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  1. #1
    Forum Member
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    May 2012
    San Diego, Ca

    A flaw in RTH...

    I figured I'd start this discussion here instead of RCG since most of the experts in FPV have migrated over here. I'll preface this by saying the incident that I had is my fault involving a power module. This plane was set up for short range and was never supposed to leave a 3000' x 3000' box. My faults are my faults, so save the banter for another thread.. The purpose of this thread is to get folks thinking and discussing what RTH does and how we can improve that critical system we rely on when the shit hits the fan. We talk about policing ourselves and I'd like this to be a constructive thread. Not a bash fest!

    Background: I had a power sag while flying FPV that browned out my RC link, Flight Controller, OSD, and GPS. I know the flight systems started coming back up because the flight controller stabilized the plane. The RC Link did its thing by going into fail-safe which engages RTH.

    The flaw here is the fact that GPS needs time to acquire satellites before the flight controller can begin navigation. During power up the flight controller erased the 'home' location and waited until GPS lock has been acquired. At that point the place where the GPS lock has been acquired is considered the home location. In my case this satellite acquisition probably didn't happen until a good 45-60 second later. At which time the plane in question has already traveled 1.5-2km from base. GPS comes on line, and the Autopilot now circles above what it now thinks is home.

    Let's take out RC link and video link out of the discussion because they are moot. Let's focus solely on RTH and how we can prevent a runaway plane when GPS lock has gone astray for a moment but is reacquired later. There is a VERY good chance that the plane would have returned to base had I gone into autonomous mode as my fail safe. That being said, should programmers of controllers that bring us RTH allow us to hard program a RTH position vs assuming where the GPS locks is 'home'. Perhaps by flipping a few switches back and forth or something.

    I'll open the discussion to the group..
    Last edited by typicalaimster; 9th January 2013 at 01:33 AM. Reason: verbage

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