EPS@ISEP | The European Project Semester (EPS) at ISEP

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report [2014/06/26 18:02] – [7.5 Prototype Implementation] team1report [2022/11/03 10:45] (current) – external edit 127.0.0.1
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 | {{ :2006_iros06-880_3_.png?100 |}} {{ :2006_iros06-880_4_.png?100 |}}| Body bends to certain shape, up- and down-motion through lift forces | Quick response and high dynamic performance | Minimum swimming speed required to utilize lift force of fins, more fragmented body architecture | | {{ :2006_iros06-880_3_.png?100 |}} {{ :2006_iros06-880_4_.png?100 |}}| Body bends to certain shape, up- and down-motion through lift forces | Quick response and high dynamic performance | Minimum swimming speed required to utilize lift force of fins, more fragmented body architecture |
 | {{ :2006_iros06-880_5_.png?100 |}} | A moving inside weight changes fish´s barycentre, thus the direction is pitched |Mechanism is set inside of body, thus the mechanism´s motion isn’t affected by water flow | Space consumption inside body, questioned effectiveness (relation of moving inside weight to overall mass) | | {{ :2006_iros06-880_5_.png?100 |}} | A moving inside weight changes fish´s barycentre, thus the direction is pitched |Mechanism is set inside of body, thus the mechanism´s motion isn’t affected by water flow | Space consumption inside body, questioned effectiveness (relation of moving inside weight to overall mass) |
-[Zhou, Cao, Wang, Tan, The Posture Control and 3-D Locomotion Implementation of Biomimetic Robot Fish, 2006. International Conference on Intelligent Robots and Systems, Proceedings of the 2006 IEEE/RSJ, Beijing, China] 
  
 The comparison reveals that there exist several different methods varying in technical complexity and effectiveness. The selection of a suitable mechanism for the developed robot will be dependent on its feasibility and the available space inside the body. The comparison reveals that there exist several different methods varying in technical complexity and effectiveness. The selection of a suitable mechanism for the developed robot will be dependent on its feasibility and the available space inside the body.
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 **Figure 29: Example of program and code** **Figure 29: Example of program and code**
  
-==== 7.5 Prototype Implementation ====+==== 7.5 Tests and Results ====
  
-At the current state (14th June, 2014) the prototypes implementation has not been completed. In this chapter it we describe in what ways and configurations our prototype will be made. We had a lot of ideas which gave us a lot of configurable parts that influence the way the robot swims, dives and looks.+A series of tests is required to experimentally evaluate if the robot is working as expected. The following tests have been performed.
  
-Body of the prototype requires a lot of additional weight to make it go under water, thus we will experiment with different ways of adding weight. As an example we might use steel bars fixed to the inside of the robot. Other idea is mounting the ballast weight to the outside bottom of the hull. Also manipulations with the weight will allow us to control the distribution of the weight and make the prototype float levelled in water.+=== 7.5.1 Test of the Tail’s Motion (dry) ===
  
-Next thing to experiment on are shapes of the two pectoral fins and bottom fin. Long pectoral fin put along the hull will work differently than wide and short fin. The case is similar with the bottom fin.+  * __Test set-up:__ Tail segments and the back fin are put together by bolts and secured by self-securing nuts (Figure 30). The spring steel shaft is led through the segments and connected to the DC motor. The DC motor is connected to the control unit and activated by turning the potentiometer on the remote control. The test is conducted in dry condition outside the water.
  
