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Parallax Servo Controller

Robert25Robert25 Posts: 53
edited 2006-03-06 22:18 in BASIC Stamp
This actually came up in another post and I was asked to repost it separately (which I kinda knew anyway)...

Speaking of the PSC... ( I know probably a different post) but I'll ask it here anyway. I was toying around to get a feel for it and the programming. I ran the "find the PSC" routine and it worked fine... reply was version 1.4. However, when I tried the ramp program, nothing happens to any servo even though the PSC red led is on and the green led blinks.

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-03-06 15:42
    Is power connected to the Green Servo Power terminals?· The PSC will respond when connected to the micro, but the servos won't move unless they have their own power.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Robert25Robert25 Posts: 53
    edited 2006-03-06 18:36
    Chris...

    Actually yes. However, when I first hooked up the servo power supply it was to a 5 volt source. After reading your response, I realized what I did and then connected them up to a 12 volt source. (I am using a powered breadboard that provides both 5 volt and 12 volt regualted outputs).

    Same result though, the green led blinks but no servo response....
  • Robert25Robert25 Posts: 53
    edited 2006-03-06 18:38
    Chris

    for your referecne I am using Parallax standard servos and I attached the test code I am using...
    bs2
    bs2
    PSC ramp servo.bs2
    349B
  • Robert25Robert25 Posts: 53
    edited 2006-03-06 19:15
    Chris,

    I also did some voltage measurements. The supply is at 12 volts and is rated at 0.5 amps. I used it to test power some steppers so I know it has got enough amps to drive one servo.

    Voltage at the servo power input is 12 volts.
    Voltage at the servo connector (center or red wire in the connector) is 1.5 volts.

    I also tried a different power suppply (9 volt supply at 1 amp) with same result. Only 1.5 volts at the red pin with servo attached.

    This lead me to trace the power supply....

    Here's what I found.... the servo power switch was coated or dirty. I cleaned the contacts and now the servo works.... hmmm
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-03-06 19:19
    Robert,

    ·· I wish I had caught this earlier...12V is well over the rating on the servos.· Every servo I have ever seen is damaged beyond repair at 12V.· Most don't make it over 9V.· The rating for our standard and continuous servos is 6V nominal.· As you go higher you reduce the life of the servos.· At a certain point the caps inside usually pop, permanently damaging the servo.· If you read the documentation to the PSC and the terminals the maximum rating for input voltage is 7.5 volts.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Robert25Robert25 Posts: 53
    edited 2006-03-06 19:40
    Thanks for that reminder...

    I changed them to 5Volt supply...

    All works fine....

    Now,,, how can you get multiple servos to activate simultaneously? Two or maybe three at the same time.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-03-06 20:20
    Send multiple commands to the PSC.· One serout could send multiple commands as well if each if terminated by a CR but if you send a certain channel a signal and follow it immediately by data for another channel you will activate them both.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Robert25Robert25 Posts: 53
    edited 2006-03-06 20:29
    Chris,,,

    Not really sure what you mean... could you please give an example (only two servos for example purposes).
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-03-06 20:35 
    pw = 1250
ch = 0
ra = 7
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", ch, ra, pw.LOWBYTE, pw.HIGHBYTE, CR]
pw = 700
ch = 1
ra = 7
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", ch, ra, pw.LOWBYTE, pw.HIGHBYTE, CR]

    This section will move channel 0 servo to 1250 and channel 1 to 700 both using a ramp (speed) of 7.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Robert25Robert25 Posts: 53
    edited 2006-03-06 22:18
    got it....

    I modified it so that three servos are working simultaneously and each goes to a different position and at different speeds....

    Chris, you're a genious
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