Alt-BEAM Archive
Message #13678
To: "'beam@sgiblab.sgi.com'" beam@sgiblab.sgi.com
From: Wilf Rigter wilf.rigter@powertech.bc.ca
Date: Wed, 19 Apr 2000 10:17:11 -0700
Subject: RE: Dummy Walker
Hi Ben,
nice progress report!
My uCrawler turns very nicely towards a light source, with a bright light on
one side it turns with a 18 inch radius small light difference cause slower
turning.
Turning should be easy with a 2 motor walker. If the walker has the front
motor at 90 degrees (up down leg motion), it's only the rear legs impart
forward motion and determine the direction. It is the vector of the center
(midway point) of the horizontal stride that determine the direction. If the
front motor is at 45 degree, it also contributes to the forward motion and
can be used together with the rear legs to decrease turning radius as shown
in the attached:
<>
Reversing a Dummy Walker is a little tricky since the two pattern generators
interact. It requires that the middle motor driver outputs are separated at
the common point of the motors (use the 2 spare drivers) and then a
conventional XOR reverser can be inserted at the inputs of the rear servo
motor drivers.
Also consider using and AC240/241/244 as a reversing motor driver. Only one
buffer is active per motor connection but should provide the same
performance with higher drive current available from the 74AC logic.
regards
wilf
> -----Original Message-----
> From: Ben Hitchcock [SMTP:ben@wollongong.apana.org.au]
> Sent: Wednesday, April 19, 2000 6:51 AM
> 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 << File: dummy.gif >> << File: nsdummy.gif >>
13679 Wed, 19 Apr 2000 10:50:22 -0700 RE: efficient launcher? "'beam@sgiblab.sgi.com'" Wilf Rigter Reminds me of the new NASA spacestation "arm" which can displace itself to
any point of the structure. Since each end of the arm can be the fulcrum, it
swings over in the direction of travel, fastens the far end, unfastens the
rear end and then swings it forward. This is also the method used by
construction cranes which pick themselves up by the "bootstraps" as the
building rises. This idea could also be applied to a stair climbing bot: the
trick is in controlling the center of gravity which in principle should
lends itself to a BEAM solution. I envision a segmented caterpillar bot that
can extend itself against the vertical part of the stair step like a ladder.
Once the upper segment is over the top of the stair, it starts to curl up,
rolling forwards over its "head" while tipping the next segment up and
forwards. Once the last segment is hauled up on the stair, the bot again
straightens itself out like a ladder and so on.
regards
wilf
> -----Original Message-----
> From: Phillip A. Ryals [SMTP:phillip@ryals.com]
> Sent: Wednesday, April 19, 2000 9:56 AM
> To: beam@sgiblab.sgi.com
> Subject: efficient launcher?
>
> I had this groovy idea, but I'm not sure if it can actually be done
> efficiently. Maybe someone could give me some pointers?
>
> I was thinking that it would be cool to implement a grappling hook type
> system to allow a robot to get over large obstacles. It would require
> some type of winch system that retracts the line, and I think this has
> already been done with 'window washers'. But what about a launcher? I
> really don't think there's an efficient way to do it with a solenoid or
> motor... I just don't think a beam cicuit could really launch anything
> very far. I think it would need to be a system where a gear motor
> wiches the hook onto a spring. Then, you would need some sort of quick
> release to get the full force of the spring. I think a big problem
> might be the friction of the line used. That might be overcome if the
> hook had some weight though.
>
>
> Is this all just wishful thinking? It sounds like a LOT of trouble to
> go to, but I think the effect would be pretty cool. Set the bot in
> front of a wall three times it's height, and watch the bot climb it.
>
>
> Any ideas?
>
>
> -phillip
13680 Wed, 19 Apr 2000 11:50:06 -0600 Re: Costings in Australia beam@sgiblab.sgi.com Dave Hrynkiw At 10:09 AM 4/19/2000 , JVernonM@aol.com wrote:
>Well, perhaps you should find the suppliers being used by other Canadian
>suppliers and kit sellers. They seem to operate just fine by calculating in
>Canadian funds.
Perhaps. The only other kit reseller we know personally is Craig, but we're
(obviously) not intimate with each other's business dealings. All I know is
what I've already stated: US funds are the currency of choice for
international transactions, both resale and wholesale.
Regards,
Dave
---------------------------------------------------------------
"Um, no - that's H,R,Y,N,K,I,W. No, not K,I,U,U, K,I,_W_. Yes,
that's right. Yes, I know it looks like "HOCKYRINK." Yup, only
2 vowels. Pronounciation? _SMITH_".
http://www.solarbotics.com
13681 Wed, 19 Apr 2000 14:41:35 EDT Re: efficient launcher? beam@sgiblab.sgi.com SkavenArmy@cs.com ok heres what ya do:
get a small childs grappling hook or whatever youre going to use. make sure
it fits inside some small pvs tubing. et a solenoid that fits also. cut a
small hole in the tubing right in front of the solenoid. now attach a motor
circuit that starts when the small lever is pulled by the string tightening.
now put it all together , integrate the touchy feely thingy to a switch that
at so high (like a pole) it would set offthe hook(at 45' of course!) and
viola! now ...all we need are some circuitry
jay z
im prolly wron here
13682 Wed, 19 Apr 2000 15:10:13 EDT new bot! Re: efficient launcher? beam@sgiblab.sgi.com BUDSCOTT@aol.com whoa, i just got a really great idea for the "odd bot" tutorial that i'm
gonna do on my page. Here's the lowdown, i'm gonna make a small grappling
hook out of some paper clips, then create some sort of grapling launcher that
would launch out the grapling and pull the bot further along, that's just the
basics, but i'll be working on it! thanks dude!
-Spencer
<http://www.botic.com/users/beamstop>
not a robot scientist
not a college major
not a grad student
not a professor
not a very organized person
just Spencer (isn't that impressive enough?)
13683 Wed, 19 Apr 2000 15:17:00 -0700 RE: new bot! Re: efficient launcher? "Phillip A. Ryals" cool. Nice idea, to use paper clips. I've spent so much time looking at
them (I work at an office supply) that I forgot them when this idea hit me.
:)
Let me know how it goes! I'll be working on my own version too.
-phillip
-----Original Message-----
whoa, i just got a really great idea for the "odd bot" tutorial that i'm
gonna do on my page. Here's the lowdown, i'm gonna make a small grappling
hook out of some paper clips, then create some sort of grapling launcher
that
would launch out the grapling and pull the bot further along, that's just
the
basics, but i'll be working on it! thanks dude!
-Spencer
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