Today I did a test flight before doing a mission. After switching to poshold, it began behaving erratically, twitching and drifting. I was able to land, but puzzled because there were no errors from the GCS.
Running auto analysis, it gave these results?
Size (kb) 8554.380859375
No of lines 114684
Duration 6 days, 22:11:00
Vehicletype ArduCopter
Firmware Version V3.2
Firmware Hash c8e0f3e1
Hardware Type
Free Mem 0
Skipped Lines 1
Test: Autotune = UNKNOWN - No ATUN log data
Test: Balance/Twist = GOOD -
Test: Brownout = GOOD -
Test: Compass = GOOD - mag_field interference within limits (8.12%)
Test: Dupe Log Data = GOOD -
Test: Empty = GOOD -
Test: Event/Failsafe = GOOD -
Test: GPS = FAIL - Min satellites: 0, Max HDop: 99.99
Test: IMU Mismatch = GOOD - (Mismatch: 0.62, WARN: 0.75, FAIL: 1.50)
Test: Parameters = GOOD -
Test: PM = FAIL - 17 slow loop lines found, max 7.20% on line 108374
Test: Pitch/Roll = GOOD -
Test: Thrust = GOOD -
Test: VCC = GOOD -
The logs show no GPS problems (Nsat and hdop) so I don't get it. Is this a communication problem with the GPS unit? Possible wiring issues?
Replies
Hi Doug,
If you still subscribed to this old thread, could you give me a hand and advice what can be done to make those 2 M8N units to report data that would be not so much different?
take a look at this log - all values communicated, speed, altitude, longitude, everything is pretty far apart.
I really wonder how it can be possible, as both units, theoretically, listen to the same set of satellites.
What can it be, in your opinion?
5.BIN
Yes, I received it and installed on a quadcopter. The first startup it took a while for the sat library to load, but after a few flights the GPS locks within 30 seconds. I don't know if the battery that's on the GPS board helps with that or not.
It does have a high x compass offset of 208, but it may be from one of the metal screws in the case (optional item) that came with it. Either way, it's still within the limit as described in the Wiki http://copter.ardupilot.com/wiki/flying-arducopter/prearm_safety_ch... sqrt(x^2+y^2+z^2) = <500 is ok Mine is 256 I believe.
A lot of people are using these GPS units as can be found here http://www.rcgroups.com/forums/showthread.php?t=2142174 Greg Covey is an honest guy that tests and uses several brands/types of GPS units. He seems to be satisfied with the performance. The CSGShop units are probably superior (I have one) but I like to test different stuff and figured at least the one from RTFQ has some history to it vs playing Russian Roulette on Ebay
Results from a long flight yesterday below:
So far it seems to be working ok for me.
@DG,
Your results look very similar to mine in that the time for the M8N to acquire and settle down it's HDOP does take some time. I found that if you connect it to UBlox's Ucenter software first that you can down load the almanac into the GPS memory and that helps for a faster acquisition of the satellites. This is especially helpful when the GPS has been off for a significant period of time.
If going about the long way (ie plug-in and sitting it outdoors) it will take a while to get it's location. Probably good to use a test battery to do this and save the good batteries for flying. Save a few milliamps in the process. :-)
I'm very interested in the newest GPS you tested from CSGShop, M8T (the round one with EMI protection)? Is it worth the extra cost? I want two GPS's on the copters, with the main one being the best available, and standard M8N vanilla brand as backup; pretty much retired the LEA 6H units.
I had 35mm smaller gps chip from same witespy shop and it used compass chip soldered under the board.
45mm board uses compass chip soldered on top of the board.
35mm board after regular calibration with 'rotation_none' never gave errors.
45mm board calibrates fine but after you move drone around it gives 'inconsistent compasses' error on MP screen and 'compass variance' error as i can understand 2 compasses axels do not match.
How all it should be configured? I want to use 2 compasses. Px4 board i use has compass chip under the board, like 35mm gps. It must be a simple offset issue but i tried all seemengly correct 'rotation' options in the calibration screen and it still gives errors.
Paul,
First of all, you can only use a second compass external to the one soldiered onto the Pixhawk board. There is NO way to disable the Pixhawk one and setup two external ones. This is annoying but it's the way the board was developed and cannot be bypassed via software. However, the software can ignore it and only use the external one. I wouldn't recommend it as your air frame would be in a world of hurt if you lost the external one. The internal one has a huge offset but should limp your drone home if the external one fails.
As for the witespy gps unit. I looked around and have to say that I'm not familiar with their setups, but I noted the label on the ceramic antenna in aligned along the longitudinal axis of the flight direction. I wasn't 100% sure if the label should be pointing forward or aft. So I think you will need to test each out and perform a low low hover test to see what your end result is.
The Toilet bowling is strictly related to compass calibration/orientation and possible EMI interference. How high is your external compass from all your electronics. Many recommend 20cm or higher for optimal results, but it could be lower if you measure the noise results after setting the test height and performing a compass calibration test.
On a separate note.. Ceramic antennas need to be pointing skyward for optimal reception of satellite signals. Any that are inverted will significantly reduce you reception of signals.
Before i had a setup with 2 gps and internal/external compasses, need to figure out what has changed. I tried it with same 35mm gps, no external compass and got almost same toilet bowl, it would not hold position. Altitude hold is stable, so it should not be compass or accelerometers in the board, it must be an issue with gps signal somehow, but not sure what it may be.
I do not believe the compass is used in Althold, strictly uses the accelerometer, gyros, and baro sensors.
Do you have a log?
I just spent may be couple hours and got to the bottom of this.
first of all, to calibrate drone with this unit on you need roll 180, it is fine.
MP software sometimes give compass variance error after that, also fine.
Toilet bowl effect I very surprisingly rendered down to my configuration of 115 kbit on the serial interface. unit from witespy is supposedly 115kbit one. alas, with 115 kbit selected I think it catches sats faster but acts crazy in the air.
I think there is a possible conflict between internal and external compass but I did 4 or 5 takeoffs after recalibration and altering interfaces and again recalibration - pos hold and loiter have slight movement in the 1.5-2 ft cube of space but overall everything stabilized.
it is with a single gps unit, bit one 45mm square that gives best and fastest sats lock.
I am thinking now if I want to mount on second gps unit for redundancy or not. probably will, as it is not going to make anything worse now, imho.
I wish we could have more redundancy for compasses - to plug in 2 external ones to get best possible approximation.
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