Workshop 16 Notes

ALAR 6712 Studio Workshop Spring 2011

Workshop 16 Notes, April 28, 2011

Hinges, Springs and Hair

PART I: Hinges and Springs

1. Hinges (see completed example hinges.mb)

Create a horizontal cylinder polygon hovering above four equidistant sphere polygons as follows.

In the Dynamics module, under the "Soft/Rigid Bodies" menu, select all of the spheres and "Create Active Rigid Body"

In the Dynamics module, under the "Soft/Rigid Bodies" menu, select the cylinder and "Create Passive Rigid Body"

Select a sphere and then the cylinder, and under the "Soft/Rigid Bodies" menu select the "Create Hinge Constraint" option.

From the front view window, move the hinge symbol so that it is on the center axis of the cylinder and sitting directly above the sphere.

Do the same operation to create hinges for all the remaining spheres.

Select all the spheres and under the "Fields" menu apply a "Gravity" field.

From the front view, adjust the location of the right-most sphere above and to the upper right of the downward location such that it will swing into the three other spheres. Change the animation to 1000 frames and play it. Note that you may need to adjust the location of the right-most sphere a few times to ensure that it hits the other three-spheres directly.

Next, select the attributes editor for the right-most sphere, select the "rigidBody" tab ("rigidBody4" in this example) and:

Set the "Mass" to 1 and the "Bounciness" to 1.2.
For the left-most sphere, set the "Mass" to 1 and the "Bounciness" to 1.2.
For the two middle spheres, set the "Mass" to 1 and the "Bounciness" to 1.0.

Assign reflective polished steel-like materials to the cylinder and spheres. Play the resulting animation.

II. Springs (see completed example spring.mb)

Create an upside down polygon pyramid sitting above the ground and a sphere sitting below it in a new scene file.

In the Dynamics module, under the "Soft/Rigid Bodies" menu, select all of the sphere and "Create Active Rigid Body".
In the Dynamics module, under the "Soft/Rigid Bodies" menu, select the pyramid and "Create Passive Rigid Body"
Select a sphere and then the pyramid, and under the "Soft/Rigid Bodies" menu select the check-box adjacent to the "Create Spring Constraint" option, and within the "Constraint Options" dialog box, set "Stiffness" to 5.0, "Damping" to 0.0, and "Rest length" to 1.0, and then select the "Create" button.

Note that the pyramid may invert to a right-side up position. If this occurs, select the Scale tool and reset it so that it is upside-down.
Add lights and materials to the model similar to the previous example of the cylinder and spheres.
Set the animation to 500 frames and play the resulting animation.

Select all the sphere and under the "Fields" menu apply a "Gravity" field. Change the "Stiffness" attribute of the spring to 2.0. Play the animation again and see the result.

PART III: HAIR

1. SIMPLE CASE. (Techniques developed after those described in The Secrets of the Pros, By Kundert-Gibbs and Dariush Drakhshani, Sybex Inc. 2005) The resulting animation is contained in the scene file hairball.mb.

1. Create a NURBS sphere.
2. With the sphere still selected, choose Hair > Create Hair.
3. In the dynamics menu, select Solvers > Interactive PLayback.
4. Create 100 frames
5. Now give some movement to the sphere, keyframing it in two locations at fame 0 and frame 30, and observe the hair performance.
6. Add keyframed scaling to the sphere surface. Keyframe it at a different scale at frame 60, and observe the hair performance.
7. Add keyframe rotation to the sphere surface. Keyframe it at a different rotation at frame 90, and observe the hair performance.
8. Select the hair and enter the attributes editor for HairSystemShape node (e.g., HairSystemShape1).
* In Clump and Hair Shape, change hairs per clump to 20. (increases strands of hair).
* In dynamics, under Solve, change Stiffness to 0.05 and replay the animation. (lowering the number increases flex in hair).
* In dynamics, under Solve, increase iterations to 6 and replay the animation (increases the iterations per time-step increasing accuracy and render time).
* In dynamics, under Forces, increase drag to 0.1 (indicates drag on hair relative to folicle. simulates friction with air - similar to water). Play the result.
* Under multi-streaks, change multi-streaks to 3 and render the result.

WE WILL SKIP THE REST OF THESE EXAMPLES BELOW IIN THE WORKSHOP UNLESS THERE IS UNEXPECTED TIME

2. ROPE 1 (Techniques developed after those described in The Secrets of the Pros). The resulting animation is contained in the scene file rope1.mb.

1. Draw an ep curve along the negative x-axis, placing points at -12 units, -8 units, -4 units and the origin.
2. Repeat this for the positive x-axis beginning at the origin. Select this second curve, and go to Edit Curves/Reserve Curve Direction. (Or, begin this curve in the reverse direction starting at 12 units, 8 units, 4 units and the origin).
3. Select both curves, and in the Dynamics module, select Hair > Make Selected Curves dynamic.
4. Both hairs are now dynamic under a single hair system.
5. In outliner, select hairSystem1Folices, select the plus sign, open the attribute editor for follicleShape1, set the point lock system to Base in the channels box.
6. Repeat step five for follicleShape2.
7. Playback animation for 60 frames, and the center of the rope should appear to drop below the origin.
8. Goto frame 60, and under Hair select Display> Current Position (this depicts the active dynamic position of the hair.)
9. To visualize the rope, create a small nurbs circle in the x-y axis from the side view window.
10. Ensure that the History option is on. Select the circle and the first hairSystem1OutbputCurve (curve3), and under Sufaces>Extrude, set style to "Tube", result position to "At path", Pivot to "Component", Orientation to "Profile Normal", and Output to Nurbs, and Apply the tool.
11. Repeat this for the second hairSystem1OutbputCurve curve (curve4).
12. Within the Outliner, select hairSystem1, and then, in the Attribute editor, select the tab for hairSystemShape1.Continuing in the Attribute editor, select the Dynamics tab, and then the Solve sub-tab, and change "Stiffness" to 0.003. Also in the Dynamics tab, under the Forces section, change gravity to 5.
13. In components mode, select the CVs at the origin from the two curves, and goto Hair>CreateConstraint>Hair to Hair.
14. Play 100 frames.
15. From the Hair menu, set Start Position to From Current.
16. In outliner, select hairConstraint1, go to frame 149, and right-clicking on the text, in the Channel box, set the key frame Glue Strength to 1.
17. Now go to frame 150, and right-clicking on the text, set the key frame for Glue Strength to 0.
18. Playback the animation and the rope breaks at frame 150.
19. Select hairSystem1 in the outliner, and in the attribute editor under hairSystemShape1, in Turbulance change Intensity to 0.2