Weekly Progress

Week One

After the initial forming of groups it was decided that a phone charger would be constructed.  The original idea was to create a system that would generate electricity from walking.  The concept was to have a generator in between two boards attached to the bottom of a shoe.  Every time the walker would place his/her foot down a system would be wound up, and upon the pick up of the foot the system would unwind causing the generator to spin and produce an electrical current. Figure 1 shows the preliminary design concept for this.

Figure 1:  Board Design

This idea was found to be not feasible for the project.  This idea was scrapped for a new concept.  The new conclusion after some brainstorming was to create a wind powered generator that would be mounted on a bike.  The windmill will be placed underneath the bike rider, in the triangular section as seen in Figure 2.  As the ride pedals the bike, wind will pass over blades of a wind turbine. As the turbine turns a a rod will turn a generator creating a current.  This current will be directed to a battery pack that can be used to charge a mobile phone.

Figure 2:  Sample Bicycle

Week Two

Going into the second week of this project the concept for the wind powered cell phone charger has had tremendous progress. Illustrated in Figure 3 shows the intended final product for the ten week project. The center mounted fan will transfer the rational movement to a AC generator. This will then be converted to DC power and charge the cell phone. The turbine design will have three blades for a good efficiency to cost ratio for the construction. The AC generator will be housed in the grey middle section where a magnet will rotate within a copper coil producing the electricity. An AC to DC converter will be purchased to change the electricity into DC that is required by the phone charger.

Figure 3: Intended final deliverable

Week Three

A main focus of this week was to improve and finalized the generator design.  Originally, the generator was going to be made from a 3 inch long piece of Schedule 40 PVC pipe.  The intended diameter of the PVC was to be 1 1/4 inches.  With this size PVC the exterior diameter will be 1.66 inches.  This PVC pipe will be fitted with end caps that will allow 22 gauge copper wire to be wrapped around the outside of the PVC without moving around.  22 gauge copper wire has a cross-sectional diameter of .0254 inches.  Through some calculation it can be determined that there will be able to be a total of 118 loops of wire (length of pipe/diameter of wire).  It is projected that it will take 615.4 inches (51.28 ft.) of wire to complete all 118 loops.  This was determined by finding the circumference of the outside of the PVC and multiplying it by the number of loops.   Inside the PVC would be two 1" x 1/2" x 1/2" neodymium magnet each with a pull force of 35.39 pounds.  Each of these magnets will have a hole drilled through the center of them so that they can be fitted to an axle.  As the axle rotates inside the PVC the magnets will also rotate.  This rotation of the magnets inside of the coils of wire will cause a current to be induced.  This idea was replaced with a new, more efficient one.  Instead of PVC a piece of aluminum pipe will be used.  This is because the thickness of the aluminum pipe is less than that of the PVC.  This will allow the magnet to be closer to the coils, thus producing a stronger current.  A new way of connecting the magnets to the axle has also been proposed.  The magnets will now be placed on opposing sides of axle, instead of the axle going through the magnet.  This method will not require the magnets to be drilled and potentially be demagnetized.  The magnets will be attached in a similar fashion as that of Figure 4.

Figure 4: Magnets on Axle

This axle will be connected to a gearing mechanism. The gearing mechanism can be seen in Figure 5.  The axle will run through from the wind turbine to the magnets.  As the turbine of the wind generator rotates, the axle will rotate with it.  The gearing mechanism that is proposed will increase the speed of rotation at the point of the magnets to 27 times the speed of the axle at the blades of the wind turbine.

Figure 5: Gearing

During this week two concrete items were constructed.  The first is a boost circuit.  This circuit takes a lower voltage and steps it up to a higher voltage.  As it can be seen in Figure 6, two 1.5 volt AA batteries are in a housing connected to the circuit.  Assuming these batteries are charged to their limit, and since the batteries are connected in series, the expected potential difference across the terminals would be 3 volts.  Figure 7 shows how the boost circuit has taken the 3 volts and stepped it up to nearly 5 volts.  Figure 6 shows how the use of a boost circuit can allow 2 AA batteries to charge an iPhone.

