John, what are you referring to with the RC RX cable? Is this the PPM
cable attaching the receiver to PPZ?
There's been a couple of crashes like this discussed on IRC recently.
I'm not sure if the fault was identified but the overloading of the 5v
PSU was suggested. This could easily happen when the servos are driven
to the limit and stall due to the hardware set up. Where ever possible
the currents drawn by the servos need to be measured when all control
surfaces are at the limit. If there are any stall conditions the setup
needs to be adjusted either physically on the air frame or by reducing
the control throws in the config file.
The 5V PSU is not only responsible for supplying the servo power but
also the 3v3 regulators power! Therefore if the 5v line drops due to too
much current being drawn then it may take out the main CPU. For my
particular setup with an 868 modem, the CPU, GPS and Modem can take upto
500mA of current. The limit of the 5V PSU is 2.25A so roughly there may
be something in the region of 1.75A left for all of the servos. That
only needs a couple of servos to stall and you could be in trouble.
Due to the above, I will be removing the 5V connection to the servos and
providing another regulated 5v directly from the battery. This will have
a limit of maybe 5-10A which is complete over kill.
I've just noticed the current-limiting switch on the hardware, this
means the servos can only draw 1A and then the switch kicks in and
notifies the CPU using GPIO. Does anyone know what the firmware does in
this instance? That therefore means that there's even less current
available for the servos and anything else which you may have connected
on the 5v rail... hmmm. I see this can trigger from 0.5A to 1.25A,
anyone ever tested this? I'm wondering now what would happen if this
were to fire, the servos would be left in their current position (or
driven back slightly from mechanical pressure). The AP might (depending
on what the GPIO signal does) try and keep driving the servos at their
current position which would mean that when the current limiter recovers
it then goes straight to the limit again?
Anyway I've rambled enough this morning!
Adam
2009/8/9 John Burt <address@hidden <mailto:address@hidden>>
Martin,
I crashed an Easystar just like that during early flight testing.
The AP (Tiny 2.11) went nonresponsive and dived into the ground,
despite my having immediately flipped the switch to manual. It would
seem that the AP processor just locked up - truly a worst case
scenario. The cause of the behavior was an undervoltage spike
condition due to sourcing the four servos and RC RX off the 5V
supply. In case you haven't already, you should always power your
hardware off a separate BEC (which begs the question of why the AP
has a 5V source anyway).
AP generated noise on the ground wire was other cause of bad AP
behavior that I experienced. This causes glitching and reduced RC
range. It has been covered ad nauseam in other posts, but I'll
repeat it: it's especially helpful to put an RF choke on the RC RX
cable. Try to wrap the wire 4+ times around the choke.
Martin P wrote:
Hello everyone!
Last weekend I had a good AUTO1 flight with my Minimag. It
reacted to pitch and roll commands, and I was able to control
the throttle. I had an attitude command in my flightplan which
was never left (as I know now).
Yesterday I tried again, without the attitude statement and
without a holding point block.
In AUTO1, it killed the throttle. Switched to manual and landed
to change battery because it was not fully charged.
Took off again. Switched to AUTO1 and it immediately stabilized
the plane. Strangely, this time it did not react to the roll
command. I flew around using the rudder. When I used the
elevator stick, the autopilot controlled the throttle. Good, so
far.
Suddenly the plane dived down vertically from an altitude of
roughly 40m. No reaction, just kept going vertical and slowly
spinning around the longitudinal axis until it crashed.
There was not as much damage done as I expected. These foamies
are awesome. All RC components including Tiny and Xbee are OK.
Except for the Lipo which is badly bent out of shape and will be
replaced for safety reasons.
Unfortunately I can't see much from the log as I had lost the
link probably minutes before. I was in stage "HOME" because I
had left the fly-too-far circle before and came back manually.
The switch was on manual so I probably tried to rescue. The Tiny
was unplugged which can have happened at the crash or before.
One aileron was ripped off and the horizontal IR was missing (I
found it in the grass).
So far, my report. The Minimag is already repaired and I'll keep
trying.
Greetz, Martin
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