OFFBOARD takeoff, land, loiter via SET_POSITION_TARGET_LOCAL_NED

1

Previously discussed here : Offboard automatic TakeOff / Landing using MAV_CMD_LAND/TAKEOFF_LOCAL - #5 by tdo

From the Mavlink receiver implemented in the PX4 Firmware, we can read that there are undocumented features for the SET_POSITION_TARGET_LOCAL_NED mavlink message.

We can see there are a Takeoff, Land, Loiter and Idle setpoints for Offboard mode.

How far are those implemented? Are those safe to use? What happens if we send a Position and a Velocity setpoint? (by ignoring neither the velocity nor the position)

2

I tested that enum under Gazebo 7, with PX4 Firmware 1.5.5

enum TypeMasks {
    MASK_POSITION =         0b0000111111111000,
    MASK_VELOCITY =         0b0000111111000111,
    MASK_TAKEOFF_POSITION = 0b0001111111111000,
    MASK_TAKEOFF =          0b0001111111111111,
    MASK_LAND_VELOCITY =    0b0010111111000111,
    MASK_LAND_POSITION =    0b0010111111111000,
    MASK_LAND =             0b0010111111111111,
    MASK_LOITER_POSITION =  0b0100111111111000,
    MASK_IDLE_POSITION =    0b1000111111111000,
};
  • MASK_TAKEOFF_POSITION ; Takeoff and go to the position after
  • MASK_POSITION ; Go to the position
  • MASK_VELOCITY; Apply that speed
  • MASK_LAND_POSITION`; Go to the position with Z=0, GUARANTEED CRASH FOR MULTICOPTER
  • MASK_LAND; Freefall, all motors off, GUARANTEED CRASH FOR ANY VEHICLE
  • MASK_LAND_VELOCITY; Going down, ignoring given Z velocity.
  • Loiter & Idle not tested

For safety, shouldn’t :

  • The MASK_LAND should be understood like MASK_LAND_VELOCITY with (0,0,0) velocities.
  • The *MASK_LAND_POSITION go for the XY position before going down ?
3

Hello,

I’m still using version 1.4.4 but I will switch to 1.5.5

As I’m landing using Offboard command, i’m using this bitmask : (0x2000 | 0b110111000011). I also set null speed for vx and vy (even if its redundant with bitfield, just to make sure)

nedSetpoint->vx = 0; /* Set Null Speed for x and y translation */
nedSetpoint->vy = 0;

Also as I request landing the first step I do in order to bouild the NED setpoint is to use the actual Local NED for North and East, hence landing vertically.

If I correctly remember, you need to set non Null speed in SET_POSITION_TARGET_LOCAL_NED message.

I’m not sure the MASK_LAND_POSITION is really usefull as the developpers are able to decompose it in two steps. In order to avoid freefall, But having a clear and simple vertical landing procedure in offboard mode will be great :slight_smile:

I don’t use Idle or Loiter (in order to achieve loiter, I continously send SET_POSITION_TARGET_LOCAL_NED message with the exact same North East Down coordonate). I do not know what Idle is intended for.

Hope it helps.

4

Hi,

Do you mean that if i where OFFBORAD, (e.g Raspberry pi connected to Pixhawk). I should use the following message SET_POSITION_TARGET_LOCAL_NED to take off??

Can I do it simply by using MAV_CMD_NAV_TAKEOFF??

Thanks

5

In offboard mode the best solution is to use the velocity setpoint.

The AUTO TAKEOFF is a part of the Waypoint system (GPS Waypoints)

6

Does that code means if we set SET_POSITION_TARGET_LOCAL_NED 's z to 0 it automatically lands untill it reaches ground?

I’m having simillar issue in gazebo & real flight test

in gazebo if I set SET_POSITION_TARGET_LOCAL_NED to 0,0,0 copter free falls

but in real flight if I set SET_POSITION_TARGET_LOCAL_NED to 0,0,0 copter surfes around ground about 5cm and doesn’t lands

I’m looking for other ways to takeoff and land is there?
how does ‘rosrun mavros mavcmd landcur’ work?

7

My method is to send a velocity setpoint of 0.5m/s up to 1m/s