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First build, first flight, first post, (first crash!), all smiles

Posted by Pete Burnett on June 27, 2012 at 10:23pm

After reading for months, then ordering all my bits, then building, I finally got properly into the air yesterday. Very Happy! Quad is standard 3DR, except I've put 880 motors on it. I hope to upgrade it to a hexa and use it with a GoPro and small gimbal once I have taught myself how to fly. Yesterday was only a few small 'hops' above head height to get a feel for the controls (very different to the simulator!).

I haven't tried any different flight modes yet, am still operating in stabilize. But I do notice oscilations in the platform when I roll particularly. I have yet to play with PID's, but was hoping someone could offer suggestions? I'm running v2.6, without any alterations yet.

And note to self - don't fly in a park when/where people walk their dogs. That was the reason for the crash, Labrador took an interest in this 'thing' and I was trying to put it down in a safe place...

And finally a note of thanks to all who are behind this forum and project, great stuff!

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  • James June 28, 2012 at 5:22am

    great stuff - my first flight lasted 22 seconds! i really should have waited for a calmer day, but i was so impatient once i had finally finished construction and setup.

    i expect that with the 880kv motors youre going to need to reduce RATE P, also the defaults have STAB I at 0.1 (i think) whilst the general consensus is that this value should be 0 - i certainly fly that way.  as for D values, there are different approaches to this, in my case i use the damping on the RATE loop with RATE D of 0.010

    as for the process to tune PIDs in flight the channel 6 potentiometer method is great, in the Arducopter config screen assign the channel 6 tuning parameter youre going to work with and the max/min range of values.  set it up so that with the dial in the centre youre at a known "good" value, one that is at least good enough to fly with, in that case if your changes produce a nasty oscillation returning the dial to centre should enable you to land and work out whats gone wrong.

    the order in which to tune parameters might vary depending on who you ask, but i would try this:

    • set STAB I = 0
    • set STAB D = 0
    • set RATE I = 0
    • set RATE D as a small value so things dont get too wobbly if RATE P is wrong, perhaps 0.002 or 0.004
    • set CH6 tuning to RATE P with min/max of 0.100/0.200 - the mid value is going to be close to the default 0.16 and youre certainly going to end up with a value in the lower half of this range.
    • take off somewhere with plenty of space and preferably long grass to cushion any failed landings.  try to hover close enough to have a good view of the quad, but not too close as to be dangerous.  now give some roll commands followed by releasing the stick and watch very closely how it returns to level, with RATE P too low it could seem slow tracking your stick movements or even oscillate slowly around level.  with RATE P too high it will oscillate rapidly around the angle commanded by stick position.  with RATE P just right it will return to level quickly with a tiny bit of overshoot, but will settle on the commanded attitude quickly and without prolonged oscillation.
    • once happy with the RATE P term, land and disarm - return to configuration in mission planner, the new value should be assigned in the PID config page, make a note of it anyway as reference.
    • next is to try and limit the overshoot with RATE I - again assign this value to CH6 tuning, with min/max values of say 0.000/0.020.
    • take off and perform the same roll followed by level commands, add RATE I until the overshoot is almost completely gone - too much and it will seem a bit slow in the last few degrees of rotation and can start feeling slow to respond to changes.  you should end up with a value of about 0.010 or 0.015
    • again, land, disarm, note new values.
    • now RATE D can smooth out the remaining wobbles, and will also add stability when performing fast descents or flying in turbulent air.  assign CH6 tune to RATE D with min/max values of 0.000/0.020.
    • fly and adjust to taste - i think the maximum value people are using is 0.012, once happy with the damping you might be able to revisit RATE P and raise it slightly for sharper control.
    • finally lowering STAB P can make things much smoother, but i have found that in gusty conditions it makes the quad "wallow" in the turbulence and is generally unpleasant.  you can try values from 3.5 to 4.5, i am currently flying with STAB P = 4.3

    there, a few pointers from one thats barely past the newbie stage himself - but ive started to get some very good results with tuning and this is the way i go about it.  dont expect to get it perfect in a day, youre likely to fail at some stage and need to undo your changes - so its useful to note down the values youre playing with.  in case things go horribly wrong return to defaults and start again :)

    james

     

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