wstech CS DataVario with GPS

[TugBoat]

(This is in the "Scale" forum because I suspect that this forum is where most of the users of this type of equipment would be.)

I have a wstech CS DataVario with the GPS receiver unit.

I am having a lot of trouble getting reliable GPS position (and ground speed) information recorded. What happens is that everything looks good on the ground, but in flight the GPS data is intermittent - sometimes for periods exceeding 700 seconds!

If you look at the plot below you can see the periods of time where the 'ground speed' is constant and these are the periods with no live GPS data.

The unit is mounted inside a fibreglass pod (sorry not a scale glider :)), and there is no carbon involved in the pod at all. I attached the GPS receiver to a small balsa 'plank' and zip-tied this to the spar as it went through the pod (photos attached).

So there isn't anything 'obscuring' the view of the receiver, other than the fibreglass, epoxy and whatever was used for the finish on the layup.

I have contacted wstech and the suggestion I got back was not that helpful. (Perhaps it is the paint/color layer or something else that makes the problem. Check operation on the ground.) There really isn't a lot of useful diagnostics other than one flashing LED - and it indicates things working fine on the ground...

So now the questions:

Has anyone else had any experience with this unit in GPS mode?
Does it provide reliable GPS data?
Are there any special installation issues that you required?
Do you have a photo of the installation?


Thanks,
Tim

[yyz]

Tim,

This is just a WAG, and you've probably already thought of it, but try taping the GPS antenna to the top of the fuselage and do the same kind (banking, etc) of flight that you did to generate the graph. It shouldn't matter but that would eliminate the gps receiver being blanketed by something in the aircraft.

Try opening the log file in Notepad and see if it's even reasonably readable. If so, post a section of that file. GPSs know the number of satellites they're "hearing" and could possibly be logging that. It might be labeled "SV" (satellite vehicle).

Another thing to try is turn the electronics on in your plane, let it sit for 5 or 10 minutes. Make sure it sits still. It takes a while for the GPS to get it's act together and it's much easier for it to do that if it's not moving.

Not a GPS nerd, just work with them quite a bit,

Mike


(This is in the "Scale" forum because I suspect that this forum is where most of the users of this type of equipment would be.)

I have a wstech CS DataVario with the GPS receiver unit.

I am having a lot of trouble getting reliable GPS position (and ground speed) information recorded. What happens is that everything looks good on the ground, but in flight the GPS data is intermittent - sometimes for periods exceeding 700 seconds!

If you look at the plot below you can see the periods of time where the 'ground speed' is constant and these are the periods with no live GPS data.

The unit is mounted inside a fibreglass pod (sorry not a scale glider :)), and there is no carbon involved in the pod at all. I attached the GPS receiver to a small balsa 'plank' and zip-tied this to the spar as it went through the pod (photos attached).

So there isn't anything 'obscuring' the view of the receiver, other than the fibreglass, epoxy and whatever was used for the finish on the layup.

I have contacted wstech and the suggestion I got back was not that helpful. (Perhaps it is the paint/color layer or something else that makes the problem. Check operation on the ground.) There really isn't a lot of useful diagnostics other than one flashing LED - and it indicates things working fine on the ground...

So now the questions:

Has anyone else had any experience with this unit in GPS mode?
Does it provide reliable GPS data?
Are there any special installation issues that you required?
Do you have a photo of the installation?


Thanks,
Tim

[TugBoat]

try taping the GPS antenna to the top of the fuselage and do the same kind (banking, etc) of flight that you did to generate the graph. It shouldn't matter but that would eliminate the gps receiver being blanketed by something in the aircraft.

Although this is a bit difficult it is on the list of things to try.

GPSs know the number of satellites they're "hearing" and could possibly be logging that.

Actually having purchased the wstech vario this is one of my minor complaints. The vario only logs the GPS lat/lon and the GPS speed, it does not log the entire GPS data stream. I knew all this prior to purchase, but had not thought of some of the consequences - it would be really nice if the unit logged all the extra data but it doesn't. It doesn't log the GPS altitude either, only the vario (air pressure) altitude.

Another thing to try is turn the electronics on in your plane, let it sit for 5 or 10 minutes.

This is an interesting point. I took a long time for the unit to adjust to being in the southern hemisphere - at least I assumed that was what it was the first time I turned it on.

Can it really take 5-10 minutes to get a signal lock on enough satellites?


Tim

[fnev]

To lock on satellites is one thing, to have the GPS figure out where it is after you moved it a fair bit after last use is an other thing. Yes it may take THAT long to run all the algorithms before it is happy with the (relative) accuracy.

