For modeling conveyor systems or any kind of freely moving goods (what is called MU in on a surface you need to use a Transport Surface.

A Transport Surface is always connected to a Drive which is controlling the speed and position. The Transport Surface needs to be placed on the object which is also including the box collider for the surface itself.

Here is a tutorial about defining your first conveyor:

Connecting Drives to Transport Surfaces

To add a Transport Surface you can use the menu or Add Component on the Gameobject itself. The Transport Surface will be added automatically to the Drive which is next (up in the hierarchy) to the Transport Surface. In some cases, you might need to change it or to add multiple Transport Surfaces to one Drive . You can do this on the Drive itself:

Drives above the TransportSurface Drive - using parent Drives

ParentDrives is only needed if IsKinematic Drives are moving TransportSurfaces in a linear direction or rotational direction, e.g. for turn tables or lifting devices.

Sometimes Unity Physics is very difficult and the solution to master it is a little bit weird. As described in Physics normal movements of a linear or rotational axis are not done based IsKinematic Rigidbodies. The transformation is done based on the Unity hierarchy and the position of Unity’s Transform because this is usually much more stable.

The Transport Surface is different from normal linear or rotational movements of an axis. It is using pure Unity physics functions for transporting the MUs.

This causes one problem. If it is for example necessary to combine a linear or rotational movement with the Transport Surface itself this will cause problems. Unity will not move the Transport Surface Collider as expected.

To prevent this the option ParentDrive is available on the Transport Surface:

This option will automatically decouple the Transport Surface upon simulation start and will make a function as expected possible. During simulation, the Transportsurface will be without a parent in the top level of the hierarchy. You can see an example in the Demo model TurningAndLiftingTransportSurface which can be found under > Scenes:

When you build up more complex kinematic structures, make sure to always keep the gameobject with the component transport surface parallel to the kinematic structure of the other drive belonging to the surface. An further expample model is MovingTransportSurface which can also be found under > Scenes. The picture below shows how to define such a structure. The parent drive of the transport surface is the one which is the lowest in the kinematic structure.

If the parent drive of the transport surface is rotating, the pivot points (centre of rotation) of both objects must be in the same position for the movement to be transmitted correctly. If necessary, an empty GameObject must be inserted to achieve this.

Constraints of transported Objects

You can choose if the constraints of objects which enter the transportsurface have to be changed or not. Setting the boolean ChangeConstraintsOnEnter or ChangeConstraintsOnExit to true will give the possibility to that.

When you change the constraints they will not be set back automatically to the former settings when the object leaves the transport surface. There you have to set ChangeConstraintsOnExit true and define the values. Choosing "None" all contraints will be removed from the object.

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