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Robotic arm — Parallax Forums

Robotic arm

ratronicratronic Posts: 1,451
edited 2009-08-31 02:06 in Propeller 1
Just wanted to show a arm I made out of the Bioloid beginner kit from http://www.crustcrawler.com/.·I am using Robotbasic from http://www.robotbasic.org/.· This really isn't a completed project (as I have no gripper).·The code is mainly Mike Gebhard's and the interface to the propeller from the PC's USB joystick via rs232 was made real easy by Robotbasic. The AX-12+ are really neat servo's and all four of these are connected with a 3 wire interface. I know it doesn't do much now but I thought I would attach a Youtube video and the code I have so far.

http://www.youtube.com/watch?v=CILzXm80rrI



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D Rat

Dave Ratcliff N6YEE

Comments

  • jazzedjazzed Posts: 11,803
    edited 2009-08-09 04:07
    Nice video! Have you given though to other control methods? Joystick is fine of course.

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    --Steve


    Propalyzer: Propeller PC Logic Analyzer
    http://forums.parallax.com/showthread.php?p=788230
  • ratronicratronic Posts: 1,451
    edited 2009-08-09 04:13
    No, I was just messing around to control the servo's. I am not much of a code writer and this is mainly a compilation of all kinds of other peoples code.

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    D Rat

    Dave Ratcliff N6YEE
  • HollyMinkowskiHollyMinkowski Posts: 1,398
    edited 2009-08-09 04:13
    Cool smile.gif

    I have been wondering lately how hard it would be to make a prop controlled robotic arm.

    I was thinking what if you used those really cheap cordless drills that are always on sale
    for the motors and made most of the arm using wood. Once painted a dull gray color with
    primer it would look the same as a metallic arm and should be very powerful because the
    cordless drill motors are very strong.

    You would need an h bridge for each motor and some kind of optical encoder thingie to tell
    position and speed of the moving parts.

    It could be inexpensive and still large and powerful smile.gif
  • StefanL38StefanL38 Posts: 2,292
    edited 2009-08-09 08:08
    this could be done with cordless-drill motors but as you mentioned to get SOME accuracy you need a feedback from the motoraxles
    by an encoder. An encoder controlled system is quite a big challenge. The challenge is the accelarating and deccelarating the motors.

    Of course in professional robots it is done exactly this way but with high complex motorcontrols with overlayed position and acceleration
    controllers as PID controllers.

    It will be easier to use steppermotors or servos. For Servos the basic control routines are already in the obex.

    To make it strong with steppermotors you could use a gear build with two wheels and a special kind of chain. I don't know the english word for it

    here is a picture bild_supertorque.jpg

    low-cost servos don't have much torque but I have an idea I find interesting:

    to move around "heavy" loads the robotarm could have some kind of balancers
    this means as soon as a load goes more to the right the balance-weight goes more to the left so the resulting torque in the axle is always minimized
    so that a relative small servo can turn it. Next thing to solve is how can the torque be measured ?

    some kind of a spring combined with a small switch or an encoder ? Or is this too complicated and just go for bigger RC-servos ?

    best regards

    Stefan

    Post Edited (StefanL38) : 8/9/2009 8:14:13 AM GMT
  • TubularTubular Posts: 4,706
    edited 2009-08-09 11:55
    Here in Australia we call it a "timing belt", commonly using a "L050" pitch.· "Timing Sprocket" for the wheel(s).·· Typically 10 to 72 teeth on the sprocket.· Certainly keeps everything taut and in nicely in sync...
    tubular
    To make it strong with steppermotors you could use a gear build with two wheels and a special kind of chain. I don't know the english word for it

    here is a picture bild_supertorque.jpg

  • SamMishalSamMishal Posts: 468
    edited 2009-08-09 16:01
    Ratronics,



    This is VERY impressive.....I like the Arm a lot.....cool stuff.

    It is also amazing that you did all this and you say that you are
    not much of a coder.....

    Samuel
  • ratronicratronic Posts: 1,451
    edited 2009-08-09 16:48
    No, I am not much of a coder. I just like·to dabble with stuff other people have done!

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    D Rat

    Dave Ratcliff N6YEE
  • WhitWhit Posts: 4,191
    edited 2009-08-09 17:20
    ratronic,

    Neat video and project. The arm responds really quickly too! My dog would go nuts...

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    Whit+


    "We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney
  • SamMishalSamMishal Posts: 468
    edited 2009-08-10 05:08
    Hi Ratronics,

    I thought that since you are so dexterous you might like to
    implement one or both of these Simulated arms in this video

    http://www.youtube.com/watch?v=AukHmkZqmys&feature=channel_page

    I am attaching·below the programs that do the simulations.

    As you can see from the video, all you need is to replace the routines that
    drive the Graphics to drive a real arm instead....all the math for moving the arms
    is already done.

    I would love to see at least the 2D one working in REAL instead of just a simulation.
    I think you are the MAN to do it.

    There was an article about the 3D arm you see in the video in the May 2009 issue of Servo Magazine.



    Regards



    Samuel




    Post Edited (SamMishal) : 8/10/2009 5:13:59 AM GMT
  • ratronicratronic Posts: 1,451
    edited 2009-08-10 19:43
    Samuel, I have never even checked out the simulator before, that's neet. But my coding skills are less than what are required for what your asking. I did figure out how to move the arm farther than I was before though. I attached another Youtube. (sorry for the bad 'arm driving', I don't even drive a car).

    http://www.youtube.com/watch?v=-xU8IUJ8SD4






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    D Rat

    Dave Ratcliff N6YEE
  • SamMishalSamMishal Posts: 468
    edited 2009-08-16 13:47
    ratronic said...
    Samuel, I have never even checked out the simulator before, that's neet. But my coding skills are less than what are required for what your asking. I did figure out how to move the arm farther than I was before though. I attached another Youtube. (sorry for the bad 'arm driving', I don't even drive a car).
    Hi Ratronics,

    Nice drivingnono.gif .....a few accidents with the PC.....tongue.gif

    When I lived in Madrid, Paris, and London I never owned a car....it was soooo nice to walk everywhere and
    take the Metro/Underground and read while sitting in the train....I miss those days....I was healthy then
    and now I have to drive everywhere I am FAT.....cry.gif and also full of fear and hate skull.gif from listening to Rush and
    Hannity et al on the Radio.

    Regards

    Samuel




    ·
  • TreeLabTreeLab Posts: 138
    edited 2009-08-16 23:30
    Hi Ratronics;
    That is very nice work, and clearly very responsive. I have never built such a device, so this is a question born out of ignorance. Is what looks to be overshoot is caused by the mechanical inertia of the arm elements or the properties of the joystick? If you force the arm to go through a mathematical sequence (no joystick) would it overshoot as well?

    Nicely done!

    Cheers!
    Paul Rowntree
  • ratronicratronic Posts: 1,451
    edited 2009-08-31 02:06
    Paul, sorry to take so long to reply, the overshoot is just a lak of programming on my part. If you look at the code, there is much that can be done to keep it within limits. I was just being lasy and haven't touched it up, just something I was playing with.

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    D Rat

    Dave Ratcliff N6YEE
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