Initial joints configuration

[charlypg]

Hello,

I use the bullet spine and I tried to change the initial positions of the joints via RobotState but it does not work. Also, self.joint_configuration does not seem to intervene anywhere in the RobotState class, and I have not found out how to set initial joints positions yet.
Is there a way to do so ? In order to obtain bent knees for example.

Thank you in advance.

[stephane-caron]

Now yes 😃 The initial joint configuration was exposed on the Python side, but not handled by the Bullet C++ spine as discussed here. It has now been added in #428 and released with v5.2.0. For instance:

import gymnasium as gym
import numpy as np
from scipy.spatial.transform import Rotation as ScipyRotation

import upkie.envs
from upkie.utils.robot_state import RobotState

if __name__ == "__main__":
    upkie.envs.register()
    with gym.make(
        "UpkieServoPositions-v4",
        frequency=200.0,
        init_state=RobotState(
            orientation_base_in_world=ScipyRotation.from_quat(
                [0.0, 0.0, -0.707, 0.707],  # SciPy convention: (x, y, z, w))
            ),
            position_base_in_world=np.array([0.1, 0.0, 0.7]),
            joint_configuration=np.array([1.0, 2.0, 3.0, 0.0, 0.0, 0.0]),
        ),
    ) as env:
        for step in range(10_000):
            env.reset()  # keep resetting to show the initial state

will keep the robot in the air with a raised left leg (first three joint angles) and a straight right leg (next three joint angles to zero).

Hoping this helps!