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.