Voyager2's Robot Fish

[voyager2]

Hi All,
Firstly this topic is for you to see my robot fish.
It has not been built yet but when I do I'll post pictures here for you.
In the mean time I'll post the schematics, diagrams and development pictures.
This is my first pic ever uploaded to Photo-bucket.

I haven't drawn in wires or sensors, so the picture is not cluttered.
Its not quite scale for instance the battery is too small and the ATmega too big.
I've clearly labeled everything in block letters (including the volume of each segment!) so everyone understands it.

The servo controller is to power the electro-magnet.
Resistor R1 is for the LEDs while R2 fools the servo controller into thinking it's centered.

EDIT:Does any one know of a good (free)3D CAD?

[madsci1016]

EDIT:Does any one know of a good (free)3D CAD?

Google Sketch-up.


http://sketchup.google.com

[TK]

Have you tried eagle cad?  I know if you are a student and you go onto the autodesk website you can get autocad for free but that may be just for highschool students....

[voyager2]

Thanks I'll try sketch-up.
I'm in year 6 so money, parts and money again come at a premium!

[voyager2]

I'm adding to the robot fish "data base" the inspirational YouTube video that started it all
Small robot fish powered by solid polymer fuel cell : DigInfo
And here is another thead dedicated to the batery

[Razor Concepts]

What is the bridge rectifier for 

[voyager2]

What is the bridge rectifier for 

The Bridge Rectifier is part of the Voltage Regulation circuit, and makes sure the voltage going into the Electro-Magnet is DC and the right polarity.
It's not really necessary but it's worth showing how  to use them

[SmAsH]

Erm... Why wouldn't the voltage be dc in the first place?

[voyager2]

I understand what you mean SmAsH, in general it makes sure the voltage going to the IC and and coil controller is the correct polarity.

[SmAsH]

Why not use a diode?

[voyager2]

A rectifier is a group of 4 diodes.
If I use a diode it won't work at all if the battery is in the wrong way, but with a rectifier the battery can be attached with any polarity.
Besides I have only 1 diode but I have plenty of rectifiers, and I get extra marks for "exotic" components

EDIT: fixed typo

[voyager2]

Hi All,
Here is a list of the parts I'm going to use:
Battery http://www.sparkfun.com/commerce/product_info.php?products_id=8818

Microcontroller http://www.sparkfun.com/commerce/product_info.php?products_id=7957

"Signaling" LED's http://www.sparkfun.com/commerce/product_info.php?products_id=528

Magnets will be hand made.

Casing will be hand made.

Tail will be hand made.

Already have the rectifier.

Already have the regulator.

Oh and the coil controller is undecided as yet.

Next Post: Specs

[Razor Concepts]

Rectifier = two diodes in circuit, which means a 1.2 volt volage drop! Lots of wasted power there.

[GearMotion]

Besides I have only 1 diode but I have plenty of rectifiers, and I get extra marks for "exotic" components

Only in a University do you get credit for a wasteful expenditure. In industry you would lose your job at worst, or be told to quit wasting money at best.

[voyager2]

Ok I'll take the rectifier out.

Next post I'll have an updated diagram and a diagram of the tail mechanism

[waltr]

If there is a possibility of connecting power in reverse polarity then the bridge rectifier is not a bad idea. The Microchip PICDEM-2 board uses a bridge rectifier on the power input. This allows a wall wart PS with either + on the tip or the ring of the coax plug to be used.
In my designs for commercial products (research lab instruments) we try to design so that a user does damage the equipment if connect wrong. We always protect the power input from reverse polarity with either a series diode, if the circuit can accept the voltage drop, or a fuze and shunt diode. We consider this cheap protection.

[voyager2]

 

If there is a possibility of connecting power in reverse polarity then the bridge rectifier is not a bad idea. The Microchip PICDEM-2 board uses a bridge rectifier on the power input. This allows a wall wart PS with either + on the tip or the ring of the coax plug to be used.
In my designs for commercial products (research lab instruments) we try to design so that a user does damage the equipment if connect wrong. We always protect the power input from reverse polarity with either a series diode, if the circuit can accept the voltage drop, or a fuze and shunt diode. We consider this cheap protection.

