1 February 2012
STORM-WATER HARVESTING SYSTEM OUTPUT SUBSYSTEM
Carolina Figueroa
RAIN-WATER HARVESTING SYSTEM —OUTPUT
Context! Design concept!
Precedents !
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Design concept!
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Hyperboloid model!
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Rod and crank mechanism modelling!
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Firefly + Arduino!
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Testing and difficulties !
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3
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Hyperboloid structure!
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Rotating gear redesign!
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Adjustments to driving definition!
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Input / Output integration!
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Further improvement!
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References !
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RAIN-WATER HARVESTING SYSTEM —OUTPUT
Context
Design concept Architecture is much about the study of space, and little or nothing of the potential movement of it. Every traditional workflow in architecture is situated in the context of three dimensions. Therefore, we think of space in terms of x,y,z coordinates. The starting point for this project was defined by a joint research on a rain water harvesting system. The concept was to develop a deployable structure to collect rain water. Whilst analysing different aspects of rain water, a critical point in the process was identified. Quality of water is greatly dependant on runoff surface pollution. The cleaner the catchment surface, the more pure water is collected. (Kinkade-Levario, 2007) A clean surface is difficult to attain, specially when by and large catchment areas are residual structures or unused parts of existing buildings. Therefore, every water harvesting system necessitates a thorough filtering and purification process if collected liquid is intended for human consumption. Following, it made more sense to design a moving structure capable of insulating its catchment surface. That first effort was framed to generate a virtual model of an actuated structure. However, it proved to be a major challenge as it was nearly impossible to find a ready made solution for designing considering movement.
Figure 2 Prototype strand 1 & 2. Configuration in anchor points generate completely different shapes
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Figure 1 Deployable structure prototype with servomotor. Early stages
RAIN-WATER HARVESTING SYSTEM —OUTPUT
A first approach included a bespoken translation of mechanical elements into mathematical idealisations inside Grasshopper. But the notion remained: every CAD and Design oriented package is programmed to take three dimensions into consideration. This research builds on top of findings from the Rain Water Harvesting System project and is framed at creating a physical prototype to incorporate movement. A physical model from the deployable structure will be constructed and actuated with a servomotor. Actuation will be controlled by an Arduino micro controller. In an effort to bridge the virtual/physical gap further, this stage is planned as a collaboration project. Whilst this work will focus on creating an actuation subsystem, an output to the main system, the other work will aim at creating a sensing submodule for the harvesting system, an input.
Precedents
Design concept This research produce a 1:30 scale prototype with the aim of exploring the working of deployable structures under dynamic systems. Every piece generated followed a simulation stage which led to the production of rapid prototyping models. This workflow facilitates production of further prototypes on different scales. Two different parts were designed and structured the schedule of this project: hyperboloid shaped deployable structure and driving gearing mechanism. In keeping with the philosophy generated in previous works, a Grasshopper definition was scripted with the purposes of simulating and testing moving mechanical parts previous to manufacturing.
Hyperboloid model For the purpose of this research, hyperboloid structure members has been classified as follows
Figure 3 Prototype strand 1 under fabrication
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RAIN-WATER HARVESTING SYSTEM —OUTPUT
The first stage followed a mathematical idealisation of hyperboloid based structures to construct a working physical prototype. Two strands were produced. The first made use of flexible material to create articulated joints in the structure. Although every deployable structure requires degrees of freedom (DOF) in joints to allow movement, incorrect definition may lead to unexpected behaviour. First prototype proved to modify its configuration when force was applied on ending nodes. Nonetheless, shape was far from resembling the one achieved though idealisation in scripting. In previous work, hyperboloid was controlled through a shift function. Two circles were used to define points in base and upper part of the shape. Shifting index in both list of points rendered the internal configuration of elements joints, i.e. distance to each other. Analysis from first prototype yielded complications in defining this shifting pattern in the same fashion. Therefore, it was concluded that a bottom-up strategy was more suited to alter and control typology. Position of intermediate joints is varied, rather than previously used top-down strategy of defining cross-reference of base point. Second hyperboloid was constructed on top of previously described analysis. Joints were redesigned to allow only one degree of freedom. Therefore, metallic pins were introduced to define freedom in rotation around plane z. Here, plane z is defined as the one perpendicular to the intersection of two rigid members. Base point joints were assembled using flexible material to allow greater degrees of freedom. As it was observed on the first prototype, these joints aid to structure internal configuration but are heavily deformed when the structure is deployed or retracted.
Rod and crank mechanism modelling In performative architecture, it is essential to consider how the moving parts of a structure can transform initial design stages (O'Sullivan and Igoe, 2004). As such, one of the objectives of this research was to use Grasshopper as a simulation tool previous to prototyping.
Figure 4 Design for crank and rod mechanism
Rod
(connected to deployable structure)
Crank Rotating link Rotating gear
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RAIN-WATER HARVESTING SYSTEM —OUTPUT
The first concept takes cues from the notion of reducing a moving mechanism to the minimal expression. Considering the simplest of all motors, a mechanical transducer was introduced to transform a rotational effort into a lineal back and forth displacement (O'Sullivan and Igoe, 2004). In turn, linear displacement would be used to elongate a circle in which the structure base points are distributed.
Figure 5 Two stages in the transformation of the crank and rod mechanism. Left is the “retracted” state. Right represents deployed stage.
