{
    "first_joint": {
        "child":"first_link",
        "axis" : "-y"
    },
    "second_joint": {
        "child":"second_link",
        "axis" : "-x"
    },
    "third_joint": {
        "child":"third_link",
        "axis" : "-z"
    },
    "fourth_joint": {
        "child":"fourth_link",
        "axis" : "-z"
    }
}