Extending Servo Leads

Discussion in 'General Electronics Chat' started by Dritech, Aug 16, 2015.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi all,

    I want to extend the servo leads to around 40m. I will be controlling the servo using the Turnigy Servo Tester. What method can I use to achieve this?
    Thanks.
     
  2. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Um... Splicing?:)
     
  3. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    But will the PWM signal work fine with a 40m lead?
     
  4. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Depending upon system parameters the lead inductance may pose a problem -- That said; it won't cost you much to try it before 'moving on' to more sophisticated/expensive approaches:)

    Best regards
    HP
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    What is the PWM frequency?
    What is the PWM amplitude?
    What are the PWM minimum and maximum duty cycles or pulse widths?
    What is the load impedance at the end of the long cable?
    Is coax cable a viable option in your application and environment?
    Is power available at the end of the long cable for a signal receiver circuit?

    ak
     
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  6. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    All crucial questions is a definitive quantitative solution required --- Tho' I be lazy:oops: So I'd just try it - if it appears to work verification of waveforms/transient response should establish reliability... My $.02

    Best regards
    HP:)
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I would also measure the voltage at the servo for the 4.6v minimum.
    The frequency is fairly low at usually 300-400Hz.
    Max.
     
  8. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    The Turnigy servo tester signal repetition rate is almost certainly 50 Hz (i.e., 20 mS). The pulse width can be between about 1 mS and 2 mS, depending on the commanded position. The exact change from a center of 1.5 mS pulse width can vary by servo and can even be adjusted by the user with some set-ups.

    John
     
  9. RichardO

    Well-Known Member

    May 4, 2013
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    I haven't looked but I would assume that you can buy an extender the same place you bought the servo.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I read somewhere for analog servos the frequency is30-50 Hz, and for digital servos it is 300 to 400 Hz.

    I have never seen one for 40m?
    That is a 150ft drum of cable.
    Max.
     
  11. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Of course it goes without saying (Re: digital systems) that transient time requirements determine the required bandwidth...

    Best regards
    HP
     
  12. RichardO

    Well-Known Member

    May 4, 2013
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    Oops. I was thinking more like 40mm. :rolleyes:
     
  13. ian field

    Distinguished Member

    Oct 27, 2012
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    Not just inductance - impedance could be an issue with that much cable, a mis match would probably cause ringing.

    Just a guess - but I'm thinking twisted pair is probably the bare minimum to get at least some sort of predictability into the characteristic impedance.
     
  14. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    My reply assumed an analog selsyn/synchro arrangement wherein transmission line phenomena would be of negligible significance -- That said, I agree that a 'proper' transmission line presenting a predictable characteristic impedance is the only way to go where any bandwidth is required:)

    Best regards
    HP
     
  15. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    If t is something like a 5 V PWM signal, RS422/485 can drive miles, but requires DC power at the receiving end.

    ak
     
  16. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    I wondered about the 40m requirement as well. The longest servo extender (for RC servos) was 900mm... That I could find
     
  17. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    @Dritech

    Oh my!:oops: Upon careful review of comments to this thread it appears my interpretation of the OP was over-general -- thus it seems you're referring to 'servos' as applied to robotics/RC models, etc...? Score another 'Litella moment' for HP (to wit: "Never mind":eek::oops::oops:

    Best regards
    HP:D
     
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  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Working with motion control and servo's, That one used to catch me out at first.
    Max.
     
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