PilotAware
British Forum => General Discussion => Topic started by: bladeslapper on November 21, 2020, 12:00:15 pm
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Just an idea of a modification for those who are happy with disassembly and soldering directly on to a board.
Don't attempt this if you are not completely happy as you are likely to damage the Pi.
I wanted to get rid of the micro USB sticking out of the side and also fit a power switch. This way I can leave the plug connected all the time.
The switch is a latching push-to-make that I have recessed into the case (bottom right of case) so it doesn’t get easily accidentally knocked.
The +ve is soldered onto PP2 on the Pi so that the supply is still protected but it's not the easiest to solder to. You could us one the many 5v feeds elsewhere on the 2 boards to make the soldering easier but then you miss the protection.
I put the -ve onto the HDMI shield as it had a decent size tab with few tracks close-by. Needs a hot iron with a suitably sized tip as the shield sinks the heat.
That switch isn't the most suitable as they are not rated as high as I would like but realistically should be ok. I drilled the hole to the larger collar size and then just used epoxy to stick it in. I've left enough wire so I can swap it if it causes any problems. It only just fits under the ADS-B adaptor and with hindsight the switch could have gone 1mm rearward which would have been better. Alternatively just move the USB plugs around (2 and 3 instead of 1 and 4). The push button only just protrudes from the side of the case so unlikely to get knocked but the oversize hole makes it easy to access when required.
I removed the 2 USB signal wires and sealed them up. I retained as much of the shielding as I could. I soldered a replacement 24AWG silicone wire onto the ground as this was easier to run. Lots of little bits of heatshrink to ensure nothing can short in there. The outer shrink is a glued one and the hole in the case is a tight fit. This keeps it nicely secure but I also added a cable tie to prevent pull-outs. 24gague silicone wire also from the switch to the Pi. (20 won't be necessary for this internal wiring and would be very difficult to solder to the tabs)
Oh and decent quality 3M double sided foam to stick the pack on - but not on the removable Rosetta cover so you can still get to the ports (just!)
Small mod that hopefully makes it much more simple to use.
UPDATE MARCH 2021
Cllick below link for a (possibly) unnecessary modification to improve GNSS reception when mounted upside down and with this battery pack attached.
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Mmmm
Not sure how efficient your GPS is going to be as you appear to have just slapped a battery pack over the top of it.
Also if using it in the vertical position as in photo the GPS antenna is not facing the sky.
You may of course be using a remote GPS but you don't say that.
Regards
Alan
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Yeah I considered that but it seems to work equally as well in all orientations on the window sill but then it can only see half the sky so not a fair test.
Therefore no particular plans for orientation, there's no reason why it has to be that way up when stuck to the window in the a/c, that was just the easiest for a photo.
I'll be sure to report any problems.
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Out of interest, when I was looking at the 'internal' GPS, I guessed that the aerial is on the side closest to the sticker/front of the rosetta? Is that correct?
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Hi bladeslapper,
The GPS antenna is the square ceramic block on what is supposed to be the ‘upper’ side of the GPS dongle.
The whole Rosetta unit is designed to sit horizontally, with the printed label uppermost, which is why the antennas are articulated - so they can be positioned vertically to minimise signal loss with the unit lying flat on its ‘back’.
That said, it might well work to a degree if mounted in a vertical orientation, but as Alan has said, it is much less likely to do so reliably with the GPS antenna sandwiched between its own circuit board and your battery pack. You could of course improve this slightly by moving the battery pack to the ‘underside’ of the unit, though it will be much better in the long run to orientate the whole unit horizontally (as intended) with the battery pack underneath.
Hope this helps. Please keep us posted.
Regards
Peter
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Thanks for the info. Yeah that was what I thought looked like the aerial.
Unfortunately the only option is to mount it on the inside of the screen/bubble either on its suckers or on a go-pro mount (I fly various heli types). The GPS aerial is therefore always going to be facing directly towards the front seats. With this in mind, while I was looking around inside the Rosetta, I was toying with the idea of moving the dongle to a better position but decided to leave it as is for now. There is plenty of space in there so I pondered turning the aerial to face the back/bottom and either leave it in the same compartment or perhaps put it under the Pi where the array of small holes are.
Having said that, I've had it attached to my office window for the past few days and it seems to be performing OK using only half the sky - currently using 6of12 sats. I have also tried turning the whole thing around 180 on the window so the dongle is at least at the top thinking this might improve GNSS reception but it doesn't seem to make a difference. I figured that having the aerials pointing straight down would be equally as good as straight up but I'm not certain about that?
