Alt-BEAM Archive
Message #13382
To: beam@sgiblab.sgi.com
From: JVernonM@aol.com
Date: Wed, 12 Apr 2000 23:47:08 EDT
Subject: Re: Ben's new bot?
In a message dated 4/12/00 7:13:09 PM Eastern Daylight Time, beh01@uow.edu.au
writes:
> The electronics work reasonably well - it chucks a hissy fit
> when I turn the light out - but I can't get it to go reliably towards the
> light.
Ben,
This is just a suggestion, but I keep thinking of those little football games
that were popular in the late 60s and early 70s. The little men moved in a
very directional way through the use of angled bristles underneath them. They
were angled back as I recall, which caused the figure to move forward.
Perhaps, little feet with small angled bristles on each side of the bot
connected directly to the vibe motor mount would work. Stiffness of the
bristle would be the area to experiment with. Just a thought, take it for
what it's worth.
See ya,
Jim
http://www.geocities.com/SoHo/Exhibit/8281/beamart.html
ICQ# 55657870
13383 Wed, 12 Apr 2000 21:25:01 -0700 RE: Photodiode use in BEAM circuits "'beam@sgiblab.sgi.com'" Wilf Rigter Hi Duncan,
You are right, photodiodes can be used in two distinctly different ways:
1. reverse biased as a photo resistor with a linear light to linear output
leakage current function over a wide dynamic range. The leakage current is
of the order of 10-100 mA in full sunlight.
2. forward biased as a photo voltaic generator (like a solar cell) with
linear light to log output voltage function. The generated photocurrent is
of the order of 100 uA in full sunlight. Some special large area PD can
generate over 10ma(sc) and 0.5V (oc)
The BEAMant and other bicore oscillators generate an alternating voltage
across the back to back PDs. Depending on the polarity of the applied
voltage during each half cycle, each reverse biased PD alternately acts like
a photo resistor to influence the time constant of that half cycle.
The photopopper appears to use forward biased photodiodes as light sensitive
voltage references in series with each SE trigger input. The balance pot is
used to compensate for small differences in PD sensitivity and 1381 trigger
levels in the left/right SE circuits under equal light conditions. During
the time the photopopper is charging the capacitor, the voltage on the cap
is applied through 50K (half of the 100K pot) and the PD to each 1381
voltage sensor. When the voltage on the cap is equal to the sum of the 1381
trigger level plus the generated PD voltage that SE will trigger shutting
out the other SE. With a light imbalance on the PDs, the SE with the lower
light level should have the lower threshold (if my understanding is correct)
and trigger first. That would mean that the PD should be mounted on same
side as the motor which it's SE controls. This would cause the popper to
steer away from shadows.
However a close examination of the photopopper 4.2 PCB shows that it's motor
are controlled by the opposite PDs which leads me to think that the polarity
of the PDs in the schematic is incorrect but I'll admit that my evidence is
tenuous at best. Still perhaps someone can give their photopopper a probe
with the old ohmmeter (hold still, this won't hurt a bit) and check the
polarity of it's PDs.
Light Dependent Resistors are similar to reverse biased PDs but are
nonlinear, have slower response (lag) and have lower effective resistance.
In some applications like the BEAMant bicore or bicore head, the PD maybe
replaced with two LDRs in series but with a 1N914 diode across each LDR and
cathodes connected back to back.
regards
wilf
> -----Original Message-----
> From: Dr. Duncan Lawrence [SMTP:duncan.lawrence@teel.co.uk]
> Sent: Wednesday, April 12, 2000 1:11 AM
> To: 'BEAM list'
> Subject: Photodiode use in BEAM circuits
>
>
> Can someone explain, or point me towards an explanation of, why in
> photovore circuits the photodiodes are connected anode-anode (via
> centralising pot)? But in BEAMAnt circuits, the photodiodes are connected
> cathode-cathode.
