Independent Design Project

The independent design project will involve the design of a line following robot. Line

following robots has many applications in the real world. The line robot will often be used in

robot races. Essentially, it involves the time it would take for the robot to transverse a particular

track. This will rely on how the robot is able to move autonomously by itself, and the time taken

to complete a particular track. This would prove beneficial in improving the design of other

robots with different applications. It can be used for many challenging scenarios such as assisting

law enforcement to locate armed criminals in an enclosed area like a building. In this regard, the

robot will often be used in reconnaissance missions, and would move following a given path

based on maps or blueprints of a particular structure that have been stored in the robot. It will

provide emergency respondents to locate criminals in a building or enclosed structure, or use it to

move in areas that are considered as risky to the human personnel (Dai & Lee, Formation control

of mobile robots with obstacle avoidance based on GOACM using onboard sensors, 2014).

There is need for the robot to be used instead if humans to prevent additional loss of life. The

robot will first be used in line following contests. This will prove the authenticity of the design,

and that it can be advantageous in a real life scenario.

Operational domain

The course for the line following robot will be white lines on a black background. This

can then be used in the control of the robot in real life scenarios. The robot’s mission will often

involve ground missions. Essentially, the robot can work autonomously and will be much easier

to achieve its goals once it advances into the mission. The course that the robot will follow is

often three quarter inches of tape placed on a white background. It would be easy to adjust the

robot’s mechanism, and it would be easy to use the black lines. There are two types of courses

that exist (Yamanoor & Yamanoor, 2014). The first is a racecourse. It is characterized by fixed

number of tiles. These have various configurations, such as the figure below:

Figure 1: Racecourse tile set for a line robot

In this regard, a box with all the above lines can lead to creation of a racecourse for any type. It

will be through a selection of various tiles, and this can be configured in any way. The final line

will entail pre-drawn elements. It will be placed on a surface or laid down with electrical tape.

Figure 2: Pre-drawn tile set

The pre-drawn tile set will prove beneficial in understanding the robot’s control mechanisms,

and application in real life. The courses will also be n three difficulty levels. This would show

the challenging courses the robot would be able to transverse. The hard difficulty was

characterized with crossings that are more than 90 degree turns. The medium difficulties will 90-

degree turns or areas where the lines cross each other. It will be able to detail the ability of the

robot to make sharp turns, and quick maneuvers (Warren, Adams, & Molle, 2011). The easy

difficulty will have gentle tracks. This is often characterized by 6-inch radius curves. Essentially,

the information will be able to detail how fast the robot will finish each difficulty.

Design

Various variables have to be met by the robot. This will be using several subsystems. The

first is that it has to be very fast. The robot also has to navigate different courses. This will detail

how the robot will handle ground applications. Essentially, the mission of the design project is to

create an autonomous, fast robot that will follow a complicated line course that is placed on a

white background (Yu, Xiangdong, Canfeng, Jiaqing, & Suxin, 2015).

Propulsion system

The are many methods that can be used in assisting the robot to move. These include tank

threads, six wheels, four wheels, three wheels, two wheels, and a single wheel. The single wheel

often appears as a robot inside a robot. Tank threads tend to be problematic, and can easily wear

out. However, they have the advantage in traversing different surfaces. However, this is not the

expected scenario for the particular robot being designed. A four-wheeler is also very similar to

three and six wheeler. The two-wheeler with a caster or tricycle is even a better alternative. In

this configuration, the sensors and the turning wheel are placed further upfront. Furthermore, the

entire weight of the robot is placed on the two back wheels. It would tremendously increase the

speed of the robot. The faster response time is also attributed to having the turning wheel at the

front. Moreover, the sensors are located in the same area, making the response much quicker. In

this regard, this is an essential element in emergencies where the robot will be used in

reconnaissance (Ceceri, 2014). The other alternative is the two side wheels. It has an independent

drives with caster or a free-spinning swivel wheel. This is an easier configuration, and will be

used for the robot.

Figure 3: Two-wheeler configuration

Design decisions section

The block diagram is necessary for the design process.

Figure 4: Block diagram

The block diagram is an outline of the robot’s design. The robot’s program will have to

contain several aspects. These are the computer, microprocessors, microcontroller, and the

software that controls them.

Input: The function is to read the black and white on the floor. It then conditions the input

signals so that they are transmitted to the computer/CPU/MPU or brain. It can be in a similar

manner to how questions are asked and a response is provided (Dai & Lee, Formation control of

mobile robots with obstacle avoidance based on GOACM using onboard sensors, 2014).

Process: This relies on the input made. The process makes a decision on what has to be changed

about the robot in regards to direction and speed. It converts the responses and decisions made

into that can change the steering and motor speed (Cook, 2015).

Output: This is involved in sending the newly or old controls signals to the steering and speed.

Storage: This is involved in storing the computer program for it to carry out the ‘process’ stage.

It will store direction, speed, and sensor readings.

Input sensor selection

There are three input sensors that can be used for the design. The first is the optical sensor. It can

use the QRB1114. It has an oval hole in the center where a bolt and nut can be inserted, making

it more adjustable (Dai & Lee, The leader-follower formation control of nonholonomic mobile

robots, 2012).

