# Send custom MAVLink message **URL:** \ **Category:** Uncategorized\ **Created:** [October 4, 2016, 1:41pm UTC](https://discuss.px4.io/t/send-custom-mavlink-message/1370 "2016-10-04T13:41:57Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![pietrop88](https://discuss.px4.io/letter_avatar_proxy/v4/letter/p/bbe5ce/32.png) [@pietrop88](https://discuss.px4.io/u/pietrop88)\ **Post date:** [October 4, 2016, 1:41pm UTC](https://discuss.px4.io/t/send-custom-mavlink-message/1370/1 "2016-10-04T13:41:57Z")
Hi, I want to send a custom uOrb message through mavlink. I follow the guide: [http://dev.px4.io/custom-mavlink-message.html](http://dev.px4.io/custom-mavlink-message.html). The class that I added to `mavlink_messages.cpp` is this one: ```auto class MavlinkStreamCaTrajectory : public MavlinkStream { public: const char *get_name() const { return MavlinkStreamCaTrajectory::get_name_static(); } static const char *get_name_static() { return "CA_TRAJECTORY"; } static uint8_t get_id_static() { return MAVLINK_MSG_ID_CA_TRAJECTORY; } uint8_t get_id() { return get_id_static(); } static MavlinkStream *new_instance(Mavlink *mavlink) { return new MavlinkStreamCaTrajectory(mavlink); } unsigned get_size() { return MAVLINK_MSG_ID_CA_TRAJECTORY_LEN + MAVLINK_NUM_NON_PAYLOAD_BYTES; } private: MavlinkOrbSubscription *_sub; uint64_t _ca_traj_time; /* do not allow top copying this class */ MavlinkStreamCaTrajectory(MavlinkStreamCaTrajectory &); MavlinkStreamCaTrajectory& operator = (const MavlinkStreamCaTrajectory &); protected: explicit MavlinkStreamCaTrajectory(Mavlink *mavlink) : MavlinkStream(mavlink), _sub(_mavlink->add_orb_subscription(ORB_ID(ca_trajectory))), // make sure you enter the name of your uorb topic here _ca_traj_time(0) {} void send(const hrt_abstime t) { struct ca_traj_struct_s _ca_trajectory; //make sure ca_traj_struct_s is the definition of your uorb topic if (_sub->update(&_ca_traj_time, &_ca_trajectory)) { mavlink_ca_trajectory_t _msg_ca_trajectory; //make sure mavlink_ca_trajectory_t is the definition of your custom mavlink message _msg_ca_trajectory.timestamp = _ca_trajectory.timestamp; _msg_ca_trajectory.time_start_usec = _ca_trajectory.time_start_usec; _msg_ca_trajectory.time_stop_usec = _ca_trajectory.time_stop_usec; _msg_ca_trajectory.coefficients =_ca_trajectory.coefficients; _msg_ca_trajectory.seq_id = _ca_trajectory.seq_id; mavlink_msg_ca_trajectory_send_struct(_mavlink->get_channel(), &_msg_ca_trajectory); } } }; ``` I appended the stream class ```auto StreamListItem *streams_list[] = { ... new StreamListItem(&MavlinkStreamCaTrajectory::new_instance, &MavlinkStreamCaTrajectory::get_name_static,&MavlinkStreamCaTrajectory::get_id_static),nullptr }; ``` Differences respect to the guide: 1. Since the constructor of class `StreamListItem` requires the `id` i added the method `get_name_static` to `MavlinkStreamCaTrajectory` class. 2. In the `send` method of class `MavlinkStreamCaTrajectory` I changed the method `_mavlink->send_message(MAVLINK_MSG_ID_CA_TRAJECTORY, &_msg_ca_trajectory);` with: `mavlink_msg_ca_trajectory_send_struct(_mavlink->get_channel(), &_msg_ca_trajectory);` because I had a compile error. Now I am able to compile the code but the function `send` is never used even if I send `ca_trajectory` uOrb message and I don’t recive any `ca_trajectory` mavlink message. I think that something is missed but I don’t no what. ---