One thing I did notice which was strange was apparent interference receiving GNSS data with the dongle plugged into USB port 2 and the ADS-B adaptor in port 3. This meant that the ADS-B aerial wire had to pass directly over the dongle's antenna rather than under and this was the only thing that I could think might be the cause. I left it for 2 hours and it managed to get 3or4 satellites out of about 6 but never managed to get a fix. Any ideas?
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Morning bladeslapper,
The antennas work equally well pointing down or up, providing they are vertical. Putting them horizontal where those in ‘other aircraft’ (or Ground Stations) are vertical results in a nominal signal loss of 3dB (i.e. it halves the effective signal in or out) - though of course actual loss varies a fair bit in practice due to normal bank angles.
I know of at lease one heli operator on the Forum who uses a GPS mouse mounted away from the unit, and several users have relocated the GPS dongle outside the case on a short USB cable to keep it horizontal where they wish to mount the unit vertically. I have also come across several instances where the user was reporting serious GPS dropouts - and on investigation found that they had mounted the unit ‘label side down’ - in one case inside a ‘spam can’ - very effectively hiding the GPS from the satellites under the metal body of the aircraft and 2 x circuit boards (it’s own and the SDR).
He was amazed at the improvement when I relocated it ‘right way up’ under a clear roof panel for him.
I haven’t personally come across the interference effect you refer to, but probably because I have only ever run the GPS dongles in the ‘upper’ ports 1 or 3 (in the Classic- Port 3 was the ‘norm’ , but this was changed to Port 1 in Rosetta as the larger Rosetta GPS will only fit in Port 1 or 2 unless you use extenders). I will take a look at this when I get a chance. Thanks for the ‘heads-up’.
Please keep us posted. We are always interested in innovation.
Best Regards
Peter
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Thanks for the additional information. All my uses of PA so far have been installs I have done in helis using all 3 external antennae, in fact I posted details of an old one on here recently:
http://forum.pilotaware.com/index.php/topic,1974.0.html (http://forum.pilotaware.com/index.php/topic,1974.0.html)
I've never used the PA as a portable unit mainly because it isn't portable enough for my user case - hence this little project.
It's still working fine in the office window but I'll be sure to post details of how well it works once I get in the air again. Does the Pi log the GNSS reception 'quality' for post flight analysis ?
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It's still working fine in the office window but I'll be sure to post details of how well it works once I get in the air again. Does the Pi log the GNSS reception 'quality' for post flight analysis ?
this information is stored in the track files
thx
Lee
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Update from today
I did a couple of hours in the heli today and the new arrangement seems to work fine despite the GPS receiver being in pretty much the worst possible position (see pic). The only thing I noticed were a few occasions where the traffic near me seemed to jump around. It did occur to me that this might be if I have lost position data and it jumped to assuming I was facing north?
How do I go about analysing the logs to quantify the quality of the GNSS data? I have them on my PC and open in notepad++ which I have identified as not ideal!
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Hi Bladeslapper
So sorry to be negative about this but short of placing your unit in a metal or carbon fibre box it is hard to envisage a worse positioning of your unit. Other than the position of your GPS which you have already acknowledged, your antennas are at such an angle as to be well out of phase with any incoming signals. You will be broadcasting your P3i signal in roughly a doughnut shape at 90 degrees to the length of your antenna and the majority of the forward transmission is angled upwards at apparently 45 degree, making it less likely for you to trigger a response from any groundstations you are approaching and seriously reducing the range of your air to air contacts I would think. Rearwards you are broadcasting into a couple of bags of water and your aircraft interior whatever that my be made of.
Is it not feasible to fit the battery to the base and lay the unit flat with the GPS towards the window and then have the room to set the antennas to vertical further away from the screen.
Regards
Alan
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How do I go about analysing the logs to quantify the quality of the GNSS data?
If you upload your track file to https://aircrew.co.uk/playback/ (https://aircrew.co.uk/playback/) (info: https://www.pilotaware.com/knowledgebase/tracks (https://www.pilotaware.com/knowledgebase/tracks)) you can view how many satellites are in view in the top left corner under "Flight Information" for any given part of the flight by dragging the slider along at the bottom. It will also show when you have no GPS lock. Typically you need at least 4 satellites in view for a fix, a good installation will get 10+.
(https://i.imgur.com/bdLebI5.png)
(https://i.imgur.com/3rEgiT4.png)
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Hi Bladeslapper
So sorry to be negative about this but short of placing your unit in a metal or carbon fibre box it is hard to envisage a worse positioning of your unit. Other than the position of your GPS which you have already acknowledged, your antennas are at such an angle as to be well out of phase with any incoming signals. You will be broadcasting your P3i signal in roughly a doughnut shape at 90 degrees to the length of your antenna and the majority of the forward transmission is angled upwards at apparently 45 degree, making it less likely for you to trigger a response from any groundstations you are approaching and seriously reducing the range of your air to air contacts I would think. Rearwards you are broadcasting into a couple of bags of water and your aircraft interior whatever that my be made of.
