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Scary iPad Ground Station BVR Flight

Discussion in 'Other DJI Multi-Rotors' started by amorrison, Jan 29, 2015.

  1. amorrison

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    As a test for a longer range flight I planned this test flight - a simple straight 1 mile out and 1 mile back. The UAV is a DJI Flamewheel F650 with A2 controller and E600 motors hereafter called "Buzzard". IPad Ground Station is 2.4GHz. I had the ground end mounted to the top of a light stand at about 7 feet, and the iPad mounted below it on the light stand. Solid Bluetooth connection.

    Take off was autonomous, no remote intervention. Launched with 8 satellites. However, it took 15 minutes to get 8, and there was a lot of 4 then 5 then 4 then 6 then 4 then 7 then 5... Etc. I wasn't exactly thrilled with the acquisition process, but we flew with 8. Cystal clear night sky at about 7pm. Little or no wind.

    Flight went perfectly to the distant waypoint at 1 mile, solid ground station signal, nice banked turn and Buzzard headed back home. Speed was about 18 mph. About a third of the way back the sat number dropped to 4 then 5 then 4 and so forth. Buzzard stopped, turn left then right and kind of wandered a bit. Still had a solid data link signal but with 4 satellites Buzzard could not find home and could not continue with the mission. Home button was no good. Then it locked on 6, re-acquired next waypoint and continued the mission a few hundred more meters. When Buzzard got the sat lock a blue line appeared and connected to next waypoint on the iPad Ground Station screen. But then Buzzard lost lock again and just wandered. IPad Ground Station crashed at this point. I started it back up but it would not connect again. OK, this was not good.

    When I looked in the direction Buzzard had taken off, I could see a tiny dot in the distance that looked like a very low star and I was hoping that was Buzzard. I picked up the remote and switched to ATTI. I yawed it around and the "star" disappeared and re-appeared. So glad for those bright navigation lights. I adjusted the yaw for max brightness and gave it 1/3 forward and waited. It seemed to be getting brighter and eventually I could see some movement. Then gave it 1/2 forward and in a minute I could make out some structure to it. Well, now I felt a lot better. Brought it on home in ATTI and did my normal hand landing. So glad to get Buzzard back in one piece.

    Lessons Learned? Always do a few test flights before attempting a long one. Just because you take off with 8 satellites doesn't mean you will keep them for the whole trip. Also, the satellites are not static. The configuration changes in just a few minutes. A nice IOS app to preview and check satellites is "GPS Plan" which is free (ad supported). It will give you very clear picture of just how the sats change over a few minutes with a slider. According to "GPS Plan" there were 8 satellites available with an elevation mask of 20 degrees. The count can get as low as 5 or 6 sometimes. It's nice to know this before you decide to try a BVR flight. No sat lock means no home lock and no go home function, there was no way to get Buzzard back but ATTI mode, and I was very lucky.

    I think the air end GS transmitter interferes with the GPS a bit too. This is apparently a known issue. DJI has a new A2 GPS Pro Plus module that supposedly addresses this. I will not be flying any more GS missions until I upgrade and test the new GPS module. And that's my story.... Buzzard survives another flight. Here is a short video of the launch and landing...

    http://youtu.be/ro8bckyquP4
     
  2. jcknows0

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    I keep thinking of getting an iPad ground station setup for my second Phantom but thoughts of this situation give me pause especially for a 200 investment
     
  3. amorrison

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    Just do some short range tests first, watch the satellite counts, and have some means to reach the MR with a transmitter if it loses satellite lock. When I get the new GPS Pro Plus I am going to run some tests and see if I get the same problem... Hopefully not.