When RTL Home Point is set

ArduCopter Copter 4.0
1

I have read through the docs but I am a little confused after a recent test flight. (https://ardupilot.org/copter/docs/rtl-mode.html)

As far as I am aware “GPS Lock” is achieved 30 seconds AFTER more that 6 satellites (by default) have been found AND this 30sec counter doesn’t start until the FC is fully booted up. Can anyone confirm this? Loiter mode only works if you have a GPS lock (which requires the 30 sec minimum wait regardless of satellite count). Side question: Is there anyway to modify this time (I am guessing its hard coded for safety reasons)?

Test Flights:

  1. Flight 1: Took off after GPS lock is achieved: The aircraft returns to where it took off. All good.
  2. Flight 2: Took off right away before GPS lock was achieved (there were more than 6 sats present at the time of ARM though), but then GPS lock was achieved in the air about 30 meters horizontally away. According to the documentation it states that the Home Point will be set where GPS lock is achieved. Last time I tested this (sorry can’t find the log) the aircraft returned to the Home Point in Flight 1. Why is this?

The reason I ask is there are times we operate in urban areas where we cannot achieve GPS lock on the ground. Once we fly up, GPS lock is easily achieved. According to the documentation the home point should be set once the aircraft gets GPS lock, but I am now worried after my test that it will try to fly back to the last time it set a home point!
Note: I am well aware even if the GPS lock is set in the air where I expect it to be, it will not be able to land by itself on the ground in this situation, but this is safer that it taking off sideways to the last home point…

2

with my frsky radio control running yappu telemetry script i can hear “GPS home acquired” after about 10-20sec of “GPS 3D fix Lock” message

3

There are no counters nor timers involved. GPS lock is achieved as soon as the signal is stable enough and the math calculations onboard the GPS receiver converge.

Enable geofence and enable all the pre-arm checks. This way you will only be able to take off when the copter knows where it is. If do not have GPS signal it will refuse to takeoff.

In order to set the home position after taking off without GPS signal you will need to use mission planner, right click on the home position on the map and select “set home here”

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