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Recharging Robot Fish

M

MooseFET

Jan 1, 1970
0
Wow...Now there's a sample of how much thought is required for making
a robot fish..

Actually, I was trying to say how much easier it would be than others
may suggest. I bet there are a dozen other ways to make them that
would be harder.
I was only thinking about an entertaining fish patrolling pattern in
the tank and achieving inductive charging...I haven't even considered
fin movement yet..

Well get moving on it. You need to get to market in time for the xmas
rush.
If I start now...I'll have swimming robot fish in say....4 years with
my spare time...
Or..I hire a bunch of engineers..maybe 1 year or less depending on how
much ping pong they play..

If you don't do it, all that spare time will just go to waste. :)
Heck..it's a fun job...anybody hiring for making robot fish??

It'll be great!
Robot fish for dentist offices and restaurants.
Kids will love it...Get the whole Finding Nemo collection!
Fake koi in Japanese fish ponds..
etc..

The only problem I see is someone else could take a computer monitor
and place it behind a skinny tank with water and air bubbles and get
much the same visual effect. The code for avoidance etc wouldn't be
all that hard to do.
 
M

MooseFET

Jan 1, 1970
0
Salt water can't that bad on alternating magnetic fields..
Say at f=20khz.

When the robot fish code detects low charge, the fish will change
routines and head toward the bottom within range of the induction
coils under the tank..Fish to coil distance maybe 1/2".

I think you can have a much greater range than that. At a few KHz,
the salt water won't have too much loss. You could use a non or less
ionic material to in place of the salt. If you used Fluorinert, the
fish could be a lot heavier but you wouldn't be able to sell the kit
for $29.95 on late night TV.

The limiting factor on the AC field strength is mostly the losses you
are willing to live with. Imagine the tank is on a stand that is
about as tall as the tank its self. If this stand is also the coil
assembly and contains a large core pointed vertically, the field
strength inside the tank could be quite high even at the half way up
point.

You need to design the electronics to make very good use of the energy
you have. Doing the tail motion seems to me to be the hardest part of
the whole design.
 
M

MooseFET

Jan 1, 1970
0
If you use RF they will always be charging.

How about using pure water and a metal plate above and below the tank.
The fish could be conductive on the top and bottom to pick up the
power. Thsi would let you go to a low enough frequency that the FCC
doesn't care. You would have a huge AC voltage between the plates but
They can be well defended against people touching them.
 
M

MooseFET

Jan 1, 1970
0
Salt water can't that bad on alternating magnetic fields..
Say at f=20khz.

IIRC, 1% salt water has a resistivity of 3 Ohm-Meters.
and Skindepth is about 500*sqrt(R/F)

Skindepth = 500*sqrt(3/20K) = 6M

If your tank is 1 meter tall, this reduces the field at the top by a
factor of
exp(1/6) = 1.18 in other words it is less than 20% reduction from
this.
 
D

D from BC

Jan 1, 1970
0
Use fuel cells and have the fish swim in ethanol?
And snap for air like real fish?

Wow! What an idea...
The fish convert the ethanol directly to electricity.
Maybe I might see fish like that someday in my lifetime..

Best to get fire insurance with that tank... :)
D from BC
 
D

D from BC

Jan 1, 1970
0
The only problem I see is someone else could take a computer monitor
and place it behind a skinny tank with water and air bubbles and get
much the same visual effect. The code for avoidance etc wouldn't be
all that hard to do.

Mmm...it's approx. $800CAD for a 24" LCD computer monitor...
A 24" monitor is about 22"x13". That would back-display a boring tank
size..
Big tanks will need larger LCD displays (arrays) costing more money..

Also, there's no true 3D view..

I think the robot fish still have a chance.
D from BC
 
D

D from BC

Jan 1, 1970
0
IIRC, 1% salt water has a resistivity of 3 Ohm-Meters.
and Skindepth is about 500*sqrt(R/F)

Skindepth = 500*sqrt(3/20K) = 6M

If your tank is 1 meter tall, this reduces the field at the top by a
factor of
exp(1/6) = 1.18 in other words it is less than 20% reduction from
this.

Salt water AC conductance?? I thought stuff like salt water
permeability and reluctance would be pop up.

Can an induction heater heat up salt water?
I think this is related to charging batteries by induction.
D from BC
 
E

ehsjr

Jan 1, 1970
0
D said:
D from BC wrote:
[snip]
The light source would be from the aquarium lighting so the fish are
active all the time.
But let's say that's not enough energy from small the solar cells.
Maybe a fix is to use intense UV light. I might dig for some data
sheets.
But solar cells on fish would add weight, probably look ugly and
there's not much area on top of a small robot fish..


Unless they are so small that they look like scales. ;-)

RF and a small signal diode array to rectify the RF to charge the
batteries. You could even let it jam their cell phones, if the RF could
be contained inside the building.



Could covering the aquarium with metal mesh fix that....
The same thing that's on microwave oven doors :)
It'll look crappy though...
D from BC

I think all you need to do is fit each fish with
a little tin-foil hat. :)

Ed
 
C

colin

Jan 1, 1970
0
D from BC said:
Scientists form Essex University try out robot fish...
http://video.google.com/videoplay?docid=7884104232255053336

Hey...this is inspiring... :)

How about robot fish aquarium as a tourist attraction?
Would you visit a tourist attraction aquarium with 100's of real fish
or 100's of robot fish?

How about robot fish for home use?
Benefits
No feeding
No dead fish
No filtering

Just charge up the fish..fill up the tank with Javex (whatever) and
presto...one maintenance free fish aquarium..