Figure 5: Optical sensor model QRB1114

Figure 6: Single Line IR Sensor R185

The figure above shows a single line IR. It is a good choice as it has onboard electronics

and has a LED status that can be used in troubleshooting. The QRD1114 is in a small package, at

about 6 * 4.38 millimeters.

Design decisions

The robot will use a line sensor. For instance, the course can be a black line on a white

background. In this regard, when the robot is programmed for ‘Right’ and is placed on the sensor

at the left of the line over the white surface. When placed over the white surface, it is told to

follow the right path until it comes to a black surface. Furthermore, the robot is told to go to the

left until the black line is no longer visible. Specifically, this robot is not really a line follow. It is

an edge follower (Hara & Pfeifer, 2003). However, a single sensor has the limitation of speed.

The robot will be spending more time bouncing off the edge of the line or turning. It would

harder to achieve more speed without an increase in accuracy. In this regard, over one sensor is

the preferable choice. In this regard, six sensors would be the best option.

Figure 7: Six line sensors

In the figure 7, the sensor is under the third sensor. It would mean that the robot would

always be at the left side of where it wants to be located. If the line is under the left sensor, it is

easier to determine that the robot is very far from the center. The sensors will provide more

information that is beneficial. Moreover, dialing a sharper turn would not be the best choice. It

will mean that the robot with overcorrect and overshoot, making the steering unstable and erratic.

However, a solution exists. The most popular solution is Proportional, Integral, and Derivative

(PID). These mathematical feedback variables can apply in the reduction of hunting and

overshooting. The second solution involves coming up with a program to know the differences

(Hunt, 2007). The first difference is in terms of returning from off a high margin to the right. The

second is in terms of moving from a perfect center position. This requires that the robot start

straightening out from the previous dominant corrective turn to the left. On the other hand, the

forts will require that the robot make a course correction to the left. It is important to note that

over four sensors will provide a smart algorithm or PID. It is much better than using two or more

sensors.

A two-sensor robot will find it hard to navigate the complex tracks. It is common with

tracks that have intersections and corners. The robot would miss the run, or would make the turn

partially turn but then it will be confused. It would then oscillate indefinitely. This occurs at

sharp 120-degree turns. On the other hand, 90-degree turns would be much easier depending on

the angle of the robot when it reaches the turn. In this regard, when the left sensor is the first to

gets over the perpendicular line, then it would take a left turn. If the right sensor got to the black

line first, it will take a right turn. If it met the intersection at a square, then it would first hesitate

and then would straight through the intersection. In this regard, the brainpower will prove

beneficial in negotiating complex paths (Hunt, 2007).

Figure 8: Completed sensor arrangement

The V shape sensor array is much better than a straight-line sensor array at recognizing 90

degree turns. It provides an advanced look of intersections. However, the straight-line array is

much better the least complicated patterns for detecting a turn.

Figure 9: Schematics for the QRD1114

The schematic has a 220-ohm resistor on the right. It plays a role as a current limiter to produce

the current for the LED (Kelly & Martinoli, 2004). In this regard, subtracting 0.7 volts that is

dropped across the LED, then the applicable formula is:

I = E/R

I = (5.0v – 0.7v) / 220 Ohms

I = 4.3v/220 Ohms

I = 0.01945 Amps

Logic design

The maximum current for the LED is 50 milliamps, but this project will use 20

milliamps. The phototransistor is the voltage divider. The light goes back to the base of the

transistor form the floor. The amount of light that is received and the base controls the flow. It

differs from the use of base bias voltage in the control of the current flow. When there is no light,

current will not be present. It acts as a switch that is open. Moreover, a voltmeter that is placed

on the output will read as 5 volts (Yamanoor & Yamanoor, 2014). On the schematics, this is

labelled as RA1. On the other hand, when the phototransistor is exposed to light, the transistor

will become saturated. It then acts as a closed switch. The current will then flow from the ground

to the resistor through the phototransistor. The output will display 0.0 Volts. It arises because the

shorted switch will make the output to appear as if it has the same potential as the ground.

Moreover, it is expected that different light levels will lead to readings that are about 0 to 5 volts.

Sensor placement 

Sensor spacing is essential to come up with accurate readings. The sensors were placed at

a distance of about 3/4 inches. In case the array moves towards any directions, the highest

number of sensors that will be activated is one (Dai & Lee, Formation control of mobile robots

with obstacle avoidance based on GOACM using onboard sensors, 2014). The readings below

show the readings from the eight sensors that might be used in the robot.

Figure 10: Line detection logic

Figure 11: Readings from eight sensors far apart

Accuracy and precision is improved by placing the sensors much closer. In this regard, the line is

exactly between two sensors, and it means that they both react (Hunt, 2007). This is shown in the

readings below.

