    grass.colorSpace = THREE.SRGBColorSpace
          grass.wrapS = grass.wrapT = 1000 // RepeatWrapping
          grass.offset.set(0, 0)
          grass.repeat.set(2, 2)
          this.physics.add.ground({ width: 20, height: 20, y: 0 }, { phong: { map: grass } })

          // add robot
          const gltf = await this.load.gltf('robot')
          const robot = new ExtendedObject3D()
          robot.name = 'robot'
          robot.add(gltf.scene.children[0])
          robot.traverse(child => {
            