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Utilities panel > Utilities rollout > More button > Utilities dialog > Choose Dynamics.
The term dynamics refers to a system of controls that generate keys to produce animation that simulates real-world physics. For example, using standard keyframing techniques to animate a bouncing ball, you create keys that move the ball down to the floor, squash the ball, move the ball back up, and so on.
Using a dynamics system, you assign physical properties to the ball and the floor (such as friction or amount of bounce), specify which object will collide against another object (for example, the ball with the floor), place an effect (such as gravity), in the scene, and then calculate a solution over a range of frames. The result is a number of keys that produce an animation in which the ball drops due to the gravity effect, collides with the floor and reacts naturally based on its surface characteristics.
A very basic simulation would involve creating a sphere and a gravity space warp, adding the sphere to a new simulation, assigning gravity as an effect on the sphere and solving the simulation. The result is that the sphere falls under the force of gravity.
You can use dynamics objects, dynamics space warp deflectors (PDynaFlect, SDynaFlect, and UDynaFlect), and space warp forces such as Gravity and Wind to add complexity to a simulation. You can use a particle stream from a particle emitter as a force on an object: the particles can collide with and be deflected by the object, as well as move it. You can attach special dynamics objects to objects, such as Spring to simulate the effects of a spring.
You can combine effects: Wind, gravity, a spring object, collision, particle deflection and collision, as well as surface properties such as friction, can all work on an object in a simulation. For a full understanding of what dynamics can do, explore this topic and areas of 3ds max that pertain to dynamics.
The Dynamics Utility is the main control center for dynamics simulations. You specify which objects are used in the simulation, what their interactivity is with each other and with the effects in the scene. The simulation is then "solved," generating the keyframes.
The effects of collisions between objects depend on the velocity of the objects and their properties. For collision to work between two objects, each object must have the other object assigned for collision. For example, when bouncing a ball, both the floor and the ball are assigned collisions.
The Material Editor: The Dynamics Properties rollout in the Material Editor lets you assign the dynamics properties to the surface of an object, like friction and bounce. Using a multi/sub-object material, you can have different surface properties at the face level of any object.
Note: You can override material surface dynamic properties with controls on the Edit Object dialog in the Dynamics utility.
Dynamics Objects, Particles and Dynamics, Dynamics Interface: Special objects like Spring and Damper, Space Warp forces like Gravity and Wind, as well as Space Warp deflectors like PDynaFlect can all influence a dynamics simulation. You must create these objects and space warps first in other areas of 3ds max before you can use them in a dynamics simulation. See the following topics for details on their creation and use:
Create panel > Geometry > Dynamics Objects
You can use the Spring and Damper objects for dynamics effects.
Create panel > Space Warps > Particles and Dynamics.
Effects (forces) are special space-warp objects that emulate natural phenomena, such as wind or gravity. In a dynamics simulation, you must place gravity in the scene if you want the objects in your simulation to fall.
Create panel > Space Warps > Dynamics Interface.
The Dynamics Interface space warps can cause particles to deflect from and affect an object in a simulation.
Combine Keyframed Objects in a Simulation: Keyframe an object and have it interact with other objects in a dynamics simulation by turning on the This Object is Unyielding check box in the Edit Object dialog for the keyframed object. Objects can bounce off of a keyframed sphere for example.
Dynamics Controller: When a Dynamics simulation is solved, a new list controller is created that holds both the generated dynamics keys and the original keys. This allows you to restore your original keys, if necessary. Undo is not supported by Dynamics.
For example, if a sphere is bouncing in a Dynamics simulation, and the sphere already contains position keys from a previous animation, the following tracks display in Track View:
Transform
Position
Dynamic Position Controller
Old Position
Rotation
Dynamic Rotation Controller
Old Rotation
Example: To create a basic simulation of bouncing boxes:
Create a thin box in the Top viewport.
Have the box almost the same height and width as the viewport. This will act as the ground plane.
In the Front viewport, create six small boxes above the "ground" box.
Position some of them to collide with each other when they fall.
On the Create panel > Space Warps > Particles and Dynamics > Object Type rollout, click Gravity.
Drag in the Top viewport to create a Gravity gizmo.
On the Utilities panel, click Dynamics.
On the Dynamics rollout, click New.
Dynamics00 appears in the Simulation Name field.
Click Edit Object List.
The Edit Object List dialog displays.
Select all the boxes in the dialog and click the > button, then click OK.
