Specifications

82
And running the ModelInformation operation will give the following feedback:
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3) List of reaction forces:
0: Main.ArmModel.Jnts.Shoulder.Constraints.Reaction(5 active of 5 reactions)
1: Main.ArmModel.Jnts.Elbow.Constraints.Reaction(5 active of 5 reactions)
2: Main.ArmModel.Drivers.ShoulderMotion.Reaction(1 active of 1 reactions)
3: Main.ArmModel.Drivers.ElbowMotion.Reaction(1 active of 1 reactions)
Total number of active reaction and driver forces: 12
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- indicating that the model is precisely statically determinate with 12 reactions corresponding to the 12 rigid
body degrees of freedom.
Having familiarized ourselves with the ModelInformation study, let us proceed to SetInitialConditions in the
next lesson
.
Lesson 2: Setting Initial Conditions
Before we look at the SetInitialConditions study, let us just notice that when the model is loaded, the
segments of the model are positioned in space according to their definition in terms of the r0 and Axes0
properties in each segment's definition. These are called the load-time positions.
In the figure below, the user has tried to position the forearm and the upper arm approximately at the right
positions and angles at load time. This is always a good idea, but it is almost impossible to get them
completely in place, and it is not necessary. Indeed, in more complicated models, you can often find the
segments and muscles in a big mess at load time. Typically, you will want to see what the model looks like
when it has been assembled correctly for time step 1. This is what the SetInitialConditions operation is for.
The load-time positions of segments in a simple arm model. Notice that the forearm and upper arm do not
meet correctly at the elbow joint.
When you run the SetInitialConditions operation, it will attempt to put the model in the position is has at