micro uav range extension - gineer uav range extension - thesis.… · partial requirements for the...

Micro UAV Range Extension

David B. Taylor


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By David Taylor (2012)

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David Brian Taylor

A thesis submitted to the Technikon SA, Florida, in fulfillment of the

partial requirements for the Baccalaureus Technologiae in Electrical

Engineering in the Department of Electrical Engineering at Technikon SA.

01 October 2012


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I declare that this thesis is my own, unaided work. It is being submitted for the Baccalaureus

Technologiae in Electrical Engineering in the Department of Electrical Engineering at Technikon SA. It

has not been submitted before for any degree, diploma or other examination at any other tertiary

education institution.

Signed: by David B. Taylor

At 10 Dione Crescent, Swindon, UK, SN25 2JW on this 1st day of October 2012


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Acknowledgements

I would like to thank Mr. Carl Joubert from African Explosives Limited, who was my mentor

throughout this study for his insight, suggestions and guidance. Without him I would not have been

able to complete this study.

I would also like to thank Ms. Kimberly Cook-Chennault from Rutgers University who gave me

permission to reference her work.


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Abstract

Unmanned Arial Vehicles (UAVs) have many capabilities limited mainly by their battery range. If a

solution could be found to extend this range or recharge this battery autonomously to enable a UAV

to extend its work beyond the line of site, many more uses may be realised.


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Contents 1. Introduction .................................................................................................................................. 11

2. Theoretical Analysis and Literature Survey ................................................................................... 11

2.1. Piezoelectric Generators ........................................................................................................... 11

2.2. Photovoltaic cell ........................................................................................................................ 13

2.3. Generator .................................................................................................................................. 13

2.4. Thermoelectric Generators ....................................................................................................... 14

2.5. Other Energy Harvesting Devices.............................................................................................. 14

2.5.1. Hydrogen Fuel Cells............................................................................................................... 15

2.5.2. UAV perching (Cory, 2010) .................................................................................................... 15

2.5.3. UAV Power Link (LaserMotive, n.d.) ..................................................................................... 15

2.6. Energy storage .......................................................................................................................... 15

2.6.1. Lithium Polymer (Li-Po) Batteries ......................................................................................... 15

2.6.2. Li-Po Battery Balancing ......................................................................................................... 15

3. Conceptual Design ........................................................................................................................ 17

3.1. Piezoelectric Generators ........................................................................................................... 17

3.2. Photovoltaic cell ........................................................................................................................ 18

3.3. Regenerative Braking ................................................................................................................ 19

3.4. Wind Turbine ............................................................................................................................ 19


4. Detailed Design ............................................................................................................................. 22

4.1. Photovoltaic Solar cells and Piezoelectric Generators .............................................................. 22

4.2. Thermoelectric Generator Matrixes ......................................................................................... 23

4.3. Battery Management ................................................................................................................ 23

4.3.1. Boost Converter .................................................................................................................... 23

4.3.2. Li-Po Shunt Battery Balancing Charger ................................................................................. 24


5. Experimental Evaluation ............................................................................................................... 25

5.1. Piezoelectric generators ........................................................................................................... 25


5.3. Photovoltaic Cells ...................................................................................................................... 28


5.5. Energy Harvesting PCB .............................................................................................................. 28

6. Discussion ...................................................................................................................................... 31


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7. Conclusion ..................................................................................................................................... 31

8. Recommendations ........................................................................................................................ 32

9. Bibliography .................................................................................................................................. 32

Appendix A. Measuring Equipment ................................................................................................... 34

Appendix B. Parts List ........................................................................................................................ 35

Appendix C. More Photos ................................................................................................................. 36


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List of Tables

Table 1: List of Abbreviations and Acronyms ........................................................................................ 10

List of Graphs

Graph 1: Power density versus voltage of novel regenerative technologies ....................................... 12

List of Illustrations

Figure 1: Tri-Copter and Tri-Rover ........................................................................................................ 17

Figure 2: Piezoelectric actuation from wheel vibration ........................................................................ 17

Figure 3: Photovoltaic cell placement ................................................................................................... 18

Figure 4: Photovoltaic cell Tracker ........................................................................................................ 18

Figure 5: In-Hub drive motor with Regenerative Braking ..................................................................... 19

Figure 6: Articulating Chassis ................................................................................................................ 20

Figure 7: Articulated Chassis with Tri-copter in wind capture position ................................................ 20

Figure 8: TEG Matrix between a Voltage Regulator and a Heat sink .................................................... 23

Figure 9: 1:1 scale Energy Harvesting PCB Track layout - TOP | Bottom .............................................. 29

List of Diagrams

Diagram 1: Voltage Rectifier and Regulator Circuit .............................................................................. 12

