urdf_parser_py: False errors reported when parsing urdf with <transmission> tags

[jbohren]

If you try to parse an urdf with urdf_parser_py it throws an error if your <transmission><joint>.. tags don't have a type attribute.

Exception: Required attribute not set in XML: type

This is an incorrect error, see http://wiki.ros.org/urdf/XML/Transmission

[adolfo-rt]

Might be related, but test-driving urdf_parser_py on REEM chokes on:

Exception: Required attribute not set in XML: upper

The only attribute named upper in the URDF spec is the joint position limit, and it's optional, see http://wiki.ros.org/urdf/XML/joint

I haven't tried on a minimal single-joint example.

[eacousineau]

I've added in a patch to set the default values for 'lower' and 'upper'. Thank you for reporting that!

And Adolfo, I tried out parsing REEM after adding the default values in. It looks like hardwareInterface has been placed as a child node of joint instead of in actuator. Should it instead be in actuator?

<transmission name="wheel_right_trans">
  <type>transmission_interface/SimpleTransmission</type>
  <actuator name="wheel_right_motor">
    <mechanicalReduction>1.0</mechanicalReduction>
  </actuator>
  <joint name="wheel_right_joint">
    <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
  </joint>
</transmission>

Sample bash session:

$ # NOTE: reem_robot and urdfdom have been placed in the same workspace
$ git clone https://github.com/pal-robotics/reem_robot.git
$ cd reem_robot
$ git rev-parse --short HEAD
2cec3cf
$ roslaunch reem_description upload_reem.launch
$ rosparam get -p /robot_description > /tmp/test.urdf
$ cd ../urdfdom/urdf_parser_py
$ git rev-parse --short HEAD
0b3e9e1
$ ./scripts/display_urdf # From param server
...
Exception: Could not perform duck-typed parsing.
Value Type: <class 'urdf_parser_py.urdf.Transmission'>
Exception: Required element not set in XML: hardwareInterface

Value Type: <class 'urdf_parser_py.urdf.PR2Transmission'>
Exception: Required attribute not set in XML: type

[adolfo-rt]

Sigh, this issue is having lots of ramifications.

The correct behavior is to specify hardware interfaces under the <joint> element, but because of a design discussion mistake, gazebo_ros_control was released into hydro parsing hardware_interfaces from the <actuator> element. In indigo, gazebo_ros_control accepts both, but the <actuator> spec is on a deprecation cycle, and will no longer be supported in J-Turtle.

To fix urdf_parser_py, one could either check that <hardware_interface> is under either <joint> or <actuator>, but I don't know if this becomes clumsy implementation-wise. Let me know what you think.

[adolfo-rt]

With #38 fixed, we can get back to the original subject (apologies for the detour):

If you try to parse an urdf with urdf_parser_py it throws an error if your .. tags don't have a type attribute.

Exception: Required attribute not set in XML: type

It seems that the <transmission> element is interpreted as a PR2-style transmission. From the ducktyping statement here, I interpret that the parser is trying to resolve the type of transmission specification (pr2_transmission vs new_transmission) from the provided elements and attributes. I don't understand the code well enough to know why it fails.

[goretkin]

I think I'm running up against this. My PR2 URDF has, for example,

  <transmission name="l_wrist_trans" type="pr2_mechanism_model/WristTransmission">
    <rightActuator mechanicalReduction="60.1714285714" name="l_wrist_r_motor"/>
    <leftActuator mechanicalReduction="60.1714285714" name="l_wrist_l_motor"/>
    <flexJoint mechanicalReduction="-1.0" name="l_wrist_flex_joint"/>
    <rollJoint mechanicalReduction="1.0" name="l_wrist_roll_joint"/>
  </transmission>

and the error I get is.

Exception: Could not perform duck-typed parsing.
Value Type: <class 'urdf_parser_py.urdf.Transmission'>
Exception: Required element not set in XML: type

Value Type: <class 'urdf_parser_py.urdf.PR2Transmission'>
Exception: Required element not set in XML: joint

It try to go up the stack trace to find out where in the file this error is, and I think it's in the part of the URDF I indicated above.

As I indicated in #58, I am under Groovy, so the actual error I'm getting is

Exception: Required element not set in XML: joint

[ugocupcic]

As far as I can tell, this should be fixed in #63.

When can we expect a new release of urdfdom to fix this?

[jacquelinekay]

The latest incarnation of the fix for this issue (#68) has been pushed to 0.2, 0.3 and master branch (targeting 0.4).

Now that the fix has been backported I will try to release a new ros-indigo-urdfdom-py and ros-jade-urdfdom-py today. After the release I will consider this issue resolved.

[ugocupcic]

👍