Issue with SET_POSITION_TARGET_GLOBAL_INT

Blue Robotics Software
1

I’ve been trying to send my sub a depth command with SET_POSITION_TARGET_GLOBAL_INT, but I’m witnessing some odd behavior that I thought I would make a forum post for.

My issue is very similar to this issue: Altitude hold and depth hold in pymavlink - #11 by kg9316
However the last activity on the post is from 2020, so I thought I’d make a new post.

To summarize, when my sub has a depth of 10m and I send it a SET_POSITION_TARGET_GLOBAL_INT message with a target of 15m, the sub will only descend 1m to 11m below the surface. If I send the exact same message again, the sub will descend to 12m and so on until I send enough messages for the sub to reach the original target.

I modified the parameters suggested in the original post to no avail. Additionally, the function calc_leash_length_z doesn’t exist anymore.

Here’s the function that I’m using to send the message:

void Plugin::_sendPositionTargetGlobal(const double alt)
{
    mavlink_message_t msg;
    mavlink_set_position_target_global_int_t ptg;

    memset(&ptg, 0, sizeof(ptg));

    MAVLinkProtocol *mavlink = qgcApp()->toolbox()->mavlinkProtocol();

    ptg.target_system = _activeVehicle->id();
    ptg.target_component = _activeVehicle->compId();
    ptg.coordinate_frame = MAV_FRAME_GLOBAL_INT;

    ptg.type_mask = POSITION_TARGET_TYPEMASK_VX_IGNORE |
                    POSITION_TARGET_TYPEMASK_VY_IGNORE |
                    POSITION_TARGET_TYPEMASK_VZ_IGNORE |
                    POSITION_TARGET_TYPEMASK_AX_IGNORE |
                    POSITION_TARGET_TYPEMASK_AY_IGNORE |
                    POSITION_TARGET_TYPEMASK_AZ_IGNORE |
                    POSITION_TARGET_TYPEMASK_YAW_IGNORE |
                    POSITION_TARGET_TYPEMASK_YAW_RATE_IGNORE;

    ptg.alt = alt;

    mavlink_msg_set_position_target_global_int_encode_chan(
        mavlink->getSystemId(),
        mavlink->getComponentId(),
        _sharedLink->mavlinkChannel(),
        &msg,
        &ptg);

    _activeVehicle->sendMessageOnLinkThreadSafe(_sharedLink.get(), msg);
}

Also, I’m using the latest version of BlueOS and ArduPilot v4.1.2.

Would really appreciate some advice on this!