RE: [Paparazzi-devel] crashed, 5V supply overloading issue

[Yves Touchette]

> It occurs to me that simply removing the aerial from the "main" part
> would turn it into a PPM demultiplexer that I could use with a BEC, if
> I needed to drive a collection of non-tiny servos. Would that be a
> (this) lazy-man's implementation of what are suggesting Yves, or have
> I misunderstood?

Personally, I doubt that the main part is just a demux as it has an antenna, etc...

> Is modulated output available from the tiny, instead of PWM (yes, I am
> that ignorant)?

The connector for the receiver as 5 pins two of which are meant to connect to an external demux. If I remember correctly, tiny1.3 had a little bug where those pins weren't routed properly, but as far as I know, they are OK on tiny 2.11.

-yvest

> --
> Chris
>
> * Like this one (I'm not seller)
> http://cgi.ebay.com.au/RC-Turborix-2-4Ghz-6-Channel-Digital-Radio-Receiver-Rx_W0QQitemZ110406182895QQcmdZViewItemQQptZAU_Toys_Hobbies_Radio_Controlled_Vehicles?hash=item19b4b8a7ef&_trksid=p4634.c0.m14.l1262
>
> On Tue, Aug 11, 2009 at 3:42 PM, Michel GORRAZ<address@hidden> wrote:
> > Hi,
> >
> > Don't forget that "Tiny" means autopilot for small aircraft equipped
> > with....small servos.
> >
> > @+
> > Michel
> >
> > 2009/8/11 Adam Spence <address@hidden>
> >>
> >> Sounds very good, anyone want to knock one up? I was going to do the half
> >> way house and still use the signals from PPZ but it may be cleaner to have
> >> the demux on board like you've suggested.
> >>
> >> 2009/8/10 Yves Touchette <address@hidden>
> >>>
> >>> I personnally think that the best solution is not to power the servos
> >>> from the AP, period.
> >>>
> >>> How about designing a PCB that would contain a servo demux (like a 4017),
> >>> be powered by the ESC BEC and have pads for both .1" connectors (regular
> >>> servos) and for pico blade connectors?
> >>>
> >>> Many of the newer good quality ESC have switching BEC's that are more
> >>> then capable of driving a reasonable server load.
> >>>
> >>> Running of the BEC will also prevent power related crashs. The BEC is
> >>> already in most planes. Those that don't have one (glow engins, etc) could
> >>> use an external BEC.
> >>>
> >>> This should be pretty easy to build without having to reroute a complete
> >>> AP.
> >>>
> >>> The two sets of connectors would alow users to choose which they prefer
> >>> and install only those.
> >>>
> >>> Does this sound good?
> >>>
> >>> -yvest
> >>>
> >>> > Date: Mon, 10 Aug 2009 08:59:29 -0700
> >>> > From: address@hidden
> >>> > To: address@hidden
> >>> > Subject: Re: [Paparazzi-devel] crashed, 5V supply overloading issue
> >>> >
> >>> > Yes, I am referring to the PPM signal from the RC receiver to PPZ.
> >>> >
> >>> > It was pretty clear that the fault was due to an overloaded 5V supply.
> >>> > On the ground I was able to faithfully re-create the AP crash
> >>> > conditions
> >>> > simply by rapidly exercising all the servos. I also did fairly
> >>> > extensive
> >>> > testing to debug this problem, including measuring current drain with
> >>> > all servos operating, which is what clarified the issue.
> >>> >
> >>> > I have suggested in the past that PPZ be updated with a higher capacity
> >>> > 5V converter, and given what you wrote below, it might also be a good
> >>> > thing to source the 3.3v line off the battery, rather than the 5V
> >>> > supply. However, the "temporary" solution is to simply use a separate
> >>> > 5V
> >>> > supply for external devices like servos, modems, etc.
> >>> >
> >>> > Adam Spence wrote:
> >>> > > 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
> >>> > >
> >>> > >
> >>> > > _______________________________________________
> >>> > > Paparazzi-devel mailing list
> >>> > > address@hidden <mailto:address@hidden>
> >>> > > http://lists.nongnu.org/mailman/listinfo/paparazzi-devel
> >>> > >
> >>> > >
> >>> > >
> >>> > >
> >>> > > _______________________________________________
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> >>> > > http://lists.nongnu.org/mailman/listinfo/paparazzi-devel
> >>> > >
> >>> > >
> >>> > >
> >>> > >
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