Figure 6: Boost Circuit

Figure 7:  Boosted Voltage

Figure 8:  Prototype Generator

The second item that was crafted was a small simple generator that was created as somewhat of a prototype.  The goal of this generator was to view the process that it takes to construct a generator.  A piece of cardboard was cut and wrapped with 20 gauge copper wire.  A nail was then taken through the center of the cardboard, acting as an axle.  The magnets were then attached to the nail as shown in Figure 4 above. The ends of the wires were connected to a light bulb in a fixture, which acted as a resistor.  The prototype generator can be seen in Figure 8.  The generator, however, did not seem to produce a current as it was expected to.  It is believed that this is due to excess space between the magnet and the copper wire loops. In the circular generator that is proposed for the future, the magnets will be much closer to the loops.

Week Four

During Week Four, another two prototypes of a generator were designed.  The first, done in lab, was a simple test generator made from K'Nex.  This generator only had 15 turns of copper wire, but it was able to produce a 20 mV potential difference.  Though this is far lower than the required 3 volts needed as the input into the boost circuit, it is a step in the right direction.  It is believed that a better coiling process with the coils closer to the magnets is the reason for the improvement. Thursday of Week Four the third prototype generator was crafted.  Figures 9 and 10 show this third generator, made from K'Nex as well.  This version was slightly larger than the first K'Nex prototype.  Oddly, this generator did not seem to draw a current.  This is believed to be due to the copper wire used to wrap the generator was believed in previous generators.

Figure 9:  Front View of Prototype 3 

Figure 10:  Side View of Prototype 3

For the upcoming week there are a few set major goals that would like to be accomplished. The first of these is test the field strength of the magnets discussed in Week Three.  Figure 11 shows the four 1" x 1/2" x 1/2" neodymium magnets.  The second goal is to determine the value of A that will be used in the theoretical calculation of Faraday's Law (Voltage Generated = -NΔ(BA)/Δt), where N is the number of turns of the wire, B is the magnetic field strength, A is the area perpendicular to  the magnetic field, and t is the time it takes to change either the field strength or perpendicular area.  Once the copper wire, which was ordered online, arrives, the construction of the actual generator will commence.  This should be completed within the next two weeks, leaving ample time for construction and modifications to the circuitry and the wind blades.

Figure 11: Neodymium Magnets

Besides the generator, the 3D Creo model of gearing box is also created. The gearing box  is 4*5*4(unit: inches). The mechanism of this gearing box is to use the radius difference between big gears and small gears. As shown by Figure 10, the fan will be connected to the cylinder which had big gear. Then the rotation of big gear will induce the rotation of small gear which connected to it. As the radius of big gear is  about 3 times bigger than that of the small gear, one rotation of big gear makes 3 rotation of small gear.  There are 3 connections between big gears and small gears in the gearing box. Thus the total gearing ratio is around 1:27.

Week Five

Week five presented a problem that slowed production of the generator.  Due to a back order of the copper wire that will be used to wrap the outside of the piping to make the generator, progress of the generator has been halted.  Within the next couple of days, the wire should arrive and construction on the generator can commence.  Though actual construction of the generator has not been able to begin, the analytical data of the generator has been finalized.  Through the use of a gaussmeter, the magnetic field strength of the neodymium magnets (B in Faraday's Law) was found to be

Figure 12: 12 Volt Generator

.55 Tesla.  The area of copper wire perpendicular to the magnetic field was determined to be .25 square meters.  The number of possible coils that will be wrapped around the outside of the piping is (N), found in week three, was 118 wraps.  As a precaution, a 12 Volt generator that runs at 6 Watts was purchased  in case there are further problems with the constructed generator.  Figure 12 shows this generator.

Figure 13: 3D Printed Blades

In this week of the project, the 3D printed fan blade turbines were returned from the printer.  Figure 13 shows the final product of the printing.  In Video One, seen below, the fan blade is being tested with the air flow from an air conditioning unit.

Figure 14: Ball Bearing

Figure 15: Revised Gearing Box 

The gearing box was also redesigned in this week and can be seen in Figure 15. In order to decrease the effect of friction from the rotation, ball bearings (Figure 14) were inserted in the gearing box on the axles.  Thus, the radius of cylinders were narrowed in order to fit the inside radius of ball bearings which is approximately 8 mm.

Week Six

This week's work resulted in a major change to the design process.  After much discussion it was decided to use the purchased generator as the power source to the phone charger.  Everything else about the system will remain the same, except for the generator.  This purchased generator will be fitted to the gearing box and will be controlled based on the rotation of the fan blade.  Two of these small generators were purchased: one that will be used in the final product and one that could be taken apart to see how it operates.  Figures 16 and 17 below show the disassembled Dynamo generator.

