david.p.mann
Second Officer
Flight distance : 18669501 ft
United States
Offline
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Gents,
One more CRITICAL item to add to your preflight check list - always, ALWAYS, go to the Map screen and make certain that the Inspire 1 AND the RC are shown on the map as being in the same (correct) coordinates where they are currently physically located.
"Close" is NOT good enough - zoom in ALL THE WAY in satellite view mode and if the location of the Inspire 1 is off by more than 10 feet, do NOT assume that the satellite map is in error. This is particularly important if you have traveled far from your last flight location or if you are in an area where the Inspire 1 and/or the RC do not have unobstructed view of the sky and access to 7+ GPS satellites. If the location of the Inspire on the satellite view is not correct, then you most likely do not have a good GPS lock on your "real position." If this is the case and you take-off in P-GPS mode, you could have a fly-away situation.
What I believe happens is this: the Inspire has an incorrect GPS position (it may only be off by, say, 15 feet; you take-off and rise up to hover 4-10 feet above ground; the Inspire GPS now gets a new (correct) GPS satellite fix; even though the Inspire has not physically moved, the flight control software thinks that the Inspire has suddenly moved from it's initial (incorrect) GPS location to it's real current (accurate) GPS position and it WILL IMMEDIATELY TRY TO RETURN TO IT'S INITIAL INCORRECT HOME POSITION. The result can be a sudden move in the direction of the incorrect initial home position resulting in a crash or injury if a person, building or tree happens to be in that direction. I don't know if this could happen, but if the initial GPS home point location error is huge (say, 1000 or more feet), this would look like a fly-away, when the flight control software is simply trying to return the UAV to it's (incorrect) initial home position. The same precaution and potential issue can occur with a Phantom 2 Vision+ UAV. I own both a P2v+ and an Inspire 1 and have experienced this issue (rarely) on both aircraft.
In 25 flights with my Phantom 2 Vision+ V3.0 (latest firmware), I have seen 15-25 feet errors in initial home position twice - both times when trying to launch from my back yard where clear view of the sky is restricted by surrounding homes and my garage. The first time I dismissed the incorrect position of my craft on the satellite view (Phantom shown 25 feet west of actual position on neighbor's home) as "map error" since I had 7 GPS satellites. When I tried to takeoff, the Phantom started bouncing sideways on the ground in the direction of the neighbor's house. I realized what was happening, shut down, moved my Phantom to a different spot in the yard, got an accurate GPS fix (confirmed by the view on the satellite view on Ground Station map) and took off without problem - straight up - 10 minutes later. The second time this happened, I did not even attempt to take-off. I just moved the Phantom to another location and waited until I had an accurate home point location shown on the satellite view map. NOTE: these errors occurred even though I showed 7 GPS satellites. Personally, I don't like to fly unless I have 10+ GPS satellites, but that is not always possible unless you are in a completely open area.
Based on my experiences with my P2V+, I now carefully check my indicated GPS position in satellite view mode on both my Inspire 1 and my P2V+ BEFORE taking off in either aircraft. In 15 flights with my Inspire, I have seen a bad GPS home point fix just one time - it was off by ~ 25 feet. With aircraft and RC turned on, but props not turning, I picked up the Inspire, walked in a 20 foot circle, set it down and now had an accurate GPS fix (i.e., location of Inspire on satellite map view agreed within a few feet of actual position).
Let me know your thoughts on the above and your personal experiences with inaccurate initial GPS home point fix. |
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