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Always goes forward, Never goes straight — Parallax Forums

Always goes forward, Never goes straight

TinkersALotTinkersALot Posts: 535
edited 2010-08-25 17:25 in Robotics
Time for my uninformed question today:

Why does my boe-bot tend to "drift to the left" when it is going forward?

Comments

  • Jessica UelmenJessica Uelmen Posts: 490
    edited 2010-08-25 11:50
    Hi TinkersALot!

    To reuse an analogy I use in the Educator's Courses: "Servos are like snowflakes; no two come from the factory the same."

    So, even though you've centered both servos to stop when sent a 750 PULSOUT duration, one may still move a little faster in one direction. And that is what's happening to you - your right servo is moving slightly faster than the left one, causing the bot to drift slightly to the left.

    The Your Turn section in Robotics with the Boe-Bot, Chapter 4 Activity #2 lends some insight on how to adjust your PULSOUT duration arguments to help your Boe-Bot move in a 'perfectly' straight line.

    Hope this helps!

    -- Jessica
  • TinkersALotTinkersALot Posts: 535
    edited 2010-08-25 14:37
    Thank you, Jessica. I'll tune up the timing on that pulse train and make it a go-straight-boe-bot!
  • ercoerco Posts: 20,256
    edited 2010-08-25 15:24
    More or less. It will never drive perfectly straight under all circumstances, including changing battery voltage. Rechargeable NiMH batteries (5, not 4, like the Boe-Boost module provides) provide a more constant voltage power supply and help reduce "drive-straight" variations.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-08-25 15:38
    With the Boe-Bot Digital Encoder and its supporting PBASIC code, the Bot-Bot will drive straight. :)

    -Phil
  • TinkersALotTinkersALot Posts: 535
    edited 2010-08-25 16:10
    Neat encoders. Doesn't look like it is readily compatible with tank tread kit though. Hmmm...
  • WhitWhit Posts: 4,191
    edited 2010-08-25 17:25
    Phil was too modest to mention the incredible pdf (written by Phil himself) that goes with the encoders (and is free to download).

    You can find it here - http://www.parallax.com/Portals/0/Downloads/docs/prod/datast/ApplyEncoder.pdf

    It explains, better than anything I've ever read, how the whole thing works.
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