Devo 8 transmitter info requested

Discussion in 'Introductions and Site Help' started by beesontoast, Jan 31, 2018.

Tags:
  1. beesontoast
    Offline

    beesontoast New Member

    Joined:
    Jan 31, 2018
    Messages:
    5
    Likes Received:
    1
    Trophy Points:
    1
    Ratings:
    +1 / 0
    New to drones and RC, but with some rusty electronics skills. Hoping to fix a Devo 8 transmitter unit that I have bought cheap as "spares or repair" and was hoping to find some info here, but there seems to be very little about this model for some reason.

    I have a specialized use in mind for drones, which I may discuss as some point, but first I need to do some learning.

    I have a Devo 8 transmitter that I bought as "spares or repair" and I'm trying to find out if it is worth repairing, or if I should use the mechanical parts and build my own circuit inside the case.

    There seems to be almost nothing on this forum or in the resources about this model - anyone know why? Better still, does anyon here have intimate knowledge of this unit?

    The unit switches on and the red LED above the switch lights, but there is nothing on the screen and no sounds. The red LED stays lit even when switched off. The same happens in all respects when I use an external power source.

    Can anyone tell me the correct battery that should be in this, as it is missing?

    I have not dismantled if further than taking the case apart so far.

    What exactly are you looking for? There is no circuit diagrams available.

    It uses a cage that holds standard AA batteries.

    Then the cage is missing. Should there be 2xAA for 3v, or 4xAA for 6 volts? The external supply looks like it will take up to 12v.

    Fault tracing info at the moment - specifically related to the power train to the display, but any board layout info would help. I can trace with an oscilloscope, but without knowing where the signals should be, it's a bit like shooting in the dark.

    No Board layouts or Circuit diagrams are made available by Walkera The best source of info on the Devo 8 would be here.

    Deviation - Home

    If you connect an external power adapter It MUST be <= 200ma Max current output. If it is over it will blow your radio.

    Walkera use the adapter to limit current. It has no internal current overload protection.

    Picture of Battery cage.

    IMG_2316.jpg

     
    Last edited by a moderator: Jan 31, 2018
  2. beesontoast
    Offline

    beesontoast New Member

    Joined:
    Jan 31, 2018
    Messages:
    5
    Likes Received:
    1
    Trophy Points:
    1
    Ratings:
    +1 / 0
    Great, thanks. If someone did plug in a higher current adaptor, which component is most likely to blow? And how fixable is this?
     
  3. bjr981s
    Offline

    bjr981s Moderator Staff Member

    Top Poster Of Month

    Joined:
    Sep 19, 2015
    Messages:
    5,367
    Likes Received:
    352
    Trophy Points:
    83
    Location:
    Sydney, Australia
    Ratings:
    +454 / 14
    If you read the devo 7 threads on this it will advise what blows.
     
  4. beesontoast
    Offline

    beesontoast New Member

    Joined:
    Jan 31, 2018
    Messages:
    5
    Likes Received:
    1
    Trophy Points:
    1
    Ratings:
    +1 / 0
    I understand that a power supply of too high voltage will be likely to blow a component, but since circuits only draw the power they need, I don't understand how connecting a power supply with a larger current capacity would affect anything. I always use power supplies with a higher supply capacity than the circuit I am powering: that is standard practice and avoids overloading the power supply. I would be grateful if you could explain why this is an issue.
     
  5. bjr981s
    Offline

    bjr981s Moderator Staff Member

    Top Poster Of Month

    Joined:
    Sep 19, 2015
    Messages:
    5,367
    Likes Received:
    352
    Trophy Points:
    83
    Location:
    Sydney, Australia
    Ratings:
    +454 / 14
    This is a common misconception. There is no "need" there is just resistance. Or more importantly Impedance.

    I = V/R

    This misconception assumes that a resistive load does not change.

    What happens when you power up an ESC? Notice the spark? This is because of the inrush current of a capacitive load. (Impedance)

    The capacitors virtually look like a short circuit until they are charged.

    The most common problem is when using a power supply to charge batteries.

    If you look at a smart battery charger it does not provide the full charge Voltage at the start of a charge cycle. It slowly steps up the Voltage to prevent an over current charge to the battery.

    So if you are designing a battery charge circuit for an RC Radio Transmitter. You can either include all the necessary electronics to deal with inrush current and a voltage step down circuit or you can use the power supply max current capability to limit the current by causing a voltage sag.

    I still = V/R but as you draw max current from the adapter, the adapter voltage sags.

    Most RX radio manuals will have a warning about only using the provided charge adapter if they ship with rechargeable batteries. The adapters will have low current output capabilities.

    Walkera radios ship with AA battery bricks but they provide a charge connector if you choose to use rechargeable batteries. But you must use a charger that has limited current supply capability.

    The Devo 7 is 50ma the Devo 8 is 8-12V 200ma. That is why it is written clearly on the radio.

    Also the range of Voltages it will accept is provided that the 200ma is not exceeded. The voltage will never be 12V as the voltage will sag to the correct voltage to supply max 200ma current.

    i.e. If you connect a 12V supply that will provide >200ma the voltage will not sag and it will draw enough current to fry the radio.

    Cheers Brian

    IMG_2324.jpg
     
  6. beesontoast
    Offline

    beesontoast New Member

    Joined:
    Jan 31, 2018
    Messages:
    5
    Likes Received:
    1
    Trophy Points:
    1
    Ratings:
    +1 / 0
    Thanks for your detailed answer, which has added to my understanding.
     

Share This Page