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Robot Arm — Parallax Forums

Robot Arm

ajwardajward Posts: 1,130
edited 2012-03-04 16:04 in Robotics
I was playing with the OWI robot arm yesterday and decided to start on one from scratch. Built with a handful of cheap 9g servos and leftover plastic from other projects.

http://bit.ly/z6IWVz

The servos are just cycling with a couple of the small servo testers Erco mentioned a while back.

Still not complete... I need another servo to add rotation at the wrist. Besides the small servos, the assembly isn't terribly strong. The whole thing is held together with 3M moulding tape... great for holding "Ranger" on the side of my truck, but it doesn't resist shear force very well.
The arm sections are too long, occasionally catching the servo wires and generally mucking things up.

Working on refining the design in AutoCad. I just about have the solid model of the 9g servo. Once I finish that, the rest should be (fairly) easy.

Hmmm... errands to run for now.

Amanda

Comments

  • ercoerco Posts: 20,256
    edited 2012-03-02 11:29
    Amanda: XLNT!

    Come on in, the water's fine! http://forums.parallax.com/showthread.php?137471-Arm-Wrist-Gripper-Uses-9-gram-servos&p=1074060&viewfull=1#post1074060

    I just received the latest ROBOT magazine with my arm construction article in it, FYI. Still have some code to finish for their web site.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-03-02 11:32
    Very cool!

    I used Lego turntables additional pivot connections when I made my popsicle stick hexapod. I thought it helped strengthen the joints a lot.
  • ajwardajward Posts: 1,130
    edited 2012-03-02 14:51
    Arrr... Back to the drawing board! Connected the arm to a BS HomeWork board to figure out the servo limits and all went well... for a bit. Then... "Basic Stamp not found"... dead battery! Replaced the battery, ran a few more cycles and "Basic Stamp not found"... another dead battery. For tiny servos, they can suck the life out a battery pretty darn quickly.

    Dragged out the bench power supply, set to 9.5 vdc. Now we're getting somewhere. The servos just snapped into position. Excellent... at least till the 3M tape gave up the ghost. :-{
    Replaced all the connections with fresh tape and the assembly lasted for about another half-dozen cycles. Seems to be too much flex and twist for the 3M.

    Gotta update the arm sections and bolt them to the servo horns.

    I love this stuff!!!!

    Amanda
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2012-03-02 16:17
    Trackball !
  • ajwardajward Posts: 1,130
    edited 2012-03-04 03:01
    @PJ... Yup, a trackball. I got tired of pushing things around on my desk with a regular mouse. :-)
  • ercoerco Posts: 20,256
    edited 2012-03-04 08:12
    9.5 VDC? That'll cook your little servos pretty quick, and rip your tape off in the process. Try 5-6V instead. Gentler motions. I'm running my arm servos off 3.6V and all's good.
  • ajwardajward Posts: 1,130
    edited 2012-03-04 11:13
    @Erco... No, no... running the H/W Board at 9.5v. Driving the servos off Vdd from the board. 9-volt batteries didn't last long supporting 4 servos.

    Interesting tho' about your servos running at 3.6v. Hafta experiment a bit.

    @
  • ercoerco Posts: 20,256
    edited 2012-03-04 14:25
    Using Vdd to drive multiple servos can also be problematic; regulator limitations and starving the Stamp for power. How about dial in 5.0 V from your power supply and run everything from that, servo supply and Stamp Vdd? Or else dial in 6.5 V for servos and also connect that to Vin on your HW board?
  • Martin_HMartin_H Posts: 4,051
    edited 2012-03-04 16:04
    With my arm I would get brown outs when moving all the servos. So I end up with two power supplies with connected grounds. The batteries seemed to last longer to.
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