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Robot Arm, Servo controller... — Parallax Forums

Robot Arm, Servo controller...

neotericneoteric Posts: 144
edited 2006-01-30 14:29 in Robotics
Considering I started working on this 3 wks ago with no heavy prior knowledge of electronics or PIC programming, I am pretty happy.· I am not using a robot kit, building a larger robot from junked parts...· using servos, bs2 stamp.· Got my 12V DC drive and the 12v stepper motors that I had working!· Thanks to all who helped me learn about the IC's it took to do this.

Now, time to build an arm.· I purchased the·Parallax servo controller, and have 5 Parallax·continuous servos.

Which leads me to my next question...· For the arm, should I have not gotten "continuous" servos?· I try to research before asking for help, and in my reading the forums last night, I have the impression now that I cannot figure out the position of the servos from the servo controller·if they are the "continous" ones.

This is a BOE board, with a servo controller attached.· I am trying to plan the whole·arm out before I begin building it and adding it to the bot.

Again, thanks for all the incredible help.· I have learned more than I ever thought an old guy like me could learn in this period.

After I get the arm built, I will go back to eating and sleeping.

·

Comments

  • Bruce BatesBruce Bates Posts: 3,045
    edited 2006-01-19 15:21
    neoteric -

    Generally speaking, continuous rotation servos are only used for driving wheels. You want ordinary servos to construct an articulated arm. I suspect Parallax will take them back, if they haven't been used.

    Regards,

    Bruce Bates
  • neotericneoteric Posts: 144
    edited 2006-01-19 16:11
    AARGHH!· The non continuous servos are backordered till March.· I cant wait till then.·

    Anyone have any ideas?· Anyone know of a Parallax distributor that has them in stock?

    Could I use the mini servo instead?·
  • Mike CookMike Cook Posts: 829
    edited 2006-01-19 16:17
    I believe that the Parallax servos are manufactured by Futaba, you can purchase them here:

    http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXH318&P=7

    Mike

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "OEM NMEA GPS Module" Now available on ebay for only $17.49

    Product web site: http://www.allsurplus.net/Axiom/
  • neotericneoteric Posts: 144
    edited 2006-01-19 16:55
    Hmm,· I will do that if I have to.· Thanks for the info.

    I'm trying to be loyal to Parallax, as they are my support structure in this....

    I have wandered the web looking for a site that has parallax servos in stock...

    Will the miniservos work?· http://www.parallax.com/detail.asp?product_id=900-00010 that is, can they be controlled from the servo controller board I bought from Parallax, and are they controlled exactly the same way?

    Thanks for the help...
  • SN96SN96 Posts: 318
    edited 2006-01-19 17:42
    I would not use mini-servos for the arm because it takes a certain amount of torque to move the weight of the arm. It depends on the size of the arm and the material used.

    Servo City has great prices on servos.
    www.servocity.com

    Here is a comparable servo to Parallax's Standard servo, except it has ball bearing support:
    http://www.servocity.com/html/hs-425bb_super_sport_bb.html

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Mike



    Post Edited (SN96) : 1/19/2006 5:51:22 PM GMT
  • ktekxktekx Posts: 71
    edited 2006-01-19 17:58
    There are different servos with different torque ratings and speeds, but the micro servos are extremely weak. I was able to use one of the micro servos to move part of a small robot arm I recently built, however, there was very little torque, it was mostly use to position the arm before the main servos moved it. One thing I found was that once the micro servos have stopped moving, they had enough "static strength" to keep the arm from moving even if force was applied to them.



    Warning 56k people, this is a short video clip: sonyplaystationonline.com/ktekx/chronobot/completed%20and%20testing/MOV01441.MPG

    DSC01433.JPG

    Top view of the arm
  • neotericneoteric Posts: 144
    edited 2006-01-19 18:25
    OK, I went with these.· Sure hope they will work with the Parallax servo controller.

    http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXH318&P=7
  • Bruce BatesBruce Bates Posts: 3,045
    edited 2006-01-19 18:52
    neoteric -

    Any standard analog R/C servo should work with the Parallax servo controllers.

    Regards,

    Bruce Bates
  • SN96SN96 Posts: 318
    edited 2006-01-19 22:39
    Just what Bruce said,

    Any standard servo will work. All standard servos work the same way. You send a pulse to the servo every 20ms and the servo moves.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Mike



    Post Edited (SN96) : 1/19/2006 10:42:21 PM GMT
  • WaldoDTDWaldoDTD Posts: 142
    edited 2006-01-26 00:57
    how are you getting your parts fabricated are you doing it yourself or do you have a custom supplier?
  • neotericneoteric Posts: 144
    edited 2006-01-26 17:36
    I am just doing it myself with parts from my home workshop and some erector sets.· Aluminum rods purchased at Lowes.· This is just a hobby/learning experience for me.
  • Kevin WoodKevin Wood Posts: 1,266
    edited 2006-01-27 11:38
    I watched the video clip that you posted, and was impressed. If you get a chance, could you post a more detailed write-up in the Sandbox? Thanks.
  • ktekxktekx Posts: 71
    edited 2006-01-27 22:52
    To fabricate and cast simple robotic parts, I've found that using plastic resins and silicon molds work pretty well. Strong and light, cure time is really fast, great for replicating multiple parts from a single mold in minutes. To avoid changing the topic of this post, I'll post some of my experiences in a new post later.
  • ktekxktekx Posts: 71
    edited 2006-01-28 12:01
    Here's the guide as promised: s95417013.onlinehome.us/ktekx/chronobot/casting.htm
  • allanlane5allanlane5 Posts: 3,815
    edited 2006-01-30 14:29
    Brilliant! Thanks for the link and the method.
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