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continuous rotation servos

Discussion in 'Robotics & Mechatronics' started by koran49, Jun 24, 2005.

  1. koran49

    koran49 New Member

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    Hello everyone I was wondering if anyone could put me in the direction of how I would program a continuous rotation servo with VB. Im somewhat new to robotics so please try not to get upset if I ask stupid questions.
    Thanks,
    Jon
     
  2. Roboticinfo

    Roboticinfo New Member

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    That is very simple but may I ask you this first.

    What microcontroller and language do you know?
     
  3. koran49

    koran49 New Member

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    http://www.imagesco.com/catalog/motors/servoboard.html
    the 8 servo board is the one I would be purchasing looks like its a PIC16FE4A. Umm as far as languages I only know a little of VB, thats one of the reasons I want to do this is so that I can learn some programming. My friend and I are doing this as a school project so we are going do our best to program this together.
     
  4. dave

    Dave New Member

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  5. Roboticinfo

    Roboticinfo New Member

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    A friend of mine owns that website, anyway that software that is included works with full rotation.

    Basicly you set the slide to 360 degrees

    Does that answer your question?
     
  6. koran49

    koran49 New Member

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    Yes I guess it does, so what your saying is set the slider to 255 and the servo should stay on continuously? Do you know how I would make the servo stop when I got it set where I want? Like say move it to 254 maybe? Also not sure if you would know the answer to this but does the setting 150 center/home the servos basically? I guess I should just order the stuff and see what I can do lol.
     
  7. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I'm rather confused about what you are wanting to do?. A servo CAN'T rotate continuously, if it does it's no longer a servo - the output shaft is connected to a potentiometer, which has a MAXIMUM POSSIBLE 270 degree rotation (it's unlikely a servo would achieve that much though?).

    It's common practice to modify a servo to give continuous rotation, particularly for small robots - however, it's then not a servo - just a motor and gearbox.
     
  8. Pommie

    Pommie Well-Known Member Most Helpful Member

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    Looking at that page, it looks like the software is prewritten and therefore will not work with VB. To get it to work with VB, you will need to know what to send to the servo board via RS232. You will also need to be familiar with the MSComm control.

    HTH

    Mike.
     
  9. NleahciM

    NleahciM New Member

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    Please don't tell me your entire post was about semantics.

    Oh wait it was.



    And of the servos I've worked with - none of them had pots that could go 270 degrees - normally they could go about 200. But one thing is for certain - you can't say they all are 270.
     
  10. koran49

    koran49 New Member

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    Okay I what I want to do is have a continuous rotating servo control a sliding ball and screw actuator and on the actuator there will be a robotic arm. http://www.imagesco.com/catalog/motors/servo.html#s-148 that is the actuator I want to use (parallax) The problem I think I'm going to run into, the provided software will not work with a continuous servo so I may need to write my own program. I know VB isn't the best "language" out there but thats the only class my school taught me. What I like about the provided software is the scripting it has I wish I knew how to write something like that, maybe someone can give me a hand doing it? I hope this helps you guys understand my big plan here.
     
  11. Roboticinfo

    Roboticinfo New Member

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    Nigel that sounds rather strange that you would say something like that.
    They sell servos with full rotation and they are easy to modify a servo todo so. In robotics a populer item to use in robotics is servos, Usually thet have two servos and they connect the wheels to the servo horn, They use them in small robots
    www.robotcafe.com and elec.
    You must not be into robotics if you ask a question like that
    Here are websites that sell wheels for servos
    www.hobbyengineering.com
    www.hvwtech.com
    www.robotstore.com
    http://www.e-clec-tech.com
     
  12. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Re: reply

    But you're modifying the servo, so it's no longer a servo! - as I mentioned previously, it's then merely a motor and gearbox - to allow continuous rotation you remove the feedback that makes it a servo.

    I'm fully aware of the use of modified servos in small robots (and even refered to it in my previous post) - but, and I'll repeat it again (as you don't able seem to understand?).

    THE MODIFICATION MEANS IT'S NO LONGER A SERVO!.

    Now that 'koran49' has actually told us what he wants, we can perhaps offer some sensible possibilities?.

    A servo requires feedback, that's what makes it a servo! - for his purpose (as I see it) the problem is to get feedback from the mechanical position of the output. Depending on the length of travel, you 'may' be able to use a slider potentiometer to replace the internal pot of the servo you modify to power it.

    BTW, the website you posted the link for clearly lists them as "Parallax Continuous Rotation Servomotor" - note the important part is MOTOR, it's no longer an operating servo. Perhaps RoboticInfo would like to try reading the page as well?.
     
  13. Roboticinfo

    Roboticinfo New Member

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    Then we should be directing him towards pwm speed controllers
    if that is what he wants.
     
  14. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I don't think he does? - as I understand him, what he wants is to be able to make a linear actuator using a screw thread. Obviously to do this you need feedback so you know where it's positioned - JUST like a servo, and it is actually building a servo if you do it in that way.

    Assuming you can get a slider potentiometer driven by the actuator? (which obviously depends on the length of travel!), an easy solution would be to modify a servo, and connect the external slider in place of the internal one.
     
  15. Roboticinfo

    Roboticinfo New Member

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    They have a rc linear servo.
     
  16. koran49

    koran49 New Member

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    I think your right on the money there Nigel. The external slider idea just might work as for the length of the screw actuator I'm not sure how long its actually going to be I'm still trying to hunt down parts and gather ideas before I begin this school project. Where could I find external sliders or how would I go about fabricating my own?
     
  17. koran49

    koran49 New Member

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    forgot to mention the approximate length for the actuator I need is going to be about 24"
     
  18. Roboticinfo

    Roboticinfo New Member

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    Well you metioned it twice :lol:

    Anyway 2ft what are you thinking?

    You can't achieve 2ft with 180 degrees

    How much pushing torqe do you need?
     
  19. koran49

    koran49 New Member

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    here is an example of the actuator I'm looking for http://www.tolomatic.com/products/axidyne_products.cfm?typeID=4
    maybe that will help us get on the right page, as for how much torque I need not sure as of yet because I have no parts yet but I would imagine that a lot of torque wouldn't be necessary because the robotic arm only weighs not more then 10-15lbs
     
  20. koran49

    koran49 New Member

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    maybe I'm just not understanding you right but when you said how am I going to achieve 24" with 180 degrees were you refering to the servo motor?
     
  21. Roboticinfo

    Roboticinfo New Member

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    What are you trying todo?

    In better words what is your project about
     

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