def render_capsule(self, at_index, p, Q, length, scale=1.0, color=[1.0, 0.0, 0.0]):
    if at_index >= len(self.cap_pool):
        # create enough to allow at_index to work
        for i in range(len(self.cap_pool), at_index + 1):  # must include at_index too
            # get primitive first
            sphere_trimesh = trimesh.creation.capsule(height=1.0, radius=1.0, count=[8, 8])
            sphere_face_colors = np.zeros(sphere_trimesh.faces.shape)
            sphere_face_colors[:] = np.array(color)
            sphere_trimesh.visual.face_colors = sphere_face_colors
            sphere_mesh = Mesh.from_trimesh(sphere_trimesh, smooth=False)

            sphere_node = Node(mesh=sphere_mesh,
                               name="capsule_" + str(i))  # , translation=np.array([-0.1, -0.10, 0.05]))
            self.scene.add_node(sphere_node)
            self.cap_pool.append(sphere_node)
    # okay now we know the node exists, just change it's position
    self.cap_pool[at_index].scale = [0.1, 0.1, length]
    self.cap_pool[at_index].translation = p
    self.cap_pool[at_index].rotation = Q

#         print("Q: " + str(Q))