Bangladesh University of Engineering and TechnologyDepartment of Mechanical Engineering

Instrumentation and Measurement SessionalCourse No: ME-362

Project Title: Terrain Hazard Optimized Robot (THOR)

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Supervised by:

Dr. M.A. Taher Alio Professor ,Dept. of Mechanical Engineering

A.K.M. Monjur Morshed

o Assistant Professor, Dept. of Mechanical Engineering

Md. Wasim Akram

o Lecturer Dept. of Mechanical Engineering,

Md. Al-Amin Khan Chowdhury

o Lecturer, Dept. of Mechanical Engineering

Abdul Motin

o Lecturer , Dept. of Mechanical Engineering

Presented by : Group A 15

Roll No Student Name

0510005 Naser Imran Hossain *

0510014 Md. Rokanuzzaman Khan

0510024 Prajnaprasun Bhattacharjee

0510033 Nahid Pervez

Dept: Mechanical Engineering

Level- 3/ Term-1

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AcknowledgementsFrom the first day we started our journey as engineering students, we’ve gone through many prescribed courses. But very few were as challenging or unique as this course. We came across a plethora of new terms, instruments, technologies and scientific observations that we had never had the pleasure of familiarizing ourselves with. Without the help of our experienced course teachers, we could’ve never made it through this challenging endeavor. So, we would like to thank the following teachers for their diligent help:-

Dr. M.A. Taher Alio Professor ,Dept. of Mechanical Engineering

A.K.M. Monjur Morshed

o Assistant Professor, Dept. of Mechanical Engineering

Md. Wasim Akram

o Lecturer, Dept. of Mechanical Engineering

Md. Al-Amin Khan Chowdhury

o Lecturer, Dept. of Mechanical Engineering

Abdul Motin

o Lecturer , Dept. of Mechanical Engineering

We would also like to mention MR. MASUDUR RAHMAN (Asst. instrumentation engineer), who gave us his utmost help throughout the course and provided necessary technical instruction whenever we faced any obstacles in accomplishing our project.

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Finally we want to thank all the lab assistants of our carpentry shop and machine shop for their continuous help though out the term in all possible ways.

Abstract:

The Terrain Hazard Optimized Robot (THOR) is a rover like robot controlled manually to

navigate through uncharted and possibly hazardous environment. Thus the nomenclature. It

is designed to vertically lift or place mission objectives with its custom designed gripper

arm and afterwards move through difficult terrain taking advantage of its pseudo-

holonomic drive and high-torque mechanism. It has a two story structure, with one

supporting the power units and the driving motors and the other with the arm-base and

gripping motors. As an additional recon measure, sensors have been used to give THOR a

sense of heat and light.

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Contents

1. Introduction ................................... .................................................... 6

2. Objective ....................................... ..................................................... 7

3. Construction of THOR .................. ........................................................ 8

3-1 Overview .................................. ............................................. 8

3-2 Mechanical Parts ...................... ......................................... 11

3-3 Electrical Parts ......................... .......................................... 15

4. Basic Mechanics behind THOR ...... ................................................. 18

4-1 Movement ................................ .......................................... 18

4-2 Gripping and support ............... .......................................... 20

5. Working Principle of the Circuit ..... ................................................... 21

5-1 Connection Diagram ................ ............................................ 21

5-2 Sensing light ........................... ........................................... 23

5-3 Sensing heat ........................... ........................................... 24

6. Applications ................................... ..................................................... 25

7. Advantages .................................... .................................................... 26

8. Limitations ..................................... ..................................................... 28

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9. Further Recommendation ............ .................................................... 29

10. Cost Analysis ............................. ................................................... 30

11. Conclusion ................................... ................................................... 31

References ....................................... .................................................... 32

1. Introduction:

Since Karel Capek (1890-1938) first used the word ‘robot’, man has been infatuated with

the creation of mechanized companions.

Our project was named after the Norse god of thunder who used to banish evil to their

demise. For it too might one day help humanity in its struggle against the evils of pollution

and contamination.

Our inspiration was the brave remote neutralization of a possible nuclear catastrophe by

one of our hon’ teachers, Professor Dr. M.A. Taher Ali, when a jammed Co-60 source of

the γ-beam irradiator at Bangladesh Institute of Nuclear Agriculture (BINA) threatened the

lives of many in the late 80’s.

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2. Objectives:

When THOR was still basically in the drawing board, we sketched up some goals we

would like to achieve with our project in due course. Our main objectives were to :-

Manually maneuver into hazardous environment.

