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Servo sounds — Parallax Forums

Servo sounds

abcdabcd Posts: 22
edited 2010-01-10 18:45 in General Discussion
I am using some new servos, but when I run them, they sound staticy. Is this supposed to happen? I know that electrical pulses control them - is it probably why?

Thanks.

Comments

  • W9GFOW9GFO Posts: 4,010
    edited 2010-01-10 03:50
    Digital servos will often chatter when holding a position. Sometimes just a touch will silent them. What kind of servos are they?

    Rich H

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    The Simple Servo Tester, a kit from Gadget Gangster.
  • abcdabcd Posts: 22
    edited 2010-01-10 05:46
    Oh, I didn't realize that I forgot to specify the servos...

    They are the standard Parallax Boe-Bot servos. I hope this is normal.

    Sorry if I sound frantic..I'm just curious :P
  • W9GFOW9GFO Posts: 4,010
    edited 2010-01-10 06:02
    Okay, not digital then. The "Standard" Bpe-Bot servos are are modified for continuous rotation so they're not really referred to as "standard" in the usual sense. Do they make the 'static' sound when moving or when holding position?

    It might be due to the program you are using and the refresh rate being too slow.

    Rich H

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    The Simple Servo Tester, a kit from Gadget Gangster.
  • abcdabcd Posts: 22
    edited 2010-01-10 16:50
    I am using the Parallax Stamp Editor and running normal scripts with PULSOUT.. 650, 750, and 850 (using BS2).

    The 750 makes no noise and no movement (my centering skills :P)

    I tried changing to a lower voltage; from the 7.5V wall wart to 6V from battery power, and I *think* it decreased in noise slightly. So, my suspicion that it might be the electrical pulse may be correct. Maybe rewire the servo to the breadboard instead so that I have a resistor?

    What is the refresh rate?
  • Mike GreenMike Green Posts: 23,101
    edited 2010-01-10 17:00
    RC servos have to see a control pulse about every 20ms or they turn themselves off until the next control pulse comes in (to save power). You should have a loop around the PULSOUT statement(s) that repeat the PULSOUT about every 20ms. That's what the PAUSE 20 is for in most typical servo programs since the other statements don't take anywhere near 20ms to execute. This "every 20ms" pulse is referred to as a "refresh" since it maintains the servo in some position.
  • abcdabcd Posts: 22
    edited 2010-01-10 17:07
    Thanks, Mike!

    I actually do have the PAUSE 20s in all of my programs (even though my teachers and classmates argue that 20ms is unnoticeable).
  • W9GFOW9GFO Posts: 4,010
    edited 2010-01-10 18:34
    Servos typically expect a pulse 50 times every second, 50 hz -or once every .020 seconds (20mS).

    To be picky, a PAUSE 20 will not allow a 50 hz refresh rate because the PULSOUT and LOOP part of the code also take a bit of time, but it is close enough if there are just a couple lines of code. As you add more code to your loop you need to reduce the PAUSE time or else the servo will start stuttering.

    The noises that servos make can be anywhere from nearly silent to down right noisy. The Parallax servos fall somewhere in between. They do make some noise while operating.

    What's the reasoning for rewiring so that you have a resistor?

    Rich H

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    The Simple Servo Tester, a kit from Gadget Gangster.
  • abcdabcd Posts: 22
    edited 2010-01-10 18:45
    Oh, that was just in case it is because of a higher DC Voltage (although my 7.5V wall wart does fall in between the 6 and 9V DC for the Bot); the noise seemed lower with 6V of batteries.

    I think your explanation make more sense, though. I forgot that it does take time for the computer (albeit that it is usually < 1s) to execute the program. I guess it does not matter that they make noise, since it would take time to find the exact (or close) PAUSE time. I did not know if the servo was going bad, lol.

    Thanks, Rich! You have been a great help! [noparse]:)[/noparse]
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