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Digital Servo Question - Hitec HS-7950TH — Parallax Forums

Digital Servo Question - Hitec HS-7950TH

LeeWLeeW Posts: 14
edited 2010-01-18 20:30 in BASIC Stamp
I have a question pertaining to the operation of a digital Hitec HS-7950TH. I have it hooked up to a BASIC stamp board along with a couple switches and a load cell. The issue is, whenever the servo is being operated, all the other functions are unable to operate. Hooking up an oscilloscope to any of the other pins, a lot of noise is seen. Using a standard analog Hitec there is no issue and the project functions perfectly.


I'm curious as to why this happens, since there shouldn't be a difference between the two, correct?

Are there different·PBASIC commands I should be using instead of Pulsout?

Post Edited (LeeW) : 1/6/2010 3:55:04 PM GMT

Comments

  • TappermanTapperman Posts: 319
    edited 2010-01-06 15:57
    This is just wild guess.· But are your bat/pwr supply stable?· Try a cap here and there accross power leads.· The fact that the analog works and digital is noisey, speaks volumes.· Digital currents are sudden and cause spikes in supply line voltage (visible on o-scope).
  • FranklinFranklin Posts: 4,747
    edited 2010-01-06 16:26
    What is the current draw on the two servos and how are you providing power?

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    - Stephen
  • LeeWLeeW Posts: 14
    edited 2010-01-06 16:42
    I'm providing power through a 9v brick to the stamp, and then 5v from the board to the servo.

    Here is the digital servo I'm using: http://www.servocity.com/html/hs-7950tg_servo.html
  • FranklinFranklin Posts: 4,747
    edited 2010-01-07 06:01
    This servo needs more power than the regulator can easily supply. You should be providing the servo with its own 7.2v power supply and only connecting the power supply grounds and the signal line to the servo. I couldn't find any spec for power but High Torque usually means high power requirements.

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    - Stephen
  • LeeWLeeW Posts: 14
    edited 2010-01-14 16:11
    Hello Franklin,

    I tried what you suggested, hooking up a power supply for just the servo. I am testing the servo on a BoE, none of the board power connected to it, just the power from the power supply. I am sending a signal to the servo from the BoE, but what happens is when I run the program the servo just keeps spinning. No matter what kind of code I try it doesn't want to change direction or slow down.


    Tapperman, I haven't tried what you suggested yet, I'll have to look into that next.
  • Spiral_72Spiral_72 Posts: 791
    edited 2010-01-14 20:25
    Man, that's a serious servo!

    So you have a continuous rotation servo? You have to send it a "center command" and adjust the pot until the servo stops. Then your pulse width to either side of center will work.

    Is the pot installed in the case? or do you have to supply your own? The reason I ask is this line from the page you linked above:

    ......continuous rotation (potentiometer is left outside the servo case)
  • LeeWLeeW Posts: 14
    edited 2010-01-14 21:10
    It's an external potentiometer included with the servo, I'll try what you suggested!
  • FranklinFranklin Posts: 4,747
    edited 2010-01-14 21:34
    Lee, you need to connect the grounds between the servo and the stamp. Without it you will not be getting a return path for your signal line.

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    - Stephen
  • LeeWLeeW Posts: 14
    edited 2010-01-18 13:08
    Franklin, I connected the grounds between the servo and the stamp.

    Spiral, a centering command would mean a pulsout of 1500? The neutral position on this server is noted as 1500 usec... would that be the same as the "center command"? When I pulsout 1500 to the servo, it doesn't move at all, but if I pulsout say 1000, the servo continously rotates in one direction and doesn't seem to want to stop regardless of the code that I send after that.

    Thanks for all your help, I'm way too used to the analog servos that you just plug into the stamp boards [noparse]:)[/noparse]
  • W9GFOW9GFO Posts: 4,010
    edited 2010-01-18 17:28
    PULSOUT 750 is the equivalent of 1500uS on a standard BS2. Each increment of PULSOUT is 2uS.

    PULSOUT 750 would be the same as the "center" command.

    Rich H

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    The Simple Servo Tester, a kit from Gadget Gangster.
  • FranklinFranklin Posts: 4,747
    edited 2010-01-18 20:30
    Somebody said...
    but if I pulsout say 1000, the servo continously rotates in one direction and doesn't seem to want to stop
    That is the correct response from a continous rotation servo. If you give it a 2000 does it go in the oyher direction?

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    - Stephen
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