edge.rit.eduedge.rit.edu/edge/P18463/public/Final Documents/P18463_Technical_… · Web viewThe device housing and modular blades were designed using SolidWorks and 3D ... A crucial

Project: P18463

Team: Stream Team

WATER POWERED USB CHARGER

Mohammad Asfar Keenan Baltunis Sarthak Tandon Ryan Barry

Lead Electrical Engineer Project Manager Lead Mechanical Engineer Facilitator

ABSTRACT

The goal of this senior design project was to develop a device that generates power using the energy from a moving body of water. Hydroelectric energy is produced all over the world on different scales using different mechanisms and turbines. However, Stream Team is one of the first group of engineering students to experiment with harnessing hydroelectricity on a personal level.

The crux of our design is the DC motor inside that is being rotated to generate power. Small DC motors found in toys, whether they have plugs or batteries, need a source of power to operate. This requires an input of electrical energy to receive an output of mechanical energy that causes the motor to run. The Trick Charger uses the same principles, but in reverse; it converts mechanical energy into electrical energy. Mechanical energy from the moving water transfers to the turbine blades that rotate the motor shaft and convert the mechanical energy back into electrical energy that can be used to charge a power bank. The power bank can then simply be used to charge any personal device that is compatible with a USB input.

The device housing and modular blades were designed using SolidWorks and 3D printed at the Construct and FabLab here at RIT. As we increased the blade size, we also increased the amount of mechanical energy available for us to convert into electrical energy. The blades were sized and angled for the device to produce enough current at a high enough voltage to charge the battery at a range of river speeds. Faster rivers and larger blades increase the amount of energy that is able to be produced by the Trick Charger.

INTRODUCTION AND BACKGROUND

This project is aimed at developing a rugged, portable, water-powered solution for charging any USB-compatible device. The device will be able to remain in a body of water for long periods of time and will be robust, waterproof, and versatile enough to function in varying bodies of water and weather conditions. The ideal result was a functioning prototype that is economical to manufacture and market in areas afflicted by unreliable power. This design also has an extension that allows the user to place the device into the body of water and avoid any contact with local wildlife. These were the key requirements our guide and customer Chris Leibfried gave us for the intended design. Customer requirements were measured and compared side by side with engineering requirements. The result is a successfully functioning prototype showcased at RIT Imagine and handed off to the customer. The

success of this project was due to the team members and the guide involved in the process. We all got along very well unlike many teams which don’t function well when they encounter setbacks.

MSD I Summarized

We started off planning a team vision for system definition and discussed on how to proceed with Phase 2. The goal was to present a feasible proposal for our system that meets all the engineering requirements from Phase 1 and any newly recognized or updated requirements from Phase 2. Several things were completed to justify a system design. We created functional decomposition and morphological charts to break down system function and possible solutions to those functions. From there, we worked to select a concept with different combinations of solutions using feasibility and Pugh chart analysis. After selecting a concept, we developed a rough plan for system architecture and created designs and flowcharts on user interaction with our system.

Figure 1: Functional Decomposition Chart

Figure 2: System Architecture

As MSD I came to an end, so did the amount of time to make crucial design decisions before the build began. To mitigate risks and problems during MSD II, the team needed to review and update the feasibility of each subsystem and focus on how the subsystems would be integrated during the build. The first and most simple sanity check is making sure all the components can spatially fit in the geometries we are envisioning. The finalized CAD file reflects the dimensions of each of the components needed for subsystem functionality.

A crucial component in ensuring the accuracy of our CAD model is comparing it to our current Bill of Materials to verify the design includes all the intended components. Each entry in the Bill of Materials needs to identify which subsystem the entry will be used for, and whether these are purely material expenses or costs associated with developing the product.

What we managed to get done this phase was update our turbine blade design and simulation, update the method of waterproofing the housing, clean up the wiring diagram, determine what accessories are needed, generate a Bill of Materials for the prototype, and update our Risks.

CFD Analysis

All theory was confirmed using FlowSim on Solidworks. The flowsim was run to ensure that the theoretical values attained in MSD I corresponded with the expected values in the model. The values within range. The table below summarizes the obtained data from the analysis from the set of blades we were testing at the time.

Five different such tables were generated to identify the best option for the turbine blades to follow. The flat bladed design turned out to offer similar/better performance than all other blade designs. However, the advantage was that it didn’t involve any complicated geometry. Hence, this design was chosen.

Since the blades are flat, most of the drag being created is through pressure drag. The thin profile of the blades prevents any sort of friction drag to be generated. However, when the blades reach steady state, most of these losses should be minimized. Even then, we knew that the max power we could attain was only 59.3% of the theoretical values. To further add redundancy, we decreased the total efficiency of the system to 40%.

As the above data table shows, the CFD analysis was run such that the resultant values would be those of torque on the blades. Through goal optimization, the ideal rpm was found so that the torque would equal zero (signaling steady state). Multiplying those two sets of values gave us the total power outputs.

Below is a visualization of the resultant velocity profile behind one our initial designs during analysis:

While our theoretical models matched with our CFD models (mostly within 10-20% margin), real world testing threw new challenges in MSD II that we were unprepared for, rendering the CFD analysis inaccurate. The analysis ended up serving as a guiding pin as to the rough values we could expect, as the model was always updated with the newer CAD files.

