RE: RE: [Paparazzi-devel] radio interference (was: downlink only)

[gisela.noci]

Hi Martin.

The balancer battery wires are probably OK, they will certainly supply 3 to
4 amps with no problem. The only thing is that the connector pins on those
balancer outputs can be iffy. Make sure they are in good shape. Also, they
servo peak currents are drawn from this connection, so any drops there will
reflect back to the PWM signals, regardless of where your ground star point
is. When debugging these things I normally connect an oscilloscope to the
power lead at the input to the device giving trouble, set to AC input and a
few hundred millivolts sensitivity, and then exercise the servos, throttle,
etc. Any noise great than maybe 100millivolts is bad. The 'scope ground lead
must be connected to the star ground point. The 'noise' on the display must
not be confused with normally battery voltage drop such as when drawing
30amps from the battery (short periods....)

Volts drops across wires are of course related to the length of wire as
well, so if the power goes from balancer connector, to 'Tiny', to RCS RX,
and then to the servos, you need ensure that the wires are of adequate cross
section. In addition, when using digital servos, the problem is worse, as
the peak currents are much higher, and the standing current tends to be
higher as well, since they are very good at holding set positions quite
closely, which means a tight servo control loop, which means a very 'active'
servo.
Having said all this, One should not even attempt to fly at all, with all
these potentional pitfalls, and even I have solved some really lousy
interference problems by deliberately creating a ground loop.....SO, the
moral is , do it by the book to start, and when that fails, experiment...

Your last comment re the foil ground is correct; just use that as the star
point, and route all peripheral ground connections from that point.

My mails are always far to  long winded....
Happy Landings..

Joe

-----Original Message-----
From: address@hidden
[mailto:address@hidden
] On Behalf Of Martin P
Sent: Wednesday, July 29, 2009 9:00 PM
To: address@hidden
Subject: Re: RE: [Paparazzi-devel] radio interference (was: downlink only)

Hello Joe,
 
this is a very good source of information, probably for all Paparazzi users.
Thank you!
 
I think the grounding concept is not that bad. I do not connect the servos
to the RX but to the Tiny. Other people route the PPM back into the RX and
let the RX decode it, and then the servos are supplied by the same cable as
the receiver. But in the "normal" configuration this is not the case. So the
ground is configured like a star with the Tiny in its center, and this is
connected to the battery.
 
I use a 2200mAh 3S LiPo and a brushless outrunner which draws 30A at full
power.
 
I have connected the Tiny to the balancer plug of the LiPo. This way I can
plug or unplug the Tiny and the ESC independently. Good for ground testing,
and the voltage drop caused by the motor pulses should not affect the rest
of the setup. Do you think that the balancer wires are too thin and
therefore cause too much voltage drop? At least from the plug to the Tiny, I
could use a thicker wire than I do now.
 
When I do that copper foil single point ground, I think this means that I
have to remove the ground connection between the Tiny and the servos?
Otherwise it wouldn't be a single point ground. Right? 

Thanks again, 
Martin
-------- Original-Nachricht --------
> Datum: Tue, 28 Jul 2009 21:25:49 +0200
> Von: "gisela.noci" <address@hidden>
> An: address@hidden
> Betreff: RE: [Paparazzi-devel] radio interference (was: downlink only)