All the objects are moved to the Objects in Simulation list on the right side of the dialog.
On the Dynamics rollout click Edit Object.
The Edit Object dialog displays.
In the list under Object, select Box01.
Turn on Dynamics Controls group > This Object is Unyielding.
Click Ok to close the Edit Object dialog.
The "ground" box won’t move when the other objects collide with it.
On the Dynamics rollout, in the Effects group, turn on Global Effects.
Click Assign Global Effects, select Gravity in the dialog and click > (right arrow), then click Ok.
This assigns gravity to all objects in the simulation.
On the Dynamics rollout, in the Collisions group, turn on Global Collisions.
Click Assign Global Collisions, select all the boxes in the dialog and click > (right arrow), then click OK.
Collisions are active for all the boxes.
Turn on Update Display with Solve, and then click Solve.
In the viewports the objects fall and collide with each other and the ground plane.
Turn on the Auto Key button, move the Time Slider to frame 15, and then select and move the "ground" box upward along the Z axis.
The ground will "move" during the simulation.
Click Solve.
The keyframed "ground" box moves up and collides with the boxes. The ability of a keyframed object to be part of a simulation is one of the useful features in 3ds max. You could use this capability to strike a ball with a bat, for example.
For further experimentation, create a spring object in Create panel > Geometry > Dynamics Objects and attach the ends of the spring object to two of the boxes and then solve the simulation. The spring will stretch and follow the bouncing boxes.
You can use the space warps in Create panel > Space Warps > Dynamics Interface, such as SDynaFlect (Spherical Dynamics Deflector) to cause a particle stream to "push" an object in a dynamics simulation.
To remove the dynamics tracks and restore the original animation tracks in Track View:
When you solve a dynamics simulation, 3ds max creates a list controller that holds both the generated dynamics keys and the original keys. This lets you easily restore the original keys. Undo is not supported by Dynamics.
To layer simulations, reverse this method. In other words, after you've solved the first simulation, copy its controllers to the old tracks, and then set up the next level of the simulation. The new simulation will base its actions on the previous one instead of overwriting it, as it normally does. You can repeat this as many times as you like to layer simulations ad infinitum.
Since Undo is not supported by Dynamics, you can also use Hold and Fetch in it’s place.
In Track View, open the Position track for an object animated by a dynamics simulation.
Select the Old Position track, and click Copy Controller on the Track View toolbar (the second button from the left).
Select the Position track (the parent), and click Paste Controller (to the right of Copy Controller).
Click OK in the Paste dialog.
The two sub-tracks and the Position parent track are replaced by a single Position track containing the original keys that were in the Old Position track.
Repeat the above steps with the Rotation track.
To set up dynamics:
Assign materials to the objects included in the simulation and adjust the surface characteristics in the Dynamics Properties rollout of the Material Editor. (For a bouncing ball, you'd use this to create a rubber-like surface.)
If you're using a linked hierarchy, set the Move and Rotate locks in the Hierarchy/Link Info panel to limit the motion and rotation of the linked objects.
Create space warp effects in the scene where needed. (For a bouncing ball, you'd need a Gravity space warp.)
Use the Dynamics utility to create a new simulation. Specify which objects are included in the simulation, which effects influence which objects, and which objects should collide with which. (For the bouncing ball, the ball and the floor are in the simulation because one collides with the other. You assign the ball the floor to collide with each other, and assign the gravity effect to the ball.)
Use the Dynamics utility to specify the range of frames to which keys will be generated, and to calculate the animation and generate the keys. (In the case of a bouncing ball, a number of position and rotation keys are generated for the ball.)
Play the animation to see if the effect is what you were looking for. If one or more objects fly off into space, or move through objects they should have bounced off, it's likely that you need to increase the Calc Intervals Per Frame value.
To reduce the number of keys generated by the Dynamics utility:
When you solve a dynamics simulation, Position and Rotation keys are generated at every frame of the specified range for every object affected in the simulation. Not only does this result in an excess of keys for later editing, but it can increase the size of the .max file tremendously. The following steps show how to reduce the number of keys using Track View.
After solving the simulation, check the animation to make sure it's what you want, and then save that version of the scene.
Deselect every object in the scene.
In the Dynamics panel > Objects in Simulation group, click the Select Objects In Sim button.
All objects included in the simulation are selected.
Open a Track View window, and then set its filter to show Animated Tracks Only and Selected Objects Only.
