What's with the toilet bowl?

[llbr22]

Sorry, I should clarify, my GPS hold is pretty solid. Shooting my buddy fly his heli was a full 5 minutes or so in one position without me correcting at all, plus being able to yaw to pan my shots. Yes, it's super solid. But I guess Im saying I still don't totally trust it from a safety stand point if I'm close to buildings or power lines. It really keeps it in place nicely, but just in case, I really still like to keep it in my sights.

If I'm in a big open flying area even if it started to circle it would be ok.

 

[DucktileMedia]

I can now safely add that flying my hex at my shop and flying it at an open field with the same settings had 2 very different results. At my shop the hex toilet bowled really badly, upward of 30'. At the open field it was within 2' max. I've seen Libr22's DJI hex and it was solidly glued in the air...which made me go out and buy one! now to get mine flying like his. I thought being on 3s was my issue but I changed nothing except for location. So this clearly has something to do with this. magnetic fields, RFI, odd un-noticeable winds? Dunno.

 

[rwijnhov]

To my experience if z for gps is off by 2cm you get toilet bowlling or not accurate hold. If Z is correct you get 10x10cm gps hold.

 

[srbell]

Went up last night with the new cog settings. Got about a 1M circle, which is a big improvement. Pretty strange weather conditions, freezing fog. Last flight of the evening I had a 1/8" layer of ice on the props. Can't believe it would even fly like that.

 

[DucktileMedia]

Something I havent seen answered is where do you measure to on the IMU? Is it the bottom or the middle? The fact that the software only allows for single decimal units makes me think it doesnt have to be THAT accurate.

 

[RTRyder]

Something I havent seen answered is where do you measure to on the IMU? Is it the bottom or the middle? The fact that the software only allows for single decimal units makes me think it doesnt have to be THAT accurate.

Measure to the center of the IMU is what DJI says and by that they mean the exact center in 3 dimensions. For the Z axis I use the middle of one of the sides as my reference point. The tolerance is +/- 1cm according to the DJI techies, one day when I had nothing better to do I changed the settings in 1cm increments away from the correct setting and in both the positive and negative directions, it didn't seem to really make that much of a visible difference. One place where it is noticeable is within a foot or two of the ground when it's getting hit with the full force of ground effect, if it's close there will little to no wobble, if it's off then there will a lot of wobble and bounce in that area.

Ken

 

[RTRyder]

While I'm thinking of it, the quad I had the severe TB problems with on Saturday appears to have gotten over whatever was going on with it. Yesterday I removed the IMU and reinstalled it with some heavier duty double sided tape and for good measure used a tie wrap around its body as well. I recalibrated the compass, measured and verified the CoG on all axis, and made sure the gain settings were the same as before I went to the field and the GPS was holding so well.

So overall I didn't really do much other than make sure the IMU is solidly on the frame, all the setup parameters are correct, and recalibrate the compass. A short while ago I went out back with a freshly charged pack and put it about 50 feet in the air then switched on GPS mode. There's a wind of about 6 to 8 mph with gusts to about 15 and it sat glued to that piece of sky for a good 6 minutes according to the timer on the TX. I brought it down, flew it around a bit and then went back up and it stayed in place for another 2 minutes before I was getting too low on battery power to keep it in the air.

So either the compass calibration was bad or something was going on at the field that caused the TB effect and near flyaway on RTH. Only thing I can do is go back at the first opportunity and see how it behaves out there now.

Ken

 

[robvree]

While I'm thinking of it, the quad I had the severe TB problems with on Saturday appears to have gotten over whatever was going on with it. Yesterday I removed the IMU and reinstalled it with some heavier duty double sided tape and for good measure used a tie wrap around its body as well. I recalibrated the compass, measured and verified the CoG on all axis, and made sure the gain settings were the same as before I went to the field and the GPS was holding so well.

So overall I didn't really do much other than make sure the IMU is solidly on the frame, all the setup parameters are correct, and recalibrate the compass. A short while ago I went out back with a freshly charged pack and put it about 50 feet in the air then switched on GPS mode. There's a wind of about 6 to 8 mph with gusts to about 15 and it sat glued to that piece of sky for a good 6 minutes according to the timer on the TX. I brought it down, flew it around a bit and then went back up and it stayed in place for another 2 minutes before I was getting too low on battery power to keep it in the air.

So either the compass calibration was bad or something was going on at the field that caused the TB effect and near flyaway on RTH. Only thing I can do is go back at the first opportunity and see how it behaves out there now.

Ken

Ken - What happens if you fly forward at a good speed in GPS mode and then let off the sticks? If I turn on GPS when I am in a stable hover, then it sits there locked in with no problems. I get the TB when I'm flying around and let off the sticks. This happens during RTH when it gets overhead but stops when it starts to descend.

 

[RTRyder]

Ken - What happens if you fly forward at a good speed in GPS mode and then let off the sticks? If I turn on GPS when I am in a stable hover, then it sits there locked in with no problems. I get the TB when I'm flying around and let off the sticks. This happens during RTH when it gets overhead but stops when it starts to descend.

