Cruise mode is a bit like FLY BY WIRE_B (FBWB), but it has “heading lock”. It is the ideal mode for longer distance FPV flight, as you can point the plane at a distant object and it will accurately track to that object, automatically controlling altitude, airspeed and heading.
The way it works is this:
- if you have any aileron or rudder input then it flies just like
FBWB. So it holds altitude until you use the elevator
to change the target altitude (at the
FBWB_CLIMB_RATErate) and it adjusts airspeed based on throttle
- when you let go of the aileron and rudder sticks for more than 0.5 seconds it sets an internal waypoint at your current location, and projects a target waypoint one kilometre ahead (note that heading lock will only activate if you have GPS lock, and have a ground speed of at least 3 m/s)
- as it flies along it heads for the target waypoint, and constantly updates that target to always be one kilometre ahead, leaving the previous waypoint as the position that you centred the aileron and rudder sticks
- as long as you don’t touch the aileron or rudder, it will run the same navigation system it uses for waypoints, including crabbing, cross-track etc, so it will very accurately hold that ground course even in the face of changing wind conditions
One of the nicer aspects of CRUISE mode is how it handles rudder. If you give it some rudder then the roll controller will keep the wings level, but the plane will yaw with the rudder. So you get a “wings level” turn, allowing you to rotate your flight to point at whatever geographic feature you want to head towards. Then when you let go of the rudder it will head straight for that point.
Note that you can configure CRUISE mode to do terrain following on PX4/Pixhawk. See the terrain following documentation.
Make sure you only fly FPV if it is allowed by your country’s flight and airspace control rules. Many countries do not allow non-line-of-sight flight without a special operating license.