I have a Kongcopter fq700 frame, KDE Direct 4014XF motors matched with their 55A ESCs, 16x5.4 Tiger Motor props, Pixhawk with v3.3.2. I have a Betview 2-axis gimbal with the W-BGC Pro alexmos controller. I had one crash and have since replaced the frame, motors, and props.
No matter how bad its handling in flight the vibrations are almost non existent. I had a 990mm custom carbon fiver frame at first and the 3 & 4 motors ran higher pwm and hotter than the 1 & 2. Switched to Kongcopter frame and initially it flew rock solid with default PIDs. I had 2 lbs of ballast weight fixed in the front to balance the battery in the back. Once I put the gimbal on, the issue with the 3 & 4 motor seemed to come back.
Troubleshooting:
Motor mounts - all motor mounts on a kongcopter frame have a tiny plastic piece to ensure that the mount is on level; that's it. Why do all these hobby frames absolutely suck when it comes to motor mounts? Anyways, there is slop in this of a max of 2 degrees. At 2kg thrust that's about 70 grams of horizontal thrust for a motor tilted by 2 degrees. What I don't understand is that I have hard mounted the plastic motor mount to the aluminum arm with exopy, but the time it flew the best is when I had not yet done that. So I know it has flown good without doing that.
PIDs - As I said, I had it flying great for a little bit on default settings. No motor overheating, no yawing. The only thing I can think that changed was the gimbal being put on. I wouldn't think that the center of mass being off would affect the yaw so much when I have these monster motors. But then again I don't know what ~100g of horizontal thrust translates to in terms of motor output to counteract it. I plan on following this tutorial this weekend to see if PID settings fixes it completely:
ESCs - We thought maybe the ESCs on motors 3 & 4 were damaged in the crash. Not by being hit (they are inside the frame) but because the CW motors were more twisted about their arms than the CCW ones. So I rotated the ESCs clockwise about the motors, so that now if they were the sole problem, a higher pwm in RCOUT as well as heating of the motors should occur on 1 & 2. That hasn't happened. As of trying to fly lately, the motors don't seem to be heating CW or CCW, but it wants to steadily yaw clockwise as soon it is free from the ground. I recently updated the firmware on the KDE ESCs as well.
I have recalibrated multiple times, compass, accel, radio. It had this problem in v3.3.1 as well. It seems to have more of an issue running on 6S than on 8S, but I'll have to swap power boards and see after I mess with the PIDs this weekend. I'm just at a loss because things seem to contradict each other when I am thinking about it. I hope its PIDs, but it flew fine once before with no tuning. That was also when the mounts weren't held firm with epoxy.
Any thoughts would be appreciated :)
Replies
What temperatures are you flying in? I've heard there may be temperature related gyro drift with one of them (can't remember which one).
Solved: As another post on the exact same issue (CW motors running hotter) proved, it was just the PID tuning. The integral term was far too low in proportion.
Current values:
P: 0.20 (max)
I: 0.250 (exact middle of allowed values)
D: 0.02 (max)
Flies like a champ, motor output signals are within 20 milliseconds of each other.
The next issue we had was that in loiter mode it dropped significantly during any semi fast roll/pitch. The aerodynamic effect of prop wash creating a lower pressure was the cause. I raised EKF_ALT_NOISE from default of 1 to 2, and also flew with the shell cover on. Much much better.