Whegs Transformer[Robotics Club]

Project By:

Aman Kumar 12085 amanku@iitk.ac.in

Nikhil Kurele 12445 nkurele@iitk.ac.in

Sandeep Maharia 12613 sndpmhr@iitk.ac.in

Pranshul Jain 12501 prajain@iitk.ac.in

Ravi Ranjan 12569 raviran@iitk.ac.in

Whegs Transformer 1

Abstract

Introduction

Objectives

Mechanical Design

Wheel Assembly

Clutch Mechanism

Leg Wheel Switching

Mechanical Components

Electronics

Electrical Components

Wireless Communication

Whegs Transformer 2

This abstract covers mechanical design, integration, and performance evaluation of a novel

four-leg/four-wheel transformable mobile robot . In contrast to most hybrid platforms that have

separate mechanisms and actuators for wheels and legs, this robot is implemented with a unique

transformation mechanism that directly switches the morphology of the driving mechanism

between the wheels (i.e. a full circle) and 2 degrees of freedom leg (i.e. combining two half circles

as a leg), so that the same system of actuation power can be efficiently utilized in both wheeled

and legged modes. The design process, Mechatronics, software infrastructure, behavioral

development, and leg–wheel dynamic characteristics are described. The performance of the robot

is evaluated in various scenarios, including driving and turning in wheeled mode, driving, irregular

terrain passing, and stair climbing in legged mode. The electronics used for transformation of

wheel to leg, and communication via X-BEE provides better controlling for a set of motion is also

discussed.

Whegs Transformer 3

LEGS and WHEELS are two widely adopted methodologies utilized by ground locomotion

platforms. After a long evolution, legs appeared on most ground animals, and these agile and

robust legs became capable of allowing animals to move smoothly and rapidly over uneven terrain.

Thus, a leg–wheel hybrid platform with great mobility on both flat ground (via wheel mode) and

rough terrain (leg mode) seems to be an adequate combination of wheel leg for flat rough

environments.

Wheeled locomotion and legged locomotion have significantly different characteristics. In

the former, interaction with the ground is smooth and continuous. In contrast, legged locomotion is

generally varying and intermittent. In contrast to most of the hybrid robots that extend the original

leg and wheel functions in a mixed manner, our paper tries to maintain the original advantages of

legs and wheels by incorporating both the functions in one robot. Furthermore, by utilizing the

same power source and transmission system, this platform provides an unusual opportunity to

explore the output variation with the same inputs.

The prototype of robot must to traverse rough terrain comfortably by switching the mode

(leg or wheel) according to environment demands.

The prototype must be able to climb stairs making it a multi utility vehicle.

The prototype must be controlled wirelessly via X_BEE with range around 30 m.

Whegs Transformer 4

Wheel Assembly:

Specifications:

Outer Diameter 15 cm

Inner Diameter 13 cm

Width 2 cm

Material Nylon

Spoke provides linear motion to wheel with the help of rack and pinion.

Housing (in which spoke moves linearly) is connected to a Pipe (OD-20mm,ID-

16mm,Length-70mm) through a coupler.

On that pipe two bearings (OD-42mm, ID-20mm, width) and one gear (provides

rotational motion via another gear connected to a motor) are mounted.

To provide linear motion to the wheel two bearings (OD-16mm, ID-5mm) are inserted

with a rod(dia-5mm, length-13cm) connected to a pinion(in contact with rack attached

on spoke).

Whegs Transformer 5

Clutch Mechanism:

During motion in leg mode pinion’s shaft and the main shaft moves with different angular

speed which causes dislocation of housing further leads to locking of wheel. So as to avoid this,

clutch is used which prevents this by engaging or disengaging both the shafts( one which rotates

the wheel and other which helps in linear motion of spoke).

Whegs Transformer 6

Leg-Wheel Switching:

Switching between wheeled and legged modes of this transformable mobile robot is

achieved by the transformation mechanism that includes a 2-DOF driving mechanism and a leg–

wheel switching mechanism.

The two half rims are joined through hinges(1cm) in which only one of the rim is attached

with spoke with the help of clamp and other is free to move about its diametric axis.

The switching between one full-circle rim (wheel mode) to two half-circle rims (leg mode)

is driven by a micro RC servo motor installed on the one half of wheel.

One half-circle rim is mounted in the spoke directly, and the other one is mounted on the

rotating horn on top of the RC servo.

The 180◦ rotational motion of the RC servo swings the half-circle rim next to the other

half-circle rim (leg mode) or away from the latter (wheel mode).

All the four micro servos mounted on each wheel will not directly powered by wires because if we

directly connect the servo with wire all the wire will wrapped around the wheel during motion leads

to the failure of project. So power will be supplied with the help of copper brush.

→Note- Before converting wheel into leg all the spoke should be in vertical position to shift the

center of wheel to the diametric opposite end of leg….