Right-click the top object in the hierarchy list (Objects), and choose Expand All.
Track View now shows all tracks in the simulation that have keys.
Go to Edit Time display mode and select all of the tracks containing keys (or right-click over the hierarchy, and choose Select All).
Double-click any key to select all keys in all tracks.
Click the Reduce Keys button, set the Threshold to what you want, and then click OK.
All selected keys are reduced.
Save the reduced version of the scene either under a new name, or by replacing the original file.
To use linked hierarchies in a simulation:
When linked hierarchies are included in your simulation, you must set locks for the children in the simulation to confine the dynamics results to specific axes. Do this on the Hierarchy panel > Link Info > Locks rollout.
The Locks rollout contains three rows of check boxes affecting the XYZ axes of the three possible transforms: Move, Rotate, and Scale. The Scale transforms are ignored, and only the Move and Rotate locks are used. When a check box is turned on, that axis of the specific transform is locked.
When you manipulate a forward-kinematics hierarchy directly using the Move or Rotate tools, you might not bother with the Link Info locks, because you can specify axis constraints using the X, Y , Z, and XY buttons in the toolbar. However, when you use that same hierarchy in a dynamics simulation, where there are several forces at work (gravity, wind, collisions), the only thing that maintains the linkage between the objects is the locks you set in the Link Info > Locks rollout. As a result, no matter what combination of Move and Rotate locks you use, you'll always want at least one Move lock in place, or your objects won’t really be linked.
The following lists all of the combinations of Move and Rotate locks that make sense within a dynamics simulation, and the effect on the link of such combinations. An asterisk (*) indicates those combinations that are more typically useful.
The format of this list as follows:
X = check box on.
O = check box off.
One group of settings is made up of the three Move check boxes over the three Rotate check boxes. Here's an example:
XXO = X and Y Move check boxes on, and Z off.
OXO = Y Rotate check box on, and X and Z off.
1 Move Lock: Turn on any single Move. (This is like a long pin sliding in a loose, long slot.) The joint can transmit force in one direction only. The objects can slide with respect to each other in two directions and rotate freely.
2 Move Locks: Turn on any two Moves. (This is like a sliding ball joint; a freely rotating joint at the end of a sliding shaft, which can slide and rotate in a hole.)
* 3 Move Locks: Turn on three Moves. (This is like a ball joint, or the theoretical "pin joint" of the statics and dynamics texts, in that it transmits any force but never transmits any torque.)
1 Move + 1 Rotate (unique): Turn on any one Move and any one Rotate, but not in the same column. (This is like two long pins, parallel, sliding in a single long slot.) The joint can transmit force in one direction only and restrain rotation about the axis of the "pins." This combination is of limited application.
2 Moves + 1 Rotate (matching): Turn on two Moves, plus one Rotate turned on that's in the same column as one of the selected Moves. (This is the same as 1 Move + 1 Rotate, above, except that the pins can no longer slide vertically in their slot.) If the assembly rotates so that one pin travels further into the slot, the other must ride higher in the slot. This is of limited application. The possible check box combinations are: XXO XXO XOX XOX OXX OXX OXO XOO XOO OOX OOX OXO
* 2 Moves + 1 Rotate (complementary): Turn on two Moves, plus one Rotate that's not in the same column as any of the selected Moves. (This is a sliding universal joint like the splined output shaft between the automatic transmission of a rear-drive car and the drive shaft.) It can transmit torque and constrain translation in two directions, both orthogonal to the axis of rotation. The possible check box combinations are: XOX XXO OXX OXO OOX XOO
3 Moves + 1 Rotate: Turn on three Moves plus one Rotate. (This is a universal joint without the sliding.) It's typical of automotive applications where the rear axle is located with the trailing driveshaft. This is an uncommon application.
* 1 Move (complementary) + 2 Rotates: Turn on one Move that's complementary to two Rotates. (This is like a hockey puck on ice.) The joint can slide anywhere on a plane, but cannot fall or tip, and it cannot leave the surface of the plane. The possible check box combinations are: XOO OXO OOX OXX XOX XXO
2 Moves (one complementary) + 2 Rotates: Turn on two Moves, one of which is complementary to one of the two Rotates that are selected. (This is like a hockey puck with a nail through it, and the nail is sliding along a groove in the ice.) It's free to travel in one direction, and to rotate about an orthogonal axis. One possible check box combination is: XXO XOX
* 2 Moves + 2 Rotates (matching): Turn on two Moves and two matching Rotates. This results in a sliding axle (a shaft that can both slide in and out of a hole, and rotate with the hole). The clear Move and Rotate axis specifies the axis along which the joint can slide and rotate. The possible check box combinations are: XXO XOX OXX XXO XOX OXX
* 2 Moves + 3 Rotates: Turn on two Moves and all three Rotates. (This is a prismatic or sliding joint.) The joint transmits no torque, and force in only one direction. You can use this in conjunction with the Push effect to make a hydraulic cylinder. The one clear Move specifies the axis of movement.
