If you do
>> rostopic info joint_states
and look at the message type (which normally should be sensor_msgs/JointState), you can then do
>> rosmsg info sensor_msgs/JointState
This should tell you the structure of the data and what is available to pick from those messages.
If for some reason your /joint_states topic is using a different message type, that may be why the timeseries is unable to find a Position field?
- Sebastian
