 # Doubt in Gurdy's basic geometry

Hi,
I’m trying to figure out the axis for each of the upperleg_joint’s in gurdy, but I am not able to understand the data quite clearly.

The links and joints image shared in the notebook has this part:

From the above picture, To my understanding the xyz near each of the upperleg_joints is the position of their origin with respect to the head_link origin.

But we are also provided another picture of the robot in the XZ Plane with the following text:

Here you have a blueprint of the distances to place the most difficult part, which is the joints between the head and the legs. The units are millimeters:

The X Z coordinates of the upperleg_joint origins from the 2nd image do not match with the ones from the 1st image.

For example:
The 1st Image has one of the joint coordinates to be `(0 0.025 -0.008)` this is one of the only joint origins to have an `x=0` so it would be a fair assumption to guess that its located at the lower end of the 2nd Image, but only the x coordinates match, the z coordinates according the 2nd Image should be -0.025 and not -0.008 as given in the 1st image.

I’m not really sure if I am assuming something wrong or if there is inconsistency in the data.
Any help would be highly appreciated.

TIA

Hi,

Yeah, The image is confussing because theblueprint image s from SolidWorks, model, which has the Z and Y swaped from Gazebo. Here you have the join deffinition of the third leg:

``````<joint name="head_upperlegM3_joint" type="revolute">
<origin xyz="0 0.025 -0.008" rpy="3.14159 0 -1.5708"/>
<limit lower="-1.55" upper="0.0" effort="1.0" velocity="0.005"/>
<axis xyz="0 1 0"/>
</joint>
``````

In SoldiWorks Blueprint you have: X = 0.0, Y= -0.008, Z= -0.025
In Gazebo you have: X=0.0, Y=0.025 , Z=-0.008

You can also see in gazebo that we have to rotate the model in Roll=3.14 and Yaw=-1.57

All this is due to the fact that the axis of the 3D mesh are not exactly the same as the ones in SoldiWorksModel.

Its a very good quiestion and didnt have it until now ;).
But this is a very common issue when you create Gazebo simulations and that why in more coplex robots, normally exporting tools are used, like SW to URDF exporter: http://wiki.ros.org/sw_urdf_exporter

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