-Another addition to the body are static fins made from plastic. We will attach additional fins to the hull to make it more stable and avoid turning along the symmetry axis of the hull.+{{::figure30.png?200|}} 
 + 
 +**Figure 30: Assembled tail segments with back fin** 
 + 
 +  * __Results:__ The tail moves as expected in dry condition. To improve the undulating movement of the tail, the shaft has been shortened so it does not connect with the last two tail segments anymore. Instead, these segments were activated by elastic bands connected to the last moving segments (Figure 31). Outside the water, this mechanism created the expected fish-like motion. Sometimes, the DC motor struggled to rotate the shaft when the tail’s end oscillated in the opposite direction than the bended shaft. This problem could be reduced by not holding the tail horizontally but vertically so that the tail hung on its support. These problems might be solved when the mechanism operates in water because of the water’s damping effect. By changing the shape of the spring steel shaft, different amplitudes could be performed. Also the amount of elastic bands on the last segments was varied. 
 + 
 +{{::figure31.png?200|}} 
 + 
 +**Figure 31: Tail with two covers and elastic bands** 
 + 
 +=== 7.5.2 Test of Controlling the steering Fins === 
 + 
 +  * __Test set-up:__ Both pectoral fins and the bottom fin are put together inside the hull. The servomotors are attached to the control unit and signals are given from the remote control by pressing “up” and “down” buttons for pectoral fins and “left” and “right” buttons for the bottom fin. 
 + 
 +  * __Results:__ The program works as expected. The fins’ rotation angles were calibrated until they seemed suitable for steering the robot sufficiently without generating too much drag. 
 + 
 +=== 7.5.3 Waterproofing Tests === 
 + 
 +  * __Test set-up for connection plastic ring/ plane cover:__ At first, the detachable connection between pipe and plane back cover, as explained in Subsection 7.3.8, was tested. The plastic ring is glued to the inside of the pipe’s end with epoxy resin. The O-ring is put into the groove and the acrylic cover attached to the ring with eight screws. Water is poured into the pipe. 
 + 
 +  * __Results for connection plastic ring/ plane cover:__ Water is dripping out at a water column of about 5 cm inside the pipe, as to be seen in Figure 32. 
 + 
 +{{::figure32.png?200|}} 
 + 
 +**Figure 32: Water dripping out of pipe with attached cover** 
 + 
 +  * __Conclusion for connection plastic ring/ plane cover:__ The sealing mechanism cannot be applied to the prototype with this combination of materials. Two possible failure causes are assumed: The plastic ring is produced by a 3D printer and thus has an uneven surface. Even after treating the surface with sandpaper there remain small grooves through which water might slip. The second problem might be the high elasticity of the acrylic cover. When tightening the screws, the pressure is not spread evenly on the connection between cover and O-ring, but the cover deforms. This problem could be solved by using a stiffer cover and increasing the number of screws to fix it. 
 + 
 +  * __Test set-up for shaft opening:__ A shaft is led through the aluminium shaft opening, as explained in Subsection 7.3.8.. Plastic material of high flexibility is attached around the aluminium piece with waterproof tape so that only the shaft sticks out at the bottom. Water is poured into the created plastic basin. The shaft is rotated manually. 
 + 
 +  * __Results for shaft opening:__ Some water is dripping from the mock-up, but it is expected to come from the plastic that surrounds the shaft opening. The test set-up is considered inadequate to examine how well the shaft opening seals. Because of the tight fitting of the O-ring inside the aluminium piece to the shaft, it is expected to seal the prototype sufficiently during submersion for short times. 
 + 
 +  * __Test set-up for entire prototype:__ The shaft openings are glued into the pipe and back cover and thus these connections are sealed. The plane plastic caps at the front and back of the pipe are sealed with duct tape in addition to the O-ring mechanism after it failed in the anterior test. The break-through of the cable that connects the control unit with the remote control is sealed with glue. The entire prototype is submerged underwater horizontally. The shaft connected to the DC motor rotates continuously, the steering  fins move occasionally. 
 + 
 +  * __Results for entire prototype:__ After operation of about 30 s the prototype is removed from the water. Through the acrylic front cover it can be observed that there is water in the bottom of the pipe, about 1 cm high. Because all electronic components inside the hull are located safe off the ground another test can be performed. After the second submersion the amount of water has increased. From the ascension of small air bubbles around the pipe it is expected that water enters through the shaft openings. Especially the opening in the back is suspected to leak, where the shaft with the smallest diameter, most rotations and highest side forces (generated by the tail segments) is located. 
 + 
 +  * __Conclusion for entire prototype:__ The applied waterproofing mechanisms are sufficient to conduct first functionality tests with the prototype. For longer submersion better solutions should be developed. In addition, the process drying the robot’s inside requires to detach an entire front or back cap and thus takes much time. A small hole on the bottom of the pipe, temporarily sealable through covering it with duct tape, could simplify this process significantly. This way, several tests underwater could be performed in a quick sequence. Nevertheless, it has to be paid high attention to not rotate the robot around its longitudinal axis in case there is water inside the pipe, because the delicate electrical components located in the top could be easily damaged. 
 + 
 +=== 7.5.4 Test of the Hull’s Immersion === 
 + 
 +  * __Test set-up:__ The entire prototype is assembled. According to the buoyancy calculation (7.3.7) weights are added into the pipe: a metal bar of approximately 3 kg and another of 1 kg. The weight’s location is at the pipe’s bottom and as far in the front as the other components inside the hull allow. The hull is sealed (7.5.3), the spherical head is attached with duct tape and the prototype is put into the water. 
 + 
 +  * __Results:__ The prototype floats on the surface and is stable around the longitudinal axis (it does not rotate upside down), but the tail sinks deep into the water while the front is floating to the surface – even more than to be seen in Figure 33.  
 + 
 +{{::figure33.png?200|}} 
 + 
 +**Figure 33: First immersion test of prototype** 
 + 
 +To balance the prototype around its transverse axis the spherical head is detached and swim supports of Styrofoam are attached sideways at the pipe’s back (Figure 34). After this adjustment the robot almost floats horizontally in the water. 
 + 
 +{{::figure34.png?200|}} 
 + 
 +**Figure 34: Prototype with swimming support** 
 + 
 +  * __Conclusion:__ This mock-up is not ideal for further functionality tests because the Styrofoam pieces generate high drag and also the prototype floats high on the surface so that the pectoral fins are just submerged. A possible solution is to locate some weight in the spherical front cap instead of the pipe to balance the robot. 
 + 
 +=== 7.5.5 Test of Tail’s Propulsion === 
 + 
 +  * __Test set-up #1:__ The prototype is entirely assembled and sealed. The tail mechanism is composed as considered appropriate in the end of the preliminary motion tests outside the water (7.5.1) with a short bended shaft and elastic bands (Figure 31). The prototype is put into the water and the shaft rotated by turning the potentiometer on the remote control. 
 + 
 +  * __Results of test #1:__ The first three tail segments that are directly actuated by the shaft move as expected. The motion of the last three segments is damped by the water and they almost trail behind without any oscillation. Also, adding more elastic bands and increasing the shaft’s bending and length do not improve the motion. Nevertheless, the tail is able to propel the robot forward slowly. The pipe (without any static fins attached) oscillates only slightly around the vertical axis and moves with a straight heading direction. 
 + 
 +  * __Test set-up #2:__ The second last tail segment is removed. The shaft directly activates all segments; there are no elastic bands. The tail segments are attached to the loose back cover and the shaft is rotated manually, first in dry condition and afterwards submerged underwater. 
 + 
 +  * __Results of test #2:__ The tail performs the desired motion when activated in the air (Figure 35 a), as already observed in Subsection 7.5.1. As soon as the tail is submerged underwater, the shaft is not able to make the segments oscillate steadily anymore. The segments tilt and block each other (Figure 35 b). 
 + 
 +{{::figure35.png?200|}} 
 + 
 +**Figure 35: (a) Tail activated in air and (b) underwater** 
 + 
 +  * __Conclusions:__ The shaft made from steel spring is assumed to be too weak to transmit forces strong enough to overcome the water’s damping forces. A shaft of a bigger diameter might be able to transfer forces sufficiently. Presumably, a DC motor with higher torque is required to rotate this shaft at a steady angular velocity. In addition, a smaller diameter of the segment’s holes, through which the shaft is led, could prevent the segments from overly tilting and blocking each other. To maintain the idea of using elastic bands for creating a smoother motion of the tail’s end, the amount of transmitted forces should be increased. This can be done by bending the end of the shaft more, using stiffer elastic bands and/or increasing the distance between the attacking point of the bands and the segment’s rotational axis to generate higher torque.
  
