Hardware

Our robot is made up of various hardware systems. These systems are as follows:

  1. Chassis
  2. Motors
  3. Sensors
  4. Microcontroller
  5. Fire Extinguishing System

A Flash animation providing a 360 degree view of our robot can be found here.

Labeled diagram of robot

Robot Diagram

Chassis:

The chassis used for Sparky is a tricycle design, with one wheel and one motor on both the left and right sides, and a trailing caster wheel in the rear. The robot's components are attached to a circular base made from 1/4" plastic. A rectangular upper level was also constucted, which provides a base for several sensors and the fan system.

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Motors:

The robot moves using two unipolar stepper motors. These stepper motors require sequences consisting of four data bits to be provided to them at a regular interval in order to operate. Looping through this sequence in order will cause the motor’s shaft to spin forward. Looping through this sequence in the reverse order will cause the shaft to spin backward. A table showing this sequence is provided below.

The stepper motors require control signals at 12V DC and 0.3 A. The HC12 is not able to provide signals at these levels, so the motors cannot be directly connected to the HC12. Instead, control circuits were constructed to amplify the signals from the HC12 and send them to the stepper motors. These control circuits make use of TIP120 Darlington transistors to amplify the control signals. Each control signal from the HC12 is sent to the base of a transistor. When this signal is high, the transistor is switched on, causing 12V to flow through the transistor and to the motors. The HC12 is protected from the motor circuitry using 7407 buffers.

Sequence Position
Line 1
Line 2
Line 3
Line 4
1
0
1
0
1
2
0
1
1
0
3
1
0
1
0
4
1
0
0
1

Motor Control Signal Sequence

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Sensors:

Three Sharp GP2D02 infrared sensors are used to determine the distance from the robot to the walls of the floor plan structure. They provide a digital distance measurement that is sent to the HC12. The GP2D02 sends out a beam of infrared light. This beam hits an object and is reflected back to the sensor’s detector, creating a triangle between the emitter, point of reflection, and the detector. The angles of this triangle vary depending on the distance from the sensor to the object. Based on these angles the sensor is able to calculate the distance from the object. The distance measurement is sent from the Sharp sensor in 8 bit serial format.

Diagram Showing Sharp Sensor Triangulation Method

Sharp Distance Sensor Triangulation Method

The Hamamatsu UVTron Flame Detection Sensor is used to detect the presence of the candle when entering a room in the floor plan. The UVTron has a bulb that can detect ultraviolet light that is emitted from a flame. When the cathode of the bulb is exposed to ultraviolet light, photoelectrons are emitted causing a discharge to take place in the bulb. The attached circuit detects this discharge and emits an electrical pulse. The process repeats as long as ultraviolet light is present. These pulses are collected by the HC12 pulse accumulator.

An infrared phototransistor is used to locate the exact position of the candle in the room. A candle, due to its heat, produces a relatively large amount of infrared light. The phototransistor outputs a voltage level proportional to the intensity of infrared light that it receives. This voltage level, in the range of 0 to 5 volts, is provided as an input to the A/D (analog to digital) converter of the HC12. The HC12 converts this value to a digital number.

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Microcontroller:

The Motorola HC12 microcontroller system is used to control the robot. It has a large array of input and output ports. The MEBI (Multiplexed External Bus Interface) provides four 8-bit I/O ports. Two 8-channel A/D (analog to digital) converters, two asynchronous serial communications interfaces, three synchronous serial interfaces, two 8-bit pulse accumulators, and eight PWM (pulse width modulation) channels are also present. Additionally, it has a large amount of available memory (256K flash EEPROM, 4K EEPROM, 12K RAM) which can store control programs, sensor data, and other information.

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Fire Extinguishing System:

A fan is used to blow out the candle using air. A fan would not be practical to extinguish a fire in a real-world situation, but the flame extinguishing system could be easily modified if a more realistic prototype was desired. The fan is made from a wooden RC (radio controlled) aircraft propeller and a 12V, .5A DC motor. The motor is turned on using a TIP120 transistor as a switch, with a signal from an I/O pin on the HC12 as input. The motor will spin as long as this control signal is high.

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Last revised: 7 May 2004

 

 

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