* 3 Moves + 2 Rotates: Turn on all three Moves, and any two Rotates. This is an axle (the most common type of joint.) The one clear Rotate specifies the axis of rotation.
All Locked: All six check boxes are on. This is a completely rigid joint.
Contains all of the surface dynamics controls.
Simulation Name—Displays the name of the current simulation. You can edit the name to rename any existing simulation.
You can create any number of simulations in your scene. Each must have a unique name and is stored in the .max file. For example, you might have a simulation named Bouncing Ball that bounces a ball down a flight of stairs, while another simulation named Paper Airplane flies a paper airplane across the room.
List—Displays the name of the current dynamics simulation, and lists all simulations in the scene. If the list contains two or more simulations, choose one from the list to make it current. All remaining panel settings are specific to the current simulation.
New—Creates a new simulation. Its name consists of the word "Dynamics" appended by a number, starting with 00. This number is incremented by one for each new simulation.
Remove—Deletes the current simulation. Dynamic simulations can use a lot of memory. Removing old or unused simulations reduces the size of your .max files. When you remove a simulation, all timings and other settings are deleted. However, any keys generated by the simulation remain.
Copy—Creates a duplicate of the current dynamics simulation. All of the settings are identical to the original simulation, with the addition of “01” appended to the name.
Lets you add and remove objects from the simulation, and edit the properties of objects in the simulation.
Edit Object List—Displays the Edit Object List dialog, which lets you specify which scene objects are to be included in the simulation.
Edit Object—Displays the Edit Object dialog.
The Edit Object dialog is the main interface for object dynamics attributes. Use this dialog to set collisions, effects, surface properties and mass for each object in the simulation.
Select Objects in Sim—Adds all objects in the simulation to the current selection set. One use for this function is to bring selected objects into Track View for further manipulation, keyframe reduction, and so on.
Specifies which effects are included in the dynamics calculation.
Effects by Object—Only effects assigned to specific objects with the Edit Object dialog > Assign Object Effects button are considered in the calculation.
Global Effects—Only effects included in the Assign Global Effects dialog (accessed by clicking the button of the same name) are included in the calculation.
Assign Global Effects—Displays the Assign Global Effects dialog.
Select effects (space warps) in the list on the left and use the > button to move them to the list on the right. Effects thus chosen affect all objects in the simulation except unyielding ones.
The Assign Global Effects dialog functions similarly to the Edit Object List dialog.
Specifies which collisions are included in the dynamics calculation.
Collisions by Object—Collisions assigned to specific objects through the Edit Object dialog > Assign Object Collisions button are included in the calculation.
Global Collisions—Collisions assigned in the Assign Global Collisions dialog (accessed by clicking the button of the same name) are included in the calculation.
Assign Global Collisions—Displays the Assign Global Collisions dialog.
Select the objects in the list on the left and use the > button to move them to the list on the right. All objects thus chosen collide with each other in the simulation.
The Assign Global Collisions dialog functions similarly to the Edit Object List dialog.
Update Display w/ Solve—Displays each frame of the solution in the wireframe viewports during the calculations. This slows down the calculation process.
Solve—Calculates the dynamics solution, generating keys over the range of frames specified in the Timing area. A progress bar appears in the status/prompt line. Press ESC to cancel the calculation.
Note: You cannot undo the generation of a dynamics simulation solution. If there's a chance you might want to restore the scene to its state prior to the solution, either save the scene or use Hold before solving it.
Lets you specify the range included in the calculation, how IK is included in the simulation, and what the air density is for the simulation.
Controls how keys are generated over time.
Start Time—Specifies the first frame to generate keys, which is the first frame to be considered for the solution. Default=0.