>
> I am assuming it has something to do with the resistance properties under
> normal and reverse bias, but exactly what that is I don't know.
>
> Secondly, can the photodiodes be swapped for Light Dependant Resistors in
> either application?
>
> Still a bit to learn yet!
>
> Many thanks
>
> Duncan
>
13384 Tue, 13 Apr 1999 19:39:21 +1000 Core-less walker beam "Ben Hitchcock" --MS_Mac_OE_3006877161_447827_MIME_Part
Content-type: text/plain; charset="US-ASCII"
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All,
Yesterday I was toying with the idea of using the position of the feedback
pot to tell the bot to stop turning the legs. After a couple of iterations
I realised that I could do away with the micro (or bi) core altogether, and
just use the position of the pot to tell the walker which way to turn its
legs.
I tested this circuit out today, and it appears to work. You have to use
schmitt triggers as the sensing elements, and I had to use a 74HC245 to
drive the motors themselves (a 74HC14 wasn't enough). This circuit will
work with hobby servos quite well because they have a feedback pot to tell
the driver what the position of the servo is.
Problems with this circuit:
If a leg gets stuck then bad luck. The circuit will stall. This is to do
with the lack of timing elements in the circuit.
Good points of this circuit:
Simplicity of debugging: You don't need to debug a complex Pulse
Neutralisation Circuit, or see how the process is walking around the core.
Just plug the leads in and go.
Simplicity of building: You don't need any more electronic elements than a
74HC14 and a 74HC245. NO other components are necessary (apart from
batteries and wire)
No leg stops: I dislike the idea of using mechanical stops to prevent my
legs from going too far. This circuit does away with them altogether - and
your legs will NEVER go too far!
I would recommend this circuit for people who want to get into walkers, but
are frightened by the complexity of a full-on microcore or bicore. About
the only thing you can get wrong with this circuit is hooking up the motors
the wrong way - and then the only thing that happens is that the motor goes
to the end of its travel and stops. Reversing the leads makes them tick
along nicely.
Right now I have two servos alternating on my desk, just the way that servos
should if they were on a walker. I haven't actually tested this by adding
legs and seeing if the thing moves, but it should work reasonably well.
In the diagram I have omitted the 74HC245 driver for clarity. I regard this
circuit as a bit of a curiosity ("I did it because I can!") rather than a
functioning piece of BEAM evolution such as the FRED.
If anyone's interested in developing this further then an idea might be to
use the remaining three inverters on the 74HC14 as a sort of 'getting stuck'
detector... if an output stays on for a long length of time then kick the
input over the other way. I haven't drawn this yet because I like the
simplicity of this drawing.
Oh and another thing, to make the walker turn just bias one of the wipers
either high or low with a 5 k resistor and the gait will change perfectly,
not hitting any end stops or making the legs do cartwheels. Not bad, eh?:-)
Any questions, comments?
Ben
--MS_Mac_OE_3006877161_447827_MIME_Part
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Attachment: coreless.gif
--MS_Mac_OE_3006877161_447827_MIME_Part--
13385 Thu, 13 Apr 2000 07:23:35 -0700 RE: Core-less walker "'beam@sgiblab.sgi.com'" Wilf Rigter
Hi Ben,
I love it! The basic principle of your design is a clear case of parallel
evolution when compared to my "earlyBEAMservo1" circuit but your arrangement
of using the three 74HC14 inverters to generate the right phase relationship
between the legs is unique.
When I look back at the basic design, I made the same observation of "no
feedback/no time out/hanging up" of the legs when hitting an obstacle. There
are lots of possibilities using reversers, switches and timeout elements and
the one that evolved for me is shown in the "earlyBEAMservo2" design which
combines a photo bridge, the basic R/C timing of an oscillator, a centering
pot with feedback from the servo pot to center the gait without springs
while allowing the legs to reverse when hitting an obstacle. The final
evolution of these servo pot feedback designs was the "uCrawler" - light
seeking - one motor/2 legged "walker" which works very well but ironically
only on short fiber carpets. The same servo pot feedback principle can
evolve to 2 and 3 motor walkers but I haven't (as yet) followed up on that.