I got an idea for recharging the fish....
When a fish dies....it drops to the bottom...(like a true dead fish :)
)
The bottom has coils that put out a power field to recharge the fish..
Once the fish electronics sense complete charging, the fish takes off
and resumes it's swimming code.

But dead robot fish on the bottom don't look good..So how else to
charge the fish?
D from BC

ultrasonics ?

Colin =^.^=
 
M

Michael A. Terrell

Jan 1, 1970
0
ehsjr said:
D from BC wrote:
[snip]

The light source would be from the aquarium lighting so the fish are
active all the time.
But let's say that's not enough energy from small the solar cells.
Maybe a fix is to use intense UV light. I might dig for some data
sheets.
But solar cells on fish would add weight, probably look ugly and
there's not much area on top of a small robot fish..


Unless they are so small that they look like scales. ;-)

RF and a small signal diode array to rectify the RF to charge the
batteries. You could even let it jam their cell phones, if the RF could
be contained inside the building.



Could covering the aquarium with metal mesh fix that....
The same thing that's on microwave oven doors :)
It'll look crappy though...
D from BC

I think all you need to do is fit each fish with
a little tin-foil hat. :)


Why not do it to the tourists? Tell them its to keep the fish from
reading their minds. ;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
M

MooseFET

Jan 1, 1970
0
Salt water AC conductance?? I thought stuff like salt water
permeability and reluctance would be pop up.

I don't think anything but the resistivity of salt water will matter
to the losses at 20KHz for lowish power levels.
Can an induction heater heat up salt water?
It won't be very good at it but if you apply a big enough dB/dT you
will get some heating from the currents.
I think this is related to charging batteries by induction.
The question is the losses you get from the salt water. It looks like
they are small enough to allow inductive charging to work quite well.

I assume that the coil on the bottom of the tank will be resonated by
a capacitor in series with it. This means that the semiconductor
driving it won't have to handle very high voltages.
 
D

D from BC

Jan 1, 1970
0
I don't think anything but the resistivity of salt water will matter
to the losses at 20KHz for lowish power levels.

It won't be very good at it but if you apply a big enough dB/dT you
will get some heating from the currents.

The question is the losses you get from the salt water. It looks like
they are small enough to allow inductive charging to work quite well.

I assume that the coil on the bottom of the tank will be resonated by
a capacitor in series with it. This means that the semiconductor
driving it won't have to handle very high voltages.

Series resonance is a nice way to get high ac current for high
magnetic strength.
I'd have to read up on resonant switchers and linear power oscillators
again..

I might try a 20Khz smps supply circuit with a U core.
D from BC
 
D

D from BC

Jan 1, 1970
0
ultrasonics ?

Colin =^.^=

It'll be the Finding Nemo jewelry cleaner too :)

The nice thing about the EM method is that the charging coil is inside
the robot fish...
With ultrasonic, wouldn't the transducer(s) need to be on the outside
of the robot fish?
(The robot fish should look like a fish with scales.)
D from BC
 
C

colin

Jan 1, 1970
0
D from BC said:
It'll be the Finding Nemo jewelry cleaner too :)

The nice thing about the EM method is that the charging coil is inside
the robot fish...
With ultrasonic, wouldn't the transducer(s) need to be on the outside
of the robot fish?
(The robot fish should look like a fish with scales.)
D from BC

well you could make the outside of the fish transparent to the frequency
used I would imagine.
or make the scales individual tiny transducers. (mems)

or how about subsonic then ?
you could cyclicly pressurize the water and an air bladder in the fish would
expand etc.
this could power a small generator, maybe even a piezo,
or better still the expansion could cuase the fishtail to flex one way and
back
making the fish swim purly mechanicaly.

or how about a dc field ?
electric eels can create it so why not, or you could even have 3 layers of
fluid,
a conductive one to say mimic the air, a thin insulating indistinguishable
from either the top or bottom layer,
and the water below.
as the fish pokes its head through to the top layer - zap it gets instant
recharge.
make it so its naturaly boyant and has to swim down under power.

I thought normal radio waves werent too good under water - hence submarines
are a job to keep intouch with.
they have to use those fancy 1km long waves.

or maybe nuclear powered is the way togo ?

how much power are we talking about anyway ?

with your coils on the bottom, they could just swim close to the botom to
get recharged rather than 'die'.

Colin =^.^=
 
D

D from BC

Jan 1, 1970
0
well you could make the outside of the fish transparent to the frequency
used I would imagine.
or make the scales individual tiny transducers. (mems)

or how about subsonic then ?
you could cyclicly pressurize the water and an air bladder in the fish would
expand etc.
this could power a small generator, maybe even a piezo,
or better still the expansion could cuase the fishtail to flex one way and
back
making the fish swim purly mechanicaly.

or how about a dc field ?
electric eels can create it so why not, or you could even have 3 layers of
fluid,
a conductive one to say mimic the air, a thin insulating indistinguishable
from either the top or bottom layer,
and the water below.
as the fish pokes its head through to the top layer - zap it gets instant
recharge.
make it so its naturaly boyant and has to swim down under power.

I thought normal radio waves werent too good under water - hence submarines
are a job to keep intouch with.
they have to use those fancy 1km long waves.

or maybe nuclear powered is the way togo ?

how much power are we talking about anyway ?

with your coils on the bottom, they could just swim close to the botom to
get recharged rather than 'die'.

Colin =^.^=

Great ideas! Except for nuclear :(
I got a chuckle from the quasi -hydraulic solution. Modulate the water
pressure.. :)

I have no idea what the power consumption of the robot fish will be..
If I start now...I might know in about 3 years...
I'll do an archive search and do a post reply in 2010. :)


D from BC
 
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