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RE: Dummy Walker

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  • Thomas Pilgaard
    Ben, on your schematic is the 68hc14 correct? - Thomas
    Message 1 of 2 , Apr 26, 2000
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      Ben,

      on your schematic is the 68hc14 correct?

      - Thomas

      > -----Original Message-----
      > From: owner-beam@... [mailto:owner-beam@...]On
      > Behalf Of Ben Hitchcock
      > Sent: Wednesday, April 19, 2000 3:51 PM
      > To: beam
      > Subject: Dummy Walker
      >
      >
      > Well,
      >
      > I've finally ironed out the bugs (I hope!) in the "getting stuck" detector
      > on my walker. Now when the walker gets stuck it will wait for a second or
      > two before spinning that motor the other way and starting the gait again.
      >
      > I tried putting a reversing circuit on it before I reached this solution.
      > This used up all the inverters, and was... interesting. When a motor
      > stalled, that motor would stop, and the other motor would swing over, it
      > would wait for a bit, then the first motor would turn. This had
      > the effect
      > of slooowwwly 'backing up' forever. If you stalled a motor when
      > backing up
      > the circuit wouldn't recover.
      >
      > This isn't to say that reversers can't be done. I'm sure that someone can
      > come up with a better solution than mine - perhaps a touch switch
      > that makes
      > the robot back up for a set time, or something. To reverse the gait you
      > have to move the inverter from the top (that is pointing left), and put it
      > in between the other two inverters, pointing right. This means that you
      > have to do away with the pairing of the two servo motors being
      > fed from the
      > one set of drivers. In other words, you use eight driver gates instead of
      > six.
      >
      >
      > There are two circuits here:
      > dummy.gif:
      > This is my original dummy walker circuit. It is simply a walker
      > circuit for
      > dummies. I couldn't get my microcore circuit to work reliably
      > (Probably had
      > something to do with the modifications I did to it! I can't just leave a
      > circuit alone!) so I made this circuit instead. I could build this one
      > without any problems. This uses two servos, a 74HC14 and a 74HC245, a few
      > batteries and that's about it. It will walk reliably, except if a motor
      > stalls for some reason (Like walking on carpet). I regard this circuit as
      > doing pretty well for the response I get out compared to the number of
      > components.
      >
      > The second circuit is nsdummy.gif. This stands for Not So Dummy
      > walker. In
      > other words, it's a bit harder to put together. I don't think
      > that this is
      > the optimum solution, but it's the best I could come up with.
      > And it works!
      > I built the thing this afternoon, and it walks fine!
      >
      > I have to say that I've been bitten by the walker bug now. I've got an
      > 8-servo 4 legged walker half built sitting on my desk that I hope
      > to control
      > with a CPU that was designed at wollongong university. I've got
      > a black and
      > white analog camera that I'm going to mount on it as well. The leg design
      > is quite different to that of Richards quadrapod, although we
      > will probably
      > be able to share control circuitry because the servos still do
      > much the same
      > thing - forward, back, up, down.
      >
      >
      > Anyway I digress.
      >
      > When building the dummy walker about the only thing that can go wrong is
      > that you get the motor polarity around the wrong way. This means that
      > instead of oscillating like any sane walker does, the motor drives to the
      > endstop and tries to keep going. Turning the power off and reversing the
      > leads on the motors fixes this. Murphy must have been looking over my
      > shoulder today because both my motors did this. What's that, a 25% chance
      > of happening?
      >
      > You can have a look at a fuzzy picture I took about an hour ago at:
      > http://wollongong.apana.org.au/~ben/nsdummy.jpg
      >
      > Although I put LDR's on the robot, and they change the center angle of the
      > front legs, I'm not convinced that the robot actually turns towards the
      > light. Has anyone gotten their walker to be light-seeking? If so, how do
      > you do it? Do you change the center position of the front or
      > back legs? By
      > how much?
      >
      > One more thing, when the circuit was breadboarded occasionally when I
      > stalled the front servo the rear one would go crazy, oscillating back and
      > forth and the front one wouldn't even move. I put this down to a high
      > reistance leak on that particular track because when the circuit was
      > freeformed the problem disappeared. Weird.
      >
      > Anyway,
      >
      > Questions, comments?
      >
      > Ben
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