2 Robot Drives

2.1.2    Motors Specifications

In our project the stepper motors provide the movement for the camera and three D.C motors for the movement of the vehicle. Stepper motors operate by producing motion in discrete steps and usually has permanent magnets on the rotor and coils on the stator. The changing magnetic field, due to the pulses supplied to different coils at different time, enables the motion of the rotor.

Motors come with extensive specifications. The meaning and purpose of some specifications obvious; below we written about the primary specifications of motors:

2.1.2.1 OPERATING VOLTAGE

All motors are rated by their operating voltage. Most motors can be operates satisfactorily at voltages lower than those specified, but it may not be as powerful as it could be, and it will run slower. Similarly, when it operates at voltage higher than those specified.

2.1.2.2 CURRENT DRAW

Current draw is more important when the specification describes motor loading. The current draw of a free running motor can be quite low .With most permanent magnet motors, current draw increases with load. If the system is designed to handle the stall current (short circuit current) it can handle anything.

2.1.2.3 SPEED

Most continuous DC motors have a normal operating speed of 4000 to 7000 rpm. However, some special purpose motors, such as those used in tape recording and computer disk drivers, operate a slow as 2000 to 3000 rpm. For just about all robotic applications, these speeds are much too high. This high speed is reduced to no more than 150 rpm by using a gear train. The speed of stepping motors is not rated in rpm but in steps (or pulses) per second. The speed of a stepper motor is a function of the number of steps that are required to make one full revolution plus the number of steps applied to the motor each second.

2.1.2.4 TORQUE

Torque is the force the motor exerts upon its load. The output torque and power from a stepper motor are functions of the motor size, motor heat sinking, working duty cycle, motor winding, and the type of driver used.

2.1.2.5 POWER

The power delivered by a motor is the product of its speed and the torque at which the speed is applied. The power of the stepper motor is a function of both the increased over-all pull-out torque and the increased stepping frequency range.

2.1.2.6    GEARS REDUCTION

The motor shaft is fitted with a gear of small radius that meshes with a gear of large radius. Depending on the mass of the robot and the performance desired, different gear ratios might be appropriate. Experimentation is probably the best way to choose the best gear train.

The DC motors that we use it in our design are already having a gear reduction box built onto the motor. When selecting gear motor, we interested in the output speed of the gearbox, not the actual running speed of the motor. Note as well that the running and stall torque of the motor will be greatly increased.

2 Robot Drives

2.1 Introduction

How to move camera?

The camera rotates to view the status of environment in front of the robot which needs a high resolution of movement.

So we use the stepper motor to achieve this requirement.

How to drive and steer the robot?

The crawler type is drived and steered by two D.C motors. When the two D.C motors rotate at the same direction for example (CW), the robot will go forward. When the two D.C motors rotate at different directions (CCW), the robot will go backward. When the left D.C motor rotate in direction clockwise (CW) and the right one on counterclockwise direction (CCW), the robot will rotate to right. When the left D.C motor rotate (CCW) and the right one on (CW), the robot will rotate left.

2.1.1 Choosing the motors

At first step, we choose what type of motors to be used. Stepper motors are motors whose rotation can be controlled with a high precision. However, they require a pretty complex controller. DC motors are the most simple to control; it dominates the field of robot, either mobile or stationary.

D.C is used as the main power source for operating the onboard electronics, and for running the motors. Few robots use motors designed to operate from A.C, even those automations used in factories.

1.2 Mechanical system specification

1.2.1 Principles of moving mechanism

There are three types of moving mechanisms; wheeled type, crawler type and legged type.

The wheeled type is the most common, but cannot overstep an obstacle larger than it's wheel diameter.

The legged type has stability difficulties and cannot be easily applied to high speed robots.

The crawler type can travel even on rough surfaces or slippery surfaces like snow and stairs with a good stability, and good speed. However, the conventional crawler type sometimes falls down when negotiating high steps on stairs or curbs. In the past, one proposed type had four crawler units, and by swinging each unit as was necessary to maintain position, it adapted to the road surfaces, the new variable shape crawler robots can move around easily without problems. Tracks turn by skidding or slipping with excellent traction, and they are best used on surfaces such as dirt that allow low-friction steering. Rubbers for the belt are common choice for medium crawler robot sizes; it's providing adequate grip for most kinds of surfaces.

Figure 1.2 The mechanical design

1.2.2 Crawler shape control

 

As shown in figure (1.3) below, driver wheels and free running wheels are mounted on both sides of the car body as part of the crawler unit supported with arms and composed of planet wheels with (Rp). By moving these planet wheels, we adapt driving to overstep the road obstacles.

Figure 1.3  Mechanical system parts

Crawler shape is altered by changing planet wheel position; the main arms which carry the planet wheels rotate around the center point between the driver wheels and free running wheels.

1.2.3 Robot body material

The main structure of our robot is made of aluminums. We choose aluminum in our design due to appearance, low weight, low cost, resistance to corrosion, availability, and so on. Onto the frame of the robot mounted motors, batteries, electronic circuit board, and other necessary components.

 

 

1.1 A Tele - Operated Robot

A tele-operated robot is one that is commanded by a human and operated by remote control. The typical tele-operated robot uses a video camera that serves as the eyes for the human operator. From some distance-perhaps as near as a few meters to as distance as several million meters the operator views the scene of interest and command the robot accordingly. Figure (1.1) shows the system component and relation between the system parts:

Figure 1.1 – block diagram show the communication between the robot and the PC.

This mobile robot can be used in security, in exploration and in other applications, to transmit picture from unstructured environment. Can be changed the work properties of his robot depending on environment that the robot will be working in. Also, a manipulator can be mounted on robot base for executing special purpose which is difficult to be done by human being.

Introduction

when we decided to make our graduated project,we thout in this way:

Since 1980, the robot has established itself in manufacturing. Now new demands for robots are spreading to other industrial fields like the construction, transportation, medical, military, and other fields.

The purpose of our project was to design a mobile robot that can overcome the terrain roughness, climb, stairs, run over trenches, … etc.

A crawler moving design was choosed for this purpose.

The movement of our robot is controlled by three D.C motors, the movement of camera is controlled by a stepper motor, and the overall system is controlled by the PIC microcontroller. RF link was used for the wireless communication between the robot and the PC. Depending on the command sent to the robot from PC, either the robot moves, or the camera moves. Image is transmitted back to the TV adapter card of a PC through the video sender unit of the wireless camera.

Our mobile robot equipped with camera mounted on top to transmit an image of environment in front of the robot.

 
This image will be received on a PC using wireless communication. An image is required to provide the required information about the environment to the operator controlling the robot movement.

Our Robot is called A Tele - Operated Robot.