How to get the axis of a revolute joint?

[2352878630]

I want to get a Vector3 type variable that represents the axis of a revolute joint.
For example, in URDF file, I already have a joint with <axis xyz="1 0 0"/>. Now I want to get a variable with a value of 1 0 0 and a type of Vector3

Thank you very much !

[jcarpent]

Unfortunately, there is not yet a direct helper to extract it.
Yet, you can recover this information partially as follows:

import pinocchio as pin
joint_model = pin.JointModelRX()
joint_data = joint_model.createData()
axis = joint_data.S[3:]

@jorisv Will you have time to add the getMotionAxis helper to all revolute and prismatic joints in Pinocchio and expose it to Python?

[jorisv]

I will check this. We also plan to use the new boost::variant eigenpy bindings to better expose joint in Python.

[2352878630]

Thank you very much!

[joao-pm-santos96]

Hi @jorisv ! Using your snippet, I get AttributeError: 'JointModelRX' object has no attribute 'createData'. Im on pin version 2.7.0. Can you help me please?

[jorisv]

Hi @joao-pm-santos96,

Sorry this code snippet is not working in Pinocchio 2. It's only working in Pinocchio 3 that should be released at the end of the month.
I don't see a way to retrieve the S content in Pinocchio 2 (the S type is not binded).

You can get a Pinocchio 3 preview version by following this instructions

[joao-pm-santos96]

Good news! I am exited to see the amazing thing pinocchio3 will bring! Keep up the amazing work! Thank you! 😃