Controlling servo with potentiometer

Discussion in 'The Projects Forum' started by susannah, Aug 1, 2013.

  1. susannah

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    Feb 14, 2010
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  2. mcgyvr

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    yes you can use a servo tester with the appropriate power supply to move a servo.

    but you didn't really define what "control" is required. but the servo testers description tells what types of modes it will do
     
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  3. susannah

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    I need to make very slow movement with servo for about 1-5 seconds then stop.

    I'm not sure which servo tester can do this.
     
  4. mcgyvr

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    I'm not either and I'm not reading the descriptions for each one..

    I'd suspect what you want is not possible with the off the shelf testers.
     
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  5. elec_mech

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    Nov 12, 2008
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    I agree with mcgyvr, I don't think the COTS (commercially off the shelf) boards will do quite what you want.

    Can you elaborate on what you want the servo to do?

    Example:
    1) Push button
    2) Servo slowly spins clockwise for x seconds
    3) Servo stops and a) stays in same position or b) returns to home (center) position?

    There are two types of servos: standard and continuous. Standard servos are like steering wheels - you can only move so far in either direction and they stop. Continuous servos are like wheels, they keep turning. The question is, which do you need?

    Do you want the servo to return to some position or do you want it always move ahead? Example for the latter, press button once, servo moves 5 degrees. Push again, servo moves 5 more degrees (10 total now), etc.

    In either case, you could use two 555 ICs - one to control direction and speed of the servo, the other to control how long the servo spins.

    If you could go into more detail about what you want the servo to do, we can offer some more help.
     
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  6. blueroomelectronics

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    OP mentioned Arduino in a past post, that would be a good choice IMO.
     
  7. mcgyvr

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    yep piece of cake with that..
     
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  8. susannah

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    Basically your 3 step example is what i want and stays in same position.

    Standard servo. Always move ahead servo.

    It needs to move left or right (depending what button i press) from current position slowly when i press button or turn potentiometer or something like that.

    No Arduino stuff please.

    I have couple of these servos but i can buy other servos too:
    HXT500 5g / .8kg / .10sec Micro Servo
    http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=663

    Thanks again

     
    Last edited: Aug 2, 2013
  9. Bernard

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    Here is a tried servo control used for a pop-up target. Use only U4; R10 & R 12 can be one 5k pot. R 9 & C 5 control approx 50 Hz clock rate, new pot controls pulse width.
     
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  10. blueroomelectronics

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    A microcontroller such as the 8pin PIC12F series could do it with little more than a handful of parts. A 555 solution is likely to be difficult to keep accurate.
     
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  11. elec_mech

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    Could you list out all your requirements? I'll give another step-by-step example with a guess as to what you want, but we really need you to write out all your requirements so we can offer a solution that meets all your needs.


    Possible Example:
    1. Servo is in center position when circuit is powered.
    2. When button A is pressed (and released), servo moves to right slowly for x seconds (30 degrees, 47 degrees, until it goes as far right as possible, etc.?)
    3. After servo stops moving it a) stays it that position until reset button is pressed, b) immediately returns to center position, c) other?
    4. Similarly, when button B is pressed, servo moves to left.
    Thus far, two buttons (right and left), possibly a third for reset. Do you need to be able to change the speed, time, etc.? Instead of buttons, you could also use a potentiometer to manually control the servo (as you turn the knob, the servo spins - the faster you turn it, the faster the servo spins).

    Please list out everything you want the circuit to do and include total number of buttons, what each does, how the servo should behave, etc. We'll only be making guesses as to your requirements until you list them out.
     
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  12. susannah

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    Feb 14, 2010
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    Hi elec_mech!

    Your example above is what i want. Servo moves as long as i press button or only few degrees when button is pressed and released. After stops moving, it stays in that position.

    Actually i think potentiometer would be perfect for my use so i could change speed. I just need to turn potentiometer to turn servo and thats it.

    Thanks
     
  13. elec_mech

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    Ah, in that case, Bernard's circuit should do the trick - the pot will allow you to manually control the position of the servo. If time allows, I'll try to build it this weekend with his suggestions and report back. I think I have a few of the same servos you mentioned as well.
     
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  14. THE_RB

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    No offense to Bernard, but you can get the basic functionality from a much simpler 555 circuit.

    These two were near the top of the google images list, and look ok;

    [​IMG]

    [​IMG]
     
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  15. djsfantasi

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    These simple circuits may not work with all hobby servos. The circuits I have seen use two 555s: one to generate a pulse of the appropriate width (1.5ms is the middle position thpically) to position the servo and a second to trigger repeating that pulse every 20ms. By varying the pulse width created by the first 555, the servo is instructed to move left, right, or center. The 20ms often can be off by a ms or two and that is how the circuits with one 555 get away with it. But your experience may be different with different servo brands.
     
  16. Bernard

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    No offense taken Roman, it does save one diode,D1, & as R9, 18k is much larger than new 5k pot, therefore D1 it is not needed, so they are the same except for different values. I tried stretching the 20 ms to see what happens-- the longer the greater the chatter, so small changes in period made little difference with the Fitec FS 5109M; M for metal gears. I'm no expert on servos, first & last RC receiver used RK 61 gas tube & rubber bands for escapement power, circ 1965.
     
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  17. THE_RB

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    Yeah the frequency is not critical as long as it is near 20mS or a bit less. I have used 15 and 16mS with no problems in PIC projects with Hitec and other cheaper servos.

    A single 555 timer can generate a variable ON period of 1-2mS and a fixed OFF period of say 18mS, so the total period is always 19-20mS regardless of servo position. It works fine with a single 555. :)
     
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  18. susannah

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    Unfortunately elec_mech seems to be too busy to "I'll try to build it this weekend with his suggestions and report back". ;-(

    So what i should do? Does any of these circuit plans in this thread work with my servos? Thanks
     
  19. John P

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    Try one of the LM555 circuits. I've built things like these in the past and they've worked fine.

    But one point to note, if you control a servo with a pot, is that you shouldn't expect too much if you want it to move slowly. What tends to happen is that the servo will move in short jerks, not with a single smooth motion that can be as slow as you want. There's probably some variation related to cost and quality of the unit, but the cheap little things I've used definitely showed this effect. They're really designed to get from point to point rapidly, not to travel slowly.
     
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  20. elec_mech

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    Roman had originally posted some links to a 556 circuit. I did give those a shot and true to John's note, the servo movement was delayed and jerky. I'm sure any of the simpler circuits posted will do the trick, but don't expect too much. The servo I had is very similar in size and appearance to the OP's, but it was a different model.

    Another option, if you don't want to build a circuit, is to use a cheap wireless RC transmitter and receiver. You can use the remote to move the servo as slow or as fast as you want. The caveat is, as soon as you release the control, the servo will return to its center position. Here is one such option.
     
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