There were some other points described in the uCrawler article but you'll
have to drag it out of the archive to find out.
regards
wilf
<> <> <>
> -----Original Message-----
> From: Ben Hitchcock [SMTP:beh01@uow.edu.au]
> Sent: Tuesday, April 13, 1999 2:39 AM
> To: beam
> Subject: Core-less walker
>
> All,
>
> Yesterday I was toying with the idea of using the position of the feedback
> pot to tell the bot to stop turning the legs. After a couple of
> iterations
> I realised that I could do away with the micro (or bi) core altogether,
> and
> just use the position of the pot to tell the walker which way to turn its
> legs.
>
> I tested this circuit out today, and it appears to work. You have to use
> schmitt triggers as the sensing elements, and I had to use a 74HC245 to
> drive the motors themselves (a 74HC14 wasn't enough). This circuit will
> work with hobby servos quite well because they have a feedback pot to tell
> the driver what the position of the servo is.
>
> Problems with this circuit:
> If a leg gets stuck then bad luck. The circuit will stall. This is to do
> with the lack of timing elements in the circuit.
>
> Good points of this circuit:
> Simplicity of debugging: You don't need to debug a complex Pulse
> Neutralisation Circuit, or see how the process is walking around the core.
> Just plug the leads in and go.
> Simplicity of building: You don't need any more electronic elements than a
> 74HC14 and a 74HC245. NO other components are necessary (apart from
> batteries and wire)
> No leg stops: I dislike the idea of using mechanical stops to prevent my
> legs from going too far. This circuit does away with them altogether -
> and
> your legs will NEVER go too far!
>
>
> I would recommend this circuit for people who want to get into walkers,
> but
> are frightened by the complexity of a full-on microcore or bicore. About
> the only thing you can get wrong with this circuit is hooking up the
> motors
> the wrong way - and then the only thing that happens is that the motor
> goes
> to the end of its travel and stops. Reversing the leads makes them tick
> along nicely.
>
> Right now I have two servos alternating on my desk, just the way that
> servos
> should if they were on a walker. I haven't actually tested this by adding
> legs and seeing if the thing moves, but it should work reasonably well.
>
> In the diagram I have omitted the 74HC245 driver for clarity. I regard
> this
> circuit as a bit of a curiosity ("I did it because I can!") rather than a
> functioning piece of BEAM evolution such as the FRED.
>
> If anyone's interested in developing this further then an idea might be to
> use the remaining three inverters on the 74HC14 as a sort of 'getting
> stuck'
> detector... if an output stays on for a long length of time then kick the
> input over the other way. I haven't drawn this yet because I like the
> simplicity of this drawing.
>
> Oh and another thing, to make the walker turn just bias one of the wipers
> either high or low with a 5 k resistor and the gait will change perfectly,
> not hitting any end stops or making the legs do cartwheels. Not bad,
> eh?:-)
>
> Any questions, comments?
>
> Ben << File: coreless.gif >>
13386 Thu, 13 Apr 2000 12:18:59 -0400 (EDT) RE: Core-less walker Wilf Rigter Dennison I Bertram Hey I just breifly checked the list today, and I saw this. I don't know
how many people remeber, but there was a servo/pot feedback circuit posted
a LONG LONG time ago. I remeber it well because it was 'big fanfair'
because it was touted as a microcore type circuit that would never
saturate and worked on PWM. This circuit looks significantly simpler
however. Very nice!
dennison
On Thu, 13 Apr 2000, Wilf Rigter wrote:
> Hi Ben,
>
> I love it! The basic principle of your design is a clear case of parallel
> evolution when compared to my "earlyBEAMservo1" circuit but your arrangement
> of using the three 74HC14 inverters to generate the right phase relationship
> between the legs is unique.
