So, as the name suggests, I've made a vehicle able to travel on land as well as water.
So, you might think whats innovative or difficult in making such a vehicle o_O
Garb two water-proof motors, a water propeller, wheels , microcontroller and there you have it...!
But, what if you have a very low budget.. and can't afford those high cost water-proof motors and propellers!Then you are in the right instructable pal.
So, my idea uses mostly cheap parts and you would be able to make your own Amphibious Vehicle within 500 Rupees(I guess it might be approximately 8-9$)
Above are the photos of the CAD models of the vehicle created in Solidworks .

Step 1: Material Needed

1) Two Motors ( I used these Plastic geared motors http://www.nex-robotics.com/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=536&category_id=13&option=com_virtuemart&Itemid=45 )
2) Nylon Rods or Aluminium Rods ( Aluminium preferably -- learnt it the hard way! I've used nylon rods, yeah they are quite light weight but are really difficult to machine whereas aluminium rods are light as well as easy to machine)
3) Acrylic sheet ( I used this, you may use any light weight material you want. I used this because i)Light weight ii)Can be easily cut into desired shapes iii)its transparent look looks good!)
4) Some wires(for motors)
5) Wheels
6) O-rings( Diameter of whose is around 1-1.5mm less than diameter of your motor shaft )
7) M-seal and Feviquick
8) If you are going to cut the acrylic sheet at home you might need a tool such as Glass cutter. Its very cheap. Costs around 15-20 Rupees. You can get this in any Hardware shop.
9) Two empty cans ( for buoyancy!)

Step 2: The Parts..!

So, the Photo above shows different parts you will have to make for your amphibian.
Looking at the CAD model Photos in further steps will make it more clear how each part has to be made.

Step 3: Motors

You need to open up your motor's casing and put in some grease which will provide lubrication as well as avoid water destroying your motor in case it gets in till there.
Solder long wires to the positive and negative terminals of your motors before hand.

Step 4: The Casing

The CAD model shows the casing for motors made in acrylic.
The dimensions and shape of this casing will vary according to the motors you use and the cuts and windows on its faces should be made according to the dimensions of your motor shaft and wire width.
The third photo shows the top view of how the motors and the shafts will be placed in the casing.
DON'T put in your motors in the casing yet, do all this in the end when you have all the parts to be made ready.

Step 5: Shaft

The photo shows the shaft which i made for my motors.
You might have to make different kind of shaft according to the desgn of your motors and wheels.
The wheels I used had a square hole. So, i came up with this design.

Step 6: Shaft Casing

This probably is the most important and difficult part of all.
This is the part which is going to protect the casing from water so, do take care while making it.
Time to grab those O-rings.
These rings are going to restrict any water letting in.
So, the casing will be made in 3 parts.(you will have to make two such casings)
The photos will show how you can make them.
After you prepare the casing put some grease on the inner surface of the casing .
This will lubricate as well as avoid water letting in.

Step 7: Construction

Put the two motors inside the casing and add the two shafts on it .(as shown in first photo)
Now put on the shaft casing and seal it with m-seal.

Step 8: Wheels

The wheels are quite easy to make.
Cut some rectangular pieces of acrylic as stick them as can be seen in the photos.
These rectangular pieces will help push water!!

Step 9: Storage Part

You can have a Storage part as shown where you can keep your battery, microcontroller,motor drivers, etc. !!
You can keep it open or closed as you wish.

Step 10: The Cans

Stick two cans as shown for buoyancy.
Stick the cans at a place such that they provide sufficient buoyancy to keep HALF of your wheels inside water(trial and error ;) )
N.B. vehicle wont run in water if entire wheel gets submerged in water( Simple Physics..!!)
PS if you want you can attach castor wheels for balancing the vehicle.