Fixed point attached to world
A Ground block represents an immobile ground point at rest in the absolute inertial World reference frame. Connecting it to a Joint prevents one side of that Joint from moving. You can also connect a Ground block to a machine Environment block.
Caution Every valid SimMechanics™ machine must have at least one Ground block.
You must connect exactly one Ground block in each machine of your model to a Machine Environment block.
Ground is a type of Body, but you can connect only one side of a Ground to a Joint block. A Ground block automatically carries a grounded coordinate system (CS). This Grounded CS is inertial, at rest in the World reference frame, with coordinate axes parallel to the World axes:
+x points right
+y points up (gravity in -y direction)
+z points out of the screen, in three dimensions
But a Ground's origin is the ground point, which in general is shifted with respect to the World origin.
Multiple Ground blocks represent different fixed points in the global inertial World. In the topology of a model, multiple Ground blocks function as a single body.
You cannot connect a Sensor or Actuator to a Ground block, because the ground point cannot be moved.
Enter the position of the ground point translated from the origin of the World CS. The position is specified as a translation vector (x,y,z), with components projected onto the fixed World CS axes. Set the Ground position units using the pull-down menu to the right. The defaults are [0 0 0] and m (meters).
Select to enable the Machine Environment port on the Ground block. This port allows you to connect a Machine Environment block to the Ground and the machine that the Ground is a part of. The default is not selected.
A Ground Without and With a Connected Machine Environment Block
If you connect a Machine Environment block to a Ground, you can adjust the mechanical environment for the machine of which that Ground is a part. Consult the Machine Environment block reference.