Changing halfcheetah's body_mass

[rgap]

Hi all,
What I'm trying to do is to change halfcheetah's head "body_mass[7]" as it does when I change its mass in the xml file half_cheetah.xml.

I've been looking aroung and found how to but it doesn't increase the head size. Is there something I'm doing wrong?

import gym
import numpy as np
from gym import utils
from gym.envs.mujoco import mujoco_env


class HalfCheetahEnv(mujoco_env.MujocoEnv, utils.EzPickle):
    def __init__(self):
        self.prev_qpos = None
        MODEL_PATH = 'half_cheetah.xml'
        mujoco_env.MujocoEnv.__init__(self, MODEL_PATH, 5)
        utils.EzPickle.__init__(self)

    def step(self, action):
        xposbefore = self.sim.data.qpos[0]
        self.do_simulation(action, self.frame_skip)
        xposafter = self.sim.data.qpos[0]
        ob = self._get_obs()
        reward_ctrl = - 0.1 * np.square(action).sum()
        reward_run = (xposafter - xposbefore)/self.dt
        reward = reward_ctrl + reward_run
        done = False
        return ob, reward, done, {}

    def _get_obs(self):
        return np.concatenate([
            self.sim.data.qpos.flat[1:],
            self.sim.data.qvel.flat,
        ])

    def reset_model(self):
        qpos = self.init_qpos + self.np_random.uniform(low=-.1, high=.1, size=self.model.nq)
        qvel = self.init_qvel + self.np_random.randn(self.model.nv) * .1
        self.set_state(qpos, qvel)
        return self._get_obs()

    def viewer_setup(self):
        self.viewer.cam.distance = self.model.stat.extent * 0.5

    def change_env(self):
        self.model.body_mass[7] = 1.5
        self.model.dof_damping[7] = 1.5


if __name__ == "__main__":

    env = HalfCheetahEnv()
    env.reset()
    env.change_env()

    while True:
        env.render()
        print(env.model.body_mass)

[jkterry1]

PR #2762 is about to be merged, introducing V4 MuJoCo environments using new bindings and a dramatically newer version of the engine. If this issue still persists with the V4 ones, please create a new issue for it.