Hi. to all...
Usually I read a lot of information from the web but that time I'm making a contribution and posting some information that can help with a tech problem I found and solve and don't find similarly info on the net, maybe I don't search on the right place. If anybody think I'm wrong or made a mistake please let me know and be free to comment. Sorry for my bad english.
Few days ago I started to build an hexa using the Tarot 680pro frame.
I built everything and finally put the pixhawk controller on their stand etc.
When I installed the arducopter and started to configure everything. I have too much trouble with the external compass..... which is 15cm+ over the frame. The internal compass works fine at home without props but I know it is near the power wires so there is a potential risk of malfunction on flight. CompassMOT solves stylishly lots of the interferences between the power wires and compas chips but I think is better to avoid a problem than generate it and then solve it. I dont like the idea of running compassmot on an hexa frame with 1355 CF props, it scare me.
After running the compass calibration, sometimes I get really bad values on the external compass. something like 5000, 4000 and 30000. Yes that crazy values. Even when y get "better" values like 700 600 600 MP constantly send compass errors of any kind
I'm using a gps compass module from an ebay seller. Its a 5883L compass and a ublox M8N. It's a really nice board ...well finished. Really nice for the price.
The gps is marvellous ... inside my house with a 40cm concrete ceiling and a really cloudy day with any kind of radio freq surrounding like the radio commander, the telem module the wifi router my phone the bluethooth etc etc...... it gets 3D fix on seconds (usually les tan 10) with lots of sats. It uses an active antena, I think it is one of their advantages over others, but that advantage is a really bad bad thing for the 5883 compass which hate it ;-) .
As you can se on the pics the active antena comes with a metal RF shield to avoid interferences.
YES... I say METAL and it's FERROUS ...... and is located just under the 5883 compass....
If you remove the antenna (you can do it with a soldering iron and les than none of skills) the compass chip becomes so happy that it will thank you with lots of goods and stable measurements for the rest ot its life ;-D
But you really need the antenna for the GPS !!!
well. There are many options to solve that, just to name a few:
1) Use another 5883 located on their own stand. I like the idea of putting the gps down ... near the controller and a stylish antena with the compass, in fact it doesn't need to be up... it can be on a leg for example or whatever yo want. Even on the top of the telemetry antena if the interference is acceptable, I don't know. But i don have a small compass only module.
2) Move the antena away 2 or 3 cm (the length of the wire). I don't think its a good idea but who knows.
3) Make the antena passive removing the metal shielding and soldering it directly to the pcb. Could be a good and easy option and maybe not too bad if the sats count is similar on cloudy days.
4) Remove the metal shielding and thanks god if no interference affect the GPS on flight. Not recommended.
5) REPLACE the ferrous metal shielding with another non-ferrous.(copper, aluminum, bronze, plumb, silver, even gold etc etc)
I choose the 5th option because I'm expecting to keep the GPS quality.
You have to choose a metal you can solder so I make a shielding cap from a thin (0.2mm) sheet of copper. If you can use scissors and a soldering iron .. it's an easy mod. Of course ... if you find it on an electronic store don't doubt to buy it but i don think it's a common piece.
I leave some pics of the final work.
I run the compass calibration process on Mission Planner without the antena near the compass chip and with the new cooper antenna shielding and the results are pretty much the same ...something like 390 50 -2. So the new shielding Is not affecting the compass anymore.
Happy Compass + Happy GPS => Happy Copter
There is a test that I don't do and it's a comparison of the gps quality reception between the too shields. Despite that ... now I get 9 sats when Im indor in my house so I dont care if previously was any better.
I saw too many GPS that uses active antennas with shieldings like mine .... and with the compass IC near the metal ferrous shielding.
Any comments are welcome.
If you already made some experiments ...tests ... or have another solution ...please share it .