OVERVIEW
A customized autonomous robot with the ability of exact localization in an unknown environment.
In this project , we aim to demonstrate the possibility of using IR wheel encoders and communicating with Robot Operating System(ROS) for location finding. An autonomous ground
vehicle must be able to locate the exact co-ordinates and navigate to it without having prior
knowledge of the environment. Considering the starting point as reference and navigating through the
path and detecting the final co-ordinates of the mobile robot.
HARDWARE USED
DC-DC step down voltage converter.
2 DC Johnson motors of 100 RPM were used for locomotion. Motor speed is varied using PWM (Pulse Width Modulation)
Using this, we can drive 2 DC motors. Basic concept is amplifying low-current control signal.
These are used to report back the change in position hence reporting the number of revolutions each wheel has made.
This is basically the brain of the bot communicating with motor driver, wheel encoders.
SOFTWARE USED
Remotely accessing raspberry pi zero w.
ROS is an advanced platform for message
passing. It consists
of publishers and subscribers for many to many communication.
MATHEMATICAL FORMULATION
Suppose that at sampling interval I the left and right wheel encoders show a pulse increment of NL and NR respectively. Suppose further that
C = π*D/n*Ce
where
C – Conversion factor that translates encoder pulses into linear wheel displacement.
D – Nominal wheel diameter (in mm).
n – Gear ratio of the reduction gear between the motor (where the encoder is attached) and the drive wheel.
Ce – Encoder resolution (in pulses per revolution).
We can compute the incremental travel distance for the left and right wheel UL,I and UR,I according to :
UL/R,I = CNL/R,I
and the incremental linear displacement of the robot’s center-point, J according to
J = ( UL,I + UR,I )/2
Next, we compute the robot’s incremental change of orientation
Ø = ( UR,I – UL,I )/b
where b is the wheelbase of the vehicle, ideally measured as the distance between the two contact points between the wheels and the floor.
The robot’s new relative orientation ØI can be computed from
ØI = ØI-1 + Ø
and the relative position of the center-point is
XI = XI-1 + JcosØI
YI = YI-1 + JsinØI
where
XI, YI – relative position of the robot’s center-point at instant I.
You can check out our code from this GitHub Repository
For a live demo of our project, you can refer this video:
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