Good question, I rarely if ever fly in GPS mode, a hangover from my MK days I guess! Thing is it didn't matter the other day if I started from a stable hover or not. Less than 30 seconds after switching to GPS mode it would start to circle, small at first and getting ever bigger with each lap, very repeatable and nothing I did that day at the field made the slighest bit of difference. The problem I had with RTH I believe was tied to whatever was happening with the quad at that point in time, unfortunately I don't have enough room here at the house to test RTH or I would have. In this case it never stopped for descent when it got overhead during RTH, it just overshot and started to circle then sped off at roughly 90 degrees to the direction it came in on.

Maybe tomorrow I can get over a local ballfield and try it out, if RTH works right then I know for certain its fixed.

Ken

 

[llbr22]

Ken - What happens if you fly forward at a good speed in GPS mode and then let off the sticks? If I turn on GPS when I am in a stable hover, then it sits there locked in with no problems. I get the TB when I'm flying around and let off the sticks. This happens during RTH when it gets overhead but stops when it starts to descend.

If I do that, it rarely stays in place.. only when I slow it down to a stationary hover can I guarantee it staying in place.

 

[DucktileMedia]

Does this invalidate a previous post concerning getting out of RTH once activated? That got me really worried to even try it out. I do know that if I hit my fail safe in hover mode it will turn off and regain control.

Another question about GPS is what happens when you fly indoors and it CANT establish any satellites? I thought I read it goes into fail safe if it detects fewer than 6 satellites? or did I get that wrong?

 

[robvree]

Does this invalidate a previous post concerning getting out of RTH once activated? That got me really worried to even try it out. I do know that if I hit my fail safe in hover mode it will turn off and regain control.

Another question about GPS is what happens when you fly indoors and it CANT establish any satellites? I thought I read it goes into fail safe if it detects fewer than 6 satellites? or did I get that wrong?

I have had no problem getting out of failsafe (I have it mixed on a switch) flipping off the switch and then changing the flight mode to atti. Other keep saying they have to switch back to manual and I have never found that as true and I have tested it a number of times.

As for flying indoors in GPS mode, you should not try it. In a perfect world the WKM is supposed to switch to atti mode if it looses too many satellites (that's what the manual says).

 

[DucktileMedia]

good to know thanks. I would not try flying in GPS mode, but didnt know if it still kicked into failsafe in atti with no satellites established. We are dealing with Chinese logic here so you never know what kind of *** backwards things can happen.

 

[UAVproducts]

What about giving us the option to adjust the Z setting with remote gain. Hmmmmm......worth a try to ask DJI I guess.
I mean if the Z is that crucial.

If no GPS it defaults to Atti. Same as if you power up switch to GPS and take off before it finds any satellites.

 

[srbell]

Glad I found this forum, some great information. I was measuring from the bottom of my IMU. There was a little voice in the back of my head saying centre of the IMU lol. I'll try it again today.

 

[Tomstoy2]

Interresting reading. I had a slight tb effect on my 4th test., as in a 2 foot slow tb, not increasing, but pretty constant. My other 3 tests she was as solid as can be. Only a couple things different from the other 3;

I finally had full-up weight, which required re-positioning the battery, so it's quite possible I didn't have her as ballanced as I did before. Which could very well be the issue.

And, I had reconfigured the z-axis to the center of the imu, also making sure to add that distance to the z-axis of the gps.

I've read elsewhere that when flying in gps it confuses the unit. That it's best to fly in att, then re-enter gps upon hovering again. This is something that I would like to see DJI work out.
Ideally, I would like to just fly around in gps, see something I want to check out for awhile, deer, nude sun-bathers, and just stop there without working switches.

Still, in my limited experience with other gps units, ( fy91q nav. system ), this one is the cats dangles!

 

[swisser]

I've read elsewhere that when flying in gps it confuses the unit. That it's best to fly in att, then re-enter gps upon hovering again. This is something that I would like to see DJI work out.
Ideally, I would like to just fly around in gps, see something I want to check out for awhile, deer, nude sun-bathers, and just stop there without working switches.
!

This is most certainly not my experience. I fly around in GPS mode and if I let off the sticks it just stays where it was, unless it has a ton of momentum in which case a touch of opposite stick checks that and then it stays put. Additionally the same thing works if I am in some other mode (manual or atti) and then flick to GPS it holds its position.

To be honest, the idea that it gets confused sounds like nonsense to me and certainly not what I see when I fly it.

 

[llbr22]

This is most certainly not my experience. I fly around in GPS mode and if I let off the sticks it just stays where it was, unless it has a ton of momentum in which case a touch of opposite stick checks that and then it stays put. Additionally the same thing works if I am in some other mode (manual or atti) and then flick to GPS it holds its position.

To be honest, the idea that it gets confused sounds like nonsense to me and certainly not what I see when I fly it.

This is only the case for me because I keep my atti gains very low for smooth almost mushy flight (and just to help keep the bumps down when flying in the wind). If I raised my atti gains I could do the same..

 

[swisser]

Yep, I tend to keep my gains on the low side too, because I like a smoother flight and am happy to correct movement with the sticks. As I said, if it has lots of momentum when I let go then it does require some stick work to stop the motion, but the GPS hold then kicks in and holds it steady. My point mainly was that the idea of switching between modes a lot is unnecessary in my experience.

 

[mitmit]

What about giving us the option to adjust the Z setting with remote gain. Hmmmmm......worth a try to ask DJI I guess.

dont you think it looks a bit funny Robert -
"since you DJI dont want to give us pid tuning ability, maybe you could at least be so kind to give us a remote z seting adjust?"