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GPS battery

Discussion in 'General Discussion' started by billflowers, Apr 28, 2014.

  1. billflowers

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    Has anyone ever changed the battery on the GPS module? Mine holds position for 5-10 min and then acts like it wants to take off to somewhere far away. I'm thinking that the BBRAM battery is getting weak. I bought the Phantom used so I have no idea how old it is, I've tested the voltage with a meter and it seems OK.
     
  2. tanasit

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    I never heard of the GPS battery before. I think the flight battery takes care of everything! ;)
    As for the problem you mentioned after 5-10 minutes position hold (not sure why one wants to do so that long?),
    did you set and confirm the home position?
    What did you do when it stared to take off?
    Did you see the low battery warning LED?
     
  3. billflowers

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    The GPS has a BBRAM battery on board. As for hovering for 5-10 minutes, obviously I'm not holding position for that long. What I meant by that is that after 5-10 it will not hold position with the controls centered. This all happens with plenty of battery power and home position locked. Any helpful info is appreciated. Also, if I take it out of GPS mode, I can regain control of the Phantom.
     
  4. OI Photography

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    The little GPS board does have a battery on it for the purpose of helping to speed up initial lock times. I've read that when tested the voltage of that batt can vary widely, and is often found to be below the 1.8v needed for it to be useful. If I remember correctly it's not easily replaced (not just pop-out-pop-in like you might expect). However, the GPS module is still supposed to work properly even if that BBRAM battery is dead or missing, it just won't retain the sat positioning references that reduce the time it takes to first acquire lock at power up
     
  5. billflowers

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    That helps, Thanks!!
     
  6. Dalite

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    I had a lot of questions and concerns about the GPS battery, and tried to get answers, refine theories and get a better understanding of what it does.

    I downloaded all the info on the uBlox website concerning the NEO-6Q GPS module

    after pouring through a lot of info that I didn't completely understand, I started putting together some questions and posed them to someone familiar with the engineering aspects of the module.

    First off, the NEO 6q module was a good choice to base the GPS board around . It uses a TCXO (Temperature Compensated Crystal Oven) and BBRAM (Battery Backed RAM) to enhance time base accuracy and speed up TTFF (Time To First Fix).

    I was concerned that the TCXO was draining the backup battery, and found that the battery only backed the RAM and the TCXO was controlled from the main power supply (lipo battery).

    I was also concerned that the battery was too small in terms of reserve current to keep the last GPS fix in RAM. I was Informed that I could compare the battery specs to the current requirements of the module to determine suitability.

    I was concerned that a low battery would cause slow reacquisition of satellites in the event of a GPS glitch. The specs for the module show that battery backup is optional. If not used, the contacts were to be bridged. If used, the battery is effective above the minimum 1.8 VDC requirement. The battery is a 3 volt battery of undetermined composition. I don't know if it is supposed to be rechargeable. I found that the presence of resistance across the BBRAM terminals of the GPS module could cause deterioration of the module's operation.

    I questioned a DJI repair tech, and found they do not check the GPS backup battery voltage as a function of repair.

    So, I still have questions, but found some of my original concerns weren't valid.

    The NEO-6Q, with a working backup battery has a 1 second TTFF; very good. This is due to correct almanac data and last fix already being present when the Phantom is powered up. But, what if the backup battery is below the 1.8 volt minimum and is seen as resistance? If the Phantom is in flight, the BBRAM is bypassed; the module feeds off the main battery. So, what could be the problem of having a low battery? From what I have been able to guess; none - other than slower TTFF due to the possibility of stored GPS data becoming corrupted between uses. That would trigger a new download of almanac data, when a flight battery is connected and the GPS acquisition routine searches for new data.

    I don't know if any of the above is useful or not.

    I will throw another variable in the mix....

    Hovering at the same motor speed with no wind could cause the vibrations of the props to start affecting other pieces of the Phantom. Sympathetic Resonance. Changing speed, small maneuvers, etc. tend to break the consistency of inherit vibrations.

    Under optimum sat lock, there is still a 2.5 meter horizontal margin of error. That would be an 8 foot square box to hover within and still be as good as it is expected to get.

    I have no answers here; just trying to share a little to think on.
     
  7. billflowers

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    Good info!! thanks! The thing that trips me out is that once it starts wandering, I can regain control by switching out of GPS mode. This tells me that there is something going on with the module. Thanks again for sharing your knowledge
     
  8. Dalite

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    You may want to look at the magnetic declination of your location and make adjustment with the compass sensor. Also, if you have the top shell off, you can carefully remove the adhesive pad, note the board orientation, them remove the GPS board to see if the ceramic antenna is cracked. It is doubtful that is the problem, but at least it woud be eliminated from the que.

    While it is apart, you can consider disconnecting the compass from the GPS and twisting the compass lead untill it has loose twist all the way down to the sensor. Don't twist so tightly that it puts pressure on the contacts on either end. You can also do this to the GPS lead where it goes into the NAZA. Also, make sure that the NAZA is firmly seared and pointed straight ahead.

    The thought process behind the twist is just a little insurance against induced interference. Straight wires are antennas. Twisting wire pairs is the oldest trick in the book for basic shielding. Look at the servo cables going from your receiver to the NAZA, and you will notice that DJI already uses this lead dress on those NAZA inputs.

    No promises any of that will give noticeable results.
     
  9. Seedler

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    Hi,

    I am also having problems with my gps. Just tested the small battery on the module. It was 0.8 volts. That to me is a dead battery. When the flight battery is connected the voltage at the battery terminals is just over 3.2 volts, so this means it is a rechargeable battery as the phantom is charging it. Don't know how long these batteries last, but I was only flying a few hours ago. I would expect them to last weeks at least for all they have to do.

    So to change it or not. I don't know if I have the nerve.
     
  10. billflowers

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    How is your GPS acting up? From what I'm gathering, the battery is not necessary for GPS function so I do not believe that it will give you issues if it's a weak battery (unless it's taking longer than normal to grab satellite signal). I have not been able to confirm the battery's function though so I might be wrong...
     
  11. Seedler

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    Hi,

    I have been finding it hard to get a good lock. Most times the best I get is 6 satellites when other devices are getting many more. Plus it can take a long time to get this. I don't know if the battery has anything to do with this. But in my mind if something isn't doing what its supposed to do there is a problem. Maybe a dead battery is a sign of an underlying battery. I cant believe it was shipped with a dead battery though. Should dji not check this before it is sent out.

    Cheers,

    Dee