Diagram 2: Photovoltaic Charging Circuit ............................................................................................. 13

Diagram 3: Simplified BLDC Regenerative ESC Circuit .......................................................................... 14

Diagram 4: 3S Li-Po Balancing Charger Circuit ...................................................................................... 16

Diagram 5: Energy Harvesting and Battery Management Circuit Diagram .......................................... 22

Diagram 6: TPS61200 Boost Converter Circuit Diagram ....................................................................... 24

Diagram 7: Piezoelectric Transducer Experiment 1 .............................................................................. 25



Diagram 10: Piezoelectric Transducer Experiment 4 ............................................................................ 26

Diagram 11: Thermo Electric Experiment ............................................................................................. 28

List of Photographs

Photo 1: Miniature Thermoelectric Generator(Custom Thermoelectric, Inc., 2011) ........................... 21

Photo 2: Tri-Copter require high current voltage regulators ................................................................ 21

Photo 3: Piezoelectric Transducer Experimental setup ........................................................................ 26

Photo 4: Model Chassis for Piezoelectric Transducer excitation. ......................................................... 27

Photo 5: Etched PCB - Top .................................................................................................................... 29

Photo 6: Etched PCB - Bottom .............................................................................................................. 29

Photo 7: Manufactured PCB - Top ........................................................................................................ 30

Photo 8: Manufactured PCB - Bottom .................................................................................................. 30


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Photo 9: Assembled Energy Harvesting with Li-Po Balancing Charger Board ...................................... 30

Photo 10: PicoScope 2204 USB Oscilloscope ........................................................................................ 34

Photo 11: My Desk ................................................................................................................................ 36

Photo 12: My Microscope/Webcam ..................................................................................................... 36

Abbreviations

Table 1: List of Abbreviations and Acronyms

Abbreviation Description

UAV Unmanned Aerial Vehicle Li-Po Lithium Polymer ESC Electronic Speed Controller BL Brushless motor DC Direct Current PV Photovoltaic or solar [cell]

Symbols

Symbol Description

The transducer damping ration in equation (1) °C Degrees Celsius (Temperature) Ω Ohm, which is the unit of electrical resistance to current flow.

Terms


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1. Introduction Unmanned Aerial Vehicles (UAVs) are very useful in many fields. More specific to this study are

Multi-Rotor Helicopters such as Quad-copters or Tri-copters. These platforms are useful due to their

stability and maneuverability. They can often carry a substantial Payload (up roughly 1 kg) while still

being very lightweight themselves (less than 500g), which make them ideal for applications requiring

Cameras, or sensors such as GPS, magnetometers (digital compass) and others as the application

requires.

The main limitations of these devices is the facts that there batteries need to be recharged or

swopped out when they run out, which, depending on the weight of the payload and/or the

conditions, might be very often. This required the UAV to return to a home base every couple of

minutes, limiting the distance it is able to operate from any pre-existing charging station.

In this study, I will be investigating whether it is possible to extend, possibly indefinitely, the range

and therefore the autonomy of a small UAV. In these devices, one of the main limiting factors is the

weight of the device and also the maximum payload it is able to carry. Therefore this study will

consider the weight (or energy density) of any charging system as one of the primary variables.

2. Theoretical Analysis and Literature Survey In this section I will be discussing the various novel ways of generating energy in a lightweight

system.

2.1. Piezoelectric Generators Piezoelectric generators harvest vibration energy from their environment.

Graph 1 shows a plot of the power density versus voltage of novel regenerative technologies

illustrating that, in some cases; piezoelectric energy harvesting can provide power density and

voltage values that are comparable to lithium and lithium-ion secondary battery technologies.(Cook-

Chennault, 2008)


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Graph 1: Power density versus voltage of novel regenerative technologies

Since energy generation from piezoelectric generators is alternating voltages, a voltage regulator

must be employed to smooth this to a DC voltage to make it useful for charging a battery. Diagram 1

depicts such a circuit.

Diagram 1: Voltage Rectifier and Regulator Circuit

For a sinusoidal excitation vibration, the electrical power generated, , by the system is given by

Piezoelectric

transducer Voltage Regulator

(1)

This graph has been

reproduced with permission

from the author.


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In equation (1), is the transducer damping ratio (

), is the natural frequency of the

system, is the amplitude of the vibration and is the excitation frequency. The maximum output

power occurs at the natural frequency of the generator. (Cook-Chennault, 2008)(Erturk, 2011)

This would mean that an ideal generator would need to select the piezoelectric transducers which

match the expected frequency that they would be disturbed by.

2.2. Photovoltaic cell While Photovoltaic (or Solar) cells have lower power density than piezoelectric generators, as shown

in Graph 1 above, a Photovoltaic cell does not require the system to be in motion, using energy, to

generate energy. It simply needs to be in the presence of ambient light, such as sunlight. To that end

solar energy would be ideally positioned to recharge any fully drained batteries.

