蘇黎世聯邦理工學院的研究人員，在木架構的構築流程之中嘗試了嶄新的數位工法，這是世界上第一個機械手臂參與大型木構協作的實際案例。這些承重的木頭模組，預先由機械手臂所組裝，之後將會組立在 DFAB HOUSE 最上面的兩層空間。
Researchers from ETH Zurich are using a new method for digital timber construction in a real project for the first time. The load-bearing timber modules, which are prefabricated by robots, will be assembled on the top two floors at the DFAB HOUSE construction site.
傳統的木頭框架構築，因為機械編程的介入而有更多的可能性。 The range of possibilities for traditional timber frame construction is
expanded by the new robotic method for digital timber construction.
Digitalisation has found its way into timber construction, with entire elements already being fabricated by computer-aided systems. The raw material is cut to size by the machines, but in most cases it still has to be manually assembled to create a plane frame. In the past, this fabrication process came with many geometric restrictions.
Researchers from ETH Zurich have built a prototype of an ultra-thin, curved concrete roof using innovative digital design and fabrication methods. The tested novel formwork system will be used in an actual construction project for the first time next year.
蘇黎世聯邦理工學院的研究人員，設計和建造了一個使用創新設計和製造方法的超薄混凝土屋面原型。該薄殼是一個屋頂單元的局部，將會於明年建構成一個名為 HiLO 的建築單元，隸屬於 NEST 大樓的一部分（the living lab building of Empa and Eawag in Dübendorf）。完工後下方的閣樓空間將成為 Empa 的客座教職員，未來生活與工作的空間。這群研究人員由 Architecture and Structures 的 Philippe Block 教授，以及 Architecture and Building Systems 的 Arno Schlüter 教授所領導，希望將嶄新的輕量化建築結構用於實際的測試，並將它與智慧和適應性建築系統結合起來。
A prototype for an ultra-thin, sinuous concrete roof using innovative design and fabrication methods has been designed and built by researchers from the ETH Zürich. The shell is part of a roof-top apartment unit called HiLo that is planned to be built next year on the NEST, the living lab building of Empa and Eawag in Dübendorf. The penthouse will provide living and work space for guest faculty of Empa. Researchers led by Philippe Block, Professor of Architecture and Structures, and Arno Schlüter, Professor of Architecture and Building Systems, want to put the new lightweight construction to the test and combine it with intelligent and adaptive building systems.
Digital Grotesque 數位洞穴（註：Grotesque《源自義大利語＂洞穴(的畫)＂的意思；指常出現在洞穴中以怪獸為題材的畫》）是第一次完全身臨其境、 實體的、 人體尺度的封閉結構，完全是以 3D 列印的技術所生成。這個結構的測量面積為16 平方米，（向量的世界裡，參數是可以不停細化直到逼近硬體的極限）這作品的細部是以人類可以感知的範圍，作為精細度的標準。這樣結構的每一個面，都是由自訂設計的演算法所演算而成。
數位洞穴這個專案，是由瑞士蘇黎世聯邦理工學院（ETH-Zurich）的電腦輔助建築設計（CAAD）研究小組所發展。其中所有的構件都是由voxeljet AG 所列印生產。數位洞穴的第一個區塊將會由FRAC中心為其永久收藏。
Digital Grotesque is the first fully immersive, solid, human-scale, enclosed structure that is entirely 3D printed out of sand. This structure, measuring 16 square meters, is materialized with details at the threshold of human perception. Every aspect of this architecture is composed by custom-designed algorithms. Please visit digital-grotesque.com for a further description. Research for the Digital Grotesque project was carried out at the Chair for CAAD at the Swiss Federal Institute of Technology (ETH) in Zurich. All components were printed by voxeljet AG. The first part of Digital Grotesque is a commission by FRAC Centre for its permanent collection.
Partners and Sponsors: • Chair for CAAD, Prof. Hovestadt, ETH Zurich • Department of Architecture, ETH Zurich • voxeljet AG • FRAC Centre • Strobel Quarzsand GmbH • Pro Helvetia Achitects: Michael Hansmeyer, Benjamin Dillenburger
Fabrication Team: Maria Smigielska, Miro Eichelberger, Yuko Ishizu, Jeanne Wellinger, Tihomir Janjusevic, Nicolás Miranda Turu, Evi Xexaki, Akihiko Tanigaito
“The whole is greater than the sum of its parts” — a catch phrase that aptly expresses the Distributed Flight Array: a modular robot consisting of hexagonal-shaped single-rotor units that can take on just about any shape or form. Although each unit is capable of generating enough thrust to lift itself off the ground, on its own it is incapable of flight much like a helicopter cannot fly without its tail rotor. However, when joined together, these units evolve into a sophisticated multi-rotor system capable of coordinated flight and much more.
In the beginning In the summer of 2008, Professor Raffaello D'Andrea at the Institute for Dynamic Systems and Control at ETH Zurich envisioned an art installation consisting of single-rotor robotic units that would self-assemble on the ground and then perform a joint task that would otherwise be impossible to achieve on its own — flight. This modular flying vehicle would then break apart in the air and then repeat the process over again, but in a new randomly-generated configuration.