Is it not feasible to fit the battery to the base and lay the unit flat with the GPS towards the window and then have the room to set the antennas to vertical further away from the screen.
Regards
Alan
Yes I completely agree but no that's pretty much the best we can do. It's the same in most helis. I've done a few semi-permanent installs now and they are much better as we can position the Rosetta elsewhere. Don't forget that most helicopters cruise with a slight nose down attitude compared to when on the ground. Not by much I admit.
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If you upload your track file to https://aircrew.co.uk/playback/ (https://aircrew.co.uk/playback/)
That's great, thanks. I looked at my outbound track and inbound track and strangely they were markedly different. Outbound (30 mins travelling west) between 5 and 8 sats and about 10 very brief moments of no GPS. Return leg East (generally) for 1 hour and between 9 and 12 sats and only 2 brief drop-outs.
I'm surprised the GPS receiver works as well as it did to be honest. I'll probably modify it anyway tho.....I can't help myself sometimes!
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Is it not feasible to fit the battery to the base and lay the unit flat with the GPS towards the window and then have the room to set the antennas to vertical further away from the screen.
I have considered this also....on a long RAM mount attached to the window with a 3D printed adaptor for the battery to connect to Rosetta on one side and the Ram mount on the other. But, I suspect I will never bother with the hassle of carrying it around with me. It's already barely small enough to take on a day of work TBH
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Hi bladeslapper,
In that case, the easiest option to improve GPS fix would simply be to put the existing GPS dongle on a short USB extender and mount it on the top end of the case between the two antennas (it fits - I have just checked). If you are worried about insulation, cover it with a bit of heat shrink or make up a 'cover' out of a bit of plastic from some scrap packaging.
Best Regards
Peter
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Yes I completely agree but no that's pretty much the best we can do. It's the same in most helis.
Actually this isn't completely true, as discussed previously on this thread, mounting the unit upside down will result in the aerials being much more vertical but may add some visual obstruction issues. I thought I would try the simple and likely worst case scenario first but I will invert it next time and see how that is.
In that case, the easiest option to improve GPS fix would simply be to put the existing GPS dongle on a short USB extender and mount it on the top end of the case between the two antennas
That would be a nice solution, and in fact if it was inverted then it could go on the other end which could be much neater if I design and print a new end cap to slide on and contain the dongle.
I'm actually surprised at how well the dongle worked with the aerial facing completely the wrong way and insulated by a battery!
I've flown again for 2 hours since and these additional logs show that it could see an average of 10 sats and no loss of GPS data for both flights.
I still might move the dongle as I'm just curious to tinker!
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An update to this mod:
As was inevitable during another lock-down, I decided I might as well move the GNSS receiver even though there seemed to be surprisingly no problem with the antennae facing completely the wrong way!
I soldered an old USB lead onto the module headers and secured it under the Pi with some carefully placed high temp UHB tape and added kapton to protect from short against the Pi (just in case it managed to work loose). It actually wedges in the space where the square of small holes is without the UHB tape but better to be safe than sorry.
It's now facing completely up to the sky in the position as normally mounted in most of the helicopter I fly.
I've done a comparative analysis between the antennae facing the back of the battery and the inside of the helicopter vs where it is now and the number of visible satellites seems to be unaffected (around 9-12) but the acquisition time is now quicker and also the number of momentary "GPS data lost" incidents seems to have gone from 1 per flight to 0.
...therefore this is a worthwhile improvement (how could it not be?!?)
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Hi bladeslapper,
Thanks for the update. That looks like a much better arrangement for the GPS. Although you’re not seeing massive improvements at the moment, the fact that you are seeing zero dropouts bodes well for if/when you have to operate at low level in mountainous terrain (like up here in Scotland) or in bad weather. You should see a definite improvement (or at least minimal deterioration) in those type of circumstances.
Excellent effort.
Best Regards
Peter
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...if/when you have to operate at low level in mountainous terrain (like up here in Scotland) or in bad weather. You should see a definite improvement (or at least minimal deterioration) in those type of circumstances.
Most of my recent flights have been grovelling around in the Pennines with the cloud sitting across the summits so I guess it's had a pretty fair test and it's performed fine - there was 1 "network error" on the radar screen only which I couldn't explain but GNSS has been fine.