-==== 7.6 ests and Results ==== 
  
  
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 In the context of starting to develop an educational toy for children, the target of this chapter was to design a biologically inspired swimming robot that has an easily controllable heading direction in the horizontal and vertical level as well as customizable features, which can teach children about the physics of floating objects. In the context of starting to develop an educational toy for children, the target of this chapter was to design a biologically inspired swimming robot that has an easily controllable heading direction in the horizontal and vertical level as well as customizable features, which can teach children about the physics of floating objects.
  
-Based on the considered biological principles and assessment of existing fish-like robots, a BCF propulsion-mechanism was adopted for the robot. The robot has along, articulated tail with a fin at its end to generate forward propulsion, a pair of pectoral fins located at the sides of the body to control the swimming depth and one at the bottom to steer left/right. The main achievement of this development is an innovative approach to actuate and change the undulating motion patterns of the robot´s segmented tail, which resembles the undulating motion along fishes´ bodies. +Based on the considered biological principles and assessment of existing fish-like robots, a BCF propulsion-mechanism was adopted for the robot. The robot has along, articulated tail with a fin at its end to generate forward propulsion,a pair of pectoral fins located at the sides of the body to control the swimming depth and one at the bottom to steer left/right. The main achievement of this development is an innovative approach to actuate and change the undulating motion patterns of the robot´s segmented tail, which resembles the undulating motion along fishes´ bodies. 
  
