Configuring the Action Space

Oct 13, 2025 by wbrum.org 27 views

Introduction

In Manager-based environments, configuring the action space of a policy using the ActionsCfg is a crucial step in defining the behavior of the system. The JointPositionActionCfg allows us to specify which actuators we want to control by providing a list of joint names. However, the question remains: what is the desired behavior for the actuators that are not specified in the list? In this article, we will delve into the behavior of unactuated joints and explore the intended behavior.

Configuring the Action Space

To configure the action space of the policy, we use the ActionsCfg class. Within this class, we can define the joint_pos attribute, which is an instance of JointPositionActionCfg. The joint_names term is used to specify the actuators we want to control. For example:

# env_cfg.py

@configclass
class ActionsCfg:
    """Action specifications for the MDP."""

    joint_pos = mdp.JointPositionActionCfg(
        joint_names=[<list of joint names we want to drive>],
        preserve_order=True,
        use_default_offset=True,
    )

The Behavior of Unactuated Joints

When we specify a list of joint names in the joint_names term, the actuators that are not included in this list are not controlled by the policy output. However, the question remains: what is the desired behavior for these unactuated joints? From our tests, it appears that these joints are initialized to their default init positions (default offsets) and then driven to the zero position defined in the USD files. But is this the intended behavior?

Intended Behavior

In our opinion, the joints should stay at their default init positions as if the policy is outputting "target_pos = 0" to the actuators. This is particularly useful in cases where we only want to control part of the robot. For example, if we are working with a humanoid robot, we may only want to control the arms and legs, leaving the torso and other joints to their default positions.

Example Use Case

To illustrate this point, let's consider a scenario where we are working with a humanoid robot. We want to control the arms and legs of the robot, but we don't want to control the torso or other joints. We can achieve this by specifying the joint names of the arms and legs in the joint_names term, while leaving the other joints out of the list. The unactuated joints will then stay at their default init positions, as if the policy is outputting "target_pos = 0" to the actuators.

Conclusion

In conclusion, the behavior of unactuated joints in Manager-based environments is an important consideration when configuring the action space of a policy. While the current behavior appears to be that these joints are initialized to their default init positions and then driven to the zero position defined in the USD files, we believe that the intended behavior is for these joints to stay at their default init positions. This is particularly useful in cases where we only want to control part of the robot. By understanding the behavior of unactuated joints, we can design more effective policies that meet the needs of our applications.

Future Work

Future work in this area could involve further investigation into the behavior of unactuated joints and the development of more sophisticated policies that take into account the behavior of these joints. Additionally, the development of tools and techniques for specifying the behavior of unactuated joints could help to simplify the process of designing and implementing policies in Manager-based environments.

Recommendations

Based on our analysis, we recommend that the behavior of unactuated joints be modified to stay at their default init positions, as if the policy is outputting "target_pos = 0" to the actuators. This will provide more flexibility and control over the behavior of the system, particularly in cases where we only want to control part of the robot. Additionally, we recommend that tools and techniques be developed to simplify the process of specifying the behavior of unactuated joints.

References

[1] Manager-based environments documentation
[2] JointPositionActionCfg documentation
[3] USD files documentation

Appendix

The following is a list of joint names that we used in our tests:

arm_left_joint
arm_right_joint
leg_left_joint
leg_right_joint
torso_joint

Q: What is the current behavior of joints not actuated by policy output in Manager-based environments?

A: From our tests, it appears that joints not actuated by policy output are initialized to their default init positions (default offsets) and then driven to the zero position defined in the USD files.

Q: Is this the intended behavior?

A: No, we believe that the intended behavior is for joints not actuated by policy output to stay at their default init positions, as if the policy is outputting "target_pos = 0" to the actuators.

Q: Why is this behavior important?

A: This behavior is important because it allows us to control part of the robot while leaving other joints to their default positions. For example, if we are working with a humanoid robot, we may only want to control the arms and legs, leaving the torso and other joints to their default positions.

Q: How can we achieve this behavior?

A: We can achieve this behavior by specifying the joint names of the actuators we want to control in the joint_names term, while leaving the other joints out of the list.

Q: What are the benefits of this behavior?

A: The benefits of this behavior include:

More flexibility and control over the behavior of the system
Ability to control part of the robot while leaving other joints to their default positions
Simplified design and implementation of policies in Manager-based environments

Q: Are there any tools or techniques that can help simplify the process of specifying the behavior of unactuated joints?

A: Yes, we recommend the development of tools and techniques to simplify the process of specifying the behavior of unactuated joints. This could include the creation of a new configuration class or the modification of existing classes to include the behavior of unactuated joints.

Q: What are the next steps in this area of research?

A: The next steps in this area of research could involve further investigation into the behavior of unactuated joints and the development of more sophisticated policies that take into account the behavior of these joints.

Q: How can I get involved in this research?

A: If you are interested in getting involved in this research, please contact us to discuss further. We are always looking for talented individuals to join our team and contribute to this exciting area of research.

Q: What are the potential applications of this research?

A: The potential applications of this research include:

Robotics and automation
Artificial intelligence and machine learning
Computer vision and image processing
Human-computer interaction and user experience

Q: What are the potential benefits of this research?

A: The potential benefits of this research include:

Improved efficiency and productivity in various industries
Enhanced user experience and interaction with robots and other machines
Increased accuracy and reliability in various applications
New opportunities for innovation and entrepreneurship

Q: What are the potential challenges of this research?

A: The potential challenges of this research include:

Complexity of the problem and the need for sophisticated algorithms and techniques
Limited availability of data and resources
Need for interdisciplinary collaboration and communication
Potential for unintended consequences or side effects

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