Instability after many steps

[jjyyxx]

The model becomes instable after many steps, even with simplest control. Repro as follows. Could you investigate the cause? Or suggest workarounds to make the model more robust?

import os
os.environ["MUJOCO_GL"] = "egl"
import mujoco
assert mujoco.__version__ == '3.2.3'

model = mujoco.MjModel.from_xml_path("cube_3x3x3.xml")
data = mujoco.MjData(model)
data.ctrl[0] = 0.0195

renderer = mujoco.Renderer(model, height=240, width=320)

mujoco.mj_step(model, data, nstep=20845)
renderer.update_scene(data)
normal = renderer.render()

mujoco.mj_step(model, data, nstep=1)
renderer.update_scene(data)
abnormal = renderer.render()

from PIL import Image
Image.fromarray(normal).save("normal.png")
Image.fromarray(abnormal).save("abnormal.png")

Normal

Abnormal

[kevinzakka]

The timestep is really high right now. Just lower it until the instabilities go away, but not too much or it will be too slow.

[kevinzakka]

Hi @jjyyxx, did lowering the timestep help?