Avoid obstacles and detours on the way using fast directional control.

Grip mission objectives with link-driven gripper

Bring objective back into safe containment area and deposit.

Sense heightened level of temperature or lack of light on due process and indicate.

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3. Construction of THOR

3-1. Overview:

CAD simulation/schematics:

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Fig 1: L.H.S View of THOR

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Fig 2. : Top View of THOR

Fig 3: Overall Look

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Real time view:

Fig 4: Real Time Top View

Fig 5: THOR- in action

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3-2. Mechanical Parts:

Ball Bearing:

Ball bearings, as shown below, are probably the most common type of bearing. They are found in everything from inline skates to hard drives. These bearings can handle both radial and thrust loads, and are usually found in applications where the load is relatively small.

Photo courtesy The Timken CompanyFig 6: Cutaway view of a ball bearing

In a ball bearing, the load is transmitted from the outer race to the ball and from the ball to the inner race. Since the ball is a sphere, it only contacts the inner and outer race at a very small point, which helps it spin very smoothly. But it also means that there is not very much contact area holding that load, so if the bearing is overloaded, the balls can deform or squish, ruining the bearing.

In our project ball bearings were also used to allow relative motion between two moving/rotating members, namely the shaft and the housing that supported them longitudinally.

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Acrylic parts:

Acrylic is a useful, clear plastic that resembles glass, but has properties that make it superior to glass in many ways. Common brands of high-grade acrylic include Polycast, Lucite and Plexiglass.

Fig 7: Acrylic Sheets

A great advantage of acrylic is that it is only half as heavy as glass. This makes working with acrylic much easier. It can also be sawed, whereas glass must be scored.

Adding to this favorable array of properties, a transparency rate of 93% makes acrylic the clearest material known . This adds to the aesthetics of a project such as ours.

A unique property of plastic is its ability to be shaped. Bow-front aquariums are beautiful examples of acrylic's wonderful properties. There are also no seams in acrylic structures, as chemical welding at the molecular level actually "melts" seams into one piece of solid material. Seams that are welded and polished are invisible.

In our project acrylic was used to build: Gripper Arm Gripper Claw Gripper Base Upper floor of THOR.

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Gear Motors:

Gearmotors are a class of motors equipped with either an integral gear box or gear reduction unit. The set of gears drive a secondary drive shaft. These motors are capable of increasing the torque generating capacity of the motor while simultaneously reducing its output speed. A major advantage that comes with the usage of gears of this type is that the driving shaft is coupled directly to the driven shaft. Furthermore, they eliminate the necessity for coupling the motor to a separate external speed reducer. These motors are common in hot melt glue pumps, conveyor drives, tape dispensers, labeling, box tapers, case erectors and heat shrink tunnels.

Fig 8: Cutway view of a Gear Motor

4 gear motors of variable RPM and torque were used to complete the structure of THOR and to support its various functions. Two motors with high operating torque were used to drive the two forward wheels. Equal RPM range was maintained to ensure uniformity of motion.

Gear motors were selected for their various tangible advantages over other motors like the stepper motor. For example, gear motors had simpler working principle, required less effort to run seamlessly, had much better operating torque and were in general , a lot more durable.

Wooden components, springs and wires:

After much deliberation, wood was included into material list. A base was built out of wood to support the weight of the power unit and the gripping tower above. Wood was also used to build the motor and shaft supports underneath the base.

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A spring was used in between the acrylic jaw to help keep them open after an ungripping operation.

Fig 9: Compressing spring and Nylon wires.

Compression springs were chosen to do this job because of their natural resistance to compression and durability.

High strength nylon wires were used to drive and control the jaw and the gripper arm.

Mild Steel Driving Shaft:

A drive shaft, driving shaft, propeller shaft, or Cardan shaft is a mechanical device for transferring power from the engine or motor to the point where useful work is applied. Most engines or motors deliver power as torque through rotary motion: this is extracted from the linear motion of pistons in a reciprocating engine; water driving a water wheel; or forced gas or water in a turbine. From the point of delivery, the components of power transmission form the drive train.

Fig 10: Gear and Shaft Coupling

Drive shafts are carriers of torque: they are subject to torsion and shear stress, which represents the difference between the input force and the load. They thus need to be strong enough to bear the stress, without imposing too great an additional inertia by virtue of the weight of the shaft.

In our project, Mild steel was chosen as shaft material because of their ductile nature and availability.

