Specifications

corresponding to a given axis and rotation angle. Therefore, we can specify:

AnySeg UpperArm = {

r0 = {0, 0.3, 0};

Axes0 =RotMat(-90*pi/180, z);

When you reload again you will see that the UpperArm is indeed rotated -90 degrees about the z axis as the

function arguments indicate. Notice the multiplication of the angle by pi/180. AnyBody identifies the word

"pi" as 3.14159... and dividing this with 180 gives the conversion factor between degrees and radians.

Angles in AnyScript are always in radians, but anywhere a number is expected you can substitute it by a

mathematical expression just like in other programming languages.

In the next section we will look at how joints can be used to constrain the movement of segments and allow

them to articulate the way we desire. So if you are up to it, let's continue onward to Lesson 3: Connecting

segments by joints.

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*In rigid body dynamics terminology, a "segment" would be called a "rigid body", but to avoid unnecessary

confusion between the rigid bodies and the total body model, we have chosen to use "segments" for the

rigid parts of the model.

Lesson 3: Connecting segments by joints

Here's an AnyScript file to start on if you have not completed the previous lesson:

demo.lesson3.any

You can think of joints in different ways. We tend to perceive them as providers of freedom, which is correct

compared to a rigid structure. However in dynamics it is often practical to perceive joints to be constraining

movement rather than releasing it. Two segments that are not joined (constrained) in any way have 2 x 6 =

12 degrees of freedom. When you join them, you take some of these degrees of freedom away. The

different joint types distinguish themselves by the degrees of freedom they remove from the connected

segments.

A segment without joints is basically floating free in space. When you connect the segments by joints, you

bind them together in some sense. But the mechanism as a whole can still fly around in space.

Not knowing where stuff is in space can be very impractical so the first thing to do is usually to ground the

mechanism somewhere. Perhaps you remember that the system added these lines somewhere in the top of

the AnyScript model:

AnyFixedRefFrame GlobalRef = {

// Todo: Add points for grounding

// of the model here

}; // Global reference frame

This is actually the definition of a global reference frame of the model. You can think of it as a coordinate

system fixed somewhere in global space. Otherwise, it is just like a segment in the sense that we can add

points to it for attachment of joints and muscles. Lets do just that. Again you can insert the objects with the

object inserter or to save time simply cut and paste the following lines into your model:

AnyFixedRefFrame GlobalRef = {

AnyDrawRefFrame DrwGlobalRef = {};

AnyRefNode Shoulder = {

sRel = {0,0,0};

};

AnyRefNode DeltodeusA = {