RE: Dummy Walker
on your schematic is the 68hc14 correct?
> -----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
> 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
> There are two circuits here:
> 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
> 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:
> 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.
> Questions, comments?