As shown in Diagram 2, to connect a Photovoltaic cell into a charging circuit, the only requirement

would be to implement a voltage regulator to smooth the voltage as this would vary depending on

the intensity of solar energy (or light) that falls on the Photovoltaic cell array. (Markvart, Tomas

(Second Editor), 2000)

Diagram 2: Photovoltaic Charging Circuit

2.3. Generator In these systems, any motor used for propulsion, can also generate power when they are set into

motion by factors external to the system. In small Multi-Rotor helicopters, Brushless DC motors are

often used for propulsion. These motors are often 3 phase motors which are ideal for use as

generators. This would entail regenerative breaking (which for multi-rotor helicopters would actually

benefit the overall system, as the breaking effect would improve the response times where motors

have to suddenly reduce their speed).(Jarrad Cody, Özdemir Göl, Zorica Nedic, Andrew Nafalski,

Aaron Mohtar, 2009)


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Diagram 3: Simplified BLDC Regenerative ESC Circuit

Diagram 3 shows a simplified Brushless (BL) DC Regenerative Electronic Speed Controller (ESC) with

the green arrows indicating the direction of current during a Regenerative Charging Cycle.

An open source implementation of such a system can be seen by visiting the Open-BLDC Project site1

2.4. Thermoelectric Generators Any heat generating components in the system would normally require heavy heat sinks or fans to

keep cool, the latter consuming even more energy. In these cases a Thermoelectric Generator allow

for superior cooling while also harvesting this energy to charge the batteries after converting it to

electricity. Because these devices are actively cooling, you would require comparatively smaller heat

sinks which would offset the weight of the addition electronics required.

Similar to photovoltaic cells, thermoelectric generators output direct voltage and current with little

fluctuation once the operating temperatures have been reached. The only requirement for a

charging circuit would be a DC to DC voltage regulator to ensure a usable voltage is being fed to the

battery (or charging circuitry).

2.5. Other Energy Harvesting Devices In this section I would like to mention some addition energy harvesting solutions that may become

effective in the near future or employed in addition to the methods discussed in this study.

Some are still in Laboratory prototype phase and/or would currently be impractical for various

reasons.

1 http://open-bldc.org/wiki/Open-BLDC

http://open-bldc.org/wiki/Open-BLDC


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2.5.1. Hydrogen Fuel Cells 1. Artificial Leaf

The artificial leaf — a silicon solar cell with different catalytic materials bonded onto its two

sides — needs no external wires or control circuits to operate. Simply placed in a container

of water and exposed to sunlight, it quickly begins to generate streams of bubbles: oxygen

bubbles from one side and hydrogen bubbles from the other. (Chandler, 2011)

Although this is a very novel way of hydrogen extraction, the additional requirement to use a

separate fuel cell to convert the captured hydrogen into electricity, and the fact that the

work is currently in prototype, the overall weight of the system will also make it un-

acceptable for use in a UAV at present.

2. Micro Fuel cell (Barras, 2009)

This device, a self-regulating hydrogen generating fuel cell, seems very promising, especially

due to the fact that the only input required is water. Provided a mechanism can be devised

to filter debris and other impurities from the water to a point where this device would be

able to make use of it, it could harvest energy from rain water or even general moister in the

surrounding air. Due to the fact that these devices are still in laboratory prototype phase, I

have excluded them from this study.

2.5.2. UAV perching (Cory, 2010) In this study a fixed wing UAV perches on a cable, which could be a High Voltage Transmission Power

Line, which would allow the UAV to charge from the electromagnetic field that surrounds it. Since

Multi-Rotor Helicopters can hover in place and allows much finer control, this method of recharging

would be very useful and possible, but High Power Transmission Lines are not always available in

every environment.

2.5.3. UAV Power Link (LaserMotive, n.d.) In this proposition the UAV is constantly or temporarily fed power via a laser beam pointed at it from

a ground based unit. Although this has been proven useful in practice, it still limits the range of the

UAV to within the line of sight of the base station.

2.6. Energy storage

2.6.1. Lithium Polymer (Li-Po) Batteries These batteries are lightweight (and thus have a high energy density) which make them ideal for

lightweight applications such as those discussed in this study. Where more than a single cell is used,

they do have to be balanced while charging to improve their lifespan, and guard against failure,

which require some additional electronics.

2.6.2. Li-Po Battery Balancing Lithium Polymer batteries (where more than one cell is used) must be balanced to ensure that each

cell remains within a couple of millivolts of the other cells to guard against malfunction and/or


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damage. All voltage generating circuits will have to feed into a balancing circuit before being fed into

the Batteries.