A bespoken three legged gear was designed and prototyped to follow this logic of operation. (Figure 3). Rotating links and rods represent one degree of freedom (DOF) joints which allow to control the extend of transmitted movement. This strategy matches with the initial hyperboloid idealisation, whereby the structure is actuated by varying the diameter of base defining circle. Keeping in line with original philosophy in this work, Grasshopper definition served the purpose of element optimisation and movement animation. Following Figure 6, a further idealisation was made to analyse ideal length of central gear and intermediate transmission members From where it can be concluded
AB1 + B1C1 = AEp AC1 = ASp 6
C1
RAIN-WATER HARVESTING SYSTEM —OUTPUT
AEp B1
A A ASp
ASp
C1
B1
Figure 6 Idealisation previous to optimisation function.
Equation has been scripted inside GH definition to be recalculated in the event of any variable change. Therefore, members dimensions are determined by the following parameters ASp = Railing starting point. Determined by retracted state of structure AEp = Railing ending point. Determined by deployed state of structure
Hyperboloid is to be actuated by transforming the position of three base points. Given the configuration of middle joints, movement will be replicated to every rigid member in the structure. Following, joints Rod 1, 2 and 3 will be used to fix structure to the gearing mechanism.
Figure 7 Arduino with servomotor on early connection tests
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RAIN-WATER HARVESTING SYSTEM —OUTPUT
Firefly + Arduino
Figure 8 Showing naming conventions for hyperboloid structure members
Anchor point (joint)
Rigid member
Base points Arduino is a micro controller board used for electronic prototyping. It is based on the ATmega 328 chip and is equipped with 32 Kb of flash memory. Furthermore, it is designed to be programmed with the Arduino software, based on a set of instructions from Processing language. Working in tandem, this specifications allows Arduino to work independently of any computer by uploading the required code directly to the ATmega chip. Firefly works by streaming code in real time to Arduino chips. In order to be able to communicate with the board, Firefly requires any board to be preloaded with the “Firefly Firmdata”, a set of Arduino code instruction translating Grasshopper-Firefly components into equivalent Arduino language instructions.
Figure 9 Final prototype under early actuation test.
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RAIN-WATER HARVESTING SYSTEM —OUTPUT
Testing and difficulties Hyperboloid structure
An initial prototype was generated using elastic material in all joints, both anchor and base points. It was determined that a better refined and constrained joints were necessary to control shape configuration. Prototype two considered rigid members in all joints. After initial testing, it was concluded that this solution for base points were compromising structure integrity, i.e. stress due to deployment was being absorbed by rigid members. A second iteration was produced to incorporate flexible joints in base points. It is concluded that stress produced during deployment is absorbed by deformation in base point joints. This assures structure integrity when being actuated. Nonetheless, base points proved to hold further complications when integrated with rod and crank mechanism. In the initial definition, structure deployment was idealised as a variation of change in base circle diameter. Although this has proven to be optimal in terms of computational resources, it is not as effective when dealing with joint design. When the structure is actuated, every base point is rotated to accommodate rigid the rigid members. Once this problem was identified, it was decided to be tackled by using an elastic material to connect the structure and gearing mechanism. However, it will be ideal to model this elements following a hinge logic. A high-detailed definition could be generated to simulate stress on this elements, leading to bespoken element which could improve actuation and structure integrity. Given the level of detail and the stress this elements would undergo, they could be prototyped using a polymer-based rapid prototyping technology.
Rotating gear redesign Following initial tests, it was determined that parameter adjustment was needed to optimise performance of physical prototype. During first performance tests, the mechanism proved to worked properly during first stages. However, it started to fail after repeating deployments. After analysis, it was determined that this problem was originated in the coupling between designed gear and servomotor. As movement is generated in the system, every component and coupling is stressed. This caused the servomotor-gear paring to fail as union was reliant on friction exerted by a screw.
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Figure 10 Fabrication process
RAIN-WATER HARVESTING SYSTEM —OUTPUT
Further inspections to the servomotor revealed a cogged paring device. Gear was redesign to incorporate a toothed coupling, thus creating a mechanical paring. Further test proved this strategy successful.
Figure 11 Physical prototype with membrane, view from top
Adjustments to driving definition Initial operating angles for servomotor had to be adjusted as unpredicted factors, i.e. member rotation in base points, led to differences in performance. Considering an initial 90 degrees of rotation, it was constrained to a further 70 degrees to allow structures to be completely deployed. These slight variations has been already scripted and are considered in the last definition accompanying this research.
Input / Output integration This research was designed as a joint effort to create an environmental dynamic system. The subsystem developed in this project comprises the actuation/output mechanism for a water catching deployable structure. A second subsystem was defined and externally developed to generate an input stream to ‘sense’ the presence of rainwater in environment. A common GH definition was developed to actuate the structure on the event of a predetermined water level threshold.
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RAIN-WATER HARVESTING SYSTEM —OUTPUT
Further improvement This project has been successful in creating a working prototype of an actuated deployable structure. Given the time and scale constrains, there are a series of variables which could be developed in further iterations. Both intermediate and base joint could be re-developed to attained a more controlled behaviour during actuation. Specially base joints could benefit from being specially tailored to deformation specification found in this prototype. Likewise, a high definition script could be developed to model and later rapid prototype this element. Membrane in original idealisation involved a shape memory mesh which could be sealed to avoid any pollution from environment. Further research could be directed in creating an independently controlled element which could serve the purpose of isolating runoff surface as to improve collected water quality. Some avenues of research include using shape memory fabric polyester.
References KINKADE-LEVARIO, H. 2007. Design for water : rainwater harvesting, stormwater catchment, and alternate water reuse, Gabriola Island, B.C., New Society Publishers. O'SULLIVAN, D. & IGOE, T. 2004. Physical computing: sensing and controlling the physical world with computers, Thomson.
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