Quadcopter - APM 2.5 v3.01 - A multitude of problems.

Hey everyone.

I'm in need of some serious help with my quadcopter (TBS discovery) as I can not get it to fly correctly at all as it has a number of problems. I have been trying to tune them out with no luck.

The first issue is it's yaw. Whenever I rotate the quad it is extremely wobbly and quit violent, it almost looks like it's going to shake itself out of the air. I can rotate slowly if I give it a tiny amount of stick but if I give it a decent amount to rotate it more quickly it is very violent. It also over compensates after having rotated clockwise but does not over compensate as much after having rotated anti-clockwise.
The logs show the YAW IN compared to the YAW having a huge difference..yaw is off the charts.

I've checked both it's vertical and horizontal balance and it's pretty much spot on..The COG is where it should be. Vibrations are also pretty good. I am using the 4 x 1/2inch square of moongel on each corner of the APM box trick and it works really well, much better than anything else I've tried.

The quad also doesn't rotate/pivot around it's COG, instead it rotates from one of the arms, ie. if it is rotating clockwise it will rotate with the front right arm as its fixed point. It's hard to explain, but if you imagine the either the left or right hand arm, depending on which direction it is rotating, being the point of axis and the rest of the quad circling around it.   Another way of explaining it: if you had a stick 30cm long, instead of the stick rotating around the middle at the 15cm point it rotates around the front at the 1cm point. I hope that makes sense?  It really is bizarre.

The second issue is the quad bounces on auto land. It generally bounces 3 times before it will settle on the ground. I have no idea how to correct this and from what I have read was supposed to be fixed in the v2.9.1 firmware? I have checked the throttle mid position and set it correctly but it did not help.

Third issue: I was out today flying and had the scariest thing so far happen. I was flying around in ALT HOLD mode, it was flying pretty well other than the yaw issues. I put a bit of horizontal speed into it and the quad basically shot itself into the ground. It went down so quickly and at such a sharp angle I could not react fast enough to pull it up. Up until that point it had been maintaining it's altitude pretty well. Luckily there was no major damage other than breaking off a landing foot and a broken prop.

The first log I had IMU logging turned on, vibrations seem pretty good to me?
The second log I have motor logging turned on. You can see at 16.3 in the second log that altitude plummets for no reason at all and that's when it crashed.

Any help would be greatly appreciated.
  Cameron

2013-09-06 13-00 5.log

2013-09-06 13-25 1.log

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Replies

  • First issue, are you using the "V" type frame in the mission planner after you install the quad firmware? Also if you look at your motors and graph them. "motor 2" seems to drop quite low, i would bet thats the one that it spins around on? Also have you done the compassmot test to see EMI on the magnetometer? ALSO calibrate your escs all at once if you havent done it.

    Second issue, the bouncing landing is the best your going to get without a sonar. The barometer doesn't know when its on the ground for sure.

    Third issue, it looks like your barometer graph is a little more bouncy than mine. Make sure its covered up from wind and light with some type of dark foam. Since you were flying in ALT hold mode when it crashed the throttle went all crazy up and down, like the barometer sent information telling it was too high, then it thought it was too low.

    Your vibes look good.

    Your yaw, and crash problems could still also be a hardware failure, faulty or bad timing esc, or a bearing seizing in a motor. Seems like there is quite a bit of roll "bounce" most of the time, while your pitch stays pretty stable.

  • Second and Third issues probably point to barometer problems relating to airflow around the APM. Where have you mounted it?

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