Diagram 4: 3S Li-Po Balancing Charger Circuit


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3. Conceptual Design Over relatively short distances, it is often more efficient to drive than it is to fly. However, flying

provides the ideal vantage point for many applications. One option would be to combine the two

ideas for best efficiency.

In this case a vehicle could drive where there are no requirements for aerial observation and then lift

off when required. The addition of drive hardware would severely increase the overall weight end

therefore reduce the flight time. To overcome this, the flying and driving system might be separate

systems that are complimentary to each other in the form of a ground based rover able to attach

and detach from a Tri-Copter.

Figure 1: Tri-Copter and Tri-Rover

In this configuration the rover should still be as lightweight as possible so that the Tri-Copter would

be able to lift it over un-drivable obstacles.

This configuration also provides additional energy harvesting opportunities as discussed later in this

section.

3.1. Piezoelectric Generators Figure 2 below shows a potential suspension configuration to capture the rolling vibration generated

when the wheels roll over the ground. Additional Piezoelectric transducers may be placed in various

locations to maximize the energy harvesting from vibrations throughout the system.

Figure 2: Piezoelectric actuation from wheel vibration

Anchor Ring

Piezoelectric transducer

Swivel joints

Anchored to chassis

Linkage Arm

Anchored to wheel


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3.2. Photovoltaic cell The Photovoltaic cell as seen in Figure 3 is placed on top of the articulating chassis (see section 3.4

below) to maximize potential for capturing light from ambient sources including the sun. Chassis

articulation and steering would allow the rover to change the angle and direction the Photovoltaic

cells are facing to become lined up with the sun to further maximize solar energy capture.

Figure 3: Photovoltaic cell placement

Figure 4: Photovoltaic cell Tracker

Using the normal steering mechanism in combination with the articulating chassis, the rover would

be capable of fully tracking the sunlight to maximize the efficiency and effectiveness of the PV cells.

In practice this improves the amount of captures energy from the PV cells by roughly 20%. An

example of the rover chassis articulated to set the PV cell angle to 30° from the horizontal can be

seen in Figure 4. This angle would be calculated from data captured by a GPS Chip to pinpoint the

current Latitude, the current time of day and the date (or more precisely the day of the year).

Photovoltaic cells


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3.3. Regenerative Braking The rovers drive power is delivered by an in-hub Brushless (BL) DC motor which is controlled by a

Brushless DC Regenerative Electronic Speed Controller (ESC). This reduces the overall weight of the

system as well as the mechanical stress in comparison with systems including gearing and drive

shafts.

Figure 5: In-Hub drive motor with Regenerative Braking

3.4. Wind Turbine An Articulated Chassis combined again with the steering system would allow the system to turn the

Tri-Copters rotors into the wind to allow for capturing wind that may be present in the environment.

This is possible because similar to the ESC used by the rover for Regenerative braking (see section

3.3 above), would be employed to control the three motors that drive the rotors.

Figure 6 shows the articulating chassis which would allow the rover to pivot up and down using the

Articulation motor which would turn a threaded shaft which is anchored to the other side. Also

visible in this figure is the Tri-Copter Docking guide. Using this mechanism, avoids the need for

complex precision landing functionality to land perfectly on top of the rover. Here the Tri-Copter

would simply land. The rover would then generally align with the front of the Tri-Copter and drive in

underneath it. The rear leg of the Tri-Copter would be captured by the docking guide to ensure the

docking alignment. The docking guide also protects the piezoelectric transducers from damage

during this procedure.

Electric brushless DC motor


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Figure 6: Articulating Chassis

Figure 7 shows the articulated chassis which pivots the Tri-Copter to be in a better position to

capture airflow.

Figure 7: Articulated Chassis with Tri-copter in wind capture position

Wind Direction

Articulation DC

drive motor

Tri-Copter

Docking

Guide


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3.5. Thermoelectric Generators Many components in a system like this are prone to generate substantial amounts of heat. This heat

may be captured by new miniature thermoelectric generators as shown in Photo 1 below (Custom

Thermoelectric, Inc., 2011).

Photo 1: Miniature Thermoelectric Generator (Custom Thermoelectric, Inc., 2011)

Devices like these could be placed on various surfaces that generate substantial amounts of heat.

These include Voltage regulators, Electronic Speed Controller power transistors, amongst others.

Photo 2 below, highlights one of the voltage regulators, which generate enough heat, on the Tri-

Copter which presents enough service area to easily place roughly 6 of these miniature devices,

which can in turn be arranged in series to increase the overall voltage generated or in parallel to

increase the overall current produced.

Photo 2: Tri-Copter require high current voltage regulators

High Current Voltage Regulator


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4. Detailed Design

Diagram 5: Energy Harvesting and Battery Management Circuit Diagram

In Diagram 5, the energy harvesting and Battery management circuit diagrams are depicted. Each

marked section depicts the different circuits required to harvest energy from the different

generators employed and will be discussed in detail for the remainder of this section.

