Workshop 11 Notes

October 26, 2017 Workshop 11 Notes

Hinges , Springs and Hair

1. Hinges (see completed example hinges.mb)

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

hinge1a

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

set active rigid body

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

create passive rigid body

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

create hinge constraint

From the front view window, move the hinge symbol so that is is just below the cylinder and sitting directly above the sphere.

hing5a

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

complete hinge constrains

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

apply gravity

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.

hinge 8a

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.

2. Spring (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.

spring

In the FX module, under the "Fields/Solvers" menu, select all of the sphere and "Create Active Rigid Body".
In the FX module, under the "Fields/Solvers" menu, select the pyramid and "Create Passive Rigid Body"
Select a sphere and then the pyramid, and under the "Fields/Solvers" 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. 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 II: 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 "nHair > Create Hair."
3. Select the menu "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.