ENGN1000: Projects in Engineering Design: Spring 2010

 

Energy Harvesting Running Shoes (EHRS)

Team: Will Ellis, Ahalya Nirmalan, Kathryn Schwink, Jake Wasserman

 

Project Summary:

Our project is to design a pair of running shoes that will power an iPod.

 

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Intro:

 

An iPod battery does not last forever. It runs out eventually, and sometimes we forget to charge it until we need it. As any person on the go knows, when that happens away from home it could be disaster unless you have brought your charger with you AND have access to an outlet. Our project solves these problems by allowing the user to always have power (and music!) as long as they are in motion.

 

This product has numerous benefits to both users and the environment. Anyone involved in a repetitive motion stepping exercise, such as jogging, hiking, or dancing, will be able to recharge their iPod battery while exercising. Not only is this convenient and time efficient, but it is environmentally friendly as well, since the combustion of fossil fuels or any other standard energy generation method is not required. With these Energy Harvesting Running Shoes, the mechanical energy of exercise is simply converted directly into usable electric power!

 

No iPod? No problem. Whatever you need to charge on the run (get it?) will work (within reason - it would take a lot of running to charge a laptop!), as long as it has a usb adapter. In addition to joggers and dancers, this product may also be targeted for hikers, day trippers, mountain climbers, or anyone with a need to charge things on the go without having to lug around a car battery or worry about finding an electrical outlet in, for example, the woods, on a mountain, or at work. Not only that, but we are hoping to make it versatile enough to let the user pump the charger with his or her hands for use on boats, airplanes, or anywhere long walks are not necessarily an option.

 

Background: 

 

While a variety of so-called Smart Shoes are already in existence, none of them meet the requirements set for our Energy Harvesting Running Shoes.

 

One such shoe uses piezoelectric materials to sense the shoe impacting the ground, and then sends information to a small computer for analysis.  Some such shoes are even capable of adjusting the cushioning of the sole of the shoe to optimize comfort and performance.  However, this design produces only a small signal and no usable power (http://findarticles.com/p/articles/mi_m0846/is_4_24/ai_n6357618/).  Another class of Smart Shoes uses piezoelectric materials embedded in the sole to generate power ( http://alumni.media.mit.edu/~nate/shoes.html).  However, despite extensive internet searches, no such shoe could be found for purchase.  Additionally, piezoelectric materials are very inefficient, produce little energy, and are very costly.

 

Existing Solutions: Pros and Cons for the User

	Pro	Con
Sensing Shoe	Commercially available	Do not generate electricity
Energy-producing Piezo shoes	Generate small amount of harnessable power	Not commercially available, expensive

 

Brainstorms:

 

Since the team's original idea was to develop an energy harvesting shoe powered by piezoelectric materials, research was performed to determine just how much energy could be harvested in this manner. Fortunately, a fair amount of publications exist pertaining to energy harvesting shoes designed for military applications. However, most publications either report that the total energy harvested was simply too small for power intensive applications or the shoes were too uncomfortable for long range missions. In order to work around these piezoelectric shortcomings, an alternate method of energy harvesting was investigated.

 

Our goal is to turn up-and-down motion into electricity using a gear system and microgenerator.  However, since our team consists of materials engineers, familiarity with gear systems was limited. While brainstorming solutions, we recalled the light-up wheel guns that we used to play with as children. We remembered squeezing a trigger linearly, which caused a wheel to spin and a bulb to light. The faster and more frequently we squeezed the handle, the faster the wheel would spin and the brighter the colors would be. Unfortunately, we were unable to find these toys.  However, this concept led us to investigate squeeze-powered flashlights as a mechanism for converting up-an-down motion into energy we could harness.

 

Here is our thought process regarding potential solutions for our problem:

 

Potential Solutions:

• Piezoelectric material
• Definition: Can generate electrical potential in response to an applied mechanical stress
• Contacted Mide company about their Volture Piezoelectric Vibration Energy Harvester (http://www.mide.com/products/volture/volture_catalog.php#peh) that produces electrical energy from high frequency vibrations of a piezoelectric material.  Unfortunately, they believe running would only produce a few to a hundred microwatts of energy, which would not be sufficient for our application.

