cd i o sustainability 2014 v final

Proceedings of the 10th International CDIO Conference, Universitat Politcnica de Catalunya, Barcelona, Spain, June 16-19, 2014.

A NOVEL ENERGY HARVESTING FLOOR: RESULTS FROM PROMOTING SUSTAINABILITY IN CDIO

Felipe Surez, Matas Alarcn, Fernando Torres, Juan Cristbal Zagal

Department of Mechanical Engineering, University of Chile Beauchef 850, Santiago, Chile

ABSTRACT Promoting sustainable development is key to new CDIO engineers. We show how students can embrace the problem of sustainability by creating new products and systems. In this case a novel energy harvesting floor was produced by a group of sophomore engineering students. The method was to build a prototype using energy manifold mechanical pressure. This method went better with every redesign process until a functional version, using digital fabrication tools, achieving convert pressure gained by pedestrian -and theoretically vehicular- traffic into energy. KEYWORDS CDIO Spaces, Fab Lab and CDIO, Non-conventional energy harvesting, Sustainability, Standards: 1, 5, 6, 7, 8. INTRODUCTION Promoting sustainable development is critical to CDIO engineering. The CDIO INITIATIVE is an innovative educational framework for producing the next generation of engineers. The framework provides students with an education stressing engineering fundamentals set in the context of Conceiving Designing Implementing Operating (CDIO) real-world systems and products. Actual problems from industry might fail at motivating students to be part of a project development, since they see themselves playing a secondary role [1] [2]. An alternative is to let students take responsibility for some long term projects, so they can explore how to maintain their tools and spaces in good condition. A great example of student involvement is given by the Fab Lab, a digital fabrication laboratory that operates since 2011 at our Engineering School. The project has gathered the attention of many students that find a new atmosphere of creativity given by their own enthusiasm together with many tools for digital manufacturing, such as 3D printers and CNC routers. Obtained results in this project were all the expected ones, getting acceptable values for the prototype whose fundamentals will be presented in the next section. This motivates to stay developing new technologies helped by students. Results can be seen in the final prototype category.


The inspiration for the work has been the Pavegen Piezoelectric Floor, whose tiles generates electrical energy due to mechanical deformation generated by the pressure made by pedestrian or vehicular traffic [3]. The new idea which will be shown wants to beat the main disadvantage of the Pavegen technology, which is the elevated production cost, trying to generate energy under the same aspect, but with a low cost. REFERENCE Another advantages besides the low cost in production, are the implementation versatility: there are a big variety of applications in the use of this technology. In the final section there is shown an alternative of use. SUSTAINABILITY PROBLEMS IN DIGITAL FABRICATION SUSTAINABLE FLOOR

The sustainable floor consists on a set of pneumatic tiles (see Figure 1). Each tile contains an array of 3x6 pneumatic cells. Stepping over a cell causes the contained air to be compressed, subsequent release allows for fresh air entering the cell. Energy is then accumulated in the form of compressed air that is stored in a cylindrical tank for future release (see Figure 2). The remainder of this section describes the different versions of pneumatic cells that were implemented.

Figure 1. Novel pneumatic energy harvesting floor created by the students. The project aims initially at providing sustainable operation for some machines at the Fab Lab. A next step is to release the tiles as an open source hardware that can be used by many people.


Figure 2. Real prototype for pneumatic tile. a, The pneumatic energy harvesting tile. b, The pneumatic storage cylinder. c, Manometer and valve assembly.

Pneumatic Cells

First prototype A pneumatic cell was implemented by utilizing a 55 mm racquetball rubber ball (see Figure 3). Two Presta valves (29mm length x 6mm width) were used for ensuring unidirectional flow of air entering and leaving the cell. Pneumatic tubing (6mm diameter) and rapid L-shaped and T-shaped connectors were used to complete the assembly. Achieving a sealed connection between valves and rubber ball was not an easy task. At first 3mm holes were drilled at two hemispheres. Then, a Presta valve was pressed into a hole leaving the screw thread end outside the ball, and the rounded smooth end inside the ball. The other Presta valve was inserted leaving the screw thread inside the ball. Finally, the smooth rounded end of one valve was connected to the pneumatic tube by heating with a heat gun. The valves were secured and sealed against the ball by gluing it.


Figure 3. Detail of Pneumatic Energy Harvesting Tile: a dynamic racquetball ball of 2,25 inches diameter, b a Presta valve that allows unidirectional air flow, c another automatic valve in the inverted position, d

6 mm pneumatic tube connected to a 90 deg elbow. At the bottom, it is completely constructed.

Second prototype

The spherical shape was convenient for the upper part of the cell but quite inconvenient for carrying the connectors in a secure and sealed way. There was designed a second prototype with an improved support. 3D printed molds and polyurethane (Sikaflex) were used for producing the soft cells (see Figure 4). The cell dimensions were 90mm by 50mm of base and 22mm height. Pairs of Presta valves, clamping valves and automatic unidirectional valve were used. Mold release was sprayed over the 3D printed molds to facilitate further demolding (see Figure 4). Two valve assemblies were attached to the molds before pouring with polyurethane. Resulting parts were ready to be used after 72 hours of curing time. The cell was finally completed by attaching the upper and lower parts.

Figure 4. 3D printed molds for producing the second prototype of the pneumatic cell. a, Mold for producing the upper part of the cell b, mold for producing the base of the cell and supporting the valves.

