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Max voltage allowable on HB-25 servo input — Parallax Forums

Max voltage allowable on HB-25 servo input

Tom CTom C Posts: 461
edited 2008-01-10 15:45 in Robotics
Hi all,

I have read the HB-25 Motor Controller manual several times and have yet to see a max voltage spec for the servo input on the controller.

Does anyone know if an RC receiver being powered by 6vdc will damage the HB-25 if it is used the drive the HB-25 servo input?

Regards,
TCIII

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If you are going to send·a Robot·to save the world, you·better make sure it likes it the way it is!

Comments

  • FranklinFranklin Posts: 4,747
    edited 2007-12-28 05:16
    On their page it says Logic Supply: N/A - Internal Regulator .

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    - Stephen
  • Mike GreenMike Green Posts: 23,101
    edited 2007-12-28 05:31
    It's unlikely, but possible that your RC receiver could damage an HB-25 since the HB-25 is designed for logic level inputs (0-5V) and, even though the RC receiver is only powered by 6V and there's probably some voltage drop in the output circuitry, without a circuit diagram of the RC receiver, it's impossible to tell for sure what the peak output voltage might be.

    If you want to play it safe, you could put two diodes in series with the RC receiver output. That would drop 6V to less than 4.6V which should still be enough to drive the HB-25.
  • Tom CTom C Posts: 461
    edited 2007-12-29 04:15
    Hi Mike,

    Thanks for the input. Much appreciated. You always give good advice.

    I was hoping that someone from Parallax with knowledge of the HB-25 might have some input too.

    Regards,
    TCIII

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    If you are going to send·a Robot·to save the world, you·better make sure it likes it the way it is!
  • Mike GreenMike Green Posts: 23,101
    edited 2007-12-29 04:31
    Most of the Parallax folk are getting a well deserved Christmas / New Year's holiday.
  • StampNut2StampNut2 Posts: 224
    edited 2008-01-04 01:21
    Just a small note here Mike Green, I have been into R/C model aircraft for over 35 yrs and most Receiver systems run on 4.8v Nicad or NIMH battery packs as standard. You can run these systems as high as 6v as you have stated. But for the HB-25 controller you should be fine with the standard 4.8v pack.

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    robosapienv2-4mem8.page.tl/
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2008-01-09 15:16
    Sorry for the late reply…The inputs are TTL compatible and require a 0-5V pulse. Now in all fairness the HB-25 was tested with several brands of R/C Receiver, however the batteries that typically come with these are not 6V but 4.8V and that is what was used. If you have the typical 4.8V battery that comes with the receiver you can certainly connect the output directly into the HB-25. Take care.

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    Chris Savage
    Parallax Tech Support
  • Tom CTom C Posts: 461
    edited 2008-01-10 03:01
    Hi Chris,

    Thanks for the input. Much appreciated.

    My Hitec R/C receiver came with a four AA cell battery holder and not the usual rechargeable 4.8 battery.

    I got the receiver to work on 5 volts by powering it from my accompanying BOE while the BOE converted the servo output of the receiver and drove the two HB-25s on my rover.

    Regards,
    TCIII

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    If you are going to send·a Robot·to save the world, you·better make sure it likes it the way it is!
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2008-01-10 15:45
    Tom,

    I had not seen one of those before, but it makes sense. Most servos are rated for 4.8V – 6V. 4AA alkaline batteries would give 6V, while 4 rechargeable AA cells would be 4.8V. Of course, most receivers will work in that range as well. Thanks for the info though. Take care.

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    Chris Savage
    Parallax Tech Support
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