Replies to This Discussion

Permalink Reply by Michael Pursifull on June 16, 2012 at 3:05pm

What other equipment do you have attached to or near the APM? In some other cases like this in the past, I've seen RF or magnetic interference preventing the GPS from locking onto enough satellites. As a test, unplug everything else from the APM, only use power (ch3) and don't even plug in the motor, and take it outside, with clear access to the sky. Make sure you don't have the RX, Telemetry, or anything else near it. Don't run the throttle, as the ESC will create a magnetic field. Make sure it is not installed inside a carbon fiber frame. Just carry the APM2, an ESC for power, and the battery outside and see if the GPS gets a lock. If so, it will suggest what the issue is. Then you can add the devices  back, one at a time, until you see it have problems. Then you will know what to move or fix.  

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Permalink Reply by Remi on June 16, 2012 at 3:30pm

Thanks for your answer Mike. I've quite classical equipments around the APM : 4 ESC that are a few centimeters above the APM, 1 2.4 GHz rx that is quite close (5mm) to the APM and while the frame is a carbon one, the APM is 1 or 2 centimeters above it. I will test the unplug of every equipment tomorrow (now it's half past midnight here in France) and I will tell you if I get better results.

Regards,

Remi

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Permalink Reply by Michael Pursifull on June 16, 2012 at 3:48pm

Yes, that very typical constellation of electronics arranged around the APM is used by many people .... and so problems with sensor noise and losing GPS lock are also very typical/common. ;)

Usually, it is easy to solve once the problem is found. Moving a transmitter a few inches away, using ferrite coils, easy things to do to solve the problem, usually. 

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Permalink Reply by Remi on June 17, 2012 at 1:19pm

Hi,

you were right Mike. I've tried removing electronics connected to the APM and finally it seems it was my rx that was causing trouble to the GPS. With the rx disconnected, I easily get a GPS lock in 30 secs with 5 or 6 sats. I tried with some turns of the APM to rx power cable (the rx is powered by the APM) and it seems to improve. I couldn't test it further because it started to rain :(

Many thanks for your help.

Regards,

Remi

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Permalink Reply by Michael Pursifull on June 17, 2012 at 1:46pm

Although it is a "receiver," it is not uncommon to find this device transmitting a low, local RF field because of the way the circuitry is designed. Your change to the power cable is one thing you can do, and you might see improvements, but that might be because the power cable is acting parasitically as an inductance driven antenna, or something like that. 

 

I bet the best improvement you can get is to move the RX a few inches farther away from the board. It most likely will not take much distance to have a dramatic improvement. 

 

On my 3DR frame, I mount the RX (which is Futaba and does not have this issue, but I mount it out away from the ESCs and telemetry for other reasons) on the underside of one of the arms. 

 

However, when I do this again, I will mount it inside the leg, and run one antenna outwards along the arm, and the other antenna down along the leg. 

 

This is one example of how you can keep your RX (or telemetry, or VTX, or anything else) away from the other sensitive receiver(s) 

 

In this case, a little bit of distance (inches) will have the biggest advantage (over shielding, etc, since both the RX and the GPS need to receive low power signals.)

 

 

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Permalink Reply by Remi on June 17, 2012 at 1:52pm

Thanks for the idea. I will try to mount it this way. It is currently very close to the APM in my mount. It is actually mounted vertically next to the APM because I don't have much room on my quad plate but with your solution it's no more a problem. Thanks again.

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ModeratorPermalink Reply by Sgt Ric on June 17, 2012 at 2:05pm

Vertically?? I have always thought that would be asking for trouble, esp when getting that all important first fix.

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Permalink Reply by Remi on June 17, 2012 at 2:09pm

I decribed it badly : it is mounted vertically on its side, like on Mike's picture. But I'll try to mount it on an arm, like Mike.

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Permalink Reply by Remi on June 18, 2012 at 6:17am

Hi,

I think I solved the problem. I mounted my receiver on an arm like Mike's, added a ferrite coil on the APM to receiver power cable, added an ubec to power the APM and I had a flight with a GPS 3d fix. I had to add an ubec because the GPS was still confused with the APM being powered by an ESC (it was working ok while being USB powered but no fix while being powered by the ESC).

Thanks again.

Remi

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Permalink Reply by Hennis de Klerk on June 19, 2012 at 2:58am

I had the same issue. Well solved my problem of the GPS not locking on. I was powering the APM2 and RX throught the OUTPUT port on the APM2 with a UBEC (as if powering it with a ESC), and GPS would not connect. So I decided to power the whole system through the RX, so I plugged the UBEC into the RX, 2 minutes later GPS connected, 3DFIX and LOCKED. The RX is the new JR DMSS 6 Channel RX with telemetry Satellite. 

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Permalink Reply by Remi on June 19, 2012 at 3:07am

Hi,

my setup is currently the one that was faulty for you : the ubec plugged on the output rail. I tried plugging it on the input port but the GPS didn't get a fix. I didn't try plugging the ubec into the rx. Anyway it's working great now.

My rx is the orange r710 DSM2 receiver (spektrum compatible). I removed it from it's case because it was ugly, big and heavy. I put the rx board into self shrinking tube and strapped it on an arm.

Regards,

Remi

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Permalink Reply by Leigh Green on July 19, 2012 at 7:18pm

...Not sure what the go is, as I have been using GPS devices for many years, I developed a tracking system with Franson many years ago and use SANav devices, and leadtek, and even Nokia...all have fantastic GPS pickup, but the Mediatek onboard seems a little insufferable.

I have seen so many suggestions of "unplug your receiver" and remove your ESC, etc...but if these are all solutions by the time I'm finished the only thing that will be in the UAV will be the APM itself - it can't be a solution to remove all other electronic equipment just to get the GPS to pick up more than 2 sats.

OK - a bit of ranting there, but then that being said early on in the evening (I'm guessing it was before the clouds rolled in.) I did have good sats (6 I think.) and was getting to within 3-4 metres without much drift...interestingly right before I got nothing I started to see my plane icon in mission planner slowly creaping north until it was over the back fence of the neighbour across the road.  Althogether not to bad really...But I suppose the reason I am posting this is...HAS ANYONE...managed to increase the pickup ability of the Mediatek GPS - whether onboard or offboard by changing the antenna...

What I've seen is every manufacturer is SO very proud that their GPS is smallest on the market with small Ceramo-helical GPS Patch antennas smaller than my thumb.   But the reality is I am not THAT void of space that I can't afford a few more mm for a bigger antenna.  SO my question really is, is there any merit or harm in creating an external antenna to attach to the GPS module...and if so does anyone have any plans/calculations like iBcrazy's CL and SP antennas...

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