> Hi Martin.
> 
> These things are never easy to remedy! It is important to try ensure that
> you do not have any ground loops though. For example, the power supply
> ground (-ve) to the autopilot may go direct to autopilot, and then to the
> RCS RX, and then to the servos from the RCS RX. This is not a good thing,
> since each time the servo is activated, it causes a peak current flow
> through the ground wire to the autopilot, and then to the power supply(
> battery) Depending on the wire thickness and the quality of the connecters
> in the path, there will inevitably be a voltage drop over these wires.
> This
> volt drop in the ground lead can have the same effect as a pulse on the
> PWM
> line to the servo, ie, the servo and/or autopilot may see a 'dip' in the
> ground lead in the same way as it does a 'peak' on the signal lead. It all
> boils down to what actually is the 'ground' reference. Routing of grounds
> is
> most often the cause of ground loops and resulting glitches. It is always
> best to try and achieve a single point grounding network, ie, have a
> single
> ground point as the main ground connection, connect your battery ground to
> this, and then lead of grounds to all the users in the system from that
> point. At this ground point and close to the case of the modem and RCS RX,
> wrap the ground wire 2 or 3 turns through a high permeability ferrite ring
> core. It is also sound practice to follow the same technique with the
> positive supply leads as well.
> 
> I implemented this method on all my planes, and do not have problems any
> more. However, a further and more serious problem stems from the brushless
> motor speed controller, although only relevant in the larger (higher
> current) motor sizes. These controllers work by switching (pulse width
> modulating) the DC to the motor, high frequencies and currents. The
> resulting square wave switching generates very wide spread high intensity
> radiated electromagnetic fields, which cover an incredibly wide range of
> frequencies, including the all important 35MHz... This normally manifests
> itself as follows.. You do a range check, a quick throttle blip, and all
> is
> well. Prepare for takeoff, and go... Full throttle, aircraft lifts of, and
> proceeds away from you, at which point the radiated emissions from the ESC
> start to exceed the 35MHz transmitter signal, as the aircraft gets further
> from the RCS TX, and suddenly you have no more control; failsafe and
> crash....
> 
> I solved this as follows :
> 
> Choose a suitable place in the fuselage where you can stick a piece of
> adhesive backed copper foil, at least 10cm X 15cm ( larger IS better..)
> use
> the center of this as the single point ground ( solder all grounds to the
> center, or fairly close to the center). Place a ferrite ring over each
> servo
> lead, at the connector and near the servo. Place a ring at the receiver
> connector inputs, on each lead into the receiver/out of the receiver. Open
> the RX case and replace the antenna wire with a thin coax cable, length
> equal to the original antenna wire, plus spare as you would require to
> route
> in the aircraft. Solder the coax center to the antenna connection, and the
> shield to the closest ground point in the RX module. ( Warrantee  , what
> warrantee....). Wrap the receiver module completely, in the same type
> copper
> foil. Using a section of the braid of some spare coax cable, solder a
> piece
> of the braid to the copper shield around the RCS RX case, and solder the
> other end of the braid to the main center ground connection.
> Fit all the bits in the Aircraft. Route the antenna coax to and through
> the
> required fuselage exit point. Leave intact about 300mm of coax protruding
> the exit point , and from this point, strip the shield from the coax, so
> that the center conducter is exposed, forming the main antenna, as before,
> and trim to the same length as the original antenna. I had no more
> glitches
> at all, with an AXI motor drawing 70amps on takeoff, 12amps at cruise.
> 
> Have fun.
> 
> Joe
> 
> 
> 
> -----Original Message-----
> From: address@hidden
>
[mailto:address@hidden
> ] On Behalf Of Martin P
> Sent: Tuesday, July 28, 2009 8:38 PM
> To: address@hidden
> Subject: [Paparazzi-devel] radio interference (was: downlink only)
> 
> Hello Joe!
>  
> Thank you for your long answer.
>  
> The cable I am talking about is the 3-wire cable with the PPM signal from
> the receiver to the autopilot and 5V supply from the autopilot to the
> receiver.
> The receiver is a Yeti Rex, 35MHz, see
>
http://paparazzi.enac.fr/wiki/Other_Hardware#JETI_REX_5_plus_.28no_MPD.29_re
> ceiver
> The onboard modem is a 2G4 / 1mW Zigbee with a Nintendo WLAN antenna.
> The autopilot is a Tiny.
> You can see the setup here
>
http://picasaweb.google.com/lh/photo/wDgwmBGefqntD2ac6ElqQA?feat=directlink