That's what I thought too Waltr, until Razor Concepts reminded me of voltage drop.

Rectifier = two diodes in circuit, which means a 1.2 volt volage drop! Lots of wasted power there.

A rectifier has four diodes in a circuit.

...Only in a University do you get credit for a wasteful expenditure. In industry you would lose your job at worst, or be told to quit wasting money at best.

GearMotion, my teacher is obsessed with us using silicon chips in our projects so weget extra marks

[waltr]

Rectifier = two diodes in circuit, which means a 1.2 volt volage drop! Lots of wasted power there.
A rectifier has four diodes in a circuit.

Yes but only two are a the voltage path, one in the negative lead the other in the positive lead. The other two are reversed so do not conduct. Sounds like you don't truly understand the full-bridge rectifier so draw it out and trace the voltage paths.

For battery power curcuits a series diode isn't the best choice because of the voltage drop and waste power. That is where a series fuze and a shunt diode gives protection without power loss.

[GearMotion]

"GearMotion, my teacher is obsessed with us using silicon chips in our projects so we get extra marks"

I'm not stopping you from doing what you need to do to get extra marks. I just wanted to point out that teacher's are very often far removed from industry. Just wanted you to pause for a moment and learn that complexity for the sake of complexity only looks good in an academic setting.

If you can justify the bridge, great. It has the benefit that you mentioned. It also has the negatives that have been mentioned. You need to weigh them against each other.

[voyager2]

I'm sure getting a diode will be fine, theirs still some silicone in them (i think)
Low voltage loss (at least less than the rectifier), serves it's purpose well too.
If sparkfun comes out with 6 v button cells @ 400mAh I'll use a rectifier...

[Soeren]

Hi,

If sparkfun comes out with 6 v button cells @ 400mAh I'll use a rectifier...

Two lithium cells stacked should do.
The consideration as to either make it "lots of silicon" or efficient in an academic setting doesn't matter much.
If you go for the inefficient, you just go critical about it in your written report.

Apart from that, if you want efficiency, either use a MOSFET or better yet, a fuse and a diode to do the protection without any loss.
After all, you have to be seriously dumb to swap polarity when you install it, with the focus you've had on it, so you'll probably never have to replace the fuse.

If you wanna go fancy with silicon, a better way would be to make it actually serve some purpose - even a teacher should be able to see through silicon added just for the teachers sake and purposefull silicon - they're not stupid, just out of synch. with the real (electronics) world.

[voyager2]

Hi,

If sparkfun comes out with 6 v button cells @ 400mAh I'll use a rectifier...

Two lithium cells stacked should do.

Thats what I'm going to do, 6v @ 200mAh is going to be fine for me.

...Apart from that, if you want efficiency, either use a MOSFET or better yet, a fuse and a diode to do the protection without any loss.
After all, you have to be seriously dumb to swap polarity when you install it...

I see what you mean, but if your in a rush polarity is the least of you worry's.
I'll just use the diode method, I'm sure I can find one, somewhere.

[voyager2]

This is the sketch-up file!

[voyager2]

What material should I make the case out of?
I thought of milk carton plastic and Silicone-Rubber.
I don't have a Laser Cutter or Vacume Forming machine so my options are limited.

[voyager2]

I found this elrctro-magnetic actuator
Electro-Magnetic Actuator
Perfect!

[Razor Concepts]

That will not be strong enough to work underwater. Even in open air, that actuator cannot move unless it is moving forwards.

[voyager2]

Thanks for pointing that out Razor Concepts.
I never really know "g-cm" means

[voyager2]

Here's a few more pictures...


Demonstrating turning.


And the updated internals.

[voyager2]

Still waiting for the milk to run out...
I hope the pictures are clear.
I'm doing the paper template today, so I should have a fish-like case within a few days.
Just found out that the last tube of silicone-rubber was used for something else

[frostyg02uk]

This is a really ambitious and cool project!

Was looking at your original design and have been wondering what materials your use to make it sufficiently water proof and how the tail will move. Are you going to use micro controllers for that? I think the tail part is such a simple and efficient design, just points out further that nature has the best designs that can be transfered to robotics (insect design of 6 legs being more stable then 2). Really looking forward to seeing this project progress, best of luck!