4.1. Photovoltaic Solar cells and Piezoelectric Generators In the above circuit, each Photovoltaic (PV) cell paired with a piezoelectric generator via a LTC3588-1

Piezoelectric Energy Harvesting Power Supply Chip (Linear Technology, n.d.) from Linear Technology.

The Piezoelectric generator is connected as a backup battery, both of which will supply the required

output voltage. In Diagram 5 the LTC5388-1 have been configured to produce a stable 3.6V output

by setting both D0 and D1 to Vin2. This achieved by the circuit allowing voltage to be built up in

storage capacitors. This voltage is then released as usable voltage.

4.1

4.2

4.3.1 4.3.2


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4.2. Thermoelectric Generator Matrixes In Diagram 5 the Thermoelectric generator (TEG) matrixes (Custom Thermoelectric, 2011) have been

arranged to form multiple strings of 4 generators arranged in series (To provide 4 Volts), each of

which are then connected in parallel to allow for more usable current to be generated.

This arrangement is depicted in Figure 8. Here you can see 16 individual TEG’s arranged in a 4 x 4

matrix. Each component is 2.5mm x 3.2mm x 1.4mm. Each component is capable of generating 1

Volt at 1 Amp.

Figure 8: TEG Matrix between a Voltage Regulator and a Heat sink

The output from all TEG matrixes are connected in parallel and also fed through another LTC5388-1

as shown in Diagram 5.

4.3. Battery Management All the outputs from the various LTC5388-1 energy harvesting circuits are fed into a single 3.6V

power rail.

4.3.1. Boost Converter This 3.6V then feeds 3 individual TPS61200 (Texas Instruments, 2008) circuits.


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Diagram 6: TPS61200 Boost Converter Circuit Diagram

Given Formula 1 in the Datasheet (Texas Instruments, 2008):

Setting R2 = 200KΩ and VFB=500mV

A standard resistor near this value is 1.2MΩ. To allow for this Resistance to be accurately set, a

270KΩ potentiometer is placed in series. This arrangement would allow the output voltage to be set

much more accurately to 4.2V.

Similarly, R3 and R4 are set according to equation 2 in (Texas Instruments, 2008):

R3 = 2.4MΩ,

R4 = 270KΩ

Which sets Vinmin ≈2.5V

Because the target Li-Po battery consists of 3 cells, each individual cell must be charged and

balanced at 4.2V. Care should be taken to isolate each of the Boost converter’s Power Ground from

the main ground, except for the one providing voltage for cell 3 as this would be grounded to the

general ground. Here each Boost converter is arranged in parallel to provide an overall maximum of

12.6 V.

4.3.2. Li-Po Shunt Battery Balancing Charger Here 3 LTC4070 (Linear Technology, n.d.) components are used that are specifically designed to

Charge Lithium-Polymer (Li-Po) Batteries at the required 4.2 V from very low current, intermittent or

continuous charging sources.

(2)

(3)


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4.4. Regenerative Braking The regenerative braking energy provided by the Electronic Speed Controllers are fed directly back

into the battery as a high enough voltage is generated to feed all 3 cells. This functionality is also

encapsulated in the Brushless DC Electronic Speed controller.

5. Experimental Evaluation The TPS6200, LTC4070 and LTC3588 are 0.5mm pitch SMD components, which make it difficult (but

not impossible) to produce the circuit boards for this system since it would in all probability never be

mass produced. Although this does allow for a very small board footprint which require less weight

as board sizes can be reduced.

Further experimentation will be carried out once the boards have been created to allow for the

small components to be soldered in place for experiments.

5.1. Piezoelectric generators 3 different configurations were tested to test the highest achievable voltage by using discrete

components.

Diagram 7 depicts a single piezoelectric transducer connected to a full wave Bridge Rectifier.

Diagram 8 shows 2 piezoelectric transducers, each rectified with a full wave bridge rectifier

connected in parallel.

Diagram 9 represent 3 piezoelectric transducers connected in a 3 phase star formation

connected to a 3 phase full wave bridge rectifier.

Diagram 10 illustrates 2 piezoelectric transducers, each connected to a full wave bridge

rectifier, connected in series.

In each of the experiments an LED load was placed in parallel with a 10µF smoothing capacitor.

Diagram 7: Piezoelectric Transducer

Experiment 1

Diagram 8: Piezoelectric Transducer Experiment 2


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Diagram 9: Piezoelectric Transducer Experiment 3

Diagram 10: Piezoelectric Transducer Experiment

4

In Photo 3 you can see the

experimental layout for Diagram 7

above. In this photo the small DC

motor is visible with off centered

weight which induced vibration at a

constant rate for consistent testing.