MSD II Summarized

Changed to modular printing. Done to avoid 3D printing issues. As design is now printable on campus, it helps lower overall design costs. After discussing the possibility and detrimental result of a single blade breaking, the team and customer agreed that the blades needed to each be separate, changeable pieces. That way, a single fin breaking does not jeopardize the entire device functionality. The team developed a 3D printed “dog bone” blade holder that connects the fins to the device and allows the user to easily switch out active blades.

Dogbone Blade Holder

New blade connection pieces that will hold the assembly such as the washer and screw setup on the motor side

Electrical subsystem tests were performed to measure generator and voltage regulator output to the power bank. Mechanical subsystem tests were aimed not only at measuring the amount of blade

rotations per minute, but also how well the housing remained waterproof in order to protect the interior electrical components.

All these subsystems were built, tested, and iterated on for improvement, particularly the mechanical tests. Both the shape of the blades and the apparatus that seals the rotating driveshaft have been heavily modified in MSD II in order to meet specifications. The team tried to perform tests and iterate quickly in order to provide other members of the team with enough time for any potential redesign work. The mechanical iterations were intended to improve fit & finish, efficiency, and waterproofing.

Designing the fins involved CFD (computational fluid dynamics) analyses through SolidWorks. With each iteration, we changed both size and pitch angle of the blades in order to maximize the rotations per minute of our final motor. It is also worth noting that the final blades are made of PLA, not ABS, due to both size constraints and limited ABS at The Construct here at RIT. The primary iterations of our blade design are shown below:

First Blade 2nd Blade Final Blade

The turbines blades were made much bigger by the final iteration compared to the previous two in order to maximize our flow area and available power. The pitch angle on the blades was also decreased in order to increase the RPM. The rounded tips have also been removed to preserve the most power we can from the limited area we can expand the size to. During testing it was also found that the blade angle was the opposite of what it should have been. The issue has since been corrected. Because previous attempts to waterproof the system with a single lip seal small shaft diameter were unsuccessful, the team implemented the use of a stuffing box (or body). A stuffing box is a common mechanism on boats that is used in order to seal boat shafts; we attempted to use these principles but on a much smaller scale. Now, there is an aluminum stuffing box that houses two lip seals, each stuffed with a pieces of greased shoelaces as a packing sealant to keep the water out. The graphite grease used help lubricate and waterproof the system for long periods of time. The stuffing body mechanism produced significantly better and more consistent waterproofing results than the single seal before.

Stuffing body with lip seals Steel Body within enclosure

Before having all components soldered and put inside the housing assembly permanently, we tested them outside on their own to see if we they gave good results. The results obtained show everything working just as expected and it was demonstrated to our guide and customer. The USB power meter greatly simplified obtaining accurate power measurements instead of using different multimeters each time. Multimeters have high internal resistance which affect our reading and USB power meter simply plugs into our cable from one side and feeds the power bank on the other. The power meter gave us a good reading after the blades hit the rpm speed of around 480-500 rpm, but the power bank starts charging at around 430 rpm.

Another major portion of MSD II was finding a motor that would allow us to meet our customer/engineering requirements. Several different motors were acquired and tested. They ranged from gearbox motors to brushless DC motors. We found that we needed to find a motor that required a low rpm to produce as much power as possible, but not so low that it wasn’t feasible to turn it with our turbine blades. After narrowing down just what exactly we were searching for, we decided upon a 2V-14V geared DC motor. We had tried geared DC motors before this one that didn’t meet our expectations. The difference is that those previous motors required too much initial force to turn the driveshaft. The motor we decided upon cost a bit more but it is much easier to turn. We did run into a problem with this motor however. Through several tests, we determined that the motor would only produce power when rotated in a specific direction. Unfortunately our turbine blades at the time were designed to the turn the motor in the opposite direction of what was needed. This meant the blade design had to be mirrored and reprinted.

USB Meter Example Electrical Testing Setup

Shown below in the table are the electrical results. As can be observed, voltage starts being measured around 450 RPM and increases steadily as the RPM rises. Around 650 RPM the voltage plateaus at just about 5V. This is due to our voltage regulator which will keep the voltage from going above 5V. Without it, the motor’s voltage output would continue to increase as RPMs increased. After soldering the USB ports into the cable and then covering the connection points with heat shrink wrap, we verified the cable successfully transmits power from one end to the other with negligible losses. This was observed when the turbine and the whole device were packaged in housing and tested using a drill machine. The electrical components functioned just as expected and the cable connections were securely soldered.

Voltage vs RPM Graph Soldered and assembled device Connections

Conclusion

The project was mostly successful. Assuming the water is moving fast enough, the turbine blades will rotate fast enough to generate the power required for the power bank to charge. Competitors such as Estream may generate power at lower blade rotational speed, but our device design is built to be more durable and allows debris to pass through more easily rather than having it interfere with device operation. Our design, which also comes with a neat anchoring solution, also allows the device to remain partially submerged for customer convenience. The power bank on shore provides customers the ability to charge whatever personal device they would like as soon as the power bank is charged. This also means that the user does not need to be near the water in order to charge their devices. Thus, our device meets most of the customer requirements and engineering requirements.