Code: from mujoco_py import load_model_from_xml, MjSim, MjViewer import math import os import numpy as np MODEL_XML = """ <?xml version="1.0" ?> <mujoco> <option timestep="0.005" /> <worldbody> <body name="box2" pos="0.1 0.1 0.4"> <joint type="free"/> <geom mass="1" size="0.05 0.05 0.05" rgba="0.8 0 0 1" type="box" condim="3"/> </body> <body name="tray" pos="0.1 0.1 0.2"> <geom name="tray" mass="1" size="0.15 0.15 0.15" type="box" condim="3"/> <joint axis="1 0 0" name="cylinder:slidex" type="slide"/> <joint axis="0 1 0" name="cylinder:slidey" type="slide"/> </body> <body name="box" pos="-0.8 0 0.2"> <geom mass="0.1" size="0.15 0.15 0.15" type="box"/> </body> <body name="floor" pos="0 0 0.025"> <geom condim="1" size="5 5 0.02" rgba="0 0.7 0.8 1" type="box"/> </body> </worldbody> <actuator> <velocity gear="1.0" joint="cylinder:slidex"/> <velocity gear="1.0" joint="cylinder:slidey"/> </actuator> </mujoco> """ model = load_model_from_xml(MODEL_XML) sim = MjSim(model) viewer = MjViewer(sim) t = 0 # set intial vel = sim.data.get_body_xvelp("tray") vel[0] = np.cos(np.deg2rad(t/2.5)) vel[1] = np.sin(np.deg2rad(t/2.5)) while True: t += 1 sim.step() viewer.render() sim.data.ctrl[0] = np.cos(np.deg2rad(t/2.5)) sim.data.ctrl[1] = np.sin(np.deg2rad(t/2.5)) Hi, When I want to generate a trajectory that doing uniform circular motion, I use the following script, however, the model will have an acceleration in the initial and then do the uniform circular motion after few steps. Even after I setting an initial velocity, it still doesn't work. Could I know if there has some way to solve this problem, please?