GPS boards and hover stability

[XterraGuy]

I'm wondering if the version of GPS board can affect hover stability given the same number of satellites? B&H just replaced a defective Solo (bundle)for me, and they built a bundle from individual components (e.g., a Solo, a gimbal, a backpack and two full sets of props). All this is fine, except the Solo has a Rev A GPS board. Flight testing it today, I noticed when compared to my other Solo which has a Rev B board in it, that it's hover stability is definitely less - even when both vehicles are locked on to 10 satellites. Taking get off in Fly mode, the new vehicle drifts more... as much as 8-10 feet laterally, with altitude varying between about 3-10 feet. My other Solo is much more stable. After flying around for 10 minutes, the new Solo thought it was 14 feet higher than it actually was. Also, after full throttle lateral flight, the vehicle tends to "slide" along another 20-30 feet (estimated) when I re-center the stick. My Rev B Solo stops it's directional motion almost immediately by comparison. All of these symptoms seem like they are or could be GPS related, and I'm wondering if that's what's happening here?

 

[IrishmanPDX]

I didn't think the GPS had anything to do with altitude hold, thought that was done via a Barometer in the pixhawk. However using the MRO gps, I still get a couple of feet lateral movement when hovering close to the ground, more than likely poor GPS lock (will be upgrading to a HERE shortly, so we'll see how that changes things). As for the full throttle lateral flight and 20 - 30 feet slide. Is this in manual mode by any chance?

 

[XterraGuy]

No, was flying in Fly mode for my test flight, so theoretically, as soon as the stick centers, the Solo should want to stay in that spot. I didn't try the pause button since I never use it, but my guess is the result would be the same. Regarding altitude hold, you may be right but I was thinking it was a combination of barometer and GPS, but I don't really know. As I sit here waiting for a Dr appt, it strikes me that I could easily swap battery trays with GPS attached and see if the flight performance I'm seeing moves to my other Solo. Then I'd know for sure. So I think I'll do that when I get home...

 

[IrishmanPDX]

Good thinking there, quick way to see differences. Course you also have to factor in weather conditions and sunspot activity, they could also affect GPS lock. Pretty sure GPS will only give you two sets of co-ordinates, not three. So it wouldn't affect altitude holding. Anyway, let us know the results of your test, also, what shielding are you using on your GPS? I'm using the V2 shields on all of mine. Strange thing is, when holding position, I will get some lateral movement of 3 - 5 feet, but if I use the RTL, it's much better at putting down within 2 feet of takeoff (something I played about with to no end with the Green Cube bird as the autoland seems to work on that one no problem!).

 

[XterraGuy]

Well, I have results. I first flew both Solos as they were: two five minute flights, one immediately after the other, using the same props and battery, lifting off with 9 sats, looking for the flight characteristics I summarized above. The older Solo with Rev B GPS held initial hover much better, both altitude and position. After flying out to about 500 feet in all directions and making numerous violent direction and altitude changes, the older Solo then hovered at 2' altitude very well and read exactly 0 feet altitude at touchdown, compared to a less stable 2' hover for the new Solo and it reading 5' altitude at touchdown. Not terrible, but definitely not as tight as the older Solo. OK, I then swapped GPS boards and flew the same missions, back to back. The vehicles flew exactly as they did before the swap: using GPS A or B made absolutely no difference. So that answers the question... the different flight characteristics can be attributed to something else, presumably the flight control system and/or associated sensors.

 

[tpsharkey]

I'm wondering if the version of GPS board can affect hover stability given the same number of satellites? B&H just replaced a defective Solo (bundle)for me, and they built a bundle from individual components (e.g., a Solo, a gimbal, a backpack and two full sets of props). All this is fine, except the Solo has a Rev A GPS board. Flight testing it today, I noticed when compared to my other Solo which has a Rev B board in it, that it's hover stability is definitely less - even when both vehicles are locked on to 10 satellites. Taking get off in Fly mode, the new vehicle drifts more... as much as 8-10 feet laterally, with altitude varying between about 3-10 feet. My other Solo is much more stable. After flying around for 10 minutes, the new Solo thought it was 14 feet higher than it actually was. Also, after full throttle lateral flight, the vehicle tends to "slide" along another 20-30 feet (estimated) when I re-center the stick. My Rev B Solo stops it's directional motion almost immediately by comparison. All of these symptoms seem like they are or could be GPS related, and I'm wondering if that's what's happening here?