Description The module consists of a base made of Sikaflex 221 polyurethane into a PLA mold and polyurethane chamber of the same material also made with a mold. The base has 2 Presta valves equidistantly inserted, following the symmetric edge associated to the long side, and two automatic valves inserted in inverted orientations. Due to this configuration, if the chamber is pressed, the air inside the chamber will be released outside it (to the pneumatic tube), and another valve will get the air from the environment. This is possible due to the properties of the


chamber: polyurethane has elastic memory, and the both of the valves allow air flow in only one direction.

Figure 5. Four-way manifold pneumatic measurement and control assembly. a Manometer, b racor end to the compression module, c storage tank connection end (closed), and d stopcock.

Figure 6. A comparison between a and b (the first two prototypes) and c - the final version of the compression module - . Note b and c have a PLA base, manufactured with a 3D Printer. Also note

Sikaflex 221 with polyurethane is a strong compound, it remains strongly bonded to the base.


Figure 7. Note a.1, a.2 mold is quite different than the first one. The image also shows b the new PLA base, c Sikaflex 221 chamber for the compression module and some of the valves: d the 6 mm valve with racor end, e the bronze valve which acts as a clamping and allows the connection between the Presta valve and d, f the automatic valve (removable Presta valve core), and g the Presta valve.

Final Prototype It consists of a PLA base (with 100 mm long, 60 mm wide and 26 mm high), a polyurethane air chamber (with 90 mm long, 50 mm wide and 32 mm high), two Presta valves (20 mm high and 6,5 mm extern wide), one clamping valve (8mm high and 9 mm extern wide), two automatic valves (29 mm high and 6 mm wide), one bronze valve (33 mm high and 16 mm wide), and a 6 mm valve with racor end. There was used also Teflon tape, and Sikaflex 221 polyurethane. The construction step begins adding Smooth-On spray into the chamber molds, it will be necessary to separate both of the parts (chamber and mold) after the drying. Base has been specially designed for allow the insertion of presta valve with a polyurethane portion to get air insulation then, if its dry, the chamber can be placed to fix in the PLA base, also using polyurethane, and using the chamber and the base wrinkled contact surface for a better fixation. Its not necessary more than 20 hours (at 20 C) to see the results. Then the automatic valves are put into the Presta valves, in this time it will be like all the past configurations: automatic valves in inverted positions. The valve which extracts air from the chamber needs to get clamped. For this reason it will be use the bronze valve. Bronze valve


was specially designed for act like a clamping valve and a good connector to the 6 mm end racor valve. Finally the clamping valve is put in another Presta valve. Its also added Teflon tape to every connection. Summarizing, module consists in an air chamber manufactured with Sikaflex 221, strongly fixed to the PLA base, it acts like the last prototype, but without leakages, and with a great durability due to the 3D printing quality.

Figure 8. A renderized view of the construction of the compression module, showing a the polyurethane chamber, b the PLA base, c the presta valve, d the automatic valve, e the bronze valve, f a clamping valve, g the 6 mm racor end valve h, a complete view of the final prototype.

Experiment The experiment was about put the final prototype under discrete values of pressure, made by a mechanical compressor with a 1.25 KPa value. This pressure is applied instantaneously, and each 1 second (see graphic 1). The objective of the experiment is to analyze the performance of the compression module when the collected pressure in the tank increases.


Graphic 1 - The results are shown in the upper graphic: the main consequence is the decreasing pressure gaining values in function of time. This is completely predictable under a common system which collects a light fluid under pressure. The values are, hereby, represented by a curve which is stabilized at the end of the pressure test.

Figure 9. Potential application as a traffic speed reducer and energy generator.


REFERENCES [1] Blikstein P., & Krannich D., (2013). The Makers Movement and FabLabs in Education:

Experiences, Technologies, and Research. IDC 13 Proceedings of the 12th International Conference on Interaction Design and Children, 613-616

[2] Scalfani V., & Sahib J. (2013). A Model for Managing 3D Printing Services in Academic Libraries.

Issues in Science and Technology Librarianship, Alabama, USA.

[3] Duarte, F., Casimiro, F., Correia, D., Mendes, R., & Ferreira, A. (2013). A New Pavment Energy

Harvest. Renewable and Sustainable Energy Conference (IRSEC), 2013 International, Ouarzazate, 408-413.


BIOGRAPHICAL INFORMATION Felipe Surez, is an electrical engineering student at University of Chile. He is interested in Digital Fabrication and Robotics. Matas Alarcn, is a construction engineering student at University of Chile. He is interested in Digital Fabrication and Robotics. Fernando Torres, Mechanical Engineer, University of Chile, 2011. Responsible of the Digital Fab Lab UChile design, implementation, operation and diffusion. During 2012 hes teaching Digital Fabrication and Open Hardware Project at the University of Chiles School of Physical and Mathematical Sciences. Juan Cristbal Zagal, Electrical Engineer (2000) and PhD in Automation (2007) from University of Chile. M.Sc. in Scientific Computing (2002) from the Royal Institute of Technology (KTH). Postdoc Mechanical and Aerospace Engineering (2010), Cornell University. Assistant Professor of Mechanical Engineering at University of Chile since 2010. Founder and Director of the University of Chile Fab Lab. Corresponding author

Prof. Juan Cristbal Zagal Mechanical Eng. Dept., University of Chile Av. Beauchef 850, Torre Central Santiago de Chile, Chile +56-22-9784545 [email protected]

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

cd i o sustainability 2014 v final

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