Hoverfly Odd GPS behavior

[Webheadfred]

This morning, I went out for a fly and had an odd anomaly with the GPS PH. First some background...

Yesterday, I had several flights without issue and I normally arm and allow the GPS to acquire on my back deck. The HEX faces approximately 020 magnetic. On those flights, the GPS acquired a good blue signal in about 15 seconds each time. Nice. Performance was excellent. This morning however, I took her out front as the sun is more dramatic there and set her up to fly. She was sitting in the driveway facing about 100 magnetic with a clear view of the sky. It took nearly 5 minutes for it to acquire a green fix and it switched several time from yellow to red. As I was watching it, it went from red to green and stayed green. Several more moments, no blue. Oh well I though and gave her a whirl. I climbed to about 30m and and engaged PH. the HEX pitched to the south and headed nearly straight south. I estimate the pitch to be 20-30 degrees as it all happened very fast. I let it go a little hoping it would correct but I had to take over and brought her back. Level again, I though I'd give her another try and it seemed to hold but I was hesitant to keep it there. I tried several more times and it seemed to hold but it was making more dramatic corrections than it should have been necessary as it was mostly calm. It seemed like it had lost it's GPS position. Thinking back after she was first built, the same thing happened and I was a little gun-shy about using GPS PH. I've probably had 15-20 flights and it's been fine. Seems like when it takes a while to lock on is when the issue shows up. Anyone else having any issue similar?

 

[Bartman]

Fred,

Can you please post a pic of the top of your heli where everything is mounted?

Could it be that some of the satellites you had been linking up to were blocked by the house? Power wires in the front?

Also, if these GPS systems are anything like their bigger siblings that we use, the position has to be redetermined after it's been moved but back yard to front yard probably isn't far enough to make a difference. Or do only LORAN and INS systems have to do that?

 

[Webheadfred]

Here ya go Bart. Maybe you see something I don't. I haven't flown again so I should be able to upload the log. I think I may have to take the wife-unit fishing so it may be a little later before I could upload the log. Thanks for taking a look.


View attachment 11090View attachment 11091View attachment 11092View attachment 11093View attachment 11094

 

[Webheadfred]

Actually Bart, the back on the deck could be blocked a little more and it acquires the fastest. Good sky coverage front and back and underground utilities. I just thought of something though and it may or may not be an issue. In the front, I armed in the driveway and there probably is rebar. Could that interfere with the SAT acquire? I know it could interfere with the compass but of course I'm airborne when engaging PH.

 

[Mactadpole]

Hey Fred,

I don't fly HF but I am fairly familiar with GPS having done a good bit of ground surveying with them and working out issues of working with them under dense and high rainforest tree canopy. One thing I see is that there is a lot of potential electrical interference in fairly close proximity to the antenna. Also it is sitting below the plane of the other electronics which may or may not cause issue due satellites low on the horizon and other electronic interference.

I think I would look at creating some sort of ground plane for the antenna and getting it up and away from electrical currents and electronics. It's just really not in a good position.

That said, here in the states there should not be much of an issue with where satellites are on the horizon or angle in the sky. Unless your in a natural or urban canyon.

My 2¢

Shawn

 

[Photronix]

View attachment 11099

From the manual

 

[Bartman]

Fred,

Have you noticed any tendencies to wander in yaw/hdg? Your GPS antenna should be up above other stuff so that other stuff can't cast a shadow onto it.

Bart

 

[Webheadfred]

Thanks Guys.... the aluminum bracket will be installed in the morning. I may just put the external magnetometer up there as well. I shall report back.

 

[Webheadfred]

Well I said I'd report back... After making a new aluminum bracket and mounting the antenna 5" above the board, I had a solid blue lock-on in about 8 seconds. Very nice. Unfortunately I also decided to put in a little vibration dampening which brought to light another problem. Bad vibration from several of the Xoar props. Everything was so tight before and the HEX flew perfectly but I could see a little standing wave sort of vibration in the video. I also noticed the #2 motor seemed to vibrate a little. So... off came the props and I checked the motors at all throttles. The Avroto motors are fine. I suppose I shouldn't have assumed the Xoar matched pairs were as perfect as they advertised. I'm now balancing them as one had a really bad hub imbalance and the others needed some attention as well. I'll try once again...