>
http://picasaweb.google.com/lh/photo/OWSuzgAoyvPwSZ5bp6QvNg?feat=directlink
> The 35MHz antenna is taped to the left wing (not seen in the picture).  
>  
> Initially, I twisted the +5V, ground and PPM wires. For a picture, see
>
http://picasaweb.google.com/lh/photo/8m9HAOhXbbx1MPgfyTj5oQ?feat=directlink
>  
> I noticed radio interference when I did a range check on the field
> (retracted antenna, 45m). I was able to control the servo (at this time,
> only one servo was connected). OK, but I had spontanous servo movements
> too,
> even when I was only 5m away.
>  
> Removed the modem, no change.
>  
> Next I strung the twisted PPM cable (including 5V supply) through a
> ferrite
> core. This defineitely improved the situation.
>  
> Next I soldered capacitors to the 5V/gnd on the receiver (in case the
> interference would be caused by the switching power supply). No
> improvement,
> removed the capacitors.
>  
> Next was the shielding of the PPM signal. The shield is connected to
> ground
> on the autopilot side only. The improvement was convincing, as I had found
> a
> spot in the apartment where the servos moved wildly, and with the
> shielding
> it was gone completely. Back on the field, I had the random servo
> movements
> again (transmitter antenna retracted) and I were still able to control the
> servos from across the field (40m).
>  
> Put in the ferrite core again. Seemed to help a little.
>  
> So what the hell, up in the air. It's an old, small, slow foamie
> (Multiplex
> Minimag) and there was nobody around to get in danger, except myself. You
> know that I know that I shouldn't do that. It was windy, too. I was so
> eager
> to see it fly.
>  
> For the next steps:
> A shielded lead from the fuselage to the actual antenna seems easy to do.
> However, in the foamie, I am not really convinced that it will help. But
> I'll try.
>  
> Ultrasonic height measurement is something I would like to do too, but in
> future. Your report of a 4m plane automatically taking off and landing is
> very impressive!
>  
> Thanks and Greetings, Martin
>  
>  
> 
> -------- Original-Nachricht --------
> > Datum: Tue, 28 Jul 2009 08:24:51 +0200
> > Von: "gisela.noci" <address@hidden>
> > An: address@hidden
> > Betreff: RE: [Paparazzi-devel] downlink only
> 
> > Hi there
> >
> > First time I am using this forum to comment on peoples comments, so hope
> I
> > get it right.
> >
> > Cannot really comment on the main content of your problem Martin, but
> the
> > last para bothers me. How did you 'shield' the 'receiver cable'? Which
> > cable
> > did you shield? Not the antenna cable , I trust. Or do you have an
> antenna
> > (whip or trailing wire) external to the fuselage, and the use a piece of
> > coax cable from the RX to the antenna? Are you using 2.4Ghz radio
> > equipment
> > ( for the radio control system, Spektrum or such like)or is it the 35MHz
> > or
> > similar stuff. If you are using Spektrum, what other equipment do you
> have
> > on the aircraft, datalink, Video transmitters, etc, and are they in the
> > 2.4GHz band as well? This is fraught with problems if so, since the very
> > close proximity of these elements WILL cause desensing of the Radio
> > control
> > RX. There is nothing you can do about that; They ALL share the same
> 2.4GHz
> > to 2.5GHz band. If the RX is in the 35MHz (or 70Mhz, etc) band, it would
> > be
> > better were is not for the fact the typical RX input selectivity is not
> > really that good, and the receiver is also desensed. I have had bad
> > experiences with JR 9 channel RX and the 9-Xtreme (900Mhz spread
> spectrum)
> > datalinks. The very broad band signal from the datalink severely
> > desensitized the RX, and range was reduced to less than 150meters!
> > However,
> > removing the RX crappy wire antenna, and and connecting a thin (2mm
> > diameter) coax cable internally (shield to RX ground) and then routing
> the
> > Coax to an exit point in the fuselage and then connecting the original
> > antenna wire to the exiting coax center wire helped a lot. I easily get
> > 600meter range now. 
> >
> > THE FIRST RULE IS : whatever you are testing, be SURE that you have a
> safe
> > and tested means of taking control of the aircraft. Sure, a component
> > failure can still foil you, but I cannot condone taking of,
> intentionally
> > or
> > otherwise(!), with your backup system ( manual RCS system)
> non-functional.
> > FIRST fix that!
> >
> > I design Spread Spectrum systems, RF datalinks, Video link, etc, as well
> > as
> > antenna systems of all types, for the aviation industry, both military
> and
> > commercial, so if there is any way I can help or advise, I will try. I
> am
> > flying Paparazzi for about 7 months now, but have designed my own ground
> > control station, and have extensively changed the autopilot - I fly V
