I loaded the 2.9.1b firmware into my APM1 and went for a test yesterday.
Quad is doing fine except for alt hold mode.
It shoots up like a rocket or falls like a brick (motors just stop).
I asked my friend to monitor the telemetry.
Before taking off we reset the alt to '0'.
Take off, stay in stabilize mode and hover around 3m.
My friend was reporting values at 25m and very heretic behaviour.
Continued the flight to collect some log data.
When landing the quad the alt value returns smoothly to '0'.
When looking at the logs we saw same heretic behaviour and even negative values.
Quite stange will the quad was in the air and not drilling a tunnel throught te ground as far as I know :-)
The sensor is covered as suggested int he wiki to prevent unwanted airflows to influence the readings.
Did someone experience similar issues? Any hints on how to solve?
I resolved the issue by taking care of the vibrations.
The way I solved it was by adding O-rings to the mount in combination with Kyosho zeal tape.
Alt hold was very smooth even got a videoof the quad.