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Flex Modifier
Flex Tests:
Flex is a simple dynamics tool that animates vertices via the Flex modifier. Here are some quick examples of what can be done with flex and brief explanations of the sets ups that were used.

Examples of projects done using flex.

Miscellaneous tests done using flex.
Flag:
Download: flag.rar
Movie: flag.mov

In this first example I have set up a flag blowing in the wind. To make this work you need to have several elements setup.

  1. The flag mesh with enough vertices that it will deform the way that you would like.
  2. A wind force.
  3. A gravity force.

Setup:

  1. Add flex to the flag and add both the wind and gravity to the Forces rollout in flex.
  2. Turn off Use Chase Springs and Use Weights.
  3. Set the solver to Runge-Kutta4 with Samples set to 5. Runge-Kutta4 is a more accurate solver then Euler but will be slower.
  4. Change to SO mode Edge Vertices and select all the vertices that are on the leading edge of the flag. These are the ones that touch the flag poll and are not to move. Or you could select just the top and bottom ones to make it look as though the flag is only tied at the two corners.
  5. Change to SO mode Weights & Springs and select all the verts in the flag.
  6. In the Advanced Springs rollout Enable Advanced Springs checkbox.
    1. In the Advanced Springs rollout open the Option dialog.
      1. Set the Spring type to Hold Shape Springs.
      2. Change the Hold Shape Radius spinner to a value around 18 for the file that I have provided. You need to play with this setting to make sure that you get the right amount of springs. To few and the flag will not keep it shape, to many and it will either blow up or be far to stiff. Note: The second time that you open this dialog it will tall you what the average edge length of the flag is, set the Hold Shape Radius to about three times the average.
      3. Press OK.
    2. Press the Add Springs Button. You can turn on the Show Springs check box and you will see all the springs in the viewport.
    3. Note the Suggested Strength, in this case it will be around 0.038.
    4. Set the Shape Str and the Shape Sway to a value the same as the Suggested Strength to start with.
    5. Turn on Hold Length and set the percent value to around 28%.
  7. With the Shape Str at the suggested strength the flag might not hold together correctly. If this is the case start to increase the Shape Str a bit at a time until the flag starts to hold it shape better.
  8. Adjust the Turbulence in the Wind force to help blow the flag around.

Notes:

Hold Length will try to stop the edges from stretching. At a value of 0% this can cause the flag to blow up as it will start to fold the flag in on itself. Let the flag stretch a little and it will start to act more naturally.

Shape Sway should generally be less then Shape Str and you should start both around the Suggested Strength value and adjust it in very small amounts from there.

Flex Amount needs to stay at a value of 1.0. If changed you will get some interesting results.

Use Chase Springs can be turned on and used to slow the effect. Set Strength to 0.0 and then adjust Sway to the desired value. Remember that Sway is really dampening, the higher the value the more the effect is damped.

There is no way to calculate self intersections so you will see the flag pass through it self. If you want to get far more accurate simulations use the cloth modifier instead.

Ball:
Download: ball.rar
Movie: ball.mov

This example needs a few elements added.

  1. GeoSphere with Segments set to 2. This is the dynamics ball to turn off Renderable in the properties. We will call this Dynamics Sphere
  2. GeoSphere with Segments set to 8. This is the ball that will render. Call this Render Sphere.
  3. Gravity force.
  4. A Deflector.
    1. Bounce 0.01
    2. Friction 100.0
    3. All others to 0.

Setup:

  1. Select Render Sphere and align it to Dynamics Sphere. I have also set the radius of the Dynamic Sphere to be a bit larger to help with objects looking like the are penetrating collision objects.
  2. Apply Skin Wrap to Render Sphere and in Skin Wrap press the Add button and select Dynamic Sphere. The Render Sphere will now be bound to it.
  3. Select Dynamic Sphere and add the Flex modifier and add Gravity to the Forces and Deflector to the Deflectors.
    1. Turn off Use Weights.
    2. Leave Use Chase Springs on but set Strength to 0.0 and Sway to 2.0.
    3. Change the solver to Runge-Kutta4 and set the Samples to 4.
    4. Change to SO mode Weights and Springs and select all the verts.
    5. In the Advanced Springs rollout turn on Enable Advanced Springs.
    6. Choose the Options button.
      1. Change the spring type to Hold Shape Springs.
      2. Change the Hold Shape Radius value to 60.0
      3. Press OK.
    7. Press the Add Springs button and turn on Show Springs to see what was added.
    8. Turn on Hold Length and set it to a value of 0.0.
    9. The Suggested Strength value will most likely be to low but set the Shape Str and Shape Sway to that value and test.
    10. Adjust the Shape Str and Shape Sway up until the ball doesn't blow up and the desired stiffness of the ball is reached.
      1. Turning Shape Str and Shape Sway down and turning Hold Length up will result in a softer ball.

Notes:

It is also possible to use Flex on FFD WSM's. This way a lower resolution calculation can be done on the FFD and a high res object can be bound to the FFD.

Flex can also be used to drive splines

Light Bulb:

Download: swingingLight01.rar
Movie: lightbulbrender.mov

In this example I first push the light bulb with a pbomb force and then with a wind with the turbulance turned up.

Elements for this tutorial are as follows.

  1. A spline the length of the cord all the way to the tip of the light bulb.
  2. A cylinder the length of the cord.
  3. A model of the light bulb.
  4. A gravity force.
  5. A wind force or pBomb. I have used both in the example.

Setup:

  1. The splines needs enough verts along it to be controlled my flex and be able to bend. Add a normalize spline to it and dial the length down till you have about 25 knots in it.
  2. Next move the pivot to the top of the spline and then reset Xform on the spline using the tool in the Utilities panel. This will allow the path deform to work correctly.
  3. Apply a Path Deform WSM to the cylinder that will be used for the cord. Press the move to spline button and make sure the axis is correct.
    1. If the cylinder isn't long enough don't use the stretch in the Path Deform but instead chang the length parameter for the cylinder.
  4. For the light bulb we can't use a Path deform as it would look very strange. So create a point helper and add an Attachment constraint to it and pick the cylinder. Use the Set Position button in the motion panel to attach the point helper to the bottom of the cylinder where the light bulb should be attached. Try to make sure that it is centered.
  5. Align the light bulb to the point helper and link it to it.
  6. To get the nice over lapping animation on the light bulb and to make it feel heavier then the cord we will need to have the light bulb look at the end of the spline.
    1. Create another point helper and this time add a Path Constraint to it and select the spline.
    2. Delete the frist key in the Path Constraint so that the point helper drops to the bottom of the spline.
    3. Select the light bulb and add a Look At Constraint to it and have it look at the second point helper.
  7. Now for setting up Flex.
    1. Add Flex to the spline.
    2. Turn off Use Weights.
    3. Set the Strength to 0.15 and Sway to 0.64.
    4. Set solver type to Runge-Kutta4 with samples at 3.
    5. Change to Edge Vertices SO mode and select the very top vertex in the spline.
    6. Change to Weights & Springs SO mode and select all the verts.
      1. Enable AdVanced Springs in the Advanced Springs rollout.
      2. Select Options and change to Hold Shape Springs with the Hold Shape Radius at around 7 for the example that I created. If you spline is longer or shorter or has more or less verts you will have to adjust this.
      3. Adjust the Shape Str and Shape Sway to the Suggested Strength value to start with.
      4. Turn on Hold Length and set it to about 7 to 10. We need it to stretch a bit or it will just start to curl up.
    7. Add gravity and wind or pbomb to the Forces menu and scrub the time line.
    8. Adjust the Shape Str and Shape Sway up slowly until you get the desired results.