Whegs Transformer 7

Mechanical Components:

1. Aluminium Sheet

2. Nylon Sheet:

3. Bearings

(I) ID-20mm; OD-42mm

Quantity: - 8 (2 For each wheel Assembly)

Use :- driving motion of the wheel

(II) ID-5mm; OD-16mm

Quantity: - 8 (2 For each wheel Assembly)

Use: - rotation of shaft (Linear Motion of Wheel)

(III) ID-12mm; OD-24mm

Quantity: - 4 (2 For each clutch)

Use: - rotation of clutch Shaft

Whegs Transformer 8

4. Gears:

All the Gears used in the bot have module 1.5 mm and cutted from a 6 mm Aluminium

sheet.

Number of teeth of gear depends upon the distance between the centre of the two

constrained gears and also the required angular velocity for respective motion.

Total of 32 gears are used in Bot.

Whegs Transformer 9

Electronic Circuit

1. Arduino Mega

Arduino is an open-source electronics prototyping

platform based on flexible, easy-to-use hardware

and software. It's intended for artists, designers,

hobbyists, and anyone interested in creating

interactive objects or environments. The hardware

consists of a simple open hardware design for the

Arduino board with an Atmel AVR processor and

on-board input/output support. The software consists of a standard programming language

compiler and the boot loader that runs on the board.

The microcontroller on the board is programmed using the Arduino programming language (based

on Wiring) and the Arduino development environment (based on Processing).

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Application in the Project:

Arduino Mega is generally used for controlling the motors i.e. DC Motors & Servo

Motors.

Example: Bot needs the specific angle rotation of servo motors which is done by Arduino.

2. Servo Motors

A servo motor is a rotary actuator that allows for precise control of angular position. It consists of a motor coupled to a sensor for position feedback, through a reduction gearbox. It also

requires a relatively sophisticated controller, often a dedicated module designed specifically for

use with servomotors. The motor is paired with some type of encoder to provide position and

speed feedback. In the simplest case, only the position is measured. The measured position of the

output is compared to the command position, the external input to the controller. If the output

position differs from that required, an error signal is generated which then causes the motor to

rotate in either direction, as needed to bring the output shaft to the appropriate position. As the

positions approach, the error signal reduces to zero and the motor stops.

→Note- Servo Motors require 6 volts so we are using 7806 for each servo to convert 12 volts into

6 volts…

Application in the Project:

Hobby servos mounted on a wheel are used for transforming wheels to legs.

These servos are not directly powered through wires since wires would roll

in main shaft and will stop the complete motion of bot. So we are using

brushes of copper to power the servo.

Use for shifting the clutch. One clutch requires one motor.

Whegs Transformer 11

3. DC Motors

A DC motor is a mechanically commutated electric motor powered

from direct current (DC). The stator is stationary in space by

definition and therefore its current. The current in the rotor is

switched by the commutator to also be stationary in space. This is

how the relative angle between the stator and rotor magnetic flux is

maintained near 90 degrees, which generates the maximum torque.

Application in the Project:

These motors are used in Bot so that it can successfully traverse rough terrains and slightly

steep obstacles depending upon the gradient of the surface.

100 rpm dc motors are used for driving motion and 10 rpm high torque dc motor used for

increase ground clearance of bot in legged mode.

4. Relay Drivers

Relays are components which allow a low-power circuit to

switch a relatively high current on and off, or to control

signals that must be electrically isolated from the controlling

circuit itself.

Application in the Project:

Since Arduino provides very less amount of current not sufficient for a DC motor, So we

are using Relay Drivers which controls two motors at a time and provides high current to a motor

as it is given power directly through Battery and signals from Arduino.

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5. Battery

Lipo (Lithium polymer) Battery is used in the project. This

battery is small in size helps in reducing the weight of Bot

and provides 5.500 amp current and a voltage of 12.5volts

which is sufficient for DC motor and for servo motor use of

7806 helps further.

Zigbee

Zigbee is a specification for a suite of high level

communication protocols using small, low- power digital

radios based on an IEEE 802 standard for personal area

networks. Zigbee is targeted at applications that require a

low data rate, long battery life, and secure networking.

Zigbee has a defined rate of 250kbit/s, best suited for

periodic or intermittent data or a single signal transmission

from a sensor or input device. Applications include wireless light switches, electrical meters with

in- home-displays, traffic management systems, and other consumer and industrial equipment that

requires short-range wireless transfer of data at relatively low rates.

Application in the Project:

The Zigbees will be used for wireless communication between the mobile robot WHEGS

and Laptop. The zigbee mount on bot transmits the data and Zigbee connected to pc act as a

receiver.

Since Zigbee works on 5 volts so we are using 7805 to convert 12 volts to 5 volts.

Whegs Transformer 13

Wiki Page:

http://students.iitk.ac.in/projects/roboticsclub/leg_wheel_transformer