3-3. Electrical Parts:

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The electrical semantics of THOR consisted of several simple circuit components (as shown below)

Fig 11: Overall view of the circuit

LM-324 Operational Amplifier:

An operational amplifier, which is often called an op-amp, is a DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output. Typically the output of the op-amp is controlled either by negative feedback, which largely determines the magnitude of its output voltage gain, or by positive feedback, which facilitates regenerative gain and oscillation. High input impedance at the input terminals and low output impedance are important typical characteristics.

Fig 12: Close-up of LM 324 Op-Amp

Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices

Light Dependent Resistor (LDR):

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A photoresistor or Light Dependent Resistor or CdS Cell is a resistor whose resistance decreases with increasing incident light intensity. It can also be referred to as a photoconductor.

A photoresistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance.

Fig 13: Light Dependent Resistors.

NTC Type thermistor:

A thermistor is a type of resistor with resistance varying according to its temperature. In our case the thermistor in use was the “Negative Temperature Coefficient” or NTC-type thermistors. From geometric POV it was a “Bead Type Thermistor. NTC thermistors are used as resistance thermometers in low-temperature measurements of the order of 10 K.

Fig 14: NTC-type ‘BEAD’ thermistor.

Variable Resistances:

Variable resistances have adjustable resistance which can be modified by changing the position of a tapping on the resistive element

Variable resistances in the range of 10KΩ were used as a means of calibration between sensor outputs and indicators.

Fig 15: Variable ResistanceResistors:

A resistor is a two-terminal electronic component designed to oppose an electric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm's law: V = IR. The resistance R is equal to the voltage drop V across the resistor divided by the current I through the resistor. Resistors in the constant range of 10 KΩ, 1MΩ and 2MΩ were used in THOR’s sensor circuit.

Fig 16: Resistor

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LEDs:

LED is a semiconductor diode that emits light when an electric current is applied in the forward direction of the device, as in the simple LED circuit. The effect is a form of electroluminescence where incoherent and narrow-spectrum light is emitted from the p-n junction.LEDs are widely used as indicator lights on electronic devices and increasingly in higher power applications such as flashlights and area lighting.

In THOR, two LEDs (one Green and one Red) were used to indicate lack of light or heightened temperature.

Fig 17: LED and its working principle

DPDT Toggle Switches:

Double Pole Double Throw (DPDT) switches were used to control the motor directions i. These switches are useful in changing the polarity of the motor inputs on operation instantaneously.

Fig 18: DPDT switch

4. Basic mechanics behind THOR

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4-1. Movement:

On our quest for fast, multidirectional movements, we came across the idea of a Pseudo-Holonomic drive. On a fully Holonomic drive, the vehicle in question can instantaneously change direction of motion and progress.

Non-holonomic robots are ones that cannot instantaneously move in any direction, such as a car. This type of robot has to perform a set of motions to change heading. For example, if you want your car to move sideways, you must perform a complex 'parallel parking' motion. For the car to turn, you must rotate the wheels and drive forward.

Non-Holonomic Movement Holonomic Movement

Fig 19: Explanation of the difference between traditional and holonomic movements.

A holonomic robot however can instantaneously move in any direction. It does not need to do any complex motions to achieve a particular heading. This type of robot would have 2 degrees of freedom in that it can move in both the X and Y plane freely

THOR’s movements weren’t completely Holonomic, thus the prefix “Pseudo”. Our project was granted the ability to turn instantaneously first and then move forward or backward. A feat otherwise considered unachievable in standard, Ackerman steering systems seen in everyday automobiles.

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Strategy:

To go forward or backward both wheel rotate in common direction

Fig 20: ‘Forward Moving’ strategy

To steer/turn, wheels are rotated in opposite directions:

Left Turn Right Turn

Fig 21: Steering Strategy

RW rotates opposite to LW to change direction and vice versa.

Smooth turns are made possible by stopping one of the wheels and resuming the other

4-2. Gripping and support:

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Gripping commences when an object is placed between the jaws of the grip. Wires are pulled from the body of THOR via a gear motor and the jaw is closed thereby entrapping the object in question.

Fig 22: Gripping Claw

When there is a need to ungrip, the wires are loosened by turning the motor in the opposite direction. The compression spring helps the claws return to their natural position..

All the time the custom designed, link-based “Gripper Arm” help keep the claw in a literally vertical position.

Fig 23: Gripper Arm

The arm is lowered or taken up via another gear motor attached to THOR’s exoskeleton. Again, wires are used to control the height of the arm.

