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Servo Controller - jittery with high servo counts — Parallax Forums

Servo Controller - jittery with high servo counts

deweycooterdeweycooter Posts: 5
edited 2010-10-29 04:59 in Propeller 1
I have the servo controller board and some custom s/w to drive the servos. All is well when I have 4 servos hooked up. Once I get to 8, I start getting some noise going to the servos. At 12 servos, it's a lot of noise and the servo response is no longer workable.

I have walwart with selectable voltage as the supply. Is it possible that it doesn't have enough amperage? If so, I'm considering using a scavenged PC power supply to apply 7V. Or am I likely looking at another issue?

Steve

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2010-10-28 15:19
    This sure sounds like a power problem. The servo controller is capable of handling more than 12 servos without jitter, but, with a single servo drawing peak currents of 1A or more, it's quite likely that you're overdrawing your power supply. I'd make sure any dedicated supply provides no more than 6V. Anything much higher and you'd wear out the motor brushes with the increased arcing from the higher voltage.
  • deweycooterdeweycooter Posts: 5
    edited 2010-10-28 15:23
    Thanks Mike, I'll give it a go. I'm going to try using the PC power supply using the +12 and +5 to make a 7V potential. I don't have anything else at my disposal and this needs to work for Sunday night. :)
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2010-10-28 15:30
    deweycooter,

    Use the +5V off of that supply rather than taking the difference... Although you may get 7V, they usually aren't meant to operate like that.

    At +5V you'll take a little bit of a power (speed) hit, but you should have plenty of current.
  • hover1hover1 Posts: 1,929
    edited 2010-10-28 16:07
    Steve,

    Are you using the old Servo Controller:
    http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/servo/List/0/SortField/4/ProductID/346/Default.aspx

    or the new one:
    http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/servo/List/0/SortField/4/ProductID/595/Default.aspx

    Also, are you using Analog or digital servos?

    Jim

    deweycooter wrote: »
    I have the servo controller board and some custom s/w to drive the servos. All is well when I have 4 servos hooked up. Once I get to 8, I start getting some noise going to the servos. At 12 servos, it's a lot of noise and the servo response is no longer workable.

    I have walwart with selectable voltage as the supply. Is it possible that it doesn't have enough amperage? If so, I'm considering using a scavenged PC power supply to apply 7V. Or am I likely looking at another issue?

    Steve
  • deweycooterdeweycooter Posts: 5
    edited 2010-10-28 19:32
    The PC supply at 5V works like a champ!!

    @hover1: I have an old board (non-propeller) and a new. I'm using the old one because the propeller-based board would always give me jittery servos, even with only one connected. (as soon as I applied power, they'd start twitching) The servos are all Futaba S3003 - I assume those are analog...?
  • hover1hover1 Posts: 1,929
    edited 2010-10-28 19:44
    deweycooter wrote: »
    The PC supply at 5V works like a champ!!

    @hover1: I have an old board (non-propeller) and a new. I'm using the old one because the propeller-based board would always give me jittery servos, even with only one connected. (as soon as I applied power, they'd start twitching) The servos are all Futaba S3003 - I assume those are analog...?

    On the Propeller based servo controller, place a 1K resistor in line with the servo signal, and that should take care of the jitters.

    Jim
  • deweycooterdeweycooter Posts: 5
    edited 2010-10-28 20:18
    hover1 wrote: »
    On the Propeller based servo controller, place a 1K resistor in line with the servo signal, and that should take care of the jitters.

    Jim

    Cool - that should help with the inevitable expansion next year. :) I ended up hacking my connectors so I could make longer runs using cat5, so adding the resistors really shouldn't be a problem. Thanks Jim!
  • hover1hover1 Posts: 1,929
    edited 2010-10-29 04:59
    This thread explains the reason for the resistor.

    http://forums.parallax.com/showthread.php?t=118121

    I just put a 1K resistor pack on all pins now.

    Jim
    deweycooter wrote: »
    Cool - that should help with the inevitable expansion next year. :) I ended up hacking my connectors so I could make longer runs using cat5, so adding the resistors really shouldn't be a problem. Thanks Jim!
    DSC00007.jpg
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