Figure 16: Bottom View of Dynamo

Figure 17: Top View of Dynamo

This is a bike dynamo two phase AC generator with two voltage outputs.  The first connection is marked as H for Headlight and the second connection is marked as T for Taillight.  The H connection output around 20-25 volts under a 8.5 Ohms load which is a 45-55 watts of power max.  The T connection outputs around 5-7 volts under shortage and we feel this wont be enough power.  This boost in power is a major step for us because our own K'Nex prototype only got us about 4 mW of power.

A final version of the gear box was also constructed.  After receiving the 3D printed gear box, the fan blade was attached to the axle.   Figure 18 shows the printed gearing box with the attached fan blade.

Week Seven

During Week Seven assembly of the entire project began.  With the fan blades attached to the gear box, an artificial wind was blown over the turbine.  This wind was created with two blow dryers.  In this testing, it was found that the blades were not creating the necessary torque to rotate the axle.  To accommodate for this, a new, larger fan is being printed.  A larger fan is capable of capturing more wind to power the rotation of the axle.  Another issue that was seen in this was that of friction.  It is believed that there is too much friction in the gearing system that is inhibiting the rotation of the axle.  To fix this issue, some gears may potentially be removed from the system.  Another change was made to the gears as well.  In order to increase the strength of the gears, the teeth were changed from a triangular shape to a rounded edge.

Another experiment was done in order to see the voltage output of the generator.  The rotating wheel of the generator was placed against the tire of a bicycle so that when the bicycle wheel was turned, the generator turned.  To measure voltage output an oscilloscope was used.  The oscilloscope would display the waves of the electrical current in a plot of voltage versus time.  At first the generator was wired directly into the oscilloscope.  The result was a sin wave from -10 to 10 volts.  A rectifier chip was then wired into the circuit before the oscilloscope.  This took the -10 to 0 volts component of the sin wave and reversed it to give a 0 to 10 volt potential difference as shown in Figure 20.  It can be seen in this figure that the frequency of the wave of the circuit with the rectifier is more than  that of the wave without the rectifier chip.  With the same rotational speed of the generator, the frequency of the wave seems to double.  This makes sense, since half of the being inverted to the other side.

Figure 19: Voltage Without Rectifier

Figure 20: Voltage With Rectifier

Week Eight

During this week, some data were collected about the generator.  The rotating end of the generator was placed against the wheel of an inverted bicycle, and the bicycle was pedaled.  The rotation of the bicycle wheel caused a rotation of the axle to the generator, therefore creating an electric current.  Due to the addition of a capacitor to the circuit, the sin wave of the voltage, as seen in Figure 20, was able to be smoothed out to a nearly straight line.  A capacitor will ensure that there is always a constant discharge of power, which creates a smooth line instead of the increasing and decreasing wave seen without the capacitor.  After getting a reading from the oscilloscope it was decided that an actual test on a cell phone was necessary.  The USB of an iPhone was plugged into the circuit and connected to the phone.  As the wheel of the bicycle was turned, the iPhone began to charge.  It was noticed that it seemed to take very little rotation of the generator to charge the phone.  This led to the idea that the gear box may not be necessary for this project.  The gear box adds extra weight without increasing efficiency due to the friction between the gears.  Further testing on the gear box to reduce friction will be needed in order to determine if the box will be used in the final deliverable.  This week, readings will be taken of how long it takes to charge a predetermined amount with a constant rotational speed.

All of the  new fan blades were returned this week, allowing for testing to find the details of the output of the generator to begin.  The new blades are essentially double the size of the original blades. Figure 21 shows the hub with one blade.  This new fan design is much heavier than the initial design.  It is believed that the extra weight may be a problem in trying to get the necessary torque to turn the fan.  A leaf blower was used to create an adequate to spin the fan.The larger of the fan blades was first tested.  The blades rotated very well, but they did not produce enough current to power the phone.  It is believed the extra weight caused a decrease in speed of the turbine.  Video 2 shows the larger blades against the wind current.

Figure 21:  Large Fan Design

Video 2

Video 3

The smaller of the two fans was next.  This managed to produce a potential difference of 8 volts at .15 amps.  This is only 15% of the current necessary to charge the phone.  Video 3 shows the smaller fan rotating.