Developer Comment by Michael Oborne on February 27, 2012 at 3:23am

 

(control_mode == CIRCLE || control_mode >= FLY_BY_WIRE_B) && (abs(home.alt - current_loc.alt) /span> 1000) && ((g.airspeed_enabled ? airspeed : g_gps->ground_speed) /span> 500 ) && !(control_mode==AUTO && takeoff_complete == false)

looking at it line by line

1. was in mode > fbw B therefor Auto = true;

2. alt from home  < 10 m? = true

3. groundspeed < 500 = true;

4. if NOT( in auto and takeoff is not complete) = true

 

the net result is true which means that throttle will not activate.

my thoughts about the one where it did try and go, one of those conditions must have been false.

so it could be any of these things. 1. the gps alt was missreading over 10 m alt from home, is posible. 2. groundspeed over 5m/s this again is determend by the gps, and is posible. 3. autotakeoff was programmed as the first mission point, and takeoff criteria hadn't been meet, so throttle went to full.

the only was to tell which one it was would be to look at the logs, from that you could see if the gps hadn't setled down, or some other thing was going on.

Comment by George Perkins on February 27, 2012 at 7:54am

Interesting stuff. Is it possible to take off from the ground, assuming the plane has landing gear and a nice smooth runway? It would obviously need to disable the 5m/s failsafe.

Comment by Don Brooks on February 27, 2012 at 8:07am

For a ground takeoff you would have to get it started with manual throttle for a couple of seconds to get speed and set direction.

Comment by Trent at MyGeekShow on February 27, 2012 at 1:31pm

An excellent discussion. I must admit, when I was doing these launches, I was a good distance from the home location, a good hundred feet or so... I didn't realize that was so important to it's sequence. I'll be more attentive to that in the future. In addition, I should also say that the GPS is poorly located with a reduced view of the sky, so it wouldn't surprise me if that were contributing to it.

 

Lastly, an observation: when I start up the APM for the first time and use stabilize during a hand launch, the plane seems to pitch down, enough that I have to take control to return it to a safe flight path. However, when I land and hand launch it again, it performs perfectly with a hand launch. I only mention this as you may have noted that during my first auto take off after setting it up, the throttle kicked in earlier than expected, but subsequent auto take-offs didn't have that effect. Interesting that the first "use" of the APMafter start up for me seems to have different results than the later uses. No big deal, just an observation.

 

Thank you guys! This is awesome stuff...

Developer Comment by Michael Oborne on February 27, 2012 at 3:52pm

if you program takeoff as your first waypoint, and are in auto, i beleive none of the above realy applies - re last line. in that code.

Developer Comment by Andrew Tridgell on February 28, 2012 at 12:02am

Hi Trent,

Regarding the pitch down on launch, the most common reason is that you have built up an I term in the pitch PID. What value do you have for PTCH2SRV_I ? If that value is non-zero then whenever you have the plane in stabilize mode it will be 'learning' the right amount of elevator to use to keep the plane level. Now imagine you are holding the plane nose up ready for a hand launch. The APM doesn't know you haven't taken off yet, so it is trying to stabilize the plane. It sees that its attempts to stabilize are failing so it tries harder and harder, building up an I term in the PID.

Now when you do finally launch it will take a while to unlearn that I term, so it will initially pitch the nose down until it learns that the I value is not needed.

This is just a guess of course, and perhaps your PTCH2SRV_I is zero, in which case the above doesn't apply. In that case if you post the tlog of the flight we may be able to work out why it is pitching down.

Comment by jjohow on February 28, 2012 at 2:38am

Hi there!

This might sound funny now - but what is so new and special about auto takeoff and landing?

I simply add the autotakeoff and landing command at the beginning and end and this is it.

As soon as I switch to AUTO, the motor kicks in and I throw the plane. I goes down the waypoints and lands

smoothly where I set the autoland waypoint.

Two things are important to know: As soon as you switch it to AUTO for takeoff, don't move your plane backwards, in my case this was the reason for the feature not to work. So be sure that you run fast enough, that the motion of your arm while running doesn't make the APM think it moves backwards. Because while running your arm holding the plane will make counter-movements to balance you body. Or, if you have a very lightweight plane, move your arm way back, switch to AUTO and throw it in one forward motion slightly nose down or level.

Second thing - for Autolanding: Your plane wont touch down exactly where you set the autoland waypoint. It will cut off throttle at this point and will be approx. 4 meter above ground, and than keep it leveled until touchdown.

Works great for me.

cheers

Joerg

Comment by George Perkins on February 28, 2012 at 2:58am

Thanks Joerg, That's very interesting.

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