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Stepper BoeBot — Parallax Forums

Stepper BoeBot

ercoerco Posts: 20,255
edited 2012-12-07 08:43 in Robotics
A little experiment in progress. A shiny new BoeBot using $2 stepper motors from Ebay China instead of stock CR servos. Ought to be a nice step up from my BS1 robot: http://www.youtube.com/watch?v=TLdkKKMfUP0 This BoeBot is not wired up yet, I just assembled the big pieces tonight to see how everything fits. Small sheet tin adapter plates to mount the steppers in the servo cutouts. Laser-cut acrylic wheels, slightly bigger diameter to keep the otherwise stock robot level (stepper motor axle shaft is 1/8" higher than orig servos). That's a ULN 2803 in the breadboard, used instead of two cheap stepper boards with ULN2003s. A 10-pin male/male header allow the stepper motors to plug right into the breadboard, and a servo extension cable brings switched power from the servo header to the motors. Two 18650 Li-Ion batteries & holder barely shoehorn in between the motors, that's where I plan to mount them. Another diversion to work on over Christmas break!
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Comments

  • Martin_HMartin_H Posts: 4,051
    edited 2012-12-07 06:06
    OK great, but there's a CONTEST on, Erco... and you're a prime mover! Time to get double duty out of Stepper BoeBot. Throw some red & green LEDs on that bad boy and get into the Hack the Halls competition!

    Just kidding. Those wheels look pretty sweet. How do you get them to grip the stepper shaft?
  • ercoerco Posts: 20,255
    edited 2012-12-07 07:10
    Good words to live by, Martin_H!

    Holes are custom cut to match the double-flatted motor shaft. Beautifully tight press-on fit. Laser cutters are amazing!
  • TtailspinTtailspin Posts: 1,326
    edited 2012-12-07 07:36
    Pretty cool erco,

    Now, if you could just do something about that caster wheel...

    Do those stepper motors have carpet shredding tourqe? can they spin the rubber off those rims?
    How are those batteries holding up? How many hours of run time? or is days of run time? :smile:
    inquiring minds want to know...


    -Tommy
  • lardomlardom Posts: 1,659
    edited 2012-12-07 08:42
    @erco, I just learned something else from you. That's the first time I've seen the tail wheel on a BoeBot. I used a tail wheel designed for rc airplanes which creates that little twist when the robot changes direction.
  • ercoerco Posts: 20,255
    edited 2012-12-07 08:43
    Will advise, Tttttttttttttttttttttttttttttttttttttttailspin!

    Neither amazing speed nor torque, just fairly predictable accuracy for dead reckoning. The ultimate limiter will be the backlash (slop) in the motors. They are $2.18 now, sans controller board: http://www.ebay.com/itm/271025308870 The boards work fine for one motor and the LEDs are useful for learning. It's a shame they used a 7-channel 2003 and let 3 channels go unused, instead of an 8-channel 2803 which can run two motors.

    The steppers get warm and consume more power than the original servos, so I figured those 18650 batteries were the way to go.

    @Lardom: yes, that tail ball is a mixed blessing. It doesn't caster, so it just skids sideways. On the other hand, it helps you hold a straight line going forward or backward. I prefer to keep the bot fairly balanced and put minimum weight on that ball for minimum influence.

    When I built Ken's Flamebot, the big aerosol can put so much weight on the ball that I had to change it to a small caster: http://www.youtube.com/watch?v=fuXMh1_-6Ag
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