I have 3 Solos that have the black shielding on the GPS but my for parts Solo I tore it down and found Rev A on the GPS. They all fly similar and hold well in GPS hoover, I have practiced manual flying (low wind) and the first time switching to manual it just hovered, not moving, I had to double check it was in manual, the barometer holds well, but flying faster there are some height movement, probably pressure changes and on centering the throttle Solo slides a little more in manual mode.

 

[RichWest]

Hover stability can be improved by applying a dampening material between the main board and the battery tray. Basically you only need 4 location to calm vibes getting to the PH. It is an attempt to reduce any resonance working through the main board.

Sorbothane has been recommended in this application, seems 3/16" thickness in 30Duro works best. A few threads on the mod and a video showing its application, "Sorbo Mod". fwiw, more is not always better, 3/8" round pads is more than enough.

 

[XterraGuy]

Thanks, I'll look into that idea. Maybe the level of barometric sensor drift that I'm seeing is within acceptable limits and I'm just spoiled by how stable my original Solo hovers and maintains calibration during flight. But it sure is nicer having it hold its position even with significant wind. If vibrations may be affecting the sensor, it's certainly worth the effort to tinker with it.

 

[XterraGuy]

Since this Solo is only a few days old, I just contacted 3DR Support and forwarded vehicle logs. Maybe they can shed some light on whether these flight characteristics are within spec...

 

[Maddog]

Hover stability can be improved by applying a dampening material between the main board and the battery tray. Basically you only need 4 location to calm vibes getting to the PH. It is an attempt to reduce any resonance working through the main board.

Sorbothane has been recommended in this application, seems 3/16" thickness in 30Duro works best. A few threads on the mod and a video showing its application, "Sorbo Mod". fwiw, more is not always better, 3/8" round pads is more than enough.

Rich- I've heard of that mod, but how does it help hover stability?

Also, I presume everybody knows the military downgrades the accuracy of civilian GPS? Don't know if that affects the ability to hover in one spot or not, but your homemade GPS-guided cruise missles won't be as accurate as the military version.

 

[skyhax]

Most of the downgrade was removed.

 

[IrishmanPDX]

All three of my solo's are now rock steady and have no positional drift whatsoever! Mainly because it's raining like heck in the PNW so they are all sitting on various shelves.....

..also, I need more shelves.

 

[RichWest]

Rich- I've heard of that mod, but how does it help hover stability?

Simple version...The PH sits between the forward and aft mounting screws on the main board. It appears there is enough weight that the board could oscillate the PH ever so slightly. The sorbo just stabilizes the board from that movement.

If you've been watching the GC release, they have supplied Sorbo and recommend its installation.... The GC weighs more than the stock cube...

 

[Pedals2Paddles]

GPS selective availability was discontinued 17 years ago. There is no degrading of GPS for civilian use. That is a myth. In fact with RTK technology, it is accurate to the centimeter. With just WAAS or other SBAS, it is accurate to a few feet and very stable.

What your #2 solo is experiencing is probably due to vibration. A bad prop or rough motor can cause that.

 

[Saijin_Naib]

GPS selective availability was discontinued 17 years ago. There is no degrading of GPS for civilian use. That is a myth. In fact with RTK technology, it is accurate to the centimeter. With just WAAS or other SBAS, it is accurate to a few feet and very stable.

What your #2 solo is experiencing is probably due to vibration. A bad prop or rough motor can cause that.

Any point attempting to put Sorbothane in the GPS bay underneath the GPS module as well? I heard microvibrations can throw that accuracy off a bit, but I've yet to see that corroborated anywhere else.

 

[Pedals2Paddles]

GPS is not affected by vibration. That would not accomplish anything.

 

[Maddog]

GPS selective availability was discontinued 17 years ago. There is no degrading of GPS for civilian use. That is a myth. In fact with RTK technology, it is accurate to the centimeter. With just WAAS or other SBAS, it is accurate to a few feet and very stable.

What your #2 solo is experiencing is probably due to vibration. A bad prop or rough motor can cause that.

Oops- my bad. I should get out more often.
Matt, have you ever seen that show "Adam Ruins Everything"? Lol!

 

[Thorsg1]

I had to send in my first Solo for warranty last year and 3DR replaced it with a refurb. I took it out of the box, updated the firmware then took it out for a test flight and it was horrible. Drifted all over the place, virtually uncontrollable, almost crashed on landing. Took it home, did compass, level and stick calibrations and that fixed it. It also had a Rev A GPS (I've since upgraded to an mRo GPS mainly to get faster lock times)

I do most of my flying in wide open spaces but I did notice the mRo module helped in situations where there were obstacles close by like trees or buildings but in open spaces, there was no difference from the Rev A. It was the calibrations that made the difference.

Your mileage may vary.