Beginner questions about flight modes..


First I would like to congratulate you guys who have developped the ArduCopter/ArduPilot kits ! I recently bought and built an AC2 from JDrones, explanations on the Arducopter Wiki were perfectly clear, and the copter behaved as I had intended !

My first test flights went perfect...until this weekend where I messed up with the simple mode (yeah, reorienting yourself to follow your copter is not a good idea...), ending in going right into a tree instead of avoiding it...hopefully my AC2 only suffered minor harm (propellers and 1 arm bent...) and should be back in the air this weekend.

Here are my (many) questions now. I looked through the Arducopter Wiki and searched through the discussions and blog articles on this site, but didn't find a crystal clear answer to these questions (I am using Arducopter 2.0.49).


1) What is your feedback about auto-mode ? Is it stable enough to use it or should I use it with care (and fear...) ?


2) About altitude of waypoints in mission planner. If I understand correctly the manual, you set waypoints altitude relative to the takeoff altitude. But how is the 'relative' and 'starting altitude' measured ? Through GPS or throught the barometer ? If through GPS, it means you have to wait for a 3D fix before launching auto-mode, right ?


3) Are auto-takeoff and landing available without a sonar ? Are these functions 'reliable' or would it be better to manually take-off and land ?

Moreover, I don't fully understand the "note: If you takeoff from the ground, your most recent Alt_hold throttle value is used as a baseline for throttle control." from the Wiki, can you explain a bit more ?


4) I remarked that my AC gets woobly when descending, even if not descending so fast (i.e. ~1m/s). What kind of descending speed should I expect when using auto-mode (and going from a waypoint to a lower waypoint) ? Should I change some PID values like explained in  the manual or just let it like that and do some tests?


5 (and last...)) I have a Spectrum DX7: When the connection between the transmitter and the receiver is lost (i.e. too far away for example), all channels on the receiver go off (Which is cool for an RC car, but maybe not so optimal for a plane...)

My question is: if I plan a flight through Mission Planner, launch the auto-mode and lose connection between transmitter and receiver during the flight, what will happen ? Will my AC just stop spinning its motors and crash or continue until planned flight is done (and maybe retrieving the connection) ??


I hope I am not too long for my first post...



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  • 100KM

    1) With care and fear.  It may act strange sometimes.  I never crashed in auto mode, but always be ready to switch back to simple and bring the copter back manually.

    2) It's always best to wait for 3D gps fix before even arming motors, if you plan to do any gps dependend modes during flight.  Home position is set when arming motors, barometer is calibrated when arming motors and I guess home altitude is also set at arming motors

    3)You could do auto take-off and landing without sonar...  But barometer is only about 1m accurate and swings up and down.  Sonar is about 1cm accurate and doesn't swing.  I think you can image why sonar is advised for auto-landing now ;-)  

    The copter needs a throttle value to hoover at.  Depending on weight, power of you motors, props, this is different for each copter.  Right now, the copter will assume that you are hoovering at constant altitude when you engage alt_hold.  So throttle value when engaging alt_hold is considered as steady hoover.  This means that if you engage alt_hold while climbing, the copter will keep climbing in alt_hold for quite a while, until it slowly corrects your throttle value.

    If you take-off from ground, there is no throttle when engaged.  So it will take the last known hoover throttle value.

    4)Mine gets wobbly to on manual descends.  In 2.0.49 automatic descends are rather slow and gentle.  There shouldn't be any "surprising" altitude drops in auto mode.  If there are, it's time to take over manually.  Try it by engaging alt_hold and then moving to full throttle to make the copter go up automatically.  Make sure you remember the hoovering stick position for when you disengage alt_hold.

    5)Try it.  Bolt or tie down the copter firmly, spin it up, go into manual and turn off your transmitter.  Normally it's advised to make the copter go into RTL, so it returns home.  I have seen few brave enough to try (fly out of radio range), and no enormous successes in that.  

    My advise : start with VERY simple missions, flying squares, then add auto-land and take-off.  Practise RTL and other automatic modes.  After 50 automatic flights, see if you're still brave enough to try out of sight flights.


    Lastly, following video might show you a bit what to expect (automatic mission in the end with waypoints at different height (5m and 8m)) :

    And BTW, I also had myself caught with the "simple mode, turn yourself around" crash.  You're not the first ;-)


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