5. Working principle of the circuit

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A small, simplistic sensor circuit powers the senses of THOR. With its help, THOR can sense heightened level of temperature or a lack of light in the ambient environment. The basic principles in action here are:-

LDR senses lack of light and indicates with a Green LED.

NTC-Type thermistor senses increase in temperature and indicates with a Red LED

Possible to calibrate sensors according to ambient variables.

In circuit “ Operational Amplifier ” ( LM-324 ) synchronizes between sensor

feedbacks and indicators.

5-1. Connection diagrams

LM-324/124

Fig 24: Schematic of the

LM-324 (TOP-View)

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Fig 25: Schematic of the Op-Amp connection

5-2. Sensing Light:

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Fig 26: Circuit diagram for the Sensing of Light

Under full incident light (spectral range of 515 nm ~ 730 nm) , LDR, with its

decreased resistance, renders the path to the LED inactive.

In darkness, its resistance increases. Op-Amp compares the feedback and lights up

the green LED.

5-3. Sensing temperature:

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Fig 27: Circuit diagram for Sensing of heat.

Under increased temperature, the NTC type thermistor resistance is decreased

rendering it inactive in the circuit. Op-Amp again compares the feedbacks and

lights up the red LED.

When ambient temperature recedes to normal, the resistance increases cutting off

power supply to the LED.

6. Applications

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Fig 28: Possibly Applications- Minesweeping (Left) & Interstellar missions (Right)

THOR at its infancy is but only an engineering project. However with proper planning it

maybe employed in a variety of useful purposes:-

Reconnoitering through possibly radioactive or hazardous environment.

Salvage mission over terrains unsuitable for human exposure.

Charting terrain as a drone for possible thermal leakage , heat flux and variation in

luminescence

Working as a multirole companion for humanitarian teams and missions.

Small scale forklifting and payload carrying.

Mapping favorable routes for friendly forces in wartime.

With interchangeable arm-mounts, THOR has been given the ability perform a

multitude of feats. For example, welding torches or surveillance cameras can be

mounted in place of the claw to execute important repair or salvaging operations.

7. Advantages:

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Our project has distinct characteristics which makes it advantageous for use under particular circumstances. For example:-

Our project was extremely cost effective. This is easily visible when logistical

considerations are made. For example over the range of -50°C to 150°C, NTC-

type thermistors offer a distinct advantage in sensitivity to temperature changes

compared to other temperature sensors like Pt-RTD.

Fig 29: Resistance Vs Temp Graph

Another smart logistical consideration was the usage of LDR to sense light.

Light Dependent Resistors (LDR) provides a comfortable range of resistive

outputs to work with.

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Fig 30: Resistance Vs Light Intensity graph

However, when logistically considering, both the NTC-type thermistor and the

LDR cost less than 0.3 USD. Certainly an economically viable consideration.

Acrylic was used instead of wood. This made the whole project lightweight and

easy to operate.

Manual control was chosen over automated maneuvering. This helped ease the

complexities of navigation make it more efficient.

THOR was coupled with a high torque mechanism. So should the need for a

heavier payload arises, our project would be able to support it on its back too.

When there is a need to take sharp turns, THOR will be able to accomplish that

using its “Pseudo-Holonomic” drive.

Where there is a strong regulation against spilling, THOR would be able to

operate because of its ingenious “Always Horizontal” gripping mechanism.

THOR was given the ability to sense heat and light. This gives the project an

edge over other similar initiatives. Because of its sensing omnipotence, THOR

is more suitable for rover-missions.

8. Limitations

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No engineering project is without flaws. There are always places and instances where and when failure may occur. It would be ludicrous to assign 100% reliability on any material in question. Likewise, our project too had limitations, limitations that restricted some of its operations, limitations that often caused failures at particularly weaker segments of its built. Some of these limitations were:-

Weak ‘Acrylic’ parts: Although lighter than more conventional materials like

‘wood’ Acrylic parts are vulnerable to sudden shock-loads. That is why there is

often a concern of structural failure when THOR is test-driven.

Connection Breakage: It was not possible to ensure a strong bondage between the

wire contacts and the motor leads. The wiring of the motors and DPDT switches

often breaks loose, rendering the motors ineffective and without power.

Transducing difficulties: The bead type thermistor is not as well responsive as the

LDR. So the signaling might be delayed. That is why the sensing of light is much

well responsive that that of heat.

Wire tension and severing: The wires used for gripper and arm-control is not that

strong in tension and might sever under much heavier payloads.

