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I need help with the propeller servo controller.. — Parallax Forums

I need help with the propeller servo controller..

FireHopperFireHopper Posts: 180
edited 2010-06-03 23:37 in General Discussion
I had it mounted in my costume. but it twitched alll over the darn place. I need help to figure out how to kill the twitching.
if I have to rewire everything shielded I can do that, I just need to know if that will help the problem. it was so bad that it wouldnt respond to any commands that the computer running psci was sending

Comments

  • kf4ixmkf4ixm Posts: 529
    edited 2010-06-01 20:05
    The twitching sounds to me to be a power problem, what are you using to power the servos and how many servos do you have connected?

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    I'm just 7*1027 atoms floating through time and space in close formation. -KF4IXM
  • FireHopperFireHopper Posts: 180
    edited 2010-06-01 20:21
    kf4ixm said...
    The twitching sounds to me to be a power problem, what are you using to power the servos and how many servos do you have connected?

    I am using 2 li-fe packs 6.6volts.. one pack to power each side. only 6 servos total. 3 on each side.

    it worked fine with the old serial servo controller. but the wires werent as convoluted.. I'm going to rewire it again, this time providing more than one ground wire, and see if that helps things.

    make the serial servo controller the main grounding point for the whole thing.
  • hover1hover1 Posts: 1,929
    edited 2010-06-01 20:25
    @FireHopper

    Try a 5k-10k resistor in line with the signal line coming off the 3-pin header, (pin marked white or W). This seems to fix most digital servo problem, ( you didn't say if you were using an Analog or Digital servo).

    Here's a recent thread:

    http://forums.parallax.com/forums/default.aspx?f=25&m=407311

    It could also be a power problem and the propeller is resetting. How is you power distributed, (seperate servo power and board power)?

    Jim
  • FireHopperFireHopper Posts: 180
    edited 2010-06-01 22:53
    hover1 said...
    @FireHopper

    Try a 5k-10k resistor in line with the signal line coming off the 3-pin header, (pin marked white or W). This seems to fix most digital servo problem, ( you didn't say if you were using an Analog or Digital servo).

    Here's a recent thread:

    http://forums.parallax.com/forums/default.aspx?f=25&m=407311

    It could also be a power problem and the propeller is resetting. How is you power distributed, (seperate servo power and board power)?

    Jim


    all analog servos. and yes seperate board and servo power

    I'm redoing it as we speak, removing switches and stuf and just wiring the batterys to the servos directly, if it still does it, then I dont know what to do.
  • FireHopperFireHopper Posts: 180
    edited 2010-06-01 23:22
    sigh, still doing it.. going to replace the propeller controller with the old serial one and see if it still does it..
  • hover1hover1 Posts: 1,929
    edited 2010-06-01 23:30
    How are you doing you board power? I just place a 5 volt regulator in the servo terminal and leave the output terminal hanging. The I wire wrap off the output leg and wire wrap to the upper center pin of the Serial In post. I have 6 volts going to the servo in terminal.

    (You have to use a LDO regulator at 6 volts input to supply the Prop circuit.)

    Jim

    Post Edited (hover1) : 6/2/2010 12:08:19 AM GMT
    Prop Servo Board.JPG
    1280 x 960 - 562K
    Servo Controller Serial-In_B.jpg
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  • FireHopperFireHopper Posts: 180
    edited 2010-06-01 23:56
    hover1 said...
    How are you doing you board power? I just place a 5 volt regulator in the servo terminal and leave the output terminal hanging. The I wire wrap off the output leg and wire wrap to the upper center pin of the Serial In post. I have 6 volts going to the servo in terminal.

    (You have to use a LDO regulator at 6 volts input to supply the Prop circuit.)

    Jim

    I'm currently using the usb to provide board power to drive the cpu. since I'm trying to get the endpoints figured out via psci
  • hover1hover1 Posts: 1,929
    edited 2010-06-02 00:23
    OK, USB power to the board should be fine if you are comfortable that is putting out the required power, Prop doesn't take much. The power and servo grounds are connected together on the board, so that's not a problem.

    I would still try a 5K resistor in line with the control signal to the servo. Here is a quote from Dave Carrier from Palallax:

    "The Propeller USB Servo Controller cannot drive loads less with than 5 kΩ of impedance. I have never seen servos that do not have high impedance inputs, but the oscilloscope traces you recorded are typical of a TXB0108 driving a low impedance load. If you do not need bidirectional communication, a series resistor of 5 kΩ or more will stop the ringing."

    It's worth a try.

    Jim
  • FireHopperFireHopper Posts: 180
    edited 2010-06-02 00:35
    hover1 said...
    OK, USB power to the board should be fine if you are comfortable that is putting out the required power, Prop doesn't take much. The power and servo grounds are connected together on the board, so that's not a problem.

    I would still try a 5K resistor in line with the control signal to the servo. Here is a quote from Dave Carrier from Palallax:

    "The Propeller USB Servo Controller cannot drive loads less with than 5 kΩ of impedance. I have never seen servos that do not have high impedance inputs, but the oscilloscope traces you recorded are typical of a TXB0108 driving a low impedance load. If you do not need bidirectional communication, a series resistor of 5 kΩ or more will stop the ringing."

    It's worth a try.

    Jim

    I dont have some 5k I have 4.7K ones though.. will try one tomorrow.. getting burnt out.. I'll also try swapping the old serial controller and see if it still does it.
  • FireHopperFireHopper Posts: 180
    edited 2010-06-02 12:02
    hover1 said...

    "The Propeller USB Servo Controller cannot drive loads less with than 5 kΩ of impedance. I have never seen servos that do not have high impedance inputs, but the oscilloscope traces you recorded are typical of a TXB0108 driving a low impedance load. If you do not need bidirectional communication, a series resistor of 5 kΩ or more will stop the ringing."

    It's worth a try.

    Jim

    I think I know what is causing the issue. on every channel there is a signal inverter, (it was made that way.) which might be causing the issue. I have wired the resistors in place and am about to try it. heres hoping..
  • FireHopperFireHopper Posts: 180
    edited 2010-06-02 12:14
    whooot.. that seems to have fixed it. will outfit the other 4 channels and see if the results are the same. need to stop by radio shack and pick up another 5 pack of 4.7K resistors.. I'm one short of the 8 I need.. need 2 for i2c, and the 6 for the 6 channels I'm using.
  • FireHopperFireHopper Posts: 180
    edited 2010-06-03 12:26
    yup that fixed it, may have to replace the one shoulder servo. its wagging a bit.. I will take it apart and look for broken gears.
  • FireHopperFireHopper Posts: 180
    edited 2010-06-03 22:44
    I think this should be added to the pdf file for the servo controller..
  • hover1hover1 Posts: 1,929
    edited 2010-06-03 22:58
    Great news that it is working!

    I agree. That quote from Dave Carrier·would save people a lot of time.

    Jim


    FireHopper said...
    I think this should be added to the pdf file for the servo controller..
  • FireHopperFireHopper Posts: 180
    edited 2010-06-03 23:37
    hover1 said...
    Great news that it is working!

    I agree. That quote from Dave Carrier would save people a lot of time.

    Jim




    FireHopper said...

    I think this should be added to the pdf file for the servo controller..

    hey beau? chip? [noparse]:)[/noparse]
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