Okay, finally gave my ArduCopter a try today. Freshly charged battery, nothing fancy, running ArduPirates code r527.

 

I've observed two major issues:

1. the yaw drift isn't really getting corrected by the magneto AT ALL - it kept drifting, usually clockwise (not sure if that's significant)

2. the y axis (i.e. altitude) oscillations made anything but short hovers (second or two, perhaps) completely impossible - i'd have it hovering stable and then it'd suddenly start dropping like crazy, touch the ground, then i'd overcompensate and it would shoot in the air to about 2-3 meters, then i'd overcompensate again and, as soon as i'd finally get it to hover, a second or two later, it would drop again. It looked like it was on a trampoline, prompting a random bystander to comment with: "That a prototype, or something?"

 

Now...

 

Re: 1 - Yes, the magneto does work, is enabled, the offset has been calibrated and its north indeed is, roughly, real north. The center stick position does correspond to center in Configurator.

 

Re: 2 - It was somewhat windy, so that might've attributed to it, but i doubt that's the sole reason for it. The oscillations were pretty regular, for one. Also, the wind was nowhere strong enough to cause any significant slewing or oscillations along other axes. Now here's the interesting bit - enabling altitude hold (barometer only, no sonar yet) kept it in one spot for a bit longer than a few seconds, with audible RPM oscillations. Then it went out of range and started oscillating just as badly as when i was handling it manually.

 

 

Finally, one observation re: propellers. The way jDrones/DIYdrones kit propellers are attached to the motor shafts makes for a REALLY bad design. Why? Because two of the motors (front and rear) rotate in such a direction (clockwise) that any torque exerted on the spinning propeller UNSCREWS the retainer screw/nut.


Net result - i've had rear propeller fly off the quad after it hit dirt during a hard landing, which was lucky (it spared the propeller); however, i've also had the front propeller unscrew itself mid-flight (good thing i was keeping the quad no higher than 2 m at all times) and catapult the nut and screw some 5 meters away.

 

And judging by the sound of the impact against a building wall and an iron fence, they make quite a nasty projectile weapon.

 

Maybe it's just me, but shouldn't pusher props also have reverse threads on their hub nuts/screws?!

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Replies

  • Found the cause of the propeller issue...

     

    One of the spinner nuts was cross-threaded.

    It *seems* like it's tight, until enough axial force (pull) gets exerted on it, at which point it just skips a thread and the whole thing flies apart.

     

    Bah... another long wait ahead of me...

  • Just a little tip on Barometer : be sure you have it well covered with a sponge or that your IMU is well under a plastic cover. You need only a small hole to compensate pressure differences. Somebody in germany (/*MK*/) uses shrink tube around a sponge leaving only the top open. Of course they have a different sensor and somehow easier to protect but it makes sense.

    The baro is very sensible to wind (air pressure of course :)), light, and temperature.
    It also has a lot of noise +- 25cm. in 1 secon range that can lead to a +-1 meter difference in just a few seconds. Of course this is the worst case, but anything in the middle can happen.

    http://www.rcgroups.com/forums/showpost.php?p=17973010&postcoun...
    This is a guy in the ardupirates who recently posted a video with alt hold. I think it is what we can expect with no data filtering and a "standard" PID control.
    TEMPERATURE.IT
  • Hmmm... It would seem my throttle issues might be caused by a fault in Turnigy 9x (w/ Th9x software).

    Right about 40-50% range, which corresponds to hover throttle, the throttle makes occasional sudden jumps to 100% (more often) and 0% (less often). Which explains sudden drops and bounces rather well.


    I've initially thought it was a stick (potentiometer) problem, but the raw ADC output suggests otherwise (i couldn't provoke it while looking at the raw output). Going to open it up again and clean it regardless, plus, maybe switch to Er9x.

  • Y-axis: in stable mode the only thing which controls this is your throttle stick, so if it's oscilating it's the pilot, you need more practise ;)

    for altitude hold: tune those PIDs to get it stable

     

    drift on yaw: do you have xbees? check heading in flight, you may have some wires creating magnetic fields while flying

  • 3D Robotics
    I've never had a prop fly off in scores of hours of quad flight. Perhaps yours just weren't tightened hard enough? As far as I know there is no quad on the market that has reverse threads on the pusher props, or any motor on the market that even offers reverse threads. I've never even seen mention of them.
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