Phantom 2 Vision 1st Flight - circular unstable motion

SkyView · Jan 20, 2014

Saturday Jan 18, 2014 was my first opportunity to fly my Phantom 2 Vision. I checked the IMU calibration and it was bang on to the required specs. Before flight, I did a compass calibration. When I lifted off to about 10 feet the Phantom hovered stable in place. However, after I made the Phantom move forward, about 5 feet to again hover, the hover was erratic where the phantom flew in circles of an ever increasing radius. I had to reduce the altitude to about 7 feet so I could grab the Phantom by hand as it flew by. I re-calibrated the compass several times only to have the same unstable flight result with each attempt.

For your information my flight attempts where at a ball field, free from power lines on a calm day at about 10c/50F in overcast skies. The Phantom did have a flashing green to mark my home point, and my iPhone showed the satellite count fluctuating between 6 and 7 satellites.

After I got home, I rechecked the calibration on the Mac Assistant Software, the IMU values where as follows:

Gyro Mod = .6
Acc Mode = 1.00
Compass (raw) =1650

What could cause this? What can be done to correct this? Could it be possible EMC problems? etc…

Thanks,

Dave

Tripnman · Jan 21, 2014

SkyView - Glad you were able to get in some stick time with the PV2.

There are plenty of threads about PV's circling in a hover if you search well enough. Finding some of those will likely give more answers than I can, but here's my experience... When I fly in large open areas with good sky coverage I usually take off with a lock on 10 or more satellites. In those situations the hover is rock solid. I'm pretty sure I could put the Tx down and walk away - the PV would stay like a well trained dog until the battery ran out.

However, when I fly in my little cul-de-sac I usually get to green-light flashing home lock with only 6 satellites due to the surrounding homes and tall trees. At 10-50 feet of altitude my PV drifts in a circle, slowly working its way closer and closer to the low-hanging branches. Copter magnets, you know. If I pop up to 100' or more, the number of GPS sats climbs to 9-10 and the circling stops. Empirically, that tells me that although you can get home lock with only 6 sats, to get a good position lock while airborne it takes a few more. From what you describe, this could be what's happening to you.

But I'm almost as much of a noob as you are. Try reading through some of these threads for the expert opinions. Good luck and happy flying.

http://www.phantompilots.com/viewtopic.php?f=5&t=2522
http://www.phantompilots.com/viewtopic.php?f=5&t=5920
http://www.phantompilots.com/viewtopic.php?f=5&t=816
http://www.phantompilots.com/viewtopic.php?f=5&t=591&p=3883

MedX172 · Jan 21, 2014

I agree with Tripnman. I've flown at two different locations thus far. One in an open field, and another adjacent to my home that is in steeper terrain near a Park trail. When I took off at the open field, I believe I was locked on 10 or 11 Satellites.

At my home, however, the smaller open area I was flying only locked on to 7-8 satellites and I noticed a distinct difference in how the Phantom behaved. I noticed it was drifting in specific directions and at times actually required counter-movements to keep it in a fixed position.

Pull_Up · Jan 21, 2014

In the IMU calibration screen hover over the question mark. it will give you the acceptable values. Your compass raw values are outside the optimal. If the mod value is outside the correct range as well then there is advice in the same popup about what you can do to rectify...

SkyView · Jan 21, 2014

Thanks for your replies, much appreciated. There is one thing I noticed and am not sure if it is normal or a defect. When I start the P2V, it will idle till I give it throttle to takeoff. When I land without turning off the motors, the P2V idles for a few seconds then gradually speeds as if to takeoff without me touching the controls. This self liftoff seems to cause the P2V to lean as if it were going to tip over rather than a stable vertical takeoff. Only when I shut off the motors and restart will the idle remain steady till I increase throttle. I was wondering if this is normal, or a Motor Speed Control defect. Also, could this be related to the circular pattern of hover as I described in my previous post.

Pull_Up · Jan 21, 2014

It's been reported by others, so I guess it's a "feature" - it might be the autoland wondering if it's truly down and having another look?! I've never come across it myself as I don't know why you'd want to sit on the ground with the props whirring? Bit of a waste of all the precious electricity... it only takes a couple of seconds to hold the throttle down to switch them off, then even less time to fire them back up again.

But I don't believe it's got anything to do with your issue - the tipping is because the aircraft is always going to be quite unstable close to the ground with throttle, in ground effect and wash. Hence why you need to give it a good push on the throttle to do a normal take-off, rather than slowly increasing it, which will put you in the ground effect and propwash and increase the time you're going to be a bit squirrely.