Tuning Large Quadcopter

Hi I’m having trouble tuning the quadcopter I built. I’m new to quadcopters and APM and I’ve got a beast on my hands for better or worse. It’s larger than most quadcopters and I optimized the frame for video work more than flight performance so I wonder if the starting parameters for APM are appropriate for me.

The issues I have are:

  1. The biggest issue is it flies ok in stabilize but if I turn on loiter it twitches back and forth and becomes increasingly unstable over the course of 20+ seconds of no input on the controls and just hovering. I had one point where it started making big swinging circles about 10’ in diameter after a few minutes of flight. I’m running the external compass and my APM is vibration isolated (I’ll admit I haven’t run a vibration data collect yet though) and I have good HDOP so I can’t see why I can’t get a smooth hover. I think the quad is overpowered so I set the slider for responsiveness all the way to the left (I think thats .06 for the gains?) and that didn’t help and I tried .2 and that seemed too responsive. My flight log records me trying various gains. I could do this is a more scientific way and record the gain for each collect. I think my data logs show some sort of roll vs rollin behavior that’s off. Are my controller gains much too low?

  2. The throttle and altitude is difficult to control. It feels like there’s a very small range where I can put the stick that isn’t shooting up into the sky or falling like a rock. I did the throttle midpoint set procedure. Alt Hold helps but when I try to descend it seems like the ESCs can’t spin the props at a stable low speed at a certain point and the quad falls in a semi-controlled manner if I try to rapidly descend. Not a huge deal breaker at the moment since I can just be patient and descend slowly.

  3. In loiter and stabilize if I yaw to the right the copter pauses for a second then wants to drift to the right. The faster and more yaw I ask of it, the more it drifts to the point where it will go 10 feet or so. The revers happens to the left. In loiter after it drifts to the side, it slowly corrects back to the yaw point. Maybe this is a related issue.

I probably should post parameters but I’m pretty much using the beginner load with the responsiveness slid all the way to the right. All these flights are with very little wind.

Here is info about my quad:

Here is my site where I’m trying to collect more info but this is really under construction right now.

Ardupilot APM 2.5
Hobby King 40A BESC
Tiger MN4012 Kv340 Motors
Maxamps 11000mAh LiPo Battery
AttoPilot Voltage and Current Sense Breakout
3DR Telemetry
3DR External Compass
Spektrum AR9010 9 Channel Rx
Immersion RC 5.8 Ghz Video Tx
DYS Brushless Gimbal
Spektrum AR610 6 Channel Rx

Weight 10lb
Size 28.4” prop center to prop center

Flight video of portion of log (sorry about really shaky vertical video - not sure if this is even useful)


Other flight video (I could dig out the logs for these if it helps):
You can see the descending problem here at about 30s:


You can see the strafe right after yaw right here at 1:12:

Graphing the roll vs rollin
It doesn’t look like the controller is asking the quadcopter to do anything. Does that mean the gains are too low?

If someone wants to make a recommendation for a starting point of parameters, I’ll go fly it and collect on board video, better 3rd person video, and cleaner logs to help tune these problems. At the moment I just don’t even know where to start though.

Obviously,your PID is too high, so there is high vibration in flight, i do not know the PID parameters, you can give us the picture of PID parameters.
You are very lucky that your quadcopter not crashed.

I’ll copy the data off my GCS computer when I get a chance but I reset all the parameters back to the default and that fixed my issues. That meant my gains needed to be higher but I don’t really understand why that would help. Maybe I messed with some parameter I shouldn’t have. The yaw problem just going away really doesn’t make any sense. I upped the altitude gain slightly from default to fix the quad losing altitude in forward flight.

I checked my vibration levels and they were within the acceptable range.

Here’s a video of a nice happy flight.