Standard analog servos able to rotate 180º

Discussion in 'General Electronics Chat' started by atferrari, Jan 2, 2011.

  1. atferrari

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    Jan 6, 2004
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    I need to buy a servo able to rotate not less than 180º.

    Since I do not need too much torque but the 180º rotation capability I browsed the list of Hitec servos at servocity.com.

    For all standard analog servos I checked so far, like this

    http://servocity.com/html/hs-422_super_sport_.html

    they seem to offer them able to rotate 180º if you pay extra 10 USD. Is my interpretation correct?

    Hitec is not clear if they analog servos are able to rotate 180º, out of the box. If so, why that extra charge?

    What servo similar to this could I buy being sure that it will be able to do that 180º (not less!) rotation? If Hitec, better (to maintain consistency with their splines).

    Just in case: I do not like to buy digital...and then a programmer and so on. No thanks.

    Really this is a new world for me!!
     
  2. jpanhalt

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    Jan 18, 2008
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    I don't have any 422's to test. My HS300's move 180°, but the thin wing servos I tried didn't. My old Airtronics and JR's seemed to go 180° too. I suggest testing the specific servo you are interested in using.

    The servo stretcher shown on that page is for extending the transmitter range of pulse widths. Cheaper transmitters may be limited in that range, but many computer transmitters let you set the full throw above 100% (e.g., 125 to 150%). That would accomplish the same thing.

    Some servos have a physical stop. In fact, one of the critical drive gears may not have teeth around its whole perimeter.

    Bottom line, pick a few servos you are interested in and see how far they will travel.

    Maybe the $10 extra for the 180° version includes a different pot, so you don't need a servo stretcher, or it may involve removing the internal stops.

    John

    Edit: My HS205's and 605's physically move a little more than 180°. I suspect the HS225's would be similar, but they are all in airplanes and can't be tested. My servo tested doesn't have a wide enough pulse range to test them electronically.
     
    Last edited: Jan 2, 2011
  3. atferrari

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    After so many contradictory info from different forums, I went to the source:

    I've been browsing your catalog but couldn't find information about this:
    Are your standard analog servos, or at least some of them, able to rotate 180º (not less than 180), out of the box?
    For my project it is crucial to have three of them rotating at least 180º. (NO bang bang, please).
    I have no intention of buying digital and associated programmers for the moment.

    Their reply:

    Hello Agustin,
    Thank you for choosing Hitec products. None of our analog servos are able to rotate 180°.
     
  4. jpanhalt

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    That's CYA bull or ignorance. The person responding may not know anything more than is in the advertising literature.

    I thought I had edited my earlier post, but guess I forgot to do that. After my post, I modified my servo driver to give a wider pulse range and was able to show that the servos mentioned in that post do in fact move and are controllable over a little more than 180°.

    I do not have any 422's to test, as mentioned previously. If there is a servo you are interested in that I have available, I would be willing to test it. The 205 and 225's are almost the same. Is the 422 the only one you are interested in? How about something a little more robust with metal gears and dual BB?

    John
     
  5. atferrari

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    Hola John,

    Thanks for your interest.

    If you happen to have a Futaba S3003 I would like to see what you find out.

    Otherwise, shortly I will be able again to generate my own signal for test.

    Gracias for that.
     
  6. Von

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  7. jpanhalt

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    Sorry, all I have is an S148. Now that I have modified my servo tester, it is portable, so I could go by the local hobby shop and see if it will let me test one. Which would you prefer the Futaba S3003 or Hitec 422?

    John
     
  8. atferrari

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    Anyone John (why not both... :))

    I appreciate your help and interest.
     
    Last edited: Jan 5, 2011
  9. jpanhalt

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    Went to local hobby shop. It only had the Futaba S3003, not the HS422. With my modified tester, the S3003 would only move about 175°, i.e., definitely a little less than 180°. It was a new, in the box unit, so I didn't want to test the mechanical limits.

    John
     
  10. sceadwian

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    Jun 1, 2009
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    I have two servo's I yanked from an ancient RC car a Ks88a (not sure of brand), and a FP148 (Futaba) both are capable of slightly more than 180 degrees between full stops, as stated you will need to feed it servo pulses outside the typical 1 to 2ms range. There has to be some sort of trimmer components in the servo though so you should be able to trim a 'normal' servo's pulse stretcher to allow the standard servo signals to do 180 degrees.
     
  11. atferrari

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    Thanks to you both.

    It seems that I have to check how far I can go sending out of the limit signals.

    I am surprised to see how much contradictory information you get in the Web about any subject. It is also frustrating to see how many sites just copy verbatim the text from another. (Look for cross correlation or autocorrelation and you will see what I say). The new trend: copy Wikipedia and you are done.

    Forgot to tell: I am programing a micro to send the control signal. Gracias again.
     
    Last edited: Jan 9, 2011
  12. jpanhalt

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    I don't think it is as much sending out-of-limit signals as it is that some transmitter manufacturers don't use all they "spec" they are allowed to use.

    In fact, I am not sure there is a "spec" from what I have read. Compare manuals from Multiplex/Graupner with Futaba and JR for example. "Spec." more likely means "typical," and of course, everyone copies the others. As an example of an "out of current spec transmitter," my old Airtronics Vision 8SP was produced in the day when servo center was changing from 1.32 mS to 1.5 mS. It allowed one to select either center position. It also allowed one to set throws at greater than what was typically 100%. That is, typical 100% for other Tx was 66% on the Airtronics. You could go to 100%, but there was a warning about exceeding the capability of some servos.

    Bottom line, I wouldn't worry about driving a servo to 180°, if it goes there freely. If you are using a transmitter that won't allow that range, you might be able to modify a servo by putting a large value resistor in parallel across the pot, so the signal it does receive will give greater movement to attain balance. NB: Some modern servos don't use pots, but they are considerably more expensive than the HS422 or S3003.

    John
     
    Last edited: Jan 9, 2011
  13. sceadwian

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    The update rate of the servo's may have to be adjusted, the pulses stretchers can tweak out if they're at the extreme's of throws. All easily experimented with using a micro controller.
     
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