1. Robot design-- Four legged walking robot Instructors: Dr. A
Robot design-- Four legged walking robot Instructors:   Dr. A. Antonio Arroyo Dr. Eric M. Schwartz TAs:  Josh Weaver Devin Hughes Andy Gray
Shaojie Ge

2. Design Overview
The robot I want to build simulates the movements of a dog. its basic function include: Walking forward and backward straight with four legs, sensing the obstacles in its way, going back when approaching an obstacle, bending over, getting up, and making some sound while walking.

3. 1. Main Structure
The robot has 4 legs and 13 degree of freedom. Each of the legs has 3 joints (3 degree of freedom), and every degree of freedom is to be accomplished by a embed servo motor. Given certain electrical pulses, the servo motor will make the joint perform the desired rotation of the joint. The last degree of freedom is located on the head part of the robot so that it can turn around its head.

4. 2. Control and sense system
I use Arduino mega 2560 r3 as the controlling board of the robot. It has a number of facilities for communicating with a computer, or other microcontrollers. The ATmega2560 provides four hardware UARTs for TTL (5V) serial communication. By using UARTs of Arduino mega 2560, I can transmit data between Arduido mega 2560 r3 and SSC-32 servo motor control board.

5. I use SSC-32 servo motor controller to control the servo motors of the robot. SSC-32 servo motor controller is connected to Arduino via a RS232 Bus for data transmission. The reason I select it is that SSC-32 can be able to control several motors at the same time. And it can make motors move at desired speed, or move within a desired period of time.

6. The sensor I want to use is the ultra red ray sensor for obstacle avoidance. A ultra red ray sensor has a transmitting tube and a receiving tube. When the red ray is reflected by obstacles, it is detected by the receiving tube and the sensor then sends a digital signal to inform the robot to go back.

7. 3.Walking Mechanism
In my robot design, I will use alternating waking mechanism.
In alternating gait, the movement of each leg can be divided into two parts. They are uplifting and advancing. When a leg’s adjacent legs begin to touch the ground, the leg starts upshifting and moving forward. Similarly, when this leg is touching the ground and starts advancing and moving backward, its adjacent legs start moving forward.
Thus, the submissive four legged walking gait can be maintained continuously.

8. Figure 1 Walking mechanism A
In figure 1, it represents the first gait the robot perform when walking straight, the lines with the same color indicate legs on the same side of the robot. The curving leg drive the robot to advance, while the stretched legs is upshifting in order to perform the next step.

9. Figure 2 Walking mechanism B
In figure 2, it represents the second gait the robot perform when walking straight, and the stretched legs of figure 1 now move backward, they become curved, this gives the robot a force to advance, while the other two legs now upshift forward for next step.

10. 4.Conclusion
So far I have designed the robot to walk straight and sense obstacles. I considered the walking mechanism of the robot. I have selected my controlling board and the sensor.

11. 5.Future work
To complete my work, I should buy the sensor and motors, I should also design and build the mobile platform properly. I have seen videos and documents talking about this walking mechanism but I found the turning mechanism of this kind of robot is rarely discussed, and that is something I should focus on in the future.