Change velocity with message to Mavlink

Question

I'm trying to move a vehicle by changing the velocity. I've been able to perform the operation successfully in Python, but for my project I can not use Python, so I'm using Android to try to make the same operation. The working functionality in Python is:

def send_ned_velocity(velocity_x, velocity_y, velocity_z):
"""
Move vehicle in direction based on specified velocity vectors.
"""
msg = vehicle.message_factory.set_position_target_local_ned_encode(
    0,       # time_boot_ms (not used)
    0, 0,    # target system, target component
    mavutil.mavlink.MAV_FRAME_BODY_NED, # frame
    0b0000111111000111, # type_mask (only speeds enabled)
    0, 0, 0, # x, y, z positions (not used)
    velocity_x, velocity_y, velocity_z, # x, y, z velocity in m/s
    0, 0, 0, # x, y, z acceleration (not supported yet, ignored in GCS_Mavlink)
    0, 0)    # yaw, yaw_rate (not supported yet, ignored in GCS_Mavlink)
# send command to vehicle
vehicle.send_mavlink(msg)
vehicle.flush()

What I'm trying to do is the equivalent code in Android:

                   // Create the message
                msg_local_position_ned msgMessageInterval = new msg_local_position_ned();
                msgMessageInterval.x = 0;
                msgMessageInterval.y = 0;
                msgMessageInterval.z = 0;
                msgMessageInterval.vx = 10;
                msgMessageInterval.vy = 0;
                msgMessageInterval.vz = 0;
                msgMessageInterval.time_boot_ms = 0;

                MavlinkMessageWrapper mavlinkMessageWrapper = new MavlinkMessageWrapper(msgMessageInterval);

                // Send the message to MavLink
                ExperimentalApi.getApi(drone).sendMavlinkMessage(mavlinkMessageWrapper);

                // Listen for the message received
                drone.addMavlinkObserver(new MavlinkObserver() {
                    @Override
                    public void onMavlinkMessageReceived(MavlinkMessageWrapper mavlinkMessageWrapper) {
                        System.out.println("MESSAGE RECEIVED="+mavlinkMessageWrapper.getMavLinkMessage().toString());
                    }
                });

What am I missing? Any help would be greatly appreciated.

Thanks.

Answer 1

I'm not familiar with Java MAVLink implementations, but you are sending LOCAL_POSITION_NED messages which are telemetry message, not the control one. You need to send SET_POSITION_TARGET_LOCAL_NED instead, like you do in Python.

Answer 2

[Closing the issue] For the future programmers who have to face the same problem here is my working code:

            msg_set_position_target_local_ned msgMessageVelocity = new msg_set_position_target_local_ned();
        msgMessageVelocity.time_boot_ms = 0;
        msgMessageVelocity.target_system = 0;
        msgMessageVelocity.target_component = 0;
        msgMessageVelocity.coordinate_frame = MAV_FRAME.MAV_FRAME_BODY_NED;
        msgMessageVelocity.type_mask = 0b0000111111000111;
        msgMessageVelocity.x = 0;
        msgMessageVelocity.y = 0;
        msgMessageVelocity.z = 0;
        msgMessageVelocity.vx = _vx * _speed;
        msgMessageVelocity.vy = _vz * _speed;
        msgMessageVelocity.vz = _vy * _speed;
        msgMessageVelocity.afx = 0;
        msgMessageVelocity.afy = 0;
        msgMessageVelocity.afz = 0;
        msgMessageVelocity.yaw = 0;
        msgMessageVelocity.yaw_rate = 0;

        MavlinkMessageWrapper mavlinkMessageWrapper = new MavlinkMessageWrapper(msgMessageVelocity);

        ExperimentalApi.getApi(drone).sendMavlinkMessage(mavlinkMessageWrapper);

        drone.addMavlinkObserver(new MavlinkObserver() {
            @Override
            public void onMavlinkMessageReceived(MavlinkMessageWrapper mavlinkMessageWrapper) {
                System.out.println("MESSAGE RECEIVED="+mavlinkMessageWrapper.getMavLinkMessage().toString());
            }
        });