[chief]

Hello,
I'm using this OP GPS http://www.ebay.com/itm/162014575951?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
 and it won't arm. The blue/yellow blink and alternate and it seems if it's not booting up, i.e. yellow light not blinking continuously. 

Getting 8 sats, and already calibrated all of the sensors.

If I reinstall the firmware with disabling the GPS, it arms and works just fine. I've spent many hours trying to figure this out.

Does anyone have any idea how to fix this?

Chief

[Wagsy]

If your mag is not displayed green it will not arm period when you have a GPS set up on it.

Is your mag green?
Are you using an external mag?
Has that GPS got an external mag.
Tha GPS may not work with the normal version of Librepilot.
You may need the beta (next) version which the boys are still working on.
Here is my video with a DJI GPS using the beta version of Libre pilot.
Getting a good external mag is the key to making it all work nice with a GPS.

[chief]

I don't believe I'm using an external mag, just the one on the board I'd assume.

Very frustrating..

[Mateusz]

I am sure this GPS is not designed by OpenPilot and heard even worst that it has no Mag and small cheap antenna.
It's just named by Chinese like that to rip off people from money who don't know what they're buying.

I never owned this one, but it looks like smaller and cheap antenna, without proper clearance around it, so you might get less sats than with properly designed GPS. Also it has no Magnetometer, and internal one on FC will not work due to interference in 99% cases. You must have your Mag/GPS combo mounted on a 14-16cm mast that is not rotating (not on single mounting screw), as rotating mast would invalidate calibration.

[hwh]

He's right, the only thing OP about that GPS is the connector is the correct one.  And it doesn't have a mag sensor.

I own two of them and don't use either one.  One died (it melted the case and the VR chip burned) after running for about 20 minutes (pictures below) and the other feels hotter than I like so I don't use it.  Someone else I know also had one that the VR chip burned on.

This probably doesn't have much to do with your current problem but you should watch how hot it gets. 

What does the GCS system health display show when it won't arm?  Mateusz is right, most of the time you can't use the internal mag and the GPS modes depend on the mag being correct.

You don't say what flight controller but I'm guessing it's a revo since you're trying to use GPS.  What type of vehicle, small quad, large quad, fixed wing?

Post your config file (file->export uav settings) with it configured so it isn't working.  Someone may be able to find something wrong with your configuration.

[chief]

I appreciate everyone's responses... I think it sums it up, cheap antenna it is! Oh well..

Where can I get the correct GPS/mag antenna or is it something that's still being worked on? I looked every where and can't seem to find it.

Either ways, I like where this is going with Librepilot!

Has anyone managed to get a GPS/mag that's currently working with revo board?

Chief

[Mateusz]

Released LP version supports Ublox GPS alone or OP GPS not produced anymore. Development branch supports DJI Naza compatible GPS+Mag and Ublox based GPS Neo6/7/8 units with I2C Mag. I recommend DJI Naza compatible and then just change connector to JST-SH 1.0 4pin.

Movie above also uses Revo + Naza DJI compatible GPS.

[chief]

Thanks,,,, I was reading on the home made antenna and decided to order the below GPS/mag unit.

https://librepilot.atlassian.net/wiki/display/LPDOC/Homemade+Helix+GPS+antenna#HomemadeHelixGPSantenna-Neo6:Patch-Helixantenna

http://www.ebay.com/itm/272291854316?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[Mateusz]

I have 3 of those GPS units and they are okeish. However, they are using I2C bus which is not as easy as DJI Naza compatible GPS I recommended earlier.

First of all using I2C bus you have to occupy another port on Revo which you might have used for something else. DJI Naza is more like old OP GPS where mag info is combined with GPS info and sent over the same serial protocol. Hence DJI would use only one port.

Second, I2C is generally not designed for long distance communication. It might be affected by noise, and depending on wire length/capacitance, pull-up resistors might be not strong enough, which would lead to occasionally reading wrong sensor data or pulling whole bus down. When it comes to Revo, on the same I2C bus is also internal baro, which might be affected if you mess up something with I2C.

Generally I2C works, but is not easy and may or may not work depending how you set it up. DJI Naza is safer option, and better as it uses just one port instead of two.

[Wagsy]

Today I flew my Quadi 400 with the OP V9 GPS and my HEXI 350 with the DJI GPS.
Both booted up very fast over many batteries.
The DJI GPS with its external mag works very good.

[Mateusz]

Today I flew my Quadi 400 with the OP V9 GPS and my HEXI 350 with the DJI GPS.
Both booted up very fast over many batteries.
The DJI GPS with its external mag works very good.

That was a good choice of GPS+Mag unit.

The OpenPilot never used I2C external magnetometers. When OP project went down and their stopped producing/selling OP GPSv9 units people started looking for alternatives. In LibrePilot the succesor of OpenPilot still in development branch, code supporting I2C mag was added, because there existed "proven" already on the market GPS+Mag units designed for APM/PixHawk using I2C bus.

I am using exact I2C Mag+GPS as above, but I can tell form scope that signal is merely acceptable and peaks are very ugly, so it may have more noise than DJI, and sometimes may not work if wires are too long. The I2C for long distance to read external mag is an unfortunate hardware design decision. It may work, but can be problematic for some users if they're not careful with wires length. And of course takes one extra port.

The DJI GPS or compatible has the same functionality as genuine OP GPSv9 and is a really good (better) replacement.

[chief]

I goofed and should of went with your recommendation.. The question is, do you really need the mag sensor for accuracy?

I'm using it on a small 200 size quad.

Will this one work? Looks like I would just have to modify the connector.
http://www.ebay.com/itm/US-FREE-Ublox-Neo-M8n-GPS-with-Compass-f-DJI-Naza-M-Lite-V2-Flight-Control-/272244668229?hash=item3f630bf745:g:ujoAAOSwXSJXOZr5

[Mateusz]

For GPS all sensors are required, not just to improve accuracy but a must. Each sensor measures something else, no other sensor knows heading only compass does it.

I2C mag will do as long as wires are not too long and will take additional port on Revo. I use that mag and it works. Just DJI one is more convenient and might be easier for new pilots.

[chief]

I was just wondering if the one mentioned above on my post will work, with just 4 wires all in one. I might order it and still use it later as I would probably use the extra port for OSD.

Thanks for the update..

[Mateusz]

Yes it should work, you just need to change connector to JST-SH 1.0 4pin as it comes with DJI's connector.