[sekollera]

snip

Actually having purchased the wstech vario this is one of my minor complaints. The vario only logs the GPS lat/lon and the GPS speed, it does not log the entire GPS data stream. I knew all this prior to purchase, but had not thought of some of the consequences - it would be really nice if the unit logged all the extra data but it doesn't. It doesn't log the GPS altitude either, only the vario (air pressure) altitude.

snip
Tim

A GPS produces time and position. Eveything else is calculated from that. There is no "extra" data stream.

Also, pressure altitude is far more accurate than GPS altitude and is how it is normally done in full-scale. A GPS altitude plot is not accepted for any form of badge flying, fyi.

Plug the data into a program like Navitar's See You and you will get all the calculated data you could ever want from the raw data, as well as a host of other features like 3D replay.Thermal averaging, time spend circling, time in cruise, netto, vario, speed, etc, etc.

http://www.naviter.si/

/Adam

[TugBoat]

Yes,

I understand that.

But there is some use for the GPS altitude - in particular obtaining a possible 'base' value for the rest of the data. At present the pressure altitude in the vario resets to zero on power up (ie. it is relative altitude) - so if you want to produce a GPX file for something like Google Earth you need to enter a manual base altitude.... which the GPS altitude would be just the thing to use.

The other aspect of not having the full GPS data stream available is that you can't investigate things like now many satelites the unit has a fix on.

So in the situation that you have a problem there is very little to go on by way of diagnosis. What I have is:

- a flashing LED on the GPS receiver unit
- the recorded, interpreted and reduced GPS data in the Vario log

This makes it just a bit difficult to "see" what is happening. If it all works fine then I agree that there isn't a problem - but if it doesn't there is little to assist in fault diagnosis.

Tim

[TugBoat]

Some additional data that may help others:

Today's test was to a short 5 minute flight, due to adverse weather.

However, I did two things:

a) Powered on the Vario & GPS and left the model sitting on the ground for 10 minutes prior to launch. The Vario announces 'GPS OK' within a few seconds of power up - but who knows exactly what this means.

b) Powered the Vario & GPS from a separate receiver pack, rather than the SBEC.

With both these changes the results were much better. The 5 minute flight appears to only have 2 'gaps' in the data and these were short (2-3 seconds). It is even possible that they are not really errors, they were just recorded log entries with identical GPS speed/lat/lon - and this is quite possibly OK.

So I don't think that it is the fuselage construction. The next step is to work out whether it is a power quality issue, or just a problem with not waiting long enough at power on for the unit to 'get its act together'...

Tim

[mosquito303]

[QUOTE=sekollera] snip
Also, pressure altitude is far more accurate than GPS altitude and is how it is normally done in full-scale. A GPS altitude plot is not accepted for any form of badge flying, fyi. snip


Accuracy isn't the reason for not accepting GPS. Tradition is. All the flight rules and all the awards before GPS were based on "calibrated" and "standard" pressure systems. To be totally truthful, these had significant errors, but as long as everybody agreed to a standard, even if not perfect, then people were playing on the same field. Well, maybe not really the same field, maybe within a hundred feet or so.

GPS has it's own difficulties. It is possible to get down to inches of accuracy. Just takes cubic money.

Dennis lennie #1731

[yyz]

Tim,

If you really want to see this through to the end, most modern gps receivers have both a data and an administrative serial interface. You may have to crack the case on the vario/flight computer -- potentially voiding your warranty -- and do some poking around and this isn't for the faint of heart.

If you can get to the administrative serial console (you'll need to build a cable), you can query the gps to see what's going on in that first, questionable 5-10 minutes. Most vendors provide software for accessing the gps at that level.

Probably not worth the trouble. Maybe just changing your pre-flight/assembly routine to 1) turn on flight computer, 2) have a beer, 3) put the wings on, etc. is the path of least technical resistance.

Happy for you that you're getting good tracking data; rules out the logger being hosed,

Mike

ps: I agree with Mosquito, it's not an issue of the gps system not having the required accuracy.

Some additional data that may help others:

Today's test was to a short 5 minute flight, due to adverse weather.

However, I did two things:

a) Powered on the Vario & GPS and left the model sitting on the ground for 10 minutes prior to launch. The Vario announces 'GPS OK' within a few seconds of power up - but who knows exactly what this means.

b) Powered the Vario & GPS from a separate receiver pack, rather than the SBEC.

With both these changes the results were much better. The 5 minute flight appears to only have 2 'gaps' in the data and these were short (2-3 seconds). It is even possible that they are not really errors, they were just recorded log entries with identical GPS speed/lat/lon - and this is quite possibly OK.