**Author:** ![pietrop88](https://discuss.px4.io/letter_avatar_proxy/v4/letter/p/bbe5ce/32.png) [@pietrop88](https://discuss.px4.io/u/pietrop88)\ **Post date:** [October 6, 2016, 8:40am UTC](https://discuss.px4.io/t/send-custom-mavlink-message/1370/2 "2016-10-06T08:40:10Z")
Solved. See [https://github.com/PX4/Firmware/issues/5597](https://github.com/PX4/Firmware/issues/5597) ---
**Author:** ![zyq1993](https://discuss.px4.io/letter_avatar_proxy/v4/letter/z/aca169/32.png) [@zyq1993](https://discuss.px4.io/u/zyq1993)\ **Post date:** [April 9, 2017, 2:55pm UTC](https://discuss.px4.io/t/send-custom-mavlink-message/1370/3 "2017-04-09T14:55:51Z")
Hello, I saw the github page [https://github.com/PX4/Firmware/issues/5597](https://github.com/PX4/Firmware/issues/5597), but I still don’t know where to put the generated directory custom\_messages in mavros package. And could you share your mavros code? Thanks a lot. ---
**Author:** ![pietrop88](https://discuss.px4.io/letter_avatar_proxy/v4/letter/p/bbe5ce/32.png) [@pietrop88](https://discuss.px4.io/u/pietrop88)\ **Post date:** [April 9, 2017, 3:39pm UTC](https://discuss.px4.io/t/send-custom-mavlink-message/1370/4 "2017-04-09T15:39:43Z")
Are you using mavros 0.17 or 0.18? ---
**Author:** ![zyq1993](https://discuss.px4.io/letter_avatar_proxy/v4/letter/z/aca169/32.png) [@zyq1993](https://discuss.px4.io/u/zyq1993)\ **Post date:** [April 10, 2017, 1:27am UTC](https://discuss.px4.io/t/send-custom-mavlink-message/1370/5 "2017-04-10T01:27:36Z")
Yes, I use mavros 0.17. ---
**Author:** ![zyq1993](https://discuss.px4.io/letter_avatar_proxy/v4/letter/z/aca169/32.png) [@zyq1993](https://discuss.px4.io/u/zyq1993)\ **Post date:** [April 10, 2017, 3:04am UTC](https://discuss.px4.io/t/send-custom-mavlink-message/1370/6 "2017-04-10T03:04:53Z")
Now, I have extended the mavros, and enabled the mavlink stream in posix-configs/SITL/init/lpe/iris, but I still can’t receive my custom mavlink messages 😢 ---
**Author:** ![zyq1993](https://discuss.px4.io/letter_avatar_proxy/v4/letter/z/aca169/32.png) [@zyq1993](https://discuss.px4.io/u/zyq1993)\ **Post date:** [April 10, 2017, 7:07am UTC](https://discuss.px4.io/t/send-custom-mavlink-message/1370/7 "2017-04-10T07:07:40Z")
Maybe my way to extend mavros is wrong, I can confirm the custom messages were sent by px4. For extending mavros, I put the directory custom\_messages that generated by pymavlink into the directory mavros/include, and added the include sentence in mavros.cpp. Do I miss anything? Thanks a lot. ![](https://discuss.px4.io/uploads/default/original/1X/494bcdf17308871619043b63714567918fc65a65.PNG) ---
**Author:** ![pietrop88](https://discuss.px4.io/letter_avatar_proxy/v4/letter/p/bbe5ce/32.png) [@pietrop88](https://discuss.px4.io/u/pietrop88)\ **Post date:** [April 10, 2017, 7:52am UTC](https://discuss.px4.io/t/send-custom-mavlink-message/1370/8 "2017-04-10T07:52:37Z")
See [this](https://github.com/mavlink/mavros/issues/166) issue. ---
**Author:** ![zyq1993](https://discuss.px4.io/letter_avatar_proxy/v4/letter/z/aca169/32.png) [@zyq1993](https://discuss.px4.io/u/zyq1993)\ **Post date:** [April 10, 2017, 2:35pm UTC](https://discuss.px4.io/t/send-custom-mavlink-message/1370/9 "2017-04-10T14:35:38Z")
I want to know how you judge whether px4 has sent the custom messages? Now I’m not sure whether px4 has sent my custom messages. ---
**Author:** ![pietrop88](https://discuss.px4.io/letter_avatar_proxy/v4/letter/p/bbe5ce/32.png) [@pietrop88](https://discuss.px4.io/u/pietrop88)\ **Post date:** [April 16, 2017, 7:29pm UTC](https://discuss.px4.io/t/send-custom-mavlink-message/1370/10 "2017-04-16T19:29:10Z")
I extended mavros and it worked. If you want to see the mavlink streaming, I think that the fast way is to use pymavlink or mavproxy.