def METHOD_NAME(parent_step, child_step, model_urdf):
    joint_name = 'joint_' + parent_step.name + '_' + child_step.name
    joint = et.SubElement(model_urdf, 'joint', name = joint_name, type = 'fixed')
    et.SubElement(joint, 'origin',
                  xyz = str(parent_step.length) + ' 0 ' + str(parent_step.height), rpy = '0 0 0')
    et.SubElement(joint, 'parent' ,link = parent_step.name)
    et.SubElement(joint, 'child' ,link = child_step.name)
    return model_urdf