Alt-BEAM Archive

Message #11936



To: beam@sgiblab.sgi.com
From: Ben Hitchcock beh01@uow.edu.au
Date: Thu, 16 Mar 2000 12:44:26 +1100 (EST)
Subject: [alt-beam] Re: FRED bread boarded...problems


Hi,

For those of you not familiar with the FRED solar engine, check out
http://wollongong.apana.org.au/~ben/fred/schematic.html. It's a solar
engine that can make a photopopper out of some pretty cheap components. I
used a slightly modified version in my seaplane (linked from that page).

> Is it possible to make some componenet changes in the FRED design. Have
> a
> 4700uf cap and 2.2k resistors instead of 4.7uf cap and 3.3 resistors?

It is possible to make lots of changes to the FRED circuit and still have
it working fine. Some changes might even improve performance. The onyl
way to tell is to actually try it.

2.2k resistors will increase the lowest light level that FRED will work
in, and raise the switch-on voltage slightly, but it should work.

4700 uF is way too high. The idea is that this cap is low enough to
charge up very quickly - otherwise there isn't much point making a FRED, a
standard FLED SE will do the same job. Use something small such as a 0.22
uF cap or 0.1 or so. You might have some of thse lying around drom a
microcore project.

> I
just bread-boarded FRED but it didn't work. The FLED would flash but the
> motor would not turn. I only bread-boarded half the circuit, or one engine.
> I don't know why this is. Where does the second wire of the FLED go? Any
> help would be appreciated.

What values are you using? Are you using a 33k resistor to bias the FLED?
If so the FLED should be very faint. Is your cap (4.7 uF) around the
right way? If you're using a 4700 uF cap then this is your problem.

> Also...
>
> If I use a larger voltage than something like a 2 or 3 volt solar panel, do
> I need a larger cap?

The FRED design will turn on at about 2.4 volts so no matter how high your
solar panel voltage is, it will never get there.

I used a calculator solar panel on my seaplane robot (See the FRED page
for a link to it).

hope this helps,

Ben



11937 Mon, 13 Mar 2000 04:43:23 -0500 Re: driving muscle wire Richard Piotter
> The thin, weak type is onlt 50 mA. Th larger stuff get's into larger
> current values in the hundreds.
>
> David Perry wrote:
> >
> > thanks for the encouragement :-) Personally i'd be happy with a 4
minute
> > stroll - could prove rather expensive though :-) I think its quite
> > possible - i think i'll use a a SE to save on weight (and batteries!)-
it
> > certainly won't be a fast moving critter though. Nitinol doesn't draw
too
> > much current (50ma) but it ain't too efficient. Should have all the
parts
> > tomorrow... See what happens. How was nitonol tricky for you?
> >
> > David
> >
> > ----- Original Message -----
> > From: "Jim Taylor"
> > To:
> > Sent: Monday, 13 March 2000 11:52
> > Subject: Re: driving muscle wire
> >
> > > ugh muscle wire......how I loved thee......I too tried to biuld a
super
> > > small walker using nitinol, some SMT parts, some really small lithium
> > > batterys, and some really thin music wire. I tried a 4 legger, a 6
> > legger,
> > > and a tilden worm. The 4 legger showed the most promise, and still
does
> > > looking back at my work. However Nitinol is very tricky stuff. You
mind
> > > as well be directly shorting the batterys. Not only do they draw alot
of
> > > current, but it doesn't transfer very well into torque. It seems
(even
> > with
> > > BORIS, and STIQUITO) no matter how small your driver, and control
board
> > is,
> > > you need alot of battery storage. Unless you like 4 minute strolls :)
> > >
> > > Don't want to discourge you though.....My mini 4 motor walker walks
fine
> > on
> > > a tether. However I don't think he will do any walking autonomously
> > >
> > >
> > > >
> > > >
> > > > > To drive a muscle wire you do not even need half of an h-bridge.
The
> > > > > second transisotr is used to provide a path for current flow. All
you
> > > > > would need is an NPN transistor with the muscle wire connected
between
> > > Vcc
> > > > > and the collector, the emitter connected to ground and the base
> > > connected
> > > > > to the input through a resistor. You will want the base resistor
small
> > > > > enough to drive the transistor into saturation and will probably
need
> > a
> > > > > resistor in series with the muscle wire to control current flow.
> > > > > I do not remember off the top of my head, but I think the 50
micron
> > > wire
> > > > > nominally needs a 100mA current. I do not remember the resistance
> > (ohms
> > > > > per unit length) off the top of my head. There are a couple sites
out
> > > > > there with properties on muscle wires (www.dynalloy.com does I am
> > sure).
> > > I
> > > > > would definitely reccomend checking them out because they give
other
> > > > > helpful hints on using the wires, especially about attaching them.
> > > > > I did a concept project a while back using muscle wires for an
> > > > > autonomous robot design class. From my experience, which is
anything
> > but
> > > > > all inclusive, I found that the technology is fun and promising
but
> > > still
> > > > > needs some work. You only get about a 5% deformation and the power
> > > > > required is still on the high side. I finally settled on a design
that
> > > > > used four muscle wires for movement of legs down and back (2
frames of
> > 3
> > > > > legs) and the reverse stroke was handled by a spring system to
save on
> > > > > power. I was using microprocessor control at the time, never got
> > around
> > > to
> > > > > trying it with BEAM control. If I find time one of these days, I
may
> > go
> > > > > back and finish that... I would be interested to hear what your
> > > experience
> > > > > with the wire is like. Best of luck.
> > > > >
> > > > > John Gonser
> > > > >
> > > > >
> > > > > On Tue, 14 Mar 2000, David Perry wrote:
> > > > >
> > > > > > Okay - haven't asked a question for a while....
> > > > > > Okay i'm making a robot, quite advanced, very, very tiny, purely
> > > because
> > > > i
> > > > > > had the idea for it and couldn't get it out of my head all day
and
> > > it'll
> > > > > > drive me mad if i don't build it.
> > > > > > The question is - what is the best way to drive muscle wire? You
> > would
> > > > only
> > > > > > use half a hbridge, (no need for switching wires) but i'm
thinking
> > > thats
> > > > > > a little too large. Perhaps a 7hc245 would suffice. I need to
drive
> > 6
> > > > > > pieces of 050 LT, any advice would be appreciated.Oh and why am
i
> > > using
> > > > > > muscle wire? - well i can't find 6x 4mm dia. gearmotors for
under
> > $31
> > > > > > :-)
> > > > > >
> > > > > > thanks,
> > > > > >
> > > > > > David
> > > > >
> > > >
> > > >
> > >
> > >
> > > James Taylor
> > > "Edgar The Hate Bug"
> > > URL: http://fly.to/springmeadows
> > > ICQ 14888587
> > >
> > >
>
> --
>
>
> Richard Piotter The Richfiles Robotics & TI web page:
> richfile@rconnect.com http://richfiles.calc.org
>
> -- Make Money by Simply Surfing the Net or responding to E-Mail!!!
> -- Click below!!!
>
> http://www.alladvantage.com/go.asp?refid=ATL147
> http://www.spedia.net/cgi-bin/dir/tz.cgi?run=show_svc&fl=8&vid=329630
>

Home