With this same setup, the various

layouts discussed above were

tested.

One concern with this experiment is

that where more than one

piezoelectric transducer is placed

close together (e.g. one above and

one below the ABS plastic strip) the

phase shift introduced during

testing may have a canceling effect

on each other.

Photo 3: Piezoelectric Transducer Experimental setup


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During experimentation, enough power was produced to turn the green LED visible in Photo 3, on

consistently at roughly 1.71V. Unfortunately I had difficulty in producing much, if at all, higher

voltage with any of the various layouts discussed above. This may however be due to the

cancellation each unit would have on the other, or that the power from each unit was not consistent

enough at the tested frequency.

Due to this complexity the individual harvesting circuits via LTC3588-1 integrated circuits (as

discussed in section 4.1), were introduced which are purpose built for this requirement and also

keep the two piezoelectric transducers isolated from one another.

Photo 4: Model Chassis for Piezoelectric Transducer excitation.

Photo 4 shows a model chassis section built to scale which would be used to push on the

piezoelectric transducers as the rover roles forward on rough terrain. Comparing this to the CAD

sketches in Figure 2 shows that this design is conceptually sound. The material used was 3.2mm and

4.8mm round tube and 1mm x 4.8mm flat strips of lightweight Compressed Polystyrene. This

produced a lightweight but rigid structure.

5.2. Thermoelectric Generators Thermoelectric generators produce a consistent voltage at a given Δt (Temperature delta).

Experimentation shows that when these cells are connected in series as depicted in Diagram 11, the

total voltage consistently doubles as expected. Similarly Current capacity doubles when the

thermoelectric generators are arranged in parallel.

These devices do however produce a very moderate voltage which makes them ineffective to drive a

load directly on their own. For this reason, as depicted in Figure 8, they should be arranged in a

matrix to allow for a usable voltage and current to be extracted from a given arrangement.


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Diagram 11: Thermo Electric Experiment

Adding these devices to the Energy Harvesting circuit depicted in 4.2 allows for useful voltage to be

extracted due to its ability to slowly charge a storage capacitor, which in turn is discharged into the

load when enough energy has built up.

5.3. Photovoltaic Cells To simplify the management of the Photovoltaic cells in terms of bypass diodes for when some are

shaded and also allow voltage to be built up to a useful voltage, they are connected directly to the

Energy Harvesting circuits in a one to one arrangement as backup to the piezoelectric transducers.

5.4. Regenerative Braking Regenerative braking as provided by Open-BLDC requires further experimentation as the devices are

not readily available at this stage in their development.

5.5. Energy Harvesting PCB To allow for the lightest weight and smallest form factor, SMD (Service Mount Device) components

were used where possible. Due to the fact that this would be a specialist application and because

the project is a prototype, or proof of concept, there is no need to produce more than one PCB

(Printed Circuit Board) at a time, which makes it impractical to have the board manufactured.

The board for testing the energy harvesting circuit discussed in section 4 was manually produced

using the toner transfer method using a laser printer. In Figure 9 a 1:1 scale copy of the toner

transfer images can be seen. Photo 5 and Photo 6 shows the resulting Etched Printed Circuit Board.

Due to the fact that the required equipment to add a Solder mask to the board was not available,

the circuit was sent to be manufactured. (Soldering SMD devices without solder mask would make

assembly very difficult and increases the possibility of errors during assembly.)

Manufacturing was done by Newbury Electronics Limited (www.pcbtrain.com) and totaled £ 65.53

(R 849.27 2) including a £ 5.00 (R 64.80) delivery fee.

2 An exchange rate of R 12.96 (ZAR) = £ 1.00 (GBP) was used.

http://www.pcbtrain.com/


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Photo 7 and Photo 8 show the top and bottom views of the manufactured board with Photo 9

showing the fully assembled board. During Testing, the base sections of the board could be tested

individually and showed that they were working in isolation. However, due to some design errors,

this revision of the circuit board is not fully operational.

This board weighs in at 20 grams, which makes it viable for use in this design. This weight level

should not change much in a later revision as all parts of the circuit work conceptually in isolation.

Figure 9: 1:1 scale Energy Harvesting PCB Track layout - TOP | Bottom

Photo 5: Etched PCB - Top

Photo 6: Etched PCB - Bottom


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Photo 7: Manufactured PCB - Top

Photo 8: Manufactured PCB - Bottom

Photo 9: Assembled Energy Harvesting with Li-Po Balancing Charger Board

Video 1: High speed video of PCB assembly (http://youtu.be/k5F6Gto3oqA)

http://youtu.be/k5F6Gto3oqA

http://youtu.be/k5F6Gto3oqA


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6. Discussion In this study we have been discussing two main types of energy replenishment. These are energy

recovery and energy harvesting.

