Altitude shoots up in Alt_hold

For anyone experienced at interpreting logs, see attached…
Had a sudden out of control throttle response in alt_hold. I’m assuming that I have a vibration issue, just wondering if anyone has any other opinions. Stabilize mode first, then switched to Alt_hold. There are times when the Acc plots are ok, but when it shoots up to full throttle in alt_hold mode, the Accz does get a little crazy, not sure if these vibrations are a cause or a result of the throttle going to max.
When I heard it go to full throttle, I brought the throttle down, but DAlt starts to climb??, even though the ThrIN is at zero. If I understand it correctly, DAlt is the desired altitude, so I don’t understand why this would be increasing?
Board is APM 2.5
Firmware is Arducopter V3.2
Any thoughts?

@Ben Willistein,
Here is an Auto Analysis of your log file:

Size (kb) 1132.4599609375
No of lines 16701
Duration 0:00:00
Vehicletype ArduCopter
Firmware Version V3.2
Firmware Hash c8e0f3e1
Hardware Type
Free Mem 0
Skipped Lines 1

Test: Autotune = UNKNOWN - No ATUN log data
Test: Balance/Twist = GOOD -
Test: Brownout = GOOD -
Test: Compass = FAIL - Large change in mag_field (225.08%)
Max mag field length (750.90) > recommended (550.00)

Test: Dupe Log Data = GOOD -
Test: Empty = GOOD -
Test: Event/Failsafe = WARN - FENCE
Test: GPS = UNKNOWN - No GPS log data
Test: IMU Mismatch = NA -
Test: Parameters = GOOD -
Test: PM = WARN - 1 slow loop lines found, max 7.30% on line 14801
Test: Pitch/Roll = GOOD -
Test: Thrust = GOOD -
Test: VCC = WARN - VCC min/max diff 0.343v, should be <0.3v

If your receiver throttle input is on RC2, there were some very large excursions on that channel prior to the Fence Failsafe.
Also, your compass has what appear to be magnetic interference issues.


I definitely think that it’s a vibrations issue. Yours are well outside nominal ranges (see … sing-logs/). From my understanding, issues with z-vibrations have been known to cause undesired climbing. The desired altitude is influenced by the accelerometers readings, so if you are having z-vibration issues then it is expected that dalt values will be affected.

the vibrations are odd, they do seem to get worse right before the climb occurs.

Are you sure verything is balanced, mounted propelry, nothing loose, no cables snagging etc.