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Gait Optimization For Talos

This folder contains the gait optimization implementation for Talos, that is used for comparison between RAPTOR and aligator.

Getting Started

Our main function is mainly at TalosSingleStepFixedPosition.cpp, where we try to solve for a trajectory that makes Talos walk forward with a user-specified step length while starting from a fixed initial configuration.

Create a data/ folder first in Examples/Talos to store all the results.

Specify the step length in singlestep_optimization_settings.yaml and run the following command in build/:

./Talos_example

This program runs the optimization and then save the trajectories and the corresponding inverse dynamics control inputs in data/solution-talos-forward-[step length].txt, over a much finer time discretization. Check line 196-210 in TalosSingleStepFixedPosition.cpp.

In Examples/Talos/python/talos_simulation.py, you will be able to find how we simulate the Talos using scipy.solve_ivp as the integrator and pinocchio to evaluate the contact dynamics. Here we apply a tracking controller in the simulation:

$$u(t) = u_{openloop}(t) + K_Pe(t) + K_D\dot{e}(t)$$

Here, $u_{openloop}(t)$ represents the open loop control input recovered from the control input sequence saved in data/solution-talos-forward-[step length].txt using zero-order hold (ZOH). We also added a simple PD control here where the desired trajectories are also recovered from data/solution-talos-forward-[step length].txt using ZOH.

For our implementation on the comparisons using aligator, please refer to our fork on aligator.

Migrating to Other Humanoid Robots

This folder provides a framework for optimizing gaits for different humanoid robots. To migrate the code, you can copy this folder and replace all instances of Talos with the name of your robot.

Below are the key modifications required for migration:

URDF Modifications

  1. URDF File Paths
    Update urdf_filename in the main files such as TalosSingleStep.cpp and TalosMultipleStep.cpp.
    You may also need to update the filepath in the same files.

  2. Floating Base Representation
    RAPTOR requires a URDF where the robot is attached to a floating base with:

    • Three prismatic joints (for translation)
    • Three revolute joints (for rotation)

    You need to manually create this modified URDF.
    Refer to talos_reduced_armfixed_floatingbase.urdf as an example.

  3. Torso Rotation Joint Name
    In line 214 of TalosDynamicsConstraints.cpp, ensure that the Rz joint (which allows torso rotation around the world z-axis) matches the corresponding joint in your URDF.

    • For example, in the same location of G1DynamicsConstraints.cpp, this joint is renamed to Rz_joint to be consistent with the corresponding URDF.

Configuration Files

Update the paths to the optimization configuration files in the main files:

  • singlestep_optimization_settings.yaml
  • multiplestep_optimization_settings.yaml

These paths appear in TalosSingleStep.cpp and TalosMultipleStep.cpp.

Robot-Related Constants

Modify the following constants in TalosConstants.h to match your robot:

  1. Joint Limits & Torque Limits
    These should be available from your robot's URDF.

  2. Ground Friction Coefficients

    • MU: Translational friction coefficient.
    • GAMMA: Torsional friction coefficient.

Feet (Ground Contact Frames)

  1. Foot Joint Names
    Update LEFT_FOOT_NAME and RIGHT_FOOT_NAME in TalosConstants.h.
    These are typically the last joints in the kinematic chain of each leg.

  2. Foot Frame Transformation
    The foot frame refers to the center of the bottom of the foot, which may not coincide with the foot joint.
    Update the transformation matrices in:

    • stance_foot_endT in TalosDynamicsConstraints.cpp
    • leftfoot_endT and rightfoot_endT in TalosCustomizedConstraints.cpp

    Where to find this transformation matrix?

    • Digit-v3: Available in its MuJoCo XML file (digit-v3.xml).
    • Talos: Defined in the URDF (same as the foot link mesh frame).
    • Unitree-G1: Defined in the URDF (foot frame is at the center of four corner spheres used for collision).

  3. Foot Size
    Update FOOT_WIDTH and FOOT_LENGTH in TalosConstants.h.

    • FOOT_WIDTH = half of the size of foot along the x axis of the foot frame.
    • FOOT_LENGTH = half of the size of foot along the y axis of the foot frame.

    Note that FOOT_WIDTH is not necessarily the short side and FOOT_LENGTH is not necessarily the long side. If the robot exhibits instability (e.g., tilting unnaturally), you may have assigned incorrect foot dimensions.

By making these modifications, you should be able to optimize gaits for your humanoid robot using this framework. One example of this migration can be found in Unitree-G1, where we duplicated the contents of this folder and modified the necessary components as outlined above.