Abstract:
Most mobile platforms or vehicles used in today are non holonomic. They only have one
or two independent degrees of freedom. Because of that its manuarability is limited and
often require much space to control like turning and parking. By improving degrees of
freedom (improving the manuarability) of a vehicle it can follow many complex
trajectories that are difficult or impossible by conventional non holonomic vehicles. Any
mobile platform that has three independent degrees of freedom in a plane is a Holonomic
platform. Independent degrees of freedom means it can change it orientation or position
with out effecting other not like car type vehicles that require turning or changing its
orientation when need to move.
Holonomic motion is very useful because its abilities such as. avoid any obstacle
while keeping its orientation same, capability to move in constrained spaces and track a
target while moving in an arbitrary trajectories etc. Because of these advantages and
capabilities some of the scientific and industrial researches are targeting to develop
holonomic mobile platforms. Already robotics community have managed to build some
working models and used in applications like robot soccer games and mobile robot
manipulations. And many different mechanisms have been created to achieve the
holonomic capability. These include various arrangements of Swedish wheels or omni
wheels, chains of spherical or cylindrical wheels, ball wheels and powered caster wheels
etc. While most of these designs are practical in indoor environments they are not
suitable for outdoor operations in large scale versions
In this research project our goal was to develop a viable design to achieve
holonomic capability that minimizes these problems and more suited for the outdoor
operations. The proposed design has a wheel arrangement much like a car but with the
capability of independent driving and steering capability of each of the four wheels. Car
type rolling and steering mechanism avoid any uneven wear of the wheels and avoid
lateral forces applied on the wheels. Wheel driving and steering mechanism was designed
such a way that wheels and be steered 360 degrees continuously with out interfering with
the wheel drive system. This enables robot to move in complex trajectories continuously
without stopping for wheel resetting. And the developed platform has increased ground
clearance that is necessary for outdoor rough terrain operations like farming.
Apart from all these benefits design comes with the requirement of complex
control system to control itself. Four independent wheels with eight degrees of freedoms
to achieve three degree of freedom motion is a redundant control problem and require
complex control system. Using inverse kinematics model of the platform and
multiprocessor design with advance microcontrollers we have tried to solve these issues
and were able to achieve successful performance.