Configurable Robot Base Location

[jrgnicho]

The system shall be able to support selecting 2 to 3 different robot base positions along the rail; selecting the base location should be configurable from the GUI, suggested solutions would be:

• Set a prismatic joint between the base and the rail and assign each base position a joint value along the rail and create a node that publishes the value of the joint to the joint_states topics and also advertises a service that allows selecting a different position for the robot base.