I have used a drone for testing out a mission I setup for my RC Helicopter. Both FW 3.5.3
The drone equipped with a cheap GoPro clone did a good job. As before with previous Missions I have loaded the same mission into the RJX520. Equipped with pixhawk, two GPSs, Sonar and a cheap 3 axis gimbal and Sony FDR-X3000. I must admit the gimbal motors are struggling now with the weight of this camera. Needs an upgrade.
After doing 4 circle around the property, with ROI, climbing gently to 72m the Heli comes down over the buildings than towards the river and looses contact to the ground station for 10 seconds. The drone was keeping to the mission programmed height of 2m above home. The Heli - pixhawk got it wrong by 1.5-2m. I watched it but did not interfere because it never happened to me before. Me and my Heli were very lucky. But in the future I will not hesitate to aboard a mission.
I mapped out the Position estimates from the Heli and the drone. That showed me that the Heli was in the wrong X Y and Z at the end of the mission.
It is not the first time I have flown this Heli with 2 GPSs. They are different brands that is why GPS_AUTO_SWITCH = 1
Not blended.
I have portions of the drone and Heli videos rendered to one 2 minutes to show what happens. The Heli misses a post in a hedge by inches. Leaves are flying but absolutely no damage. The white spin-blades had a lot of green color, that’s all.
Still not 100% sure why the Position estimate went that much wrong down there.The drone was ok all the way with 1 GPS.
Both aircraft in this video : https://www.youtube.com/watch?v=bX201xZGOHk
Wow. Yes indeed, GPS is not 100% accurate 100% of the time. We had a moderate geomagnetic storm in the northern latitudes a few days ago that caused really beautiful aurora’s at night and GPS position estimates were off by up to 75 feet with professional-grade Trimble mapping units for one whole day. We had one unit that could not get a differential correction signal for 24 hours even though we tried two different antennas on it 
I will take that GPS1 off because it let me down this time. The GPS2 will be GPS1 and the only one for a wile.
By having a short flying brake I go for the change of the DDVP tail wiring to test the FW for it. Thanks Chris.
Do you know if it is a repeatable problem with the dual GPS?
The GPS accuracy spec is with a global average user range error (URE) of ≤7.8 m (25.6 ft.), with 95% probability. Actual performance typically exceeds the specification. However, the URE is not user accuracy. User accuracy depends on a combination of satellite constellation geometry at your location, and local factors such as signal blockage, atmospheric conditions, multi-pathing of signals, and receiver design.
Many folks think GPS is 100% accurate and reliable. It is far from it. As a pilot this is the best approach:
Chris, I just feel not comfortable with this GPS unit. (from China) The second is a original 3DR unit but older with latest FW .
I wanted to have two just for redundancy.
If I go for two again I will make sure that those are of the same make and I will use blending parameter. Which has been proven to be more accurate than 1 unit on its own.
But I also agree with you regarding the specification accuracy of those ‘cheap’ units. Over the time I was sometimes stunted about the accuracy after the Heli came back down on RTL. The camera was running from takeoff until the landing.
The footage of the video showed me it landed with such stunning accuracy back home.
During the last mission which was completed by my drone as expected. I will admit my complacency, yes, stupidity. Never again, I will and I must aboard. I wanted this to be seen by others who could have a similar situation.
Most of the time the consumer-grade units are pretty good. But there are anomalies that can cause quite significant position error. Pilots that use GPS navigation must always be ready to take over manually when it fails. Not only in RC, but full-size aircraft as well.
Even the TSO’d units that cost $20,000+ in full size aircraft can have horizontal position variance of 25 feet with CAT III precision approaches, which is under the required visual range for those approaches. However NO full-size aircraft use GPS for altitude. The tried and true Category I ILS with localizer and glideslope is still the gold standard in precision approaches for full-size aircraft, despite modern technology. Cat II and III instrument approaches all use radio altimeter for altitude and decision height on the approach. Using GPS for altitude is nuts and it’s not if you’ll crash into the ground, it’s when. I see a trend in RC pilots and drone manufacturers placing WAAAAY too much faith in that GPS.
Thanks for the info. Will keep that in mind.