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Recharging Robot Fish

Discussion in 'Electronic Design' started by D from BC, Apr 21, 2007.

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  1. D from BC

    D from BC Guest

    Scientists form Essex University try out robot fish...

    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?
    No feeding
    No dead fish
    No filtering

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

    I got an idea for recharging the fish....
    When a fish 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
  2. MooseFET

    MooseFET Guest

    Bleach has a funny color. How about just adding a whole bunch of

    The fish could remain upright and the range that the power from the
    coils covers could allow the fish to get recharged just by hanging
    around in the bottom of the tank.

    If you use a "super cap" as the storage, the charging could be only
    partial. The fish could be designed so that they always try to swim
    upwards slightly. The amount of "up bubble" and swim speed PWM could
    be a couple of some simple random functions. A fish that randomly
    hangs about at the bottom for a while, would get a bigger charge. Its
    thrust would be higher so it would go up to the top of the tank and
    swim up there for a while. Others would make only short trips up from
    the bottom.
  3. D from BC

    D from BC Guest

    It's been awhile since I looked at bleach... :)
    Salt water sounds good... IIRC fungus, bacteria,bugs, snails and algae
    shouldn't survive in salted tap water.
    Fish corrosion risk??

    Nice idea, so.....
    The fish could just "chill out" with low activity near the bottom...
    It's not as entertaining but it's better than dead still on the
    bottom. (More funny if the programming put the fish upsidedown when
    Once charged, it can dart around until it has to "rest" again and
    cruise the bottom for charging... ( bottom feeders :) )

    I think I understand your other charge up idea..
    How it randomly charges determines how it swims.. Ex: A random deep
    dive (very close to the coils) will make a more active fish.
    D from BC
  4. Donald

    Donald Guest

    I don't think the charge connection would work well through water. Salt
    water even worse.

    Some experiments are in order.


  5. Lightning?

    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
  6. D from BC

    D from BC Guest

    Were you thinking of running a current through the water?

    I think recharging by induction might work.
    Power coils (perhaps water cooled by the aquarium) put out a
    recharging field for the fish.

    I've come up with another charging idea..
    A fish docking station.. :) Somehow the fish plug in, charge up and
    then swim away.
    D from BC

  7. And some fish drop to the bottom of the tank with a dead battery,
    while waiting their turn?

    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
  8. D from BC

    D from BC Guest

    Just like in nature ...Survival of the fitest. :)

    But let's say the fish have RFID technology too..
    Fish #1 can be ordered to dock..then fish 2 and so on..
    But there might be something fishy about that idea too.
    D from BC

  9. Fitest? I'd rather see survival of the "Fittest", or even "Fattest".

    How about an electric eel to recharge them? ;-)

    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
  10. D from BC

    D from BC Guest

    Damn..goofed that joke with bad spellling..
    Survival of the spellist... :)

    Electric eel....mmmm..then what charges the electric eel?

    Maybe solar powered robot fish might work..?
    D from BC

  11. Use a real eel. It'll keep the tourists from trying to steel your
    robots, too. ;-)

    During the day. What happens if they all fall into a pile in one
    corner while trying to get the last ray of sunlight?

    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
  12. D from BC

    D from BC Guest

    Aha! steal ...not steel... :p

    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
    But solar cells on fish would add weight, probably look ugly and
    there's not much area on top of a small robot fish..
    D from BC
  13. MooseFET

    MooseFET Guest

    This is my second try on saying this. It looks like google groups
    lost the other post. If you see another that makes the same points,
    you will know that google found the lost one. I will add a few new
    ideas in here.

    I was thinking that the randomness was in the PWM with no feedback.
    This means that a more charged battery automatically makes the fish
    faster and therefor on the average up.

    If the center of thrust is below the center of drag, the thrust will
    tilt the fish up and make it swim up. This increases the degree to
    which the charge on the battery makes the fish swim upwards.

    The whole swimming motion could be just one motor with a crank or
    cam. It could also be a pair of electromagnets. The body would be
    made of some flexible material so that just driving one point would
    create the curved shape of the fish motion.

    The coupling from the motor to the externals would be springy. This
    with the resistance of the water would reduce the peak to peak motion
    of the tail. To turn, the motor's power is pulsed off briefly as the
    tail hits one extreme.

    At the extremes the tail also bends so that it creates a down force,
    tipping the front up. Up down control is by pausing the power briefly
    at the extremes or the center point to either increase or decrease
    this effect.

    The light on the top of the tank can be pulsed so that the following
    works. I will explain it as though it is steady light but the
    sunlight may prevent this from working without the modulation.

    The fish can have 3 photodiodes. The two eyes each cover a 120 degree
    area that nearly overlaps. The third photodiode is hidden at the back
    of the mouth and only sees a narrow forward view.

    An improvement to this idea is to use 3 pairs of photodiodes with
    little masks over them so that a point light source switches between
    them as it moves across the field of view. This would give a better
    signal for the below.

    When the fish changes relative position WRT some object, this will
    cause the light falling on the eyes to vary. The more rapid the
    variation, the closer the object must be so the tail control will be
    commanded to swim away from whichever eye has the more rapid
    variations. I think a simple highpass filter and rectifier would
    serve as the measurement and a comparison would be the logic. There
    is no need for a linear control. There would be sort of a noise based
    PWMing happening on this control.

    Variations in the photocell signal in the mouth are used to raise the
    gain of the above process. Earlier I had suggested that it just made
    "right rudder" into "full right rudder". I think I can improve on
    this idea with this observation:

    The changes in the mouth's photocell will happen at the same time as
    whichever eye points more at the nearby object in front of the fish.
    Some nearby object behind the fish may cause the light on the other
    eye to vary at some other time. If the gain for the rectifier was
    raised when the change happened, this would bias things towards the
    fish avoiding objects in front. If the tails of the fish are made
    with the right sort of reflective and color properties, you can make
    the fish strongly avoid running into each other.

    Now if we make the various feedbacks have a high and very nonlinear
    gain with some memory in them, the result will be chaos. This would
    make the logic a lot simpler because the chaos would serve in place of
    the randomizer.

  14. I had to let you get even.

    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.

    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
  15. D from BC

    D from BC Guest

    Wow...Now there's a sample of how much thought is required for making
    a robot fish..
    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..

    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..'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..
    D from BC
  16. D from BC

    D from BC Guest

    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
  17. jasen

    jasen Guest

    water shouldn't be much of a problem, but salt water is packed with ions that
    are going to respond to the EM waves from the charger.

    deodorised kerosene might work better, but the hazmat issues may be a barrier.

  18. D from BC

    D from BC Guest

    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".
    It'll do low energy swimming, soak up some mag energy and then take
    off into action again once charged.

    D from BC

  19. If you use RF they will always be charging.

    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
  20. Use fuel cells and have the fish swim in ethanol?
    And snap for air like real fish?
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