•  Compressed air from a bellow within the shoe to power a micro generator.

• Contacted Ferguson Engineering regarding their air-powered micro motors.
• Connect the micro motor to an electrical generator to produce electricity.
• Could potentially destroy the functionality of the running shoe due to the bellow in the sole of the shoe as well as the bulkiness and weight of the proposed system.

• Squeeze system made up of a flywheel and a dynamo (an electrical generator that converts mechanical rotation to electrical current via magnetic induction).

• Idea: Taking apart a squeeze flashlight and re-engineering the gears to account for the change from side-to-side motion to the up-and-down motion in a running shoe.
• Technology: A dynamo generator works by rotating a magnet about a stationary coil of wire, inducing a current in the wire.  A gear mechanism placed inside the sole of the shoe will convert the up and down motion of jogging into a rotary motion to spin the magnet.
• http://en.wikipedia.org/wiki/Dynamo
• This could be inexpensively built by purchasing and adapting an already existing product.  Due to the low prices, we could also buy multiple versions of squeeze flashlights in order to see which would be most optimal for our design.
• Cranking the flashlight for one minute provides 15 minutes of power to the LED light, suggesting that there is sufficient power for our application.

 

Our Proposed Solution:

 

We have decided to use a squeeze flashlight system that can be built into a running shoe.  We have ordered several different squeeze flashlights that we can take apart and reverse-engineer.

 

The following pictures show several types of flashlights, including images of their internal mechanisms.

 

 

 

 

 

 

Requirements:

 

• This system MUST generate power through the motion of running.
• The functionality of the shoe MUST be maintained.
• The charger SHOULD operate between 4.75-5.25 V (http://www.instructables.com/id/How-To-Make-Your-Own-USB-Car-Charger-For-Any-iPod-/)
• The shoe SHOULD be comfortable.
• The shoe SHOULD be successfully connected to an iPod.
• The shoe MAY generate sufficient power to play an uncharged iPod while running.

 

Intellectual Property:

 

An extensive patent search has been conducted in order to ensure the novelty of our idea.

 

A commonly-patented variety of smart shoes is one that uses a pressure sensor in the insole to send data regarding the forces on the shoe and the number of steps taken to a computer.  An example of one such patent can be found at http://www.google.com/patents?id=v3InAAAAEBAJ&printsec=abstract&zoom=4&source=gbs_overview_r&cad=0#v=onepage&q=&f=false

 

Another variety of smart show uses a spring system in the heal to store the energy of the down step and use this stored energy to add power to the up step http://www.google.com/patents?id=Fok2AAAAEBAJ&printsec=abstract&zoom=4&source=gbs_overview_r&cad=0#v=onepage&q=&f=false

 

Another patent is for an athletic shoe outfitted with an electrostrictive polymer, which is basically an extremely flexible piezoelectric material, in the sole.  When the sole and polymer deform, energy is harvested. http://www.google.com/patents?id=EDILAAAAEBAJ&printsec=description&zoom=4#v=onepage&q=&f=false

 

A patent does exist for an energy-harvesting outfit, including a shoe.  This system appears to utilize mechanical, hydraulic, and pneumatic methods of energy harvesting.  Our approach is different because of its focused and well-defined nature.  http://www.google.com/patents?id=ACoIAAAAEBAJ&printsec=abstract&zoom=4#v=onepage&q=&f=false

 

Preliminary Work: 

 

March 1, 2010: Today we measured the voltage coming directly from the energy generating device of the blue flashlight.  This value was measured to fall within a range of approximately +3 volts to -3 volts per pump.  In the flashlight, the wires leading from the generator device terminate at a circuit board that allows for the connection of a rechargeable battery pack, an on/off switch, and LED lights. The voltage measured on the connections of the LED after passing through the chip was found to be less than 500mV. Our plan is to remove this chip in order to receive the maximum voltage from the generator.  We also found a large capacitor that we will be able to use to test the charging capability of our system. 

