mjbWorld program - User guide - Kinematics

This allows you to program motion into the 3d models.

The program supports may different ways to program motion. Interpolators can be used for simple repetative motions (see tutorial animation a hand), this method is more powerful for similating physics because:

  1. The movement continues until explicitly stopped (Newtons first law!) unlike interpolators which must have start and end points.
  2. Velocities and Accelerations can be explicitly input

This uses the KinematicsBean (here we are doing forward kinematics as opposed to inverse kinematics- inverse comes later!). Ie motion can be defined for any Transformgroup in the tree and the resultant positon will be detemined by combining all the transforms below.

First start the program. We need a shape to move so we will get a box from the quick shape window (any other shape under a TransformGroupBean will do).

So to get a shape to work on, open the quick shape window,

Select the boxBean and drag it into the tree view (or instead of dragging hit the + button)

Now we want to add a kinematicsBean below the transformGroupBean. So,

  1. Open the Insert view.
  2. Select the transformGroupBean in the tree vindow
  3. Select the kinematicsBean in the insert/add view
  4. Drag the kinematicsBean to the transformGroupBean (or just hit the + button)
  5. Close the insert view

Select the kinematicsBean in the tree view:

Set the initial Distance, initial velocity and initial Acceleration to suitable values (for example as below)

select front view in 3D view so that we can see the animation.

Open the timeline window and hit play (green arrow) to see animation.

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see also:


Keyframing Theory

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