I was setting up my new airplane with me new APM2 and noticed that I had a very unsteady display on the Mission Planner. The artificial horizon and other parameters were jumping around a little. This was with both USB and telemetry connection.
I had the GPS mounted on top of the APM2. I found that if I unplugged the GPS that everything was steady. I hooked up my old 
Media Tech GPS and all was well. Has anyone else had this problem?
Next order I will have to get a longer GPS cable and relocate the new GPS to see if that solves the problem. The problem is that the new 3DR/uBlox GPS very HUGE and it’s not easy to find room for it.
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I've been getting a regular twitch in my copter since installing the ublox GPS. Seem to be at about 2hz. If I unplug the gps, the twitch is greatly reduced. I tried unplugging all of my other components (bec, video tx, moving my radio rx far away etc) but unplugging the GPS is the only thing that seems to really make a difference to the twitch.
Another interesting observation - AHI goes bananas only when GPS gets fix - not while it's searching for sats.
is it even possible that this is some bizzare software bug related to decoding the ublox protocol ?
With all the information people wish, we must admit that the MAX7456 is not good enough in the long run - the more you display, the more cluttered the screen gets - and - we are completely missing analog indicators, they are considered much more readable.
For really cool graphics, and audio warnings - take a look at this project;
http://forums.openpilot.org/topic/6736-openpilot-osd-prototyping/
Fortunately it's open source too - it would be sweet to make that read mavlink...
For what it's worth - I have same problems with my APM2.5 + LEA6H's.
Tested (outdoor) USB powered - 8GPS, very solid fix - still the AHI jumps around a little.
Tried a GPS cable of twice the length of the original/included one - no big improvement.
Tried a Mediatek GPS - to my big surprise, same problem.
Veryfied that my APM1's AHI is 100% stable with GPS
Connected LEA6H to APM1 - and AHI on APM1 was as bad as APM2 !
how can this be explained ? - LEA6H may cause more noise/interference or harmonics for AHI than Mediatek, - and APM2 (it's sensor) is more sensitive to noise than APM1 was ?
Anyway - with jumps up to 10% on roll, pitch, yaw axis - no kind of stable flight can be expected unless the aircraft is really heavy/sluggish.
I noticed the same thing and the problem is caused by the increased sensitivity of the new gps. The AHRS code in version 2.50 uses the gps velocity in calculating accelerations for x/y drift control. GPS gets velocity information from slight doppler shift of the carrier signal. When you are indoors you are getting multipath reflections that are messing with the velocity readings and thus causing jitter in the ahrs display. Take the unit outside away from walls and see if the jittering stops. The only thing wrong with the new ublox is that it's antenna is too sensetive.
Maybe they will redesign the circuit board to provide improved shielding. A nice plastic box would also be good.
My old Media Tek GPS is working excellently so I think that I will just fly that and forget about the new 3DR GPS until they get the bugs worked out. They definitely have some work to do to make it usable for everyone – especially for those with small aircraft.
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I think, I have the same problem http://diydrones.com/forum/topics/attitude-issue-with-gps?commentId...