-After selecting suitable components it was started to implement a prototype. At the current status (14th June, 2014) this process has not been completed. The experimental evaluation of the prototype´s functionalities will be added to this document as soon as obtained.+After selecting suitable components a prototype was implemented. During the experimental evaluation of the prototype´s functionalities, some flaws of the waterproofing mechanisms became apparent. Nevertheless, first tests in the pool revealed the potential of the new tail mechanism to effectively propel the robot forward. A list of possible adaptations was proposed to improve the tail functionalities in the future. The main modification will be to increase the dimensions of component to improve the transfer of forces. Also, the prototype’s longitudinal mass distribution needs to be improved and the tests of steering and submersing performed, which was not possible in the time available for performing tests. 
 + 
 +As soon as also these tests have been performed successfully, the prototype can be considered a fully functional swimming robot with submerging capabilities and an innovative propulsion system.
  
 ===== 8. Conclusions ===== ===== 8. Conclusions =====
 +
 +
 +The main purpose of this report was to start developing a construction kit for a swimming robot with biomimetic features in order to arouse children´s curiosity and enthusiasm for technology. The research focused on enabling children to experiment on the physics of floating objects and drawing attention to sustainability problems of the oceans. During the entire development, the team had to bear in mind the marketability of the final product, sustainability issues as well as ethical and deontological concerns.
 +
 +At first, this chapter presents and discusses the main achievements obtained during this project. Finally, an outlook on future developments is going to be provided.
 +
 ==== 8.1 Discussion ==== ==== 8.1 Discussion ====
-//Provide here what was achieved (related with the initial objectives) and what is missing (related with the initial objectives) of the project.//+ 
 +In the beginning of this project, detailed knowledge about the research field has been gathered. Analyzing several natural and manmade mechanisms and products served as groundwork for the product development and confirmed the innovative character of the toy in the market. 
 + 
 +Before starting to develop the actual product, several preparations were performed. The team successfully elaborated and applied project management tools to create a positive, effective and efficient working atmosphere that helped to finish deliverables in time. The marketing plan helped to define the final product in detail. It was revealed that the construction kit for children of eight to twelve years has a unique combination of educational values. A market survey was conducted and plans for a successful product´s promotion and selling developed. In addition to that, research on eco-efficiency measures for sustainability revealed the importance of addressing these topics in order to create a profitable company. As a final preparation, ethical concerns regarding this project were addressed. 
 + 
 +Based on this groundwork, a prototype was developed in theory that resembles a fish successfully, ensures steering with a command-response pattern that is easy to handle and makes experimenting on the physics of floating objects possible. A user’s manual has been prepared to guide children through experimenting on their final toy. The key concept is an innovative tail mechanism that required functional tests due to its novelty character. Therefore, a prototype has been implemented that is able to float on the water surface. Due to the short amount of time available for the experimental evaluation, not all functionality tests could be performed. Nevertheless, the tail mechanism already revealed its potential to propel the robot forward. It is expected that its efficiency can be increased significantly by applying a list of proposed adaptations to the mechanism. 
 + 
 +If the future experimental tests confirm the expected high feasibility and efficiency of the robot with its new propulsion mechanism, this project has not only performed first step towards developing an innovative educational toy for children, but also made an important contribution to the scientific research field of biologically inspired swimming robots. 
 ==== 8.2 Future Development ====   ==== 8.2 Future Development ====  
-//Provide here your recommendations for future work.//+ 
 +Following this project, the proposed modifications to the tail mechanism can be performed. They mainly consist of increasing the dimensions of the spring steel shaft and torque of the DC motor that activate the tail segments. When also the longitudinal balance of the prototype is improved, the remaining functionality tests for steering left/right and submersion can be performed. At this state, the prototype will fulfil the initially proposed requirements. 
 + 
 +In addition, different fin models (varying in shape and size) can be experimentally tested in order to detect their effectiveness of steering and stabilizing the robot´s locomotion. Also, it is important to develop easier and safer waterproofing mechanisms because children are expected to easily loose their enthusiasm if water leaks inside the robot and components break. 
 + 
 +Finally, the other proposed features of the toy, which are to teach mechanics and programming, can be further elaborated by providing a user´s manual for the assembly and templates for programming. Before the final toy is ready for sale, the amount of toxic materials and harmful pieces has to be minimized, holding paramount the enhancement of safety for the user.
  
  
 ===== Bibliography ===== ===== Bibliography =====
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 ===== Appendices ===== ===== Appendices =====
 +
 +The following survey was done in the “EscolaSecundária do Agrupamento de Escolas de ÁguasSantas” in Porto, Portugal. The results were displayed in the marketing plan in Chapter 4.
 +
 +{{::survey_portugues.pdf|}}

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