Robot Fish Battery

[voyager2]

Hi all,
I have decided to make my own robot fish.
Bellow is a YouTube video of my inspiration.
http://www.youtube.com/watch?v=bVTpINHJeaY&feature=PlayList&p=B82E7D0174883419&playnext_from=PL&index=5#wsSmall robot fish powered by solid polymer fuel cell : DigInfo
And here is the URL

Code: [Select]

http://www.youtube.com/watch?v=bVTpINHJeaY&feature=PlayList&p=B82E7D0174883419&playnext_from=PL&index=5I have everything worked out except the battery and how to protect the ATMega8 chip from magnetic-radiation.
My first thought was lead, to protect the chip then i ran out of ideas.
For the battery i though of Li-Ions or 10F super capacitors (available from Little Bird Electronics)

[Razor Concepts]

The mega8 should not be affected by magnetic radiation - i have swiped neodymium magnets right over these chips with no effect.

[voyager2]

Thanks, now just the battery...

[Joker94]

a couple of 3v coin batteries should suffice like the following ones (just as an example)

http://en.wikipedia.org/wiki/Button_cell

they are really small so it should not take alot of weight or room. i havent used them personally but i have seen them used in micro swarm bots. Google micro bots and you might find some useful stuff (i say this as i gather you want the electronics to be pretty small).

[voyager2]

The Electronics are based on the $50 robot with an additional two transistors to drive the tail.
I am using TIP 31B/C Power Transistor NPN, will these suffice?
http://www.dse.com.au/cgi-bin/dse.storefront/4c0e3cac02febe38273fc0a87e01067e/Product/View/Z2020

Thanks for all the help so far, Stay Tuned!

[waltr]

Just an FYI on :

I have everything worked out except the battery and how to protect the ATMega8 chip from magnetic-radiation.
My first thought was lead, to protect the chip then i ran out of ideas.

Lead will do nothing to a magnetic field. Lead is good to block nuclear radiation however.

To shield something from a magnetic field one needs to use a material that has a high magnetic permeability such as Iron and some other materials. and the shielding material shape needs to be carefully designed.

But as Razor said, "The mega8 should not be affected by magnetic radiation" ans so it is not needed.

[Soeren]

Hi,

For batteries, you might wanna consider Zinc/air (if you have enough air abord for the runtime).
Else, Lithium cells in some form would be the sensible choice.

[voyager2]

For batteries, you might wanna consider Zinc/air (if you have enough air abord for the runtime).
Else, Lithium cells in some form would be the sensible choice.

Hi Soeren, I thought of Li-Ions but I remembered Admin's battery tutorial.
"Lithium forms large quantities of hydrogen when put in contact with water."
I an more concerned with the battery exploding than frying my electronics!
I'll consider sealing it with silicone-rubber. 

[Admin]

I'd recommend just using a NiMH battery.

If you really really need high current, use LiFe. Its like a Lipo, but without the thermal runaway issue and half the mAh.

[Soeren]

Hi,

Hi Soeren, I thought of Li-Ions but I remembered Admin's battery tutorial.
"Lithium forms large quantities of hydrogen when put in contact with water."
I an more concerned with the battery exploding than frying my electronics!
I'll consider sealing it with silicone-rubber. 

What do you think happen to electronics in general when it gets wet?

A fish should be watertight (or else it would drown )

[voyager2]

...A fish should be watertight (or else it would drown )

 

...

Hi Soeren, I thought of Li-Ions but I remembered Admin's battery tutorial.
"Lithium forms large quantities of hydrogen when put in contact with water."
I an more concerned with the battery exploding than frying my electronics!
I'll consider sealing it with silicone-rubber. 

What do you think happen to electronics in general when it gets wet?...

I didn't mean the electronics, I got 10 free sample ATmega 168s from ATmel so their not a problem,
I meant the battery.

"Lithium forms large quantities of hydrogen when put in contact with water."
O.k. this did sort of sound concerning, but the battery is sealed anyway
If water gets in whos to say I don't make a model Hindenburg

[Razor Concepts]

Lipo cells are complegely sealed. You can drop one in water and it won't explode. Putting it in water is actially one method of disposing the battery. This is also why cell phones dont explode when dropped in water 

[Admin]

Lipo cells are complegely sealed. You can drop one in water and it won't explode. Putting it in water is actially one method of disposing the battery. This is also why cell phones dont explode when dropped in water 

Drop it in water and let the two battery leads short. Then say that

(assuming the Lipo doesn't have some form of built in short protection)

[Soeren]

Hi,

Lipo cells are complegely sealed. You can drop one in water and it won't explode. Putting it in water is actially one method of disposing the battery. This is also why cell phones dont explode when dropped in water 

Drop it in water and let the two battery leads short. Then say that

(assuming the Lipo doesn't have some form of built in short protection)

Why would that be any bit worse than doing it out of the water - sounds a bit reckless to me, whatever the ambient fabric.

[Admin]

ehhh I didn't explain myself properly . . . was implying that a water leak in the fish could result in the leads shorting . . . and as soon as the battery waterproofing melts off, thats when the fun starts

[Soeren]

Hi,

[...] was implying that a water leak in the fish could result in the leads shorting . . .

Shorting? You must have very very very low impedance water in your end of the world

As I didn't see any "Folks, don't try this at home", I'll see if I can find a suitable "fish size" LiI-on, when I get past my home some time this week.  This needs some hard evidence - Would a salinity of 40g/l (sea water is around 35g/l) be OK, or were you referring to The Dead Sea? 


Lots of young people carry their Li-Ion driven cell phones in their trouser pockets, which means they are often very steamy inside (i.e. an RH of around 99%) during the summer. I have seen plenty of gold plated PCB's with the copper oxidizing through the gold at every trace edge, from sweat that is slightly less saline than sea water - I haven't heard of any spontaneous combustions though.

Too bad I gave up having an aquarium - that would have been the ultimate test lab, with bright colored cat food swimming around the potential nuke 
Well, I'll see what setup I can come up with.

[voyager2]

Too bad I gave up having an aquarium - that would have been the ultimate test lab, with bright colored cat food swimming around the potential nuke 
Well, I'll see what setup I can come up with.

I still have my fish tank, with one googly eye Goldfish(called Google),  and he's survived for nearly 1 year.
Thanks to my expert care and my second favourite website, kokosgoldfish.com he should survive another year!

[Soeren]

Hi,

I still have my fish tank, with one googly eye Goldfish(called Google), 

So, it wouldn't be rude to tell you to "go fish" if you need info? 

[Admin]

This needs some hard evidence - Would a salinity of 40g/l (sea water is around 35g/l) be OK

Please film it! Have the leads right next to each other, of course . . . Various websites listed sea-water resistance from 0.5 ohms to 200 ohms. For a fully charged 7.2V LiPo at the lower end of resistance, you'd get a 15W short.

Lots of young people carry their Li-Ion driven cell phones in their trouser pockets, which means they are often very steamy inside (i.e. an RH of around 99%) during the summer.

If someones pants get *that* wet, he already has other problems

Actually, I saw one guy freak out in front of me and run to the bathroom, then came out a bit later saying the lead-acid AA batteries in his pocket somehow began leaking. He then went on to explain that it probably happened because its so hot in his pants . . . not sure what he meant by that . . .