The Archimedean Amphibian (ArchAm) is an manualy controlled all-terain submersible vehicle working on screw propulsion mechanism. This works best over water,snow,sand and other soft surfaces,although it can work as effectively over solid surfaces.It was sponsored as an SOE for Shasstra08 and was the first underwater SOE made.
Contents
[hide]
* 1 Purpose
* 2 Scope
* 3 Earlier Attempts
* 4 Systems
o 4.1 Propulsion
+ 4.1.1 Motor
+ 4.1.2 GearBox
+ 4.1.3 Conveyor Screws
+ 4.1.4 Gear-switching motor
o 4.2 Buoyance varying mechanism
+ 4.2.1 Air column
+ 4.2.2 Bellow
+ 4.2.3 Motor
o 4.3 Electronics and Control systems involved
+ 4.3.1 Control Circuitry
+ 4.3.2 Communication
# 4.3.2.1 ATMega 16 microcontroller
# 4.3.2.2 Multiplexer for Polarity change
# 4.3.2.3 H-Bridge
# 4.3.2.4 The Porgram
+ 4.3.3 Controller Program
# 4.3.3.1 The Controller Program
+ 4.3.4 Possible technical glitches
* 5 Team
o 5.1
* 6 Cost
o 6.1 Inventory list
* 7 See Also
o 7.1
* 8 External Links
[edit] Purpose
The main aim of the project Archimedean Amphibian was to develop a propulsion mechanism(screw propulsion) which can move over almost all terrain and also on and underwater.We looked forward to build a submersible multi-terrain amphibious vehicle on the principle of conveyor screw propulsion.
[edit] Scope
This technology cannot used commercially, but can find a large scope in fields such as military and surveillance.it can also be used to propel vehicles in inaccessible terrain such as snow, marsh, deserts etc.It can be used to traverse unexplored terrains where the nature of terrain in unknown
[edit] Earlier Attempts
Such a project has rarely been attempted around the world.One such vehicle was apparantly used by the Russian military, although very few information regarding it can be found.There also exit a toy marketed as Terrain Twister which works on a similar propulsion system.The British exploration team Ice Challenger used the same propulsion mechanism in their Snowbird 6 vehicle(a modified bombardier tracked craft) to traverse the ice floes in the Bering Strait.They claim it to be first landbased vehicle to successfully cross the frozen Bering Strait from America to Russia.In fiction, it is also the propulsion system for Metal Gear Solid 3's Shagohod.However no vehicle this propulsion system could be found which can go on terrains and on/underwater simultaneously.
[edit] Systems
The project can primarily be divided into three subsystems namely propulsion system,buoyance variation and controllling circuits
[edit] Propulsion
This system contains four sub-systems namely the motor, the gearbox, the conveyor screws and gear-changing motors.
The gear changing mechanism was actuated by powering the high torque motors. This made the gear box slide from one state to another. When the gear box was in the first state and the main motors were turned on the conveyor screws rotated with the same rpm and hence the same torque as the main motor. When the small high torque motors are actuated, the position of the gearbox is changed and now the conveyor screw rotates with a speed 4 times more than that of the driver motor. This mechanism was neccesary since high torque is required on land and high rpm is required in water.
[edit] Motor
The main motors used for the project were 2 TVS Lucas-5SW60 wiper motors. Each was a 12V DC motor. The motors provided a torque of 18N-m at 48rpm.
[edit] GearBox
The gearbox consists of an arrangement of gears which facilitates changing the rpm. The gearbox has two states, one which keeps the rpm same and another which increases it four times. The gear box was mounted on a slider mechanism taken out of a pronter and was free to move in one direction.
[edit] Conveyor Screws
These form the core of the propulsion system. These were made using tinned Aluminium sheets (Galvanase sheets) screwed to plastic pipes. Their dimensions were 50 cm long, 70 cm inner diameter, 95 cm outer diameter.
[edit] Gear-switching motor
Consists of two high torque, 30 rpm motors, each of which is fitted to a 10 cm bolt. The corresponding nut is attached to the gearbox itself. The motors themselves, along with the bolt were clamped firmly to the base.
[edit] Buoyance varying mechanism
Consists of three sub-systems, namely an air column, a bellow, and a motor. When the motor is actuated, the lower part of the air column moves with respect to the base. Hence, effectively, the bellow gets compressed or expanded.This changes the volume of air trapped in the column and hence the buoyancy of the vehicle. The surface area of our air coulmn was about .04 cubuc metres. About 5 cm of the bolt length was being used for buoyancy variation. Hence we were able to achieve a buoyancy variation of about 2 litres/2 kgs.
[edit] Air column
The main source of buoyancy on the vehicle is a sealed air colmn with a fixed upper side .
[edit] Bellow
The bellow is an extension of the air column and it effectively gives the air column a movable lower side. This lower side can be moved upwards or downwards with respect to the upper side which is rigidly attached to the base. This provides a way to vary the buoyancy which enables the vehicle to move in and out of water.
[edit] Motor
This is used to actuate the bellow or the lower face of the air column. A high torque, 10 rpm motor was used for this purpose. Such a low rpm was chosen so as to achieve neutral buoyancy underwater. This motor was attached to a 8 cm bolt. And its nut was rigidly attached to the base of the vehicle. The motor itself was rigidly fixed to the lower movable part.
[edit] Electronics and Control systems involved
The ArchAm control system consist of two parts :
* Control Circuitry
1. Communication(RS-232->TTL level converter and UART)
2. ATMega 16 microcontroller
3. Multiplexers for polarity change
4. H-bridge circuitry for driving motors
* Controller Program, running on a computer
[edit] Control Circuitry
[edit] Communication
For communication the RS-232 protocol was used (9600 baud, 2 stop bits, even parity). A level converter (MAX-232) was used to convert RS-232 levels to TTL levels. The outputs from the MAX232 were connected to the ATMega16’s UART thus allowing it to communicate with the computer. The program for the ATMega16 was written in C using Programmer’s Notepad and compiled using avr-gcc. It was burned into the microcontroller using AVRdude. Following is the source code for the program running in the micro:
[edit] ATMega 16 microcontroller
For controlling the gearbox, bellow and screw motors, the ATMega16 microcontroller was used. For controlling the speed of the screw motors, the micro’s internal PWM circuitry was used. For controlling the polarity of the screw motors pin A0 and A1 were used. For changing the polarity of the motors the state of the pins was reversed. The pins A0 and A1 were connected appropriately to the inputs of two multiplexers
[edit] Multiplexer for Polarity change
The inputs were connected to A0 and A1 of the microcontroller appropriately and the outputs of the multiplexer were connected to the PWM circuitry.
[edit] H-Bridge
Two 5A 24V H-bridges were fabricated and used for controlling screw motors. Two L293D motor drivers were used for controlling the bellow and gearbox motors.
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