Support for multiple degrees of freedom joints

[AlpenAalAlex]

Description

Implements a TODO in joints.py:
Update spring and damping once the user changes these values in custom properties

Added joint types:

• gearbox - a constraint for two revolute joints

  • parameters:

    • gearbox reference body - this is another joint
    • gearbox ratio
    • axis
    • axis2

  • In Gazebo the child of a gearbox joint does no longer collide with other links. If you know how to fix this please let me know

• ball - a ball and socket joint

  • parameters:

    • axis
    • limit

  • Limit will be applied to upper and lower limit
    These parameters are not yet supported by Gazebo but apparently by other programs

• universal - a ball joint with a constrained axis

  • parameters:

    • axis
    • axis2
      each with:
      • lower limit
      • upper limit
      • max effort
      • max velocity
    • spring constant
    • damping constant

  • axis and axis2 are free. The missing axis is constrained

• screw - a joint with rotational motion coupled to sliding

  • parameters:

    • axis
    • lower limit
    • upper limit
    • max effort
    • max velocity
    • screw thread pitch

  • The screw can slide along the axis and will rotate around that axis
    The rotation is determined by the thread pitch given in meters per revolution

Related Issue

#195

Motivation and Context

So far phobos only supports 1-DOF joints. SDF provides other joint type definitions.

How Has This Been Tested?

To test create a simple model with each of these joints, export as sdf and import into gazebo
The gearbox is a constraint between two joints. The links can be in this order:
|root_link
|-parent_link - revolute joint
|--gearbox
|---child_link - revolute joint
|-reference_body - fixed joint

If you change the custom properties joint/dynamics/damping and joint/dynamics/spring_stiffness you can see damping and stiffness is updated in the physics tab

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.

[hwiedPro]

Really cool I'll check this at my end!