg69_RRA_residuals_motors.xml. Click OK.
- Check the External Loads box and specify the file you created for Inverse Dynamics (e.g., leg69_right_GRF.xml).
- Save your settings to an RRA setup file (e.g., leg69_Setup_RRA_stance.xml) and click Run.
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- Re-run RRA with the adjusted model making sure to close and re-open the RRA Tool to ensure the most recent adjusted model is always used.
- Adjust the pelvis COM and mass in accordance with the RRA Tool output messages.
- Increase the tracking task weights for coordinates that show poor tracking.
- Decrease the tracking task weights for coordinates that are within 1 degree, since the optimizer can then use these coordinates to reduce the residual forces.
- Iterate until the requested change in pelvis mass is less than 1 kg and the residual forces and coordinate errors follow the suggested thresholds in the table at the bottom of the Getting Started with RRA page.
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You should see the pelvis mass stabilize after about 5 iterations. If you are completing this exercise for a course, don't spend a lot of time aiming for perfection; "OKAY" results are okay. |
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- One common way for CMC to fail is when the tool is unable to find a set of muscle forces that can accurately reproduce the joint dynamics. Consider reducing the tracking weights until your run successfully completes. Make sure to re-run RRA and use the adjusted model output from the RRA Tool in CMC when you adjust the tasks.
- Check the troubleshooting tips at the bottom of the Getting Started with CMC page.
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Next: Questions: Leg Muscle Force Estimation Home: The Strength of Simulation: Estimating Leg Muscle Forces in Stance and Swing |