9. Further recommendation

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After the completion of any project, the question that first arises is “How to optimize the current configuration?” Our project too has many optimization and improvement opportunities. Such as:-

Replacing acrylic parts with stronger materials, like HDPE (High Density Poly

Ethylene) or Aluminum. This would retain THOR’s lightweight built while

increase strength/unit length ,

Integrating radio frequency control and servo drives. RF controlling would

bring a new degree of freedom to THOR’s navigation relieving the operating

hand of the concern of wire tangling.

Incorporating solar-power for prolong operation. With a depletable power

source like integrated DC batteries, THOR remains vulnerable to power

shortage when operating times are increases. That is why photovoltaic cells

empower by solar power maybe embedded later on to give THOR a whole new

dimension.

Automating directional commands via microcontrollers. Automation, although

prone to system failures, is none the less a very efficient method to accomplish a

pre-set sequence of objectives. So if the necessity arises for such an objective,

THOR’s circuits can be coupled with a programmable microcontroller.

Replacing LDR with more sensitive sensors such as phototransistors. This

would increase THOR’s sensitivity to light and make it more responsive in

crucial times.

10. Cost Analysis

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Item No. Name Quantity Price(Tk.)1. Acrylic Base 2*(9 inch * 6 inch) 3202. Acrylic Arm 4 links + Claw 3003. Gear Motor 4 pieces 16004. Solid rod of Mild steel 3 feet 2405. Nuts & Bolts 150 pieces 1806. Bearing 10 pieces 1507. Spring & Washers --------- 308. Battery 1 piece 4009. Bread Board 1 piece 25010. DPDT switch 4 pieces 20011. Extension Wires 7 gauges 14012. IC(LM-324) 1 piece 1613. LDR 1 piece 1014. NTC type Thermistor 1 piece 1515. LED 2 pieces 416. Machining Cost ------- 50017. Others ------- 845

Total 5200

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11. Conclusion

Throughout our sessional course we came across many difficulties. We entered as freshmen in the science of instrumentation and by the end of the semester we had transformed into much more potent engineers.

We were able to successfully carry out all the objectives we initially set out to achieve.We learned much throughout the semester, about mechanical and electrical components and most importantly about human resource management. However, the finalé which included the joy of accomplishment would remain radiant in our memories for ever. All in all that was quite a delightful experience

Finally, we would like to say that THOR has many scopes for improvement. We hope our juniors or any other interested reader would be able to improve and revitalize our project furthermore in the future. We would be highly delighted to help out anyone seeking general & technical help, information or suggestions regarding our project. Anyone interested about our project can reach us at the following website: http://project-thor.pbwiki.com

References

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1. Report on salvage of a jammed cobalt-60 source of the gamma beam irradiator at Bangladesh Institute of Nuclear Agriculture (BINA), Mymensingh, Bangladesh - S M F Karim, K O Awal and M A T Ali http://www.iop.org/EJ/abstract/0952-4746/17/1/004

2. The International Journal of Robotics Research, Vol. 4, No. 1, 3-12 (1985) DOI: 10.1177/027836498500400101. Control and Geometrical Considerations for an Articulated Robot Hand - Hiroaki Kobayashi

3. “JOINT COUPLING DESIGN OF UNDERACTUATED GRIPPERS” - Aaron M. Dollar and Robert D. Howe. Proceedings of IDETC/CIE 2006 ASME 2006 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference September 10-13, 2006, Philadelphia, Pennsylvania, USA

4. Robot Mechanisms and Mechanical Devices Illustrated- Paul Sandin. Publisher: McGraw-Hill/TAB Electronics; 1 edition (June 27, 2003). ISBN-13: 978-0071412001

5. Johnsson, M., & Balkenius, C. (2007). LUCS Haptic Hand III - An Anthropomorphic Robot Hand with Proprioception. LUCS Minor 13.

6. ASME “Magazine of Mechanical Engineering” Aug 2000 Issue http://www.memagazine.org/backissues/membersonly/aug00/features/fact/fact.html

7. Society of Robots http://www.societyofrobots.com/robot_omni_wheel.shtml

8. Digital Temperature Measurement http://www.educypedia.be/electronics/circuitssensortemp.htm

9. Mechatronics Wiki http://hades.mech.northwestern.edu/wiki/index.php?title=Main_Page

10. Negative Temperature Coefficient Thermistors http://www.designinfo.com/cornerstone/ref/negtemp.html

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