 

March 3, 2010: Today we successfully charged a capacitor to 5V (the correct operating voltage to charge an iPod) in 4 pumps.  Each pump resulted in approximately 1.25V.  After 16 pumps, the capacitor was charged to 10V.  After successive pumping, the capacitor would not charge past 12.84V.  We are investigating the reason behind this.

 

This week, we are ordering new flashlights, some USB connectors, and several voltage regulators in order to prepare for the design and testing of the housing system to connect the charging components to the iPod.  

 

We have conducted significant research into the problem of successfully connecting our apparatus to an iPod.  We have been able to find useful internet resources, as shown below.

• Purchase a USB-A female connector and a voltage regulator.

•       Wire both devices to the system and then solder the connections to make them permanent.

•       The voltage regulator will allow us to make sure the voltage produced is between 4.75 and 5.25 Volts and the USB-A female connector will allow the consumer to plug their iPod into our charger using the USB cord that comes with the iPod.

      Refer to http://www.reuk.co.uk/Solar-iPod-Charger.htm and http://yosemiteoutside.com/m/Blogs/02EA4A6B-8893-4F3E-87A8-C1E4B24C3AAB.html for other projects where an energy harvesting system was used to build an iPod charger.

 

March 5, 2010:  We placed an order for 3 additional flashlights, 5 USB-A female connectors, and a used 2nd generation iPod nano on which we can perform our tests.

 

March 14, 2010: We began assembling the circuitry of our first prototype after our parts finally arrived.  Without a capacitor, we were unable to produce enough power to charge the iPod when connected.  We need to look into adding capacitors and diodes to improve our output.

 

First Prototype:

 

March 15, 2010: Today we successfully created and tested our first prototype that produced a voltage that the iPod recognized.

 

Circuitry: Using two capacitors, a 5V voltage regulator, a diode, and a USB-A female port we were able to successfully connect the generator to the iPod via the apple USB charging cable.  The circuit diagram below shows the circuit design.

The circuitry elements were connected on a large stationary breadboard, and we used an oscilloscope to view the output voltage from the system. 

 

 

By manually pumping the generator, an output voltage from the circuit of 5V was obtained.  However, the voltage was only held at this value for a fraction of a second before beginning to drop down, as shown in the oscilloscope below.  The capacitors helped to stabilize the voltage and remove noise, but more optimization is needed.  Our next step is to condense the circuitry onto a smaller, more portable breadboard and connect all elements using solder.

 

 

Shoe/Mechanics: For the first prototype, we are more concerned with functionality than appearance. We therefore began by using a hack-saw to strip away all unnecessary parts from the flashlight other than those that house the gearing system and the generator since they are aligned well in this housing. We then tested multiple placements of the system on the shoe and tested each one for optimal comfort, ease of use, and for the placement that would make best use of the mechanical energy of each step. We considered the toe, heal, center inside and center outside of each side of the shoe as the location for the generator.  The best placement we found that optimized all above requirements was the inside, slightly towards the heal; however this spot will most likely be changed, since when the system is on the inside of the shoe it is liable to be kicked by the other foot, especially if we decide we want one on each foot. Thus we may decide that the outside, slightly towards the heal, is the best spot. For now the system remains on the inside for the first prototype and is held on by duct-tape.

 

 

The next step is to connect all components of the system to the shoe using a permanent and stylish mechanism. As of now small screws are being considered.

 

During the in-class presentation, the device was tested to failure, as a couple of the wires pulled out of the circuit board while running.  These wires, along with all of the other connections, have been re-soldered and checked so that this does not happen again. Our model that was presented in class utilized rubber bands in order to strap the breadboard to the user's leg. In order to make the device more portable and less bulky, the breadboard was cut into a smaller piece and will be permanently attached to the shoe in the future.  This completes our first prototype.

