Title pretty much says it all. I had it autotuned with 3.1rc8 + a little mods to throttle gain and it had an absolutely perfect land and RTL. Zero bounces. Now after going to 3.1 stable, everything seems to be normal, with the exception that I get 2-3 bounces after landing. It will set down as normal, then after it is grounded for .5 seconds, it will hop up and set down.
I would just flash back to 3.1rc8 and forget about it, but I’m curious what could have happened so i might be able to fix it in the future.
JrLane,
That’s very odd because -rc8 and the official AC3.1 are nearly identical. There were a few changes for the Pixhawk/PX4 but only one small change for the APM2 which shouldn’t have affecting the landing…
I think i’d need to see some logs…
Okay after a few more flights i am now getting bounce with 3.1rc8. Somehow i lost the logs comparing 3.1 to 3.1rc8 but it would seem that point is moot now since i’m seeing bounce with 3.1rc8 now.
This is my latest flight with a land at the end. Conditions were 5mph wind landing into 3-4 inches of soft snow (I have no landing gear, bare DJI 450 frame)
JRLane,
I had a look at the logs and compared the CTUN message’s Baro Alt to the GPS messages’s RelAlt (which is actually the barometer+accelerometer based altitude estimate, it has nothing to do with the GPS).
…anyway, they don’t line up well which means that the altitude estimate that it’s using for missions, LAND, RTL, etc are all quite far off from reality. Normally this is caused by vibration on the frame. There’s some wiki pages which talk about how to measure the vibration by enabling the IMU message: copter.ardupilot.com/wiki/ac_measuringvibration/
I wonder if perhaps the method used to mount the flight controller to the frame has been changed or if there's been some damage to a prop or motor or something like that that may have increased the vibration levels.
I had wondered about that so i did try that via the method used on the site. I actually have screenshots of the flights. What i got out of the reading was, the levels of vibration are within range but just barely. Would you say after seeing these, it is the most likely cause of my ailment. BTW the difference between the screenshots, one is after replacing a motor that i noticed had noisy bearing.
JR,
Yes, I’m pretty sure that it’s vibration. As you say it’s within the guidelines (-15m/s/s ~ 5ms/s) but it’s a little high. This plus the difference in the inertial nav alt estimate and the baro estimate makes me think that it’s just go to be vibrations.
I’d vote for a better vibration dampening method. Maybe moongel or DuBro foam on the 4 corners of the board.