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My Robot Challenge — Parallax Forums

My Robot Challenge

ercoerco Posts: 20,256
edited 2011-11-30 21:38 in Robotics
See my obscure challenge buried in this thread: http://forums.parallax.com/showthread.php?136008-Black-Friday-Deals&p=1054736&viewfull=1#post1054736

Just feeling frisky at the time. Did I rush into this? Was I in error? Should I retract? Logoff forever?

Nah, I'll stick. My spider sense in tingling.

Comments

  • TtailspinTtailspin Posts: 1,326
    edited 2011-11-26 20:13
    The pen lifter on my Scribbler2 is "homemade", does that count?? If it does, then I am yer huckleberry...:cool:

    -Tommy
  • ercoerco Posts: 20,256
    edited 2011-11-26 20:18
    Get Caster the Friendly Bot rolling in a square! :)
  • al1970al1970 Posts: 64
    edited 2011-11-27 00:50
    So Erco, how did your robot do running the 8 ft. square?
  • ratronicratronic Posts: 1,451
    edited 2011-11-27 09:37
    erco how close do you get with using one wheel encoder?
  • ercoerco Posts: 20,256
    edited 2011-11-27 11:17
    Ain't built it yet, but I have it working perfectly in my head. :)

    More of a mechanical solution than electronic, and the BS1 has plenty of power. I'm a minimalist!

    I will be building over Christmas break. Not holiday break.

    CHRIST-mas break! :)
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-11-27 11:20
    Hmmm. Two wheels: one encoder. I smell a differential being cooked up!

    -Phil
  • ercoerco Posts: 20,256
    edited 2011-11-27 11:29
    You are wise, Phillipi. Sort of a sideways dual-differential drive, with 1/4 the parts and backlash. Always start with good mechanicals and then minimum support electronics is all you need!
  • Martin_HMartin_H Posts: 4,051
    edited 2011-11-27 16:06
    erco wrote: »
    You are wise, Phillipi. Sort of a sideways dual-differential drive, with 1/4 the parts and backlash. Always start with good mechanicals and then minimum support electronics is all you need!

    Ah so this is the long rumored improvement to the dual differential drive. I can't wait to see it.
  • AImanAIman Posts: 531
    edited 2011-11-28 21:57
    "Nah, I'll stick. My spider sense in tingling."

    One of my first programable robots was the Arobot that ran a BS2 and after some goading from some guys in the robotics club I reprogrammed the thing to go in a square and do figure eights going backwards. I will place odds on your simple robot being rather accurate if you take the time to think it out.

    ... of course having done it myself helps my faith in your position
  • ercoerco Posts: 20,256
    edited 2011-11-29 00:39
    AIman: I bought an Arobot last year from a local off Craigslist. Just added it to my collection, never even fired it up. Its car-type steering seems kinda flimsy, so I didn't have high expectations for its repeatability, but I knew that before I bought it. Nice to hear that you had good results with yours. One day I'l get around to using it... :)
  • Martin_HMartin_H Posts: 4,051
    edited 2011-11-29 06:49
    If I was going attempt this challenge, I'd find the single encoder to be the biggest problem. So I would have a robot that could only drive straight and use a single encoder to calculate distance traveled. It would turn by having a servo controlled jack with a servo controlled foot that rotated the whole robot 90 degrees. Once the problem was reduced to mechanics I'd be left with little need for computational resources.

    I suppose you could take things a step farther and eliminate a microcontroller entirely by using something like a counter IC to trigger the jack. The jack would use 555 timers to create the servo wave forms to lever the robot up and rotate it.

    But I'm a software guy and prefer the malleability of software with a two encoder differential steering robot.
  • ercoerco Posts: 20,256
    edited 2011-11-29 08:40
    One year at TCFFHRC, a robot chassis had 2 different sets of 4 wheels, aimed 90 degrees apart. He would dead reckon without turning doing multiple 90 degree segments. Drive forward on the A wheels for X units. Stop. Raise the A wheels & lower the B wheels. Roll left Y units. Stop. Raise the B wheels and lower the A wheels... Lather, rinse, repeat.

    Neither fast nor accurate, just complicated. PITA! KISS!

    Acronyms rock. DYT?
  • Martin_HMartin_H Posts: 4,051
    edited 2011-11-29 10:39
    I would love to have seen that robot. Omni wheels at 90 degrees apart sound like a better idea than raising and lowering the wheels.
  • Cluso99Cluso99 Posts: 18,069
    edited 2011-11-29 17:08
    I have the Tamiya 70168 double gearbox motors and 70101 36mm wheels (just arrived). Now for the electronics. But don't hold your breath as I have too many other projects running that this is just for the lazy times.
  • ercoerco Posts: 20,256
    edited 2011-11-29 19:56
    @Cluso99: You got a 10x10 open floor area on your sailboat for testing? :)
  • AImanAIman Posts: 531
    edited 2011-11-30 21:38
    FYI - I had a project that I needed a much greater degree of accuracy then running a coder on the wheel, so what happened was the coder was mounted on the motor shaft prior to the main gear reduction box and was able to get much greater accuracy. Accuracy will depened on the gears used, where the coder is placed in the gearing and the size of the wheel used.

    My project placed the coder between the second and third gears giving an accuracy greater then 1/1000 of an inch because of the rpm the motor kicked out. Given the math, accuracy to 1/65,000 of an inch was theoritcally possible. Orginally the coder was going to be placed straight on the motor shaft, but that rpm made the coder wheel turn to fast.
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