Could IK solver called by arm_navigation auto-generated file work for 5 DOF manipulator

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If you have a 5DOF arm and keep the target pose orientation within the reachable space of your arm, IK should work. If however, you for example rotate the target pose around the axis of the missing sixth DOF (if it's rotational), IK will naturally fail.

I can recommend the OpenRAVE ikfast module and it's 'TranslationDirection5D' IK option for such a scenario. It is also shortly talked about here.

I documented how I generated the IK for our 5DOF arm, so here goes:

Generating a OpenRAVE-Collada robot model (assumes you have OpenRAVE installed):

roscd hector_arm_urdf/urdf
rosrun xacro xacro.py hector_arm_ax12_5dof_standalone.xacro > hector_arm_ax12_5dof_standalone.urdf
rosrun collada_urdf urdf_to_collada hector_arm_ax12_5dof_standalone.urdf hector_arm_ax12_5dof_standalone.dae

In the next step, a OpenRAVE scene description file has to be created in the same directory. For this example, this would be "hector_arm_ax12_5dof_standalone.xml". With following contents:

<Robot name="hector_arm_ax12_5dof_standalone" file="hector_arm_ax12_5dof_standalone.dae">
  <Manipulator name="hector_arm_5dof">
    <base>arm_base_link</base>
    <effector>endeffector_yaw_link</effector>
    <direction>1 0 0</direction>
    <translation>0 0 0</translation>
  </Manipulator>
</Robot>

You can do a visual inspection of the model by starting OpenRAVE and then loading the OpenRAVE scene description XML file created above. The endeffector should look as described here when using the red arrow tool to the top right and clicking on the robot.

roscd openrave/bin
export PYTHONPATH=$PYTHONPATH:`./openrave-config --python-dir`
./openrave.py

Finally, generating 5DOF IK:

roscd openrave/bin
export PYTHONPATH=$PYTHONPATH:`./openrave-config --python-dir`
./openrave.py --database inversekinematics --robot=/home/stefan/rosext/hector/ros/stacks/hector_arm/hector_arm_urdf/urdf/hector_arm_ax12_5dof_standalone.xml --iktype=TranslationDirection5D

The generated IK library or .cpp can then be used for calculating inverse kinematics in ROS. This of course is an option that needs a little more effort than relying on the KDL based iterative solver provided with the ROS tools.