AMPHIBIAN BOT

INTRODUCTION

An Amphibian Bot represents an amphibious robot which has the following features:

• A robot which is viable on land as well as on (or

under) water.

• A robot which uses the principle of buoyancy to vary

its depth while in water.

WHY AMPHIBIOUS?

• An amphibious robot, apart from being very

attractive and challenging, has a very broad

application and can be useful in complex working

environment.

• It can even be made to walk on rough ground,

maneuver underwater and pass through transitional

terrain such as sand and mud, simultaneously.

• Amphibious legged robots can be useful in many

search, rescue, and recovery tasks.

• It also enables non-intrusive environmental

monitoring.

BASIC IDEA

• Animals are able to exploit large degrees of freedom

in their limbs to efficiently generate thrust without

the need to take their limbs out of water during

swimming.

• Replicating this in an amphibious robot requires a

large number of motors, which adds to the robot s complexity and cost. So this idea is not used in robots.

• Instead, to prevent the cancelling of the thrust force,

robots take their limbs out of water during the

portion of swimming stroke when the limbs are not

pushing the water back. Limbs are reinserted into the

water to push the water back, which creates a large

splash.

BUOYANCY

Definition: Buoyancy is the upward force exerted by the

fluid on a body that is immersed.

Buoyant force: When an object displaces water, the

water surrounding it has the tendency to try to fill in the

space the object now occupies. The water pushes

against the object, exerting pressure and force on it.

Positive, Neutral, and Negative Buoyancy: A submerged

object like a ROV will float or sink depending upon the

net effect of the weight of the object and the buoyant

force generated by the object.

Three possible conditions for the object:

1. Positive buoyancy: Buoyant force > Weight => object

floats

2. Neutral buoyancy: Buoyant force = Weight => object

neitherfloats nor sinks

3. Negative buoyancy: Buoyant force < Weight =>

object sinks

Center of Buoyancy: The shape of the displaced water is

exactly the same as the shape of the vehicle. The Center

of Buoyancy (CoB) is located at the Center of

Gravity(CoG) of the volume of displaced water.

Why Things Tip or Flip Over in Water: When the object is

completely submerged in water, if CoB lies below CoG, it

creates an unstable equilibrium i.e. a slight tilt leads to

tipping/flipping of the object. To avoid that, design

should be such that its CoG lies above its CoB (which can

be done by making the object denser in the bottom than

at the top) so as to avoid tipping/flipping.

Although, if the object is partially submerged, itmay

remain stable even if the CoG is above the CoB; provided

that when disturbed from the equilibrium position, the

CoB moves further to the same side that the CoG moves,

thus providing a positive righting moment.

WATERPROOFING

One of the major issues which occur with amphibian bots

is percolation of water due to which short circuiting can

occur.

• Liquid silicone rubber, commonly known as Liquid

Rubber, can be used to provide an efficient

waterproofing. It employs a new, impenetrable,

rubber technology and is used for waterproofing

many electronic devices.

• Waterproof servos and ESC (electronic speed control)

can also be used. They are highly useful.

More alternatives: Following waterproof gels can also be

used:

• RTV silicone gel

• Aquarium Sealant Silicone

• Marine epoxy white paste

Rust proofing: Rust-proof gels and sprays can be used.

SEALING

• The biggest glitch faced in building an amphibious

robot is sealing it, because bot swims in water which

can cause short circuiting due to the water

percolating inside the bot.

How sealing is done?

• Chassis of carbon fiber material can be used.

• Silicon sealant can be applied on the edges from

outside.

• PVC can also be used for the material of body.

• The holes can be filled with bondtite.

An example of sealing- SUGRU

• The Sugru handles as any other modeling clay and

you have 30min to one hour to get the shape right.

With Polymorph its hot wet and you have to work

fast.

• The Sugru comes in many bright colors and you can

blend it to any shade by combining colors. Polymorph can be colored, but it s a pain and you can t really get the color your after..

• The Sugru bonds to almost anything. Polymorph

bonds to almost nothing.

• The Sugru when cured has a rubbery and flex to it,

Polymorph is hard and glossy.

• As the Sugru is softer to work with and will fill gaps

and give you more detail imprints than Polymorph.

AMPHIBIOUS LOCOMOTION:

• Amphibious robot relies mainly on walking and

swimming.

• A unique combination of propeller and legs can be

used.

Legs can be designed in a way that they can be used as

wheels when on land and as fins when in water.

PROPELLER

A propeller is a type of fan that transmits power by

converting rotational motion into thrust. A pressure

difference is produced between the forward and rear

surfaces of the airfoil-shaped blade, and a fluid (such as air

or water) is accelerated behind the blade.

Propeller dynamics can be modeled by both Bernoulli's

principle and Newton's third law. A marine propeller is

sometimes colloquially known as a screw propeller or

screw.

Controllable pitch propeller-

One kind

UNDERWATER LOCOMOTION

• Underwater locomotion is achieved by taking the

robot inside water using a central propeller.

• This uses the principle of conservation of angular

momentum.

GYROSCOPE

PROPULSION MECHANISMS FOR VARIOUS

AMPHIBIOUS ROBOTS

HOW TO DESIGN?

• The effort should be to minimize as much as possible,

the splashing of water during its motion.

• This would help reducing the inefficiency in

swimming and minimize the disturbance created in

the environment.

• Take an example of a turtle, which is able to both

walk and swim. Its legs are designed to include

passive compliant components, which act as one-way

valves to control water flow and allow the robot to

keep its legs in the water while swimming.

• This leads to splash-free swimming without

increasing the robot cost.

CONTROLLING OF AMPHIBIOUS ROBOT

• Controlling for such a bot is quite difficult, because of

a high level of attenuation is encountered in

controlling them.

• That s why wire-controlled bots are preferred over

wireless ones in the case of underwater bots.

• But still low-frequency transmitters can reduce the

problem, and hence are a better option.