74*245 Motor Driver

H-Bridge Driver

Simple PWM Gen.

Handy Method Measuring RPM

Measuring RPM via Photo reflector

Introduction to Robotic

DC, Stepper,and Servo Motor

Microcontroller Tutorial

Computer Interface
Tutorial
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6.2 Communication

Information could be sent from the beacon to the robot for further instructions. Sending ASCII characters at 1200 baud was successful between two PIC microcontollers with programs written in Basic showing that this is possible. A range of about 15 feet between beacon and receiver was possible during testing of thisidea. The implementation of communication with the robot itself has not been done at this time.

6.3 Multi-frequency Required

One problem that presented itself during testing was infrared from the beacon at the same frequency (38kc) interfered with the obstacle avoidance sensors of the robot. Using sensors operating at a different frequency of modulation should help with this problem. Panasonic IR sensors are available at other frequencies of 36.7, 40 and 56.9 kilohertz.a Panasonic PNA4602, made to respond only to 38
kilohertz. The range of detection depends on the reflectance of the obstacle and is in the range of 3 to 12 inches. The sensor, after detecting IR, outputs a low state and remains in this state briefly. This delay allows the microcontroller to pulse the IR LED, then check for the response of the sensor without doing both at the same time.

7 Remote Control

Some kind of remote control was desirable when the robot was off on its own during behavior tests. Sometimes the robot would wander into a dangerous situation and had to be “rescued”. Between IR obstacle avoidance routines the IR sensors are free to sense from other sources such as a remote control. If the robot receives IR during this time, the robot was programmed to turn right. With a little skill, an operator can steer the robot out of trouble. An IR remote (fig. 5) using the same pulse modulation frequency of 38 kilohertz was constructed with another 16F84 PIC and programmed in Basic.

Figure 5 Remote Control

8. Bells and Whistles

To help follow how the program progressed as it ran and for trouble shooting purposes, various auditory and visual indicators were added. Small green leds were added to each IR obstacle avoidance modules to indicate an object was encountered. A bright blue LED was useful to warn people of its prescience when the robot was allowed to interact with the pubic. A piezo beeper and speaker were added to beep at different points of the program. Children and adults alike found the beeping and flashing lights very attractive.

9. Behavior

9.1 Getting Around
The priority of the robot was to move forward, avoid obstacles, and move toward people. Before making a move the program sends a burst of 38 kilohertz IR from the IR LED’s, then immediately checks the state of the IR receivers. If the way is clear, a forward motion is made. Forward motion continues until an object is encountered. If only the right or left IR sensor found something, then the robot would first backup a bit, followed by a right or left turn, depending on which sensor was activated. Backing up helps clear an area for a turn. The program keeps track of the number of backups attempted before returning to forward motion. After a preset number of backups occur, the robot makes a right turn, in an attempt to get around an obstacle. Forward motion is counted as how many times the forward motion subroutine is accessed and saved as a variable. A reset of this count occurs on each backup, or turn.

9.2 Scanning
Once a clear path has been taken, the robot stops to scan for both the beacon and heat radiated by people. First rotation is made in quick steps clockwise and scans are made for the beacon. If the beacon is found, forward motion starts. After scanning for the beacon the robot then scans for heat, rotating counterclockwise back to its starting position. The robot pauses for a few seconds during each rotation to allow the PIR to react. If heat is detected forward motion starts. The forward motion counter variable resets to zero and forward motion continues until an object is encountered.

9.3 Watchdog
If no encounters have been made with objects and many scans have been completed, the robot takes a rest in “watchdog mode”. During this time, all servos are turned off to conserve power, however the PIR sensor remains active. Upon detection of heat, the robot “wakes up”, makes sounds, flashes the blue LED and starts to move forward. Holding down the mode switch while switching on the power, starts watchdog mode immediately, making the robot a handy security device.

10 Conclusion
Building a two-wheel robot provided a different and challenging way to maneuver a robot around. Maintaining balance was found to depend on weight distribution and proved to be no problem with this design. Changes in wheel diameter, weight distribution, and width of the base need to be addressed. Larger designs may require gearhead motors for greater torque and perhaps a method for sensing attitude for controlling balance. Students at the high school level or at a local robotics club could build the two-wheel robot design. Since the robot is made from materials that are commonly available, it is possible to build and program with very little investment.

Supplemental Photos

Fig. 6 Wheel Spacers mounted on CD disc

Fig. 7 Bottom View of Rollie

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