 

Second Prototype:

 

For our second prototype, we modified the apparatus of the first prototype.  The soldered breadboard is now securely taped to the back of the shoe, as shown in the two images below.  This will prevent wires from disconnecting while the shoe is in use. Furthermore, we used electrical tape to hold some of the wires tightly against the breadboard in order to eliminate the strain on the connections.

 

 

 

 

This prototype was recognized by the iPod as a charging mechanism, as the charging symbol on the iPod was visible during use.  Unfortunately, charging was inconsistent, as the symbol flashed on and off.  This leads us to believe that the generator we are currently using is not producing enough power to continuously charge the iPod. Other generators will be investigated for the next prototype.

 

 

Third Prototype:

 

Prototype three focuses on overcoming the problem of generating sufficient voltage to maintain steady charging of the iPod.  As mentioned in the requirements section, the iPod must receive a minimum of 4.75V DC in order to charge properly.  The difficulties encountered with the second prototype resulted from the fact that the voltage output from the circuit dropped below this threshold. 

 

In order to receive more charging power, we are investigating ways to attach two generators to the circuit, one located on each shoe.  Although this approach would likely provide the additional power needed, it threatens to hinder the functionality of the shoe, as it would require wires to run up both legs to a circuit board located on a belt at the waist.  In order to avoid this problem, we investigated alternate gearing systems and generators.  We did not have much luck finding a steel gearing system that was small and light enough for our application.  We also had difficulties finding higher quality generators.  Professor Daniels was able to locate a larger generator, but after testing its output with our gearing system, the resulting voltage was even less than that from the original generator taken from the flashlight.

 

After this disappointment we reverse-engineered a second hand pump flashlight that utilized a modified mechanism for generating power.  Upon inspection of the second flashlight, it became apparent that the linear motion of the hand pump is geared so that it spins a magnet around a large coil of copper wire.  When connected to an oscilloscope, the mechanism successfully delivered over 6 V.  What was more impressive than the 6 V was the timescale over which the voltage was produced.  Although not shown in the picture below, the voltage was held above 6 V for approximately 2 seconds (the picture below shows more than 7 V for 786 milliseconds).  The length of the generated voltage can be attributed to the nature of the mechanism.  The gear spins the magnet which has a flywheel effect because it continues to spin even as the hand pump is released.  This means that power continues to be generated between pumps.  This is demonstrated in the video below. 

 

 

The previous generator, on the other hand, only produced a voltage while the hand pump was being squeezed.  In addition, unlike the original generator, the function generated from the second generator was close to a perfect sine wave, as shown below.

 

 

By measuring the voltage drop across a resistor of known value, we were able to calculate that this flashlight generator outputs a power of 0.33 W.

 

With these exciting results in mind, we attached the new mechanism to our circuit board.  The result was extremely satisfying.  While pumping the handle, the charging light of the iPod stayed lit continuously for the entire duration of use.  Now that we have proved we have enough power to charge an iPod, our next goal is to figure out how long it will take while walking or running in the shoe to fully charge an iPod that has been completely drained. 

 

 

Troubleshooting of the Third Prototype

 

 

Unfortunately, at some point following the initial success of the third prototype, a problem occurred that removed the functionality of the apparatus. The iPod was unable to hold a continuous charge, although it very sporadically showed the charging symbol when the generator was pumped extremely quickly.

 

Due to this problem, we decided to test a couple of different circuitry options in order to see if we could harness any more power from our flashlight generator system.  Using four diodes and a capacitor, we created a full-wave rectifier (as shown in the first photo below).  This rectifier converts the entire sinusoidal wave form into one of constant polarity at its output, and thus should be more efficient.  However, after testing this system with a function wave generator, we found that it could only obtain 5V DC output from the voltage regulator with a 15 V PP input into the circuit from the generator.  Since our system only produces 10V PP, we decided against this circuit design since it is less efficient than our original circuit. 

 

 

We also tried a circuit system that used two flashlight generators (one to be attached on each shoe), but it also did not successfully improve our final voltage output.  See the following two photos for this two-generator system.