>
> When I look back at the basic design, I made the same observation of "no
> feedback/no time out/hanging up" of the legs when hitting an obstacle. There
> are lots of possibilities using reversers, switches and timeout elements and
> the one that evolved for me is shown in the "earlyBEAMservo2" design which
> combines a photo bridge, the basic R/C timing of an oscillator, a centering
> pot with feedback from the servo pot to center the gait without springs
> while allowing the legs to reverse when hitting an obstacle. The final
> evolution of these servo pot feedback designs was the "uCrawler" - light
> seeking - one motor/2 legged "walker" which works very well but ironically
> only on short fiber carpets. The same servo pot feedback principle can
> evolve to 2 and 3 motor walkers but I haven't (as yet) followed up on that.
> There were some other points described in the uCrawler article but you'll
> have to drag it out of the archive to find out.
>
> regards
>
> wilf
>
> <> <> <>
> > -----Original Message-----
> > From: Ben Hitchcock [SMTP:beh01@uow.edu.au]
> > Sent: Tuesday, April 13, 1999 2:39 AM
> > To: beam
> > Subject: Core-less walker
> >
> > All,
> >
> > Yesterday I was toying with the idea of using the position of the feedback
> > pot to tell the bot to stop turning the legs. After a couple of
> > iterations
> > I realised that I could do away with the micro (or bi) core altogether,
> > and
> > just use the position of the pot to tell the walker which way to turn its
> > legs.
> >
> > I tested this circuit out today, and it appears to work. You have to use
> > schmitt triggers as the sensing elements, and I had to use a 74HC245 to
> > drive the motors themselves (a 74HC14 wasn't enough). This circuit will
> > work with hobby servos quite well because they have a feedback pot to tell
> > the driver what the position of the servo is.
> >
> > Problems with this circuit:
> > If a leg gets stuck then bad luck. The circuit will stall. This is to do
> > with the lack of timing elements in the circuit.
> >
> > Good points of this circuit:
> > Simplicity of debugging: You don't need to debug a complex Pulse
> > Neutralisation Circuit, or see how the process is walking around the core.
> > Just plug the leads in and go.
> > Simplicity of building: You don't need any more electronic elements than a
> > 74HC14 and a 74HC245. NO other components are necessary (apart from
> > batteries and wire)
> > No leg stops: I dislike the idea of using mechanical stops to prevent my
> > legs from going too far. This circuit does away with them altogether -
> > and
> > your legs will NEVER go too far!
> >
> >
> > I would recommend this circuit for people who want to get into walkers,
> > but
> > are frightened by the complexity of a full-on microcore or bicore. About
> > the only thing you can get wrong with this circuit is hooking up the
> > motors
> > the wrong way - and then the only thing that happens is that the motor
> > goes
> > to the end of its travel and stops. Reversing the leads makes them tick
> > along nicely.
> >
> > Right now I have two servos alternating on my desk, just the way that
> > servos
> > should if they were on a walker. I haven't actually tested this by adding
> > legs and seeing if the thing moves, but it should work reasonably well.
> >
> > In the diagram I have omitted the 74HC245 driver for clarity. I regard
> > this
> > circuit as a bit of a curiosity ("I did it because I can!") rather than a
> > functioning piece of BEAM evolution such as the FRED.
> >
> > If anyone's interested in developing this further then an idea might be to
> > use the remaining three inverters on the 74HC14 as a sort of 'getting
> > stuck'
> > detector... if an output stays on for a long length of time then kick the
> > input over the other way. I haven't drawn this yet because I like the
> > simplicity of this drawing.
> >
> > Oh and another thing, to make the walker turn just bias one of the wipers
> > either high or low with a 5 k resistor and the gait will change perfectly,
> > not hitting any end stops or making the legs do cartwheels. Not bad,
> > eh?:-)
> >
> > Any questions, comments?
> >
> > Ben << File: coreless.gif >>
>
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