So I don't think that it is the fuselage construction. The next step is to work out whether it is a power quality issue, or just a problem with not waiting long enough at power on for the unit to 'get its act together'...

Tim

[TugBoat]

Hi Mike,

I am sure that I could open up the unit, but at this stage I am trying to avoid that.

---

So onwards with the testing.

Last Sunday's test was to reconnect the Vario+GPS to the SBEC supply. Again I left the model sitting on the ground with the power on for 11 minutes before launching.

In this configuration I got extremely erratic operation of the Vario+GPS. There are lots of gaps in the data recorded in the Vario.

So it looks like it is out with the scope and look at the quality of the power being delivered by the SBEC.

The SBEC is not an 'expensive' one, so I suppose the power quality may be an issue - I will report back in due course.

Tim

[TugBoat]

Like all problems I am sure that this one will make complete sense once understood. But at this stage I am somewhat confused.

I put the scope onto the power line and there was a bit of noise. Not enough I would have thought to cause any problem. Anyway, in line with my current theories I added a 2200uF low-ESR electrolytic and a 0.1uF monolithic bypass to the system.

The result was a significant reduction in what noise there was. However, it made no difference to the performance of the GPS. The GPS data contained lots of gaps.

Of course, one problem with the testing is that without hacking into the GPS data I can't easily test the behaviour on the ground. The unit is stationary and there is no way of seeing whether GPS lock is lost. So I am limited to inflight testing.

There is a connector between the GPS receiver and the vario - so I could try and source some connectors and then I am sure I could make a cable to access the GPS data which must be there as logic level serial data.

About the only other thing I can try is to decouple the vario from the SBEC power with an LC filter, or perhaps us a separate linear regulator to power the vario/GPS.

More experimentation required, I will probably put the separate battery in next time and just make sure that that really did fix the problem and it wasn't just a fluke!

Tim

[TugBoat]

Well I have to say that this issue has me beaten - or at least very confused.

I have been testing with a separate battery powering the vario+GPS - but with mixed results. Last weekend I had a 20 minute flight with perfect GPS tracking for the entire flight. Yesterday I had a 20 minute flight with about 40% of samples lost and some very wrong samples thrown in for good measure.

Both were is similar conditions with good soaring. The data last weekend tracked all the circleing, you could see the drift as I tracked with the thermals etc. - just fantastic. Yesterday's flight was just a mess...

In both cases the unit was given 10 minutes on the ground to get 'in sync'.

It is really hard to see exactly what the factor/factors are that affect this problem: same equipment, in same aircraft, ...

About the only thing I can think of is that most of my testing has been at the one field in Sydney, last weekend was at Bathurst (about 180km away). Why that should be relevant I have no idea!

If I work out exactly what is happening I will report back. In the meantime I have to say that I am slightly disappointed with the GPS part of the vario - I had hoped to get information similar to what I got last weekend on a reliable basis.

When this works it really works and is just fantastic - when it doesn't work it is really difficult to work out why.

It is a great pity that the vario does not record just a little more of the GPS data in the vario log file. Based on my experience it needs to record:

- GPS altitude (so that you get a reference for where '0' pressure altitude is)
- GPS time (otherwise the log only contains relative time from turn on)
- some additional GPS diagnostic information (# of satelites in view etc)

The first two would make it much easier to produce GPX (or other files) that are portable. Currently you need to 'know' the start altitude and time to produce a valid GPX file.

The third would permit some sort of diagnosis of problems.

As I said I will report back if I work anything out.

Tim

[h.eberbach]

Tim,

have you been in contact on your issue with the designer/ seller of the CS Vario?
Mr. Schreiner is a very nice guy and a modeller himself (also with some experienced model sailplane flyers in his neighbourhood) and in my judgement, he will be very interested to read your findings and help to solve them.

AFAIK, he does not follow RCG on a regular basis.

Herbert

P.S. My GPS module is still in its box, unused - I am just too lazy to try it.... ;-))

[TugBoat]

Hi Herbert,

Yes, I did contacted Mr. Schreiner about the issue initially - his suggestion was that it could be something about the skin of the aircraft. And I should check the monitoring LEDS with the unit inside & outside the aircraft on the ground.

I don't think that the fueslage material is the issue, it is standard epoxy/glass construction. I probably need to try one more experiment with the GPS unit mounted on the outside of the aircraft - but I need to pull it all out to do that.

I think that I have now got sufficient information to report back to him with a lot more detail. Something I plan to do in the few days. I will see if he has any other suggestions.

Tim