Tip: If you set a start time that's later than a keyframe-animated object's last animation frame, you may get unexpected motion during the interim frames. For example, if you animate a box's position from frames 0 to 10, and then use the box in a dynamics simulation that starts at frame 20, the box will move between frames 10 and 20 because of the Bezier controller's default interpolation. To avoid this, before solving the simulation, set the last animation keyframe's Out tangent type to Linear or Step; see Bezier Controllers. Alternatively, set the last key of the keyframed "input motion" after the start time of the simulation, or set a start time before the last key.
End Time—Specifies the last key considered for the solution. This spinner is set to the last frame of the active segment when you create a new simulation. For example, if your active segment ends at frame 200, when you click New to create a new simulation, End Time is set to 200.
Calc Intervals Per Frame—Specifies how many calculations are performed for each frame of the simulation time range. Range=1 to 160.
Finding the right number for this spinner is a matter of experimentation. As a general rule, the faster things are moving in the simulation, the higher you should set this value.
Note: If you find that some objects aren't colliding properly with others (they're going through them), increase the Calc Intervals Per Frame value.
Keys Every N Frames—Specifies the frequency with which keys are generated, per object. If this were set to 2, keys would be generated in every other frame.
Warning: When you reduce the key count by increasing this setting, important information can be lost. For example, if a collision occurs on frame n, the Dynamics utility normally sets keys at frames n, n+1, and n-1. But if you've set Keys Every N Frames to 2, a keyframe for the impact itself might not be generated, while keys for the sudden reversal of motion would be generated on either side of the (missing) impact. Thus, the motion controller is left to interpolate motion in a region where the motion should be sharply defined. When this happens, motion can be incorrect and the remainder of the solve is affected. In the aforementioned example, a key describing the impact is lost and the motion controller interpolates motion so that objects that should collide actually intersect, ruining the simulation.
Time Scale—Slows down or speeds up the overall effect of the simulation. It applies a linear scale factor to the outside forces affecting each object (gravity, wind, and so on).
The default value of 1 results in normal speed. You can scale down the simulation (make it slower) by using values below 1 (from 0.1 to 1), and you can scale up the simulation (make it faster) by using values greater than 1 (from 1 to 100). If you speed up your simulation and objects begin to behave incorrectly (going through objects, for example), increase the Calc Intervals Per Frame value to compensate.
Relates to IK settings and the transfer of momentum.
Use IK Joint Limits—Uses the current IK joint limit settings as constraints for hierarchies in the simulation.
Use IK Joint Damping—Uses the IK damping settings as constraints for hierarchies in the simulation.
Density percent—Sets the air density in the simulation. A setting of 100 is the air at sea level. A setting of 0 is a total vacuum.
When anything moves, it hits air resistance (except in space). The faster it moves, the higher the relative air resistance with the square of the speed. Thus, air resistance imposes an upper limit on the speed of things that are falling with gravity, and also makes objects tumble due to the effect of air resistance on each face of the object.
Close—Closes the Dynamics utility.
The three spinners in the Dynamics Properties rollout in the Material Editor let you specify surface properties that affect the animation of an object upon collision with another object. If there are no collisions in your simulation, these settings have no effect.
Because the Dynamics Properties rollout is available at the top level of any material (including sub-materials), you can specify different surface dynamic properties for each face in an object. There are also controls in the Dynamics utility that let you adjust the surface properties at the object level, but only the Material Editor lets you alter the surface properties at the sub-object level (through use of a Multi/Sub-Object material).
As a default, the values in the Dynamics Properties rollout provide a surface that's similar to Teflon-coated hardened steel. This is with values of Bounce Coefficient equal to 1; with both Static Friction and Dynamic Friction set to 0.
Bounce Coefficient—Determines how far an object bounces after pressing a surface (the higher the value, the greater the bounce.) A value of 1 represents a bounce in which no kinetic energy is lost.
Static Friction—Determines how difficult it’s for an object to start moving along a surface (the higher this value, the more difficult the movement.) If something weighs 10 pounds and sits on Teflon (a static friction of near zero), it takes almost no force to make it move sideways, On the other hand, if it sits on sandpaper, then the static friction might be very high, around .5 to .8.
Sliding Friction—Determines how difficult it’s for an object to keep moving over a surface (the higher this value, the more difficult for the object to keep moving.) Once two objects begin to slide over one another, static friction disappears and sliding friction takes over. Generally, sliding friction is lower than static friction due to surface tension effects. For example, once steel starts sliding over brass (a value of static friction that might run from .05 to .2), the sliding friction drops to a significantly lower value: .01 to .1.
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