Alt-BEAM Archive
Message #12242
To: beam@sgiblab.sgi.com
From: Bruce Robinson Bruce_Robinson@telus.net
Date: Mon, 20 Mar 2000 18:29:03 -0800
Subject: [alt-beam] Re: ....yet again.....
"Scolman,Jim" wrote:
>
> ... in the enclosed diagram, one of the power leads goes to the
> (+ plus) sign, where does the other go? ... where is the (- neg)
> symbol?
On the '240 chip, pin 10 is negative, or ground (Wilf used a little
downward pointing triangle). Pin 1 (labelled 1G) and Pin 19 (labelled
2G) are the two "enable" pins are connected to ground as well; this
basically turns the two halves of the chip "on".
> Is this a Bicore, MicroCore, or UniCore?
Microcore. This is typical Wilf :) The microcore couldn't be built on a
'240 chip, it needed a Schmitt inverters; then Wilf came up with this
circuit to prove the experts wrong. Here's his quote from the original
message that accompanied this circuit:
"Here is a tested 74HC240 microcore (no not a bicore)
circuit which behaves just like a 74HC14 type microcore
and motor driver combined."
> ... All the "stuff" inside the outline of the chip ... is that internal
> to the chip or are those parts and connections to be fabricated and
> soldered?
The inverters (large triangles with a dot on the pointy end, labelled
"1" and "2") are internal to the chip. The four capacitors labelled C1
(three drawn inside the chip outline, one outside) are external
components.
> ... I still don't understand about ground ...
Just another way of refering to the negative connection of your power
supply. I has it's roots way back in the days of vacuum tubes.
> ... where do you connect the 1G and 2G pins? The R1 resitors that
> just end in an arrow head......where do they connect?
Those little down arrows are just a symbol for "ground", or the negative
connection of your power supply.
> I am electronically challenged ...
We're all on the learning curve, just at different places. There's
always someone a little higher up the curve :)
A tip to help figure out the GND (negative) connection is this. On most
of the 74-series chips (everyone I've ever encountered so far), the two
power supplies are diagonally opposite. Positive is the highest numbered
pin (directly across from pin 1), and negative is in the opposite row of
pins, at the other end of the chip. If a person is using a symbol for
GND that you aren't familiar with, identifying the ground pin this way
helps you figure out what symbol is being used.
Bruce
12243 Mon, 20 Mar 2000 18:28:15 -0800 [alt-beam] Re: Aesthetics beam@sgiblab.sgi.com Bruce Robinson Sathe Dilip wrote:
>
> ... Now thinking about it, I have seen some bands of flexible
> PCB-like material in older dot matrix printers to connect to
> the print head. May be someone who has a junked printer can
> report on the suitability of using that material in some way?
I completely forgot about that stuff. I've got a piece right here, this
one salvaged from a defunt hard drives. It was used to connect the head
assembly to the chassis. And yes, the ends are soldered directly, so it
can obviously withstand heat. The problem with the piece I have (and
probably the stuff in a printer) is that it has the base material on
both sides of the traces. Probably necessary to prevent short circuits.
I doubt you could make much use of the salvaged material -- it's just a
way to carry a bunch of parallel traces. It would be very interesting to
get hold of a sheet of raw material and see if it can be etched.
Bruce
12244 Mon, 20 Mar 2000 21:41:57 -0800 [alt-beam] Re: Question about vibra-popper mechanics alt-beam@egroups.com David Simmons Ben,
Nice idea, when you get it going are you going post info so the rest of
us can try the little guy out?
See below...
Ben Hitchcock wrote:
>
> All,
>
> I have been working on a 'crunch-resistant' robot for about a month, off and
> on. I finally got the circuit working to my satisfaction, but the damn
> mechanics are driving me crazy!
I happened to have a single pager motor with the eccentric still on so I
thought I would try a few things. First, the kinetic energy produced by
the motor will always follow the path of least resistance. This being a
given I tried playing around with the motor. With the motor free and
power applied the motor jumped in one direction, change the polarity and
the motor jumped the other direction. Simple enough, so it should work
the same way on your bot. But it won't, the balance of energy being
applied is just off the center of the motor axis. Therefore with the
motor at the back of your frame the energy is being applied to the back.
Regardless of motor direction you should see almost the same resultant
movement. To try this I taped the motor to the side of a lego block
(isn't having kids toys around great). It didn't seem to matter much
what direction the motor turned the brick moved towards the motor almost
every time.
When I centered the motor on the Lego brick it would change directions
according to the direction of the motor. Still this seemed a little
weak. So I clamped the wires between two bricks, allowing the motor to
swing back and forth. This provided the most interesting movement so
far. The weight of the motor gives a good kick in the direction you want
to go and the spin keeps it going. I would have liked to have tried two
motors, but perhaps on the weekend.
My solution to your movement problem would be to pinion the motors at
the wire end and allow them to move back and forth inside the case you
plan on making. I would guess at 15 degrees of freedom in each direction
with the pinion centered on the center line of the body. Try different
ground contact points until you get the movement you like best.
If you are not going to try this, or at least not right away, Kyle would
be interested in the circuit you are using so he can try this out. He
likes the idea of a low profile bot, with a strange type of movement.
Regards,
Dave
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