 

 

 

It was later discovered that the problem that occurred was actually due to the manner in which we were pumping the generator. In order to receive enough power from the new generator/gearing system, the device must be pumped at a certain rate and with a certain amount of force, which was more than we were applying when we believed there was a problem with this  prototype.  Fortunately, the force due to running on the hand crank is more than sufficient to make the device function to our required specifications. As a result, we have decided to continue using the original circuit system.

 

Final Prototype:

 

The final prototype implements several important improvements.  First is the housing of the apparatus.  We planned to greatly improve the appearance of the shoe by using either the full casing of the flashlight or alternatively by using CAD to design an original housing.  The use of CAD proved to be difficult due to the precision required to properly align the gearing system with the generator.  Furthermore, no one in our group has any CAD experience.  An alternate option we considered was using an epoxy resin for the housing.  This option would have allowed for a more elegant shoe but could have easily interfered with the gearing mechanism.  However, the current housing from the flashlight fits the generator perfectly (as it was designed for this purpose) while at the same time it is lightweight and does not hinder running.  As a result of these benefits, we decided to utilize the housing provided by the flashlight.

 

As mentioned previously, in the second prototype the device was positioned on the inside of the shoe.  However, this caused functionality issues since there was a tendency for the runner to kick the generator with her other foot while running.  As a result, in the final prototype the generator is positioned on the outside of the shoe.  This improves appearance as well as functionality (again the positioning will be optimized for comfort and functionality as before by utilizing duct tape to make minute changes before the final position is determined). 

 

 

We came up with several ideas on how to attach the flashlight generator to the shoe without the use of duct tape.  We explored the use of several types of glue, small screws, brackets, tape, etc.  The final prototype uses a combination of plastic strapping with small screws and epoxy resin (a high-strength glue).  The smaller, improved circuit board was also attached to the shoe with epoxy.  These supplies were obtained from Home Depot and allowed us to create a much more aesthetically-pleasing look compared to the previous prototypes, which used duct tape.  Thus, our final prototype gained the advantage of looking nice without losing any of its functionality.  A picture of the final design is shown below.

 

 

Final Results:

 

To determine the success of our final prototype, we ran for 20 minutes while wearing the Energy Harvesting Running Shoe.  We attached a partially charged iPod to the shoe and observed the battery symbol over the length of the run.  The iPod maintained the green charging symbol throughout the duration of the run, indicating that we have achieved our requirement of generating power through the motion of running.  This is further supported by additional tests using a voltmeter and oscilloscope throughout the design process.  A voltmeter showed that hand-cranking our generator produced a output voltage of about 4.8 V.  Throughout the running test, the shoe proved to be very comfortable and functional, satisfying two more requirements.  Since it was difficult to film the charging while running, the below video shows the iPod maintaining charge while running in place.

 

 

To investigate the last requirement, one more test was performed in order to determine whether or not a fully discharged iPod could be turned on in a reasonable amount of time.  During a 18 minute run, the iPod displayed charging symbols (either the Apple or low battery symbol), but was unable to charge sufficiently to turn on.  A video of the end of this run is shown below.

 

 

Analysis of Original Requirements:

• This system MUST generate power through the motion of running. - SATISFIED
• The functionality of the shoe MUST be maintained. - SATISFIED
• The charger SHOULD operate between 4.75-5.25 V. - SATISFIED (We reached a final voltage output of about 4.8 V)
• The shoe SHOULD be comfortable. - SATISFIED
• The shoe SHOULD be successfully connected to an iPod. - SATISFIED
• The shoe MAY generate sufficient power to play an uncharged iPod while running. - FURTHER TESTING NEEDED.   

   

   

Future Improvements:

 

Our final prototype successfully proved that the motion of running can produce power at an extremely low cost (approximately $15 excluding the price of the shoe).  Despite our successes, we were unable to satisfy our last requirement of turning on an uncharged iPod due to the inefficiency of the generator.  We believe that this requirement could be easily achieved by replacing the "squeeze flashlight" generator with a high quality microgenerator and gearing system.  This would increase the price of the shoe, but the improved performance would outweigh this cost.  The packaging and appearance of the running shoe could also be streamlined.