 

[Bartman]

Fred,

I'm trying to get my hands on some golf club weighting tape, apparently it's lead tape and should be perfect for balancing the hubs. Out of ten Xoar props, two will be perfect, six will need a little hub balancing, and two will need mroe than you'd expect. it's the nature of natural materials.

Bart

 

[Webheadfred]

Hey Bart... I think I've fount a pretty good solution for the hub. I bought from HD a little 5 minute epoxy. It's the little two tube thing and I drop a dab or so and mix it up. With a tooth pick for fine adjustment or the end of a clipped zip tie for heavier adjustment I'll apply it and check it as it sets up. I never thought of the golf club tape...hmmmm maybe a trip to Edwin Watts this afternoon!

 

[Bartman]

Fred,

Is that one of Rusty's frames? DO you have any issues with heading fluctuations?

Bart

 

[Webheadfred]

Yeah, it's a Rusty's frame. I didn't have any heading problems until that last flight but with so much vibration, I figured that was the issue. Still balancing and should be able to test again before dark.. I'll let ya know.

 

[Webheadfred]

Well, after spending the better part of two days balancing the Xoar props, I've discovered that I need WAY lower gain than the APC's to fly smoothly. In fact, I've reduced the gain down about 25 points in the transmitter. I hate to say it, I think I like the APC's better. I've been flying 11x47's APC and I tried 11x5 Xoar. Lifting up, there is just tremendous vibration. I can see the gimbal vibrating. Each time, I landed, lowered the gain and took off again. Repeat. I did get it somewhat smoother the more I lowered the gain and it was flyable. The GPS acquires perfectly with the new bracket but I haven't been able to test it much with the vibration issue. I think tomorrow I'll balance up some 12x38 APC's and compare. Maybe with the more flexible props, it'll be another step in the right direction. Not sure what I was thinking with those Xoar. Oh well.

 

[Bartman]

i just dont' get it, i'm using Xoar props and they're wonderful. other people use them and they're a problem. are yours snug on the prop shafts?

 

[Webheadfred]

They fit very snug on the shaft. I think it has something to do with the flex. I'm guessing though. The only way to tell I suppose, is to compare them to the APC's. Anyone have any experience with 12x38's as compared to 11x47's. I'm thinking I should get slightly more time. I don't know though.

 

[hondajd7]

I've been following this thread closely and made me wonder about my compass calibration.

How accurate do you need to be when flipping the craft end over end? I ask because at 19lbs, mine is rather difficult to rotate perfectly on my own.

 

[Webheadfred]

Lets see... I balanced up some 12x38 apc's and put them on. I have to say its much more smooth than the Xoar's. I even got about a minute longer flight time. Still some vibration in the video though but a huge improvement. What I've done now is to go to a smaller gimbal. I was using a RusticWave with some HiTech servos. I've switched to a Jakub Gimbal since I've only my GoPro Hero2 that I use. I have it all mounted and ready to go but this dang thing called work snuck up on me. Hopefully with the smaller gimbal and less to vibrate, it'll be smoother. We'll see.

How accurate do you need to be when flipping the craft end over end? I ask because at 19lbs, mine is rather difficult to rotate perfectly on my own.

Good question and I've thought of this too. I know where 'North' is in my yard as I just look for Polaris and called it a day. I think tomorrow, I'll pull out the compass and get a magnetic fix and redo the magnetic compass and see how that works. With the bracket I made, I'm still getting really good satelite lock-on on power-up. When all this is sorted out, I hope to post a video showing the vibration and each step I took and the incremental result. Fingers crossed for tomorrow morning smooth video.

 

[Bartman]

Fred

Are you using the latest firmware by any chance? if so have you redone all the calibrations?

 

[Webheadfred]

Yes, I'm using the latest firmware. I didn't recalibrate the accelerometers or temperature as I had done that as an X8. No change in firmware so I figured I was good to go. I did re-do the compass calibration as I took off the external magnetometer and stuck with the internal one. I'm going to re-do the compass tomorrow, verifying magnetic north with my hiking compass.