Tuesday, August 30, 2016

Two uBlox GPS & Compass combo-modules for Pixhawk compared

Both of these are advertised as being "GPS combo-modules" with uBlox NEO-M8N GPS and a HMC5883L compass. They are both pinned with Molex PicoBlade for easy PixHawk use. The content of this post started as a rant/complaint, but I've decided to present it as a Comparison, so I can offer a suggested alternative. Ok, so first the bad ...

Beitian GPS & Compass combo-module (white):

Looks pretty on the outside right? Well, looks can be deceiving.

For starters, it only works intermittently. Initial testing revealed it gets more erratic as it warms-up. Inside, we first find a conventional uBlox chipset missing. However, if you look through the hole, you see a chip with uBlox printed on it ... so who knows if it's all real. Not sure if that is a battery or super-capacitor, but it's spot-welded in. Also interesting that the magnetometer is apparently under the metal shield ? (the other side is just the ceramic GPS antenna).

Then I noticed that instead of using the available (dependable and industry-standard) Molex PicoBlade connector, they have instead decided to hard-wire solder the tiny cable wires directly to the module's PCB. Seems this miss-step allowed the real problem (below) to even manifest itself in the first place. It might not have been so bad if the assembly technician knew how to solder.

Yes, the real surprise inside is the soldering (zoom in or "open in new tab/window"). The wires are frayed and barely attached. Not only that, but all the connections are poor, dull, and obvious "cold solder" connections that aren't always making good contact. Everyone knows what happens if your GPS or compass becomes disconnected or glitched in flight ... right, the aircraft flies-away or crashes. I think this poor soldering is why the module works intermittently, worse as it warms-up, clearly un-reliably, and completely unfit for its purpose.

Finally, there is no obvious indication or arrow pointing forward. Neither on the module's outer case or inner PCB. The compass chip is not visible either.

EDIT 11-2017
I needed a GPS (and external compass) for a new PixRacer quad I'm putting together. So, instead of wasting $20 on this, I decided to try to fix it (it's a challenge right ? :) and good micro-soldering practice). I think the main problem was the poor solder job.

The cable itself has a nice molded strain-relief.  I was temped to just splice-in a Pico-Blade 6-pinner, but that's more hacky-work and the designer went the other way for some reason. Instead, I removed the wires, cleaned the holes, and carefully re-stripped and tinned the thin wires. I think the wires should go through the holes, and then solder (like a normal hole-thru part).

Here is what it looks like now. It looks "rough" but it's functionally solid. Seems to work fine so far. Wow, GPS on uBlox 8-series is so much better than 6-series (even in poor conditions). And yes, the compass/magnetometer works fine (even under the metal shield). The "S" points to the front, and the "B" is to the back of quad.

GR-BD uBlox GPS & Compass combo-module (black):


I had this NEO-M8N unit, out on porch getting "warmed-up" for a recent test flight. I was getting SATS:15 & HDOP:0.8 . So, good performance and as expected ... much better than my uBlox 6-series units in same environment.


This GR-BD GPS module is much better built. Inside you find a more standard looking uBlox chipset. They also use a properly crimped cable connector to match the one provided on the PCB. This provides a much better connection to vital sensors like these (compared to the white Beitian unit) . In hours of testing, I have never seen this GR-BD module fail. While the proper direction is already clearly marked, the compass chip is also visible. I like the visible blue status led also. I'm in the USA, so not sure about performance when using alternate GLONASS (GNSS).

In summary, I guess the real advantage of this black GR-BD one, over the white Beitian one ... is that it actually worked without first being opened and repaired :)


  1. Did you do anything to enable GLONASS sats reading? My M8N looks not authentic and shows hardware version 00070000 in U-center which I assume stands for M7N model.

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  3. I reworked the Beitian unit and it appears to be working. I think I might have salvaged it.


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