> > tails,
> > with ONLY rudder/elevator, ie, no ailerons, as well as a 4 meter
> wingspan
> > homebuilt A/C, fitted with ultrasonic height detection. This A/C does
> > auto-takeoff and auto-land (beautifully!). But I cannot help with any of
> > the
> > issues related to the A/C  / GCS communication and control, since I have
> > done my own....Found the Paparazzi GCS very emcopassing and complete,
> but
> > far to complex, and impossible to certify , even in part, for use in
> > restricted civil airspace.
> >
> > HAVE FUN, be safe...
> >
> > Joe
> >
> > -----Original Message-----
> > From:
> address@hidden
> >
>
[mailto:address@hidden
> > ] On Behalf Of Martin P
> > Sent: Monday, July 27, 2009 10:46 PM
> > To: address@hidden
> > Subject: Re: [Paparazzi-devel] downlink only
> >
> > Hi,
> >
> > I do not intend to do any settings via the transmitter.
> >
> > However, I do not seem to have 2-way-communication via the modems.
> > Although
> > I saw something with the scope, I am not able to use neither the
> settings
> > tab in the ground station nor the settings dialog from the tools menu.
> The
> > latter shows an empty window.
> >
> >
> > On the field I used a modified flight plan which does not stop at the
> > holding point. First of all, uplink seems not to work an secondly, most
> of
> > the time I am alone on the field.
> >
> > Usually, when ground testing, the throttle reacted to the stick in
> AUTO1.
> > Yesterday I switched to AUTO1 and the plane throtteled up and took off
> > before I expected (I use a landing gear). Switched to MANUAL and
> climbed,
> > then back to AUTO1. No throttle. Probably this is because I put the
> > vmode="throttle" in the takeoff block to get executed anyway.
> >
> > I havent't seen any vmode statements other than specifying "throttle".
> > What
> > are the valid values for vmode?
> > Could I automaitcally set the vmode to pitch in AUTO1?
> >
> > Managed to land manually, in spite severe radio interference. Radio
> > interference in spite having changed the receiver cable to a shielded
> > wire.
> >
> > So, I am still struggling and learning. Every help is greatly welcome.
> >
> > Greetings, Martin
> >
> > -------- Original-Nachricht --------
> > > Datum: Fri, 24 Jul 2009 19:00:32 +0200
> > > Von: Pascal Brisset <address@hidden>
> > > An: address@hidden
> > > Betreff: Re: [Paparazzi-devel] downlink only
> >
> > > Hi,
> > >
> > > Martin P wrote:
> > > > I was wrong, I do have 2-way communication. Looked at pins 2 and 3
> > with
> > > the scope. (Could have done that earlier)
> > > >
> > > > Then I do not know why I was stuck in holding point block (before I
> > > commented it out).
> > > >
> > > > With or without 2-way-communication, I am still interested in flying
> > > without GCS interaction. Which means that, for the time being, I can
> > only
> > > follow a pre-determined track and then (attempt to) land.
> > > >  
> > >  The code to do a setting from RC channel is still there:
> > >
> > >
> >
>
http://paparazzi.enac.fr/wiki/Telemetry#R.2FC_Transmitter_Data_Uplink_.28Obs
> > olete.29
> > >
> > >  But.
> > >  It has not been tested for months (years ?).
> > >  We will remove it asap
> > >
> > > --Pascal
> > >
> > >
> > >
> > > > Greetz, Martin
> > > > -------- Original-Nachricht --------
> > > >  
> > > >> Datum: Mon, 20 Jul 2009 23:11:58 +0200
> > > >> Von: "Martin P" <address@hidden>
> > > >> An: address@hidden
> > > >> Betreff: [Paparazzi-devel] downlink only
> > > >>    
> > > >
> > > >  
> > > >> Hello,
> > > >>
> > > >> it seems that I have a common problem: GCS doesn't send to the
> plane.
> > > >> Removing the datalink section didn't help.
> > > >>
> > > >> Anyway, I am not so much interested in the uplink. When I am alone
> I
> > > >> cannot watch the plane and the computer screen at the same time. I
> > know
> > > that
> > > >> Pascal Brisset strongly advises against removing the holding point
> > > block from
> > > >> the flight plan, but I might do just that.
> > > >>
> > > >> My starting procedure would be like this:
> > > >> Switch on the transmitter and switch to MANUAL, throttle off.
> > > >> Power the plane.
> > > >> Wait for GPS and do GeoInit.
> > > >> Instantly go to Takeoff (a beep or LED signal would be nice).
> > > >> As I am still in MANUAL, the propeller doesn't spin.
> > > >>
> > > >> I don't know how to go on from this point. When I switched to AUTO2
> > > >> (without propeller, for safety) I expected the motor to start, but
> it
> > > didn't.
> > > >> Does the autopilot wait for a "launch" command which it doesn't
> get?
> > > Does the
> > > >> autopilot wait until I have stared manually?
> > > >>
> > > >> Can you take off from the lawn (with a landing gear) or do you need
> > to
> > > >> throw the plane?
> > > >>
> > > >> Greetings, Martin
> > > >>
> 
> 
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