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.

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 critical miss-step allowed the real problem (below) to even manifest itself in the first place.



But 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. 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.

Lets see what the seller has to say, and I will report back.


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

http://www.banggood.com/Ublox-NEO-M8N-Flight-Controller-GPS-with-Protective-Shell-for-PIX-PX4-Pixhawk-p-1005394.html?p=NR1603976533201412HJ 

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.

In summary, I guess the real advantage of this black GR-BD one, over the white Beitian one ... is that it actually works :-)

2 comments:

  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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    1. No, I did not. By the way, I'm in the USA.

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