I have a urdf file for NAO robot . I converted it to XML using compile with options collision= "predefined". inertiafromgeom="true" and integrator="RK4. When I simulate the converted XML , I cannot see effect of gravity on the entire body. Only the limbs are moving due to gravity. But the entire bosy remains a fixed position. What options should I to get gravity act on the entire body? Here is the link to the drive containing the mesh folder and the urdf file. https://drive.google.com/drive/folders/1BySb9Zd00jrjQEShUs81AnuH-FSej6Hz?usp=sharing [edit] This is solved by adding joint of type free to the torso. But there are random vibration in the limbs when the robot lands the floor like in this gif.