Energy recovery happens when energy is spent and waste energy is recovered from systems that

expel heat and/or excessive movement.

1. The piezoelectric transducers recover kinetic energy from the rover traveling over rough

terrain, but this can only happen when energy is spent to drive the rover forward.

2. Thermoelectric generators are only useful where circuitry heats up from usage to drive other

systems on the rover or the tri-copter. One possibility to improve this is to bring

Thermoelectric generators in contact with heat sources in the environment where the

system is deployed in places that would support this such as places with hot climates or in

heavy industry where heat sources are easily accessible.

3. Regenerative breaking again requires the rover to have been brought into motion,

expending (in most cases) more energy than can be recovered from stopping this motion.

Energy Harvesting is the mechanism of taking energy from the environment and converting this to

usable energy without spending even more energy.

1. The main way discussed in this study would be to utilize the photovoltaic solar cells when

the rover is stationary and the rover is landed to harvest energy from radiation from the son.

Once the rover batteries are replenished, some of this energy may be used to charge the tri-

copter batteries.

2. Using the regenerative breaking in the Wind Turbine configuration, as discussed in section

3.4 would be another viable option for energy harvesting without expending more energy.

In this study, energy recovery would only prolong the time the system would be operational

between full battery recharges. Once the batteries are fully discharged the system would however

have to be stationary until the batteries can be fully recharged from the environment, such as the

son, heat or wind.

7. Conclusion Micro unmanned aerial vehicles like Tri-Copters have an average battery lifespan between 20 and 45

minutes.

In this study we discussed the possibility of extending the useful mission time of a system like this to

near indefinite time. In addition to this, this design putts no additional limitations onto the systems

and therefore creates new possibilities for Micro-UAV’s using the superior stability and agility on

prolonged missions.

These could include missions centering on surveillance, exploration, mapping and many more. Using

the system in this configuration would also make it completely independent of grid supplied energy

and therefore carbon and energy neutral.


32

8. Recommendations In this study, only some aspects of the full design of a system like this was looked at. Many issues

remain before a system like this can be implemented in the real world. These include:

1. Autonomous Docking System: Some way must be devised for the tri-copter to dock with the

rover which hosts the photovoltaic and energy harvesting circuitry. This has been discussed

at a high level here and would see the tri-copter perform a relatively simple landing on level

and accessible terrain. The rover would then drive underneath the tri-copter and dock with

it. This solution would expend much less energy that a precision landing maneuver.

2. Once the rover has docked with the tri-copter, some mechanism must be devices for the

two vehicles to lock together to allow the tri-copter to lift the rover and carry it over

potential impassable terrain.

3. Once the rover and tri-copter have docked, the batteries from both systems must be

connected to allow them to be fully recharged.

a. Some thought should be given to the fact that the PV cells are covered when the tri-

copter is docked onto the rover, so a more elaborate connecter system should be

employed or the system should charge each part independently.

b. An alternative could be to employ a light magnetic connector, which would allow

the battery connection to remain connected while allowing the rover to back out

from underneath the tri-copter. This magnetic connector would however be easy to

disconnect if the tri-copter would lift off or if the rover moved out of the range of

the cabling. (This system could also guard against connecting batteries the wrong

way around).

4. The chassis and wheels themselves would also need to be constructed from lightweight

material

9. Bibliography Barras, C., 2009. World's smallest fuel cell promises greener gadgets. [Online]

Available at: http://www.newscientist.com/article/dn16370-worlds-smallest-fuel-cell-promises-

greener-gadgets.html

Chandler, D. L., 2011. ‘Artificial leaf’ makes fuel from sunlight - MIT News Office. [Online]

Available at: http://web.mit.edu/newsoffice/2011/artificial-leaf-0930.html

Cook-Chennault, K. A., 2008. Piezoelectric Energy Harvesting. [Online]

Available at: http://www.rci.rutgers.edu/~cookchen/Publications_files/Piezoelectric Energy

Harvesting.pdf

Cook-Chennault, K. A., 2008. Powering MEMS portable devices. [Online]

Available at: http://www.rci.rutgers.edu/~cookchen/Publications_files/A Review.pdf

Cory, R., 2010. The Perching Glider. [Online]

Available at: http://groups.csail.mit.edu/locomotion/perching

Custom Thermoelectric, Inc., 2011. Mini TEC's. [Online]

Available at: http://www.customthermoelectric.com/mini-tecs.html


33

Custom Thermoelectric, 2011. Custom Thermoelectric. [Online]

Available at: http://www.customthermoelectric.com/tecs_mini/pdf/00801-9X30-

10RU3_spec_sht.pdf

Erturk, A., 2011. Piezoelectric Energy Harvesting: Modelling and Application. s.l.:Wiley-Blackwell.

