Phantom + Lightbridge - Freefall

DavidN

Member
I have a Phantom 2 with Lightbridge and a H3-3d. Default Gains except as you suggested ATTI is at 120. Compass is correctly adjusted. All firmware is up to date. RC is a Taranis.

I take the Phantom up to 75 or 100 feet with GPS (no less than 8 satellites) hoover for short while then begin to descend straight down at a constant moderately slow speed by holding the throttle in a steady position a little below midpoint. At some point in the descent the drone will essentially go into a free fall. Sometimes if I throw the throttle all the way up and I will get the drone to slow down and begin an ascent. I have swapped the FC from a Phantom Vision Plus thinking I had a FC issue. Same pattern has happened. Issue has also happened with different batteries. Does not seem like an antennae problem as I have replicated the issue with the Phantom in several different orientations. Thank goodness for some very dense unmowed grass as a couple of times the Phantom has dropped fifteen or twenty feet to the ground.

I am not sure where to go from here.
 



hjls3

Member
don't know much about the phantom, however - descending straight down not really a good idea - when you do so, you are descending thru your turbulent air. prop wash. I fly a bunch at high altitude, live at 8500. When I go up to say 10k or so, you really have to be super careful about how you descend.
 

Tahoe Ed

Active Member
Does the Phantom wobble on descent? If so you are descending in your own prop wash. That will cause instability. If you are the newest firmware then your descent is limited to 2m/sec. You can try the 9450 DJI props. That may help the situation. However, it is better to descend with some forward or sideways movement. I like to circle if I need to descend quickly.
 

FlyGirl

Member
The original poster said it went into free fall though, not wobbles, almost like the copter was disarming the motors? Is that true DavidN? After you calibrated the transmitter in the assistant software, did you have full range on the throttle stick in the assistant software?
 

Tahoe Ed

Active Member
The original poster said it went into free fall though, not wobbles, almost like the copter was disarming the motors? Is that true DavidN? After you calibrated the transmitter in the assistant software, did you have full range on the throttle stick in the assistant software?

True, he does not state if his cutoff is Immediate or Intelligent.
 


DavidN

Member
True, he does not state if his cutoff is Immediate or Intelligent.

The freefall is likely VRS. VRS was caused by me doing repeated descents straight down as part of some testing I was doing.

Let me add another piece to my story. The reason I was doing these vertical descents was I was trying to replicate something else I have experienced with this Phantom 2 but not with my slightly lower weight Phantom Vision. I had on a couple of occasions been where the Phantom 2 would fly fine in any horizontal or vertical movement but after 7 or 8 minutes of flying would ascend only at very slow speed or not at all. Even with the throttle all the way up. Sometimes even descending with the throttle all the way up. It was these uncontrolled but slow descents that got me doing the vertical drops that I now know were causing VRS. But what was going on in the other case of the less than normal throttle response? The Phantom Vision has none of these issues of sub par throttle response.

I live at 8000 feet and I have a Lightbridge unit attached so some added weight. That might explain the low throttle response but what would explain the throttle sometimes being fully able to lift the Phantom 2 vertically at a nice clip and the next minute full up throttle and the drone is barely rising or even sinking. I stumbled in VRS while trying to figure out what was going on with the occasional throttle issue. Now I need to get an understanding of this minimal lift issue. Is the Phantom 2 + Lightbridge + H3-3d + GoPro + 8000 feet a weight and thin air combination part of this issue. But why then is most of the time vertical lift is just fine. Other times definitely not so much. I could try the new 9450 prop. But again why the current variability in ascending power? Firmware is 3.06. Same issue with various batteries.
 

Bartman

Welcome to MultiRotorForums.com!!
David,

It sounds like the helicopter wouldn't climb because the batteries were nearly dead? Flying at 8000 ft is going to deplete the batteries much more quickly than flying at sea level would.

Bart
 

Tahoe Ed

Active Member
David, that is why DJI introduced the 9450 props. High altitude or heavy quads. I would try them I think you will be surprised at how well they perform with the latest firmware.
 