Figure 12: Readings from eight sensors closer together

In the second scenario, the sensors provided more readings that were accurate. The spacing used

is about half an inch between all sensors. On the board with a spacing of 0.100 between the

holes, then the sensors are placed 5 holes apart. The best configuration in this case would be

eight sensors. The white line on board will have the ground bus (Warren, Adams, & Molle,

2011). The white line will have the five-volt bus line. The 200 Ohm (red, red, brown, gold) and

10 Ohm (Brown, black, orange, gold) resistors will be placed here. The sensors will also be

placed in the same direction. The phototransistors (small round white circle) will go to the right

while the LEDs (small black rectangle) will go to the left.

Based on figure 8, the assembly has white, yellow, red, and green leads. The bottom-left

green and red leads are the ground and power (5v). They are going to a 2-prong connector placed

at a right angle. The white leads are signal leads for the four left-hand sensors. They end at a 4-

prong connected at a right angle. The yellow leads are hidden below the white leads. They act as

signal leads for the right-hand sensors. They also end at a 4-prong connector at 90 degrees.

Testing

The sensors are tested before assembly. One of the sensors will be first wired to a board.

It is then powered up, and the output is sent from the RA1 to the voltmeter. The next step will

involve using a white paper. It is filled with a black line measuring three-quarters of an inch. It

acts as a reflector for testing purposes. The sensor is then placed on the paper facing downwards.

It is then passed back and forth on the black line. The results will be able to show the voltage

change during this activity (Hara & Pfeifer, 2003). The sensor will then be held over an inch. It

will produce a constant voltage change of about 4.2 volts. It shows that the phototransistor is not

getting any light (or just the ambient reflection), or that the switch is open. It is considered as the

high voltage reading that means there is no reflection.

The sensor is also placed at about half an inch from the paper. It should produce a change

immediately. It would provide constant voltage readings of about 0.12v. It is a confirmation that

the phototransistor is saturated and conducting within a maximum range. Moreover, when the

sensor is moved slowly across the black line, the voltage will increase to almost 4.12 volts. It

would mean that the black line is not reflecting minimal or nay light back to the phototransistor

(Warren, Adams, & Molle, 2011). Light conditions in a room can easily affect the readings based

on the position of the sensor. The array should easily be adjusted to ensure that the robot would

work based on different light conditions.

Assembly

The motor chosen will be one with four gear ratios. The caster is mounted to the robot

base. The sensors will be placed at the front of the caster while facing downwards. Furthermore,

there should be minimal clearance between the ground and sensor covering

Figure 13: Position of sensor and caster

The battery will then be connected to the circuit. The batteries will comprise tow 3.7 Li-ions

cells that are connected in series. It will allow the robot to move for about four minutes.

Figure 14: Circuit diagram of a line following robot

The motor driver circuit and potential will then be attached. The threshold of the LDR

should be adjusted when the sensor is placed on the black surface. It should be below 0.5 volts. If

the motors are rotating in a reverse direction, then the polarity of the motors are changed. It is

soldered to a different general-purpose board. It is then placed on top of the chassis. It will make

it easier to adjust the potentiometer.

Figure 15: Final robot

Conclusion

In conclusion, the independent design project will come up with a simple line following

robot. Many aspects have to be put into consideration during the design. It includes the number

of sensors to be used, mode of locomotion and the motors used. Once assembled, the robot will

be able to follow autonomously a black line on a white acrylic surface. The robot can prove

beneficial in carrying out other complicated tasks. It can be used for reconnaissance in areas

where it is dangerous and risky for humans. The robot will use eight photovoltaic sensors. Two

sensors on the bottom will detect the black line, and this will allow the robot to move along the

lines on its own.

References

Ceceri, K. (2014). Making Simple Robots Exploring Cutting-Edge Robotics with Everyday Stuff.

New York, NY: Sebastopol O'Reilly & Associates.

Cook, D. (2015). Robot building for beginners. New York, NY: Apress.

Dai, Y., & Lee, S. G. (2014). Formation control of mobile robots with obstacle avoidance based

on GOACM using onboard sensors. International Journal of Control, Automation, and

Systems, 12(5), 1077-1089.

Dai, Y., & Lee, S.-g. (2012). The leader-follower formation control of nonholonomic mobile

robots. International Journal of Control, Automation, and Systems, 10(2), 350-361.

Hara, F., & Pfeifer, R. (2003). Morpho-functional Machines: The New Species : Designing

Embodied Intelligence. Tokyo: Springer Japan.

Hunt, J. A. (2007). Robot kinematics and the Gantry-Tau parallel machine. The Industrial Robot,

34(5), 362-367.

Kelly, I., & Martinoli, A. (2004). A scalable, on-board localisation and communication system

for indoor multi-robot experiments. Sensor Review, 24(2), 167-180.

Warren, J.-D., Adams, J. S., & Molle, H. (2011). Arduino robotics. New York, NY: Apress.

Yamanoor, S., & Yamanoor, S. (2014). Raspberry pi mechatronics projects hotshot. London:

Packt Publishing.

Yu, L., Xiangdong, J., Canfeng, Z., Jiaqing, C., & Suxin, H. (2015). Welding robot system

applied in sub-sea pipeline-installation. The Industrial Robot, 42(1), 92-83.