Jarrad Cody, Özdemir Göl, Zorica Nedic, Andrew Nafalski, Aaron Mohtar, 2009. Regenerative Braking

In An Electric Vehicle. [Online]

Available at: http://www.komel.katowice.pl/ZRODLA/FULL/81/ref_20.pdf

LaserMotive, n.d. UAV Power Links. [Online]

Available at: http://lasermotive.com/products/uav-power-links/

Linear Technology, n.d. Li-Ion/Polymer Shunt Battery Charger System. [Online]

Available at: http://cds.linear.com/docs/Datasheet/4070fc.pdf

Linear Technology, n.d. Piezoelectric Energy Harvesting Power Supply. [Online]

Available at: http://cds.linear.com/docs/Datasheet/35881fa.pdf

Markvart, Tomas (Second Editor), 2000. Solar Electricity Second Edition. England: John Wiley & Sons

Ltd.

Texas Instruments, 2008. Low input voltage synchronous boost converter with 1.3A switches.

[Online]

Available at: http://www.ti.com/lit/ds/symlink/tps61202.pdf


34

Appendix A. Measuring Equipment This section lists the various measuring equipment used during experimentation for this project.

1. Digital Multi-meter

a. Model: DT9205A

2. Oscilloscope

a. Model: PicoScope 2204

i. 2 Channel

ii. AWG (Arbitrary Waveform Generator)

iii. 10 MHz bandwidth

iv. 100 MS/s

b. Source:

http://www.picotech.com/entry-level-oscilloscopes.html

Photo 10: PicoScope 2204 USB Oscilloscope

http://www.picotech.com/entry-level-oscilloscopes.html


35

Appendix B. Parts List Most parts used in this design are off the shelf components as listed below. The mini thermoelectric

generators are more difficult and not broadly available in the small size required by this design. They

are however in stock and available for direct order and purchase from CustomThermoelectric.com.

Due to their specialist nature they are also significantly more expensive.

Costs are listed in South African Rand below the local cost, calculated using the following exchange

rates:

1. R 12.96 (ZAR) = £ 1.00 (GBP) , and 2. R 8.26 (ZAR) = $ 1.00 (USD)

Mftr. & Part No. Description Unit Price Supplier

TEXAS INSTRUMENTS - TPS61200DRCT

CONVERTER, BOOST SYNCH, 1.5A, SMD

£ 3.50 [R 45.35]

uk.Farnell.com

LINEAR TECHNOLOGY - LTC4070EMS8E#PBF

BATTERY CHARGER, LIION/POLY, 8MSOP

£ 4.76 [R 61.68]

uk.Farnell.com

LINEAR TECHNOLOGY - LTC3588EMSE-1#PBF

IC, PSU, ENERGY HARVESTING, 10MSOP

£ 6.79 [R 87.98]

uk.Farnell.com

MURATA POWER SOLUTIONS - 11R223C

INDUCTOR, 22UH, 10% 0.65A TH RADIAL

£ 0.24 [R 3.12]

uk.Farnell.com

MURATA POWER SOLUTIONS - 11R222C

INDUCTOR, 2.2UH, 20% 1.9A TH RADIAL

£ 0.24 [R 3.12]

uk.Farnell.com

BOURNS - 3296Y-1-254LF TRIMMER, 250K £ 2.08 [R 26.95]

uk.Farnell.com

VISHAY SPRAGUE - 293D105X9035A2TE3

CAPACITOR, TANTALUM, 35V, 1UF £ 0.16 [R 2.13]

uk.Farnell.com

MULTICOMP - MCCTC106M025

CAPACITOR, CASE C, 10UF, 25V £ 0.68 [R 8.81]

uk.Farnell.com



uk.Farnell.com


CAPACITOR, TANTALUM, 20V, 4.7UF £ 0.07 [R 0.84]

uk.Farnell.com

VISHAY SPRAGUE - TR3C476K016C0350


uk.Farnell.com

VISHAY FORMERLY I.R. - 10BQ015TRPBF

SCHOTTKY RECTIFIER, 1A £ 0.14 [R 1.78]

uk.Farnell.com

KINGBRIGHT - KP-1608MBC

LED, SMD, 0603, BLUE £ 0.52 [R 6.74]

uk.Farnell.com

Custom Thermoelectronic - 00801-9X30-10RU3

Mini Thermoelectronic generator $ 33.50 [R 276.82]

Custom Thermoelectric

SANYO - AM-8801CAR-SCE SOLAR CELL £ 11.68 [R 151.35]

uk.Farnell.com


36

Appendix C. More Photos

Photo 11: My Desk

Photo 12: My Microscope/Webcam

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