DavidN

Member
David,

It sounds like the helicopter wouldn't climb because the batteries were nearly dead? Flying at 8000 ft is going to deplete the batteries much more quickly than flying at sea level would.

Bart

According to the Lightbridge OSD, I have had the issue with 45 and 50% on different batteries. I have five batteries. None have been cycled more than twenty times. Lowest I have ever run a battery down to is 23%. At 8000 feet with my configuration the batteries are at about 30% after 11 or 12 minutes. Thanks
 

Tahoe Ed

Active Member
According to the Lightbridge OSD, I have had the issue with 45 and 50% on different batteries. I have five batteries. None have been cycled more than twenty times. Lowest I have ever run a battery down to is 23%. At 8000 feet with my configuration the batteries are at about 30% after 11 or 12 minutes. Thanks

David I can tell you from experience flying at altitude that below 50% you can have issues. That is why I recommended the 9450 props.
 

DavidN

Member
David, that is why DJI introduced the 9450 props. High altitude or heavy quads. I would try them I think you will be surprised at how well they perform with the latest firmware.

Yes last night I found out about these newer props. I ordered some early this morning.

Does not I think explain the variability in lift. Sometimes quick snappy lift on throttle up and other times little or no lift even on full throttle. The minimal lift does seem to happen not at the beginning of a flight but after several minutes of flight. But also not so late in a flight to be in a low battery situation either. Thanks
 

DavidN

Member
David I can tell you from experience flying at altitude that below 50% you can have issues. That is why I recommended the 9450 props.

Maybe a Phantom 2 + Lightbridge + gimbal + GoPro is right on the edge of acceptable weight and air density at this altitude. When new props come in that will change one variable and maybe deal with the issue.
 

jdennings

Member
I am at 5500 feet only, yet with a phantom 2 loaded with gimbal + go pro + extra rx + iosd + vtx the weight does get up there, and the power required to stop a fast descending copter with marginal power can never be under-estimated.
Sounds from what you've been saying that it could be a combination of both too much down speed and some VRS.

One way you could find out your limits is to get up high and see how low on the throttle you can get away with. Definitely, er, stressful ...
I did that and ran a few tests a while back to check out limits on mine, see how fast down I could get away with and what were "safe" limits. I found out that in some instances I could not stop the copter by throttle only if in pure or fast freefall. Something I can definitely do with others, not quite stop but reduce speed a lot. Hard to say if it was VRS with the Phantom, inadequate power, or both ... Immediately switching to manual with throttle up to the max, and simultaneous strong and fast lateral movement via pitch or roll, always worked though, as expected to get out of a vortex ring.
 

DavidN

Member
The 9450 props are a definite improvement at my altitude of 8000 feet for my Phantom 2 + Lightbridge + Gimbal and Gopro. Only had time to do a little testing with one battery but quad is flying and just maybe the throttle issue is cured or much better.
 

Toni Mas

New Member
Hi there. I have the same problem than David with my phantom 2. It seems that at some point the phantom looses power and goes down and goes on a free fall. Sometimes before hitting the ground responds to the controls and I am able to recover altitude. It seems that something into the phantom 2 gets over heated and at some point does not respond the controls. Just waiting from a response from the Dji tecnical support but not lucky at the moment.
 

GorData

New Member
I weighed my phantom 2 with H4-3D gimbal with GoPro 4 and light bridge and it was 1345 grams. Not too bad.


Sent from my iPhone using Tapatalk 2
 

Does anyone have any new info on this problem? My phantom 2 is doing the exact same thing. I have a h32d gimbal, iso mini, and dji video downlink. I've added an orange rx8 through the s bus and use a spectrum dx9, and run carbon fibor props it flew great about 10 times, then randomly started losing throttle control and drops uncontrollably, Its not ring vortex, or low battery. I've tried switching to manual and giving it full throttle but no help. It's not losing signal because it doesn't go into failsafe, which I've tested and that works....I'm at 180' above sea level.
 

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