Feasibility studyThe number of challenges faced in designing and implementing such a system are many. We first wanted to be sure, however, that the concept was indeed feasible. Making some realistic assumptions about the system we performed some back-of-the-envelope calculations and created a linear dynamics model of the vehicle in order to provide us with some intuition about its physical dynamics. From this, a control strategy was devised. We then simulated the closed-loop system under a variety of disturbances, providing us with a general understanding of the physical requirements needed to successfully execute the project.
2008 年的秋天，這個物理系統的設計與實現其實還只是 ETH Zurich 校園，內某個進行中的設計專案的一部分。這專案包括八位來自機械、 電氣、 軟體工程領域的研究生，以及技術人員和教員，包括我自己在內。我們的任務是為設計和構建一個具有特別功能的原型，主要需具備三個關鍵的能力：（1）對接（2）地面上的協調與移動性和（3）協調飛行。在每完成一個任務之後，我們都會反過來驗證我們的模型和控制策略，來檢測一些我們可能沒有預料到的，可能會侷限系統的變數。
Design and implementation of the physical system began in the fall of 2008 as part of a design project class at ETH Zurich.The class consisted of eight graduate-level students from mechanical, electrical, and software engineering, as well as technical staff and instructors, including myself. Our task was to design and build a functional prototype that would demonstrate three key abilities of the system: (1) docking, (2) coordinated ground mobility, and (3) coordinated flight. In accomplishing each of these tasks, we would in turn validate our model and control strategy, and likely discover limitations to the system we did not foresee.
The project was no doubt challenging, and the timing constraints imposed by the class did not work in our favour. Our initial hope was to demonstrate each of the key abilities using a single set of vehicles and to demonstrate coordinated flight in several configurations. Our goals were too ambitious under the framework of this class and therefore loosened our requirements. By the summer of 2009 (a few months after the class had ended), we succeeded in demonstrating each of these key abilities, and ultimately, the project's feasibility.
Towards the end of the above video, you will notice one of the many limitations of the system: its inability to control its altitude (or height off the ground). You may also notice that both flying and driving capabilities were separated in order to make the vehicle lighter for flight. Its primary limitation, however, was its inability to demonstrate coordinated mobility for randomly assembled configurations. The units themselves lacked the ability to communicate on each of their sides, and even if this were possible, we did not yet have any way of automatically generating the appropriate control strategy for the assembled configuration. For our demonstration, each unit was pre-programmed for a particular configuration and the controller was tuned by hand. This, however, was just the tip of the iceberg for the long list of requirements needed to successfully achieve our final goal.
Design iterationsWith the design project class under wraps, and feasibility of the system demonstrated, the next step was to engineer a truly modular system capable of coordinated mobility — both on the ground and in the air. This was by no means a straightforward process; if it was, it wouldn't be considered research. One additional revision of the vehicle was created prior to arriving at the current design.
In designing Revision 1, one of our major goals was to integrate both driving and flying capabilities. This required us to rethink the mechanical chassis and to design with a sufficient thrust to weight ratio in mind. Although light-weight and mechanically robust, the ethyl polypropylene foam chassis we used in the proof-of-concept vehicle was difficult to manufacture and our experience led us to switch to a different material. We opted instead for constructing the chassis out of laser-cut acetal plastic, a higher-powered flight motor, and a new propeller. This resulted in a very robust chassis, which was easy to fabricate in-house, and it provided sufficient thrust for the purposes of lift and control effort. What we failed to consider, however, was the stiffness of the chassis and manufacturing variability of the rotors. Only after completing the design of Revision 1 and producing several units did we discover that the vibrating modes in the chassis caused by aerodynamic turbulence from the propellers saturated the onboard rate-gyroscope sensors, which was needed for closed-loop control.
六個接合面都具備傳輸溝通的能力，也是這一個修訂版本中很重要的一個里程碑。我們成功地安裝紅外收發器到每個連接介面上。然而，我們後來發現進行實驗時，紅外線系統會與我們裝置環境的 3D 運動捕獲系統（用於地面測量）發生干擾，由於它使用類似頻率的紅外燈來照亮，會被辨識為跟蹤的標記。
It was also important in this revision to demonstrate communication on each of its six sides. We successfully accomplished this using infrared transceivers mounted to each connection interface. However, we later discovered interference issues when conducting experiments with our vehicle within the environment of a 3D motion capture system (needed for ground truth measurements), which uses a similar frequency of infrared light to illuminate markers that it tracks in order to estimate the pose for the object of interest.
On top of this was the need to shrink the size of the electronics such that it would fit within the protected volume of the chassis. We were motivated by recent manufacturing possibilities in creating flexible printed circuit boards, and locked on to this scheme. When it came around to producing the boards, however, the lead-time for such services in relatively small quantities was much too long for our requirements — we wanted to be able to prototype and have a quick turn-around on our designs. We therefore had to redo parts of the design for a standard printed circuit board.
當系統第一次使用 3D 運動捕獲系統進行試飛時，透過回傳的測量訊息，我們得到了一些具建議性的資料。這些測量是非常精確和相對快速的，我們可以利用電路板上的功能直接估計問題，並只專注于這些問題的控制。事實上，我們主要在處理兩個項目：（1）如前面所述，從 3D 運動捕獲系統發出的紅外燈，會造成單元相互溝通時的干擾；（2）測量資訊 （或控制資訊） 在操控的前提下需要以無線的方式進行傳送，而在一般的發展（使用 WiFi）下，會產生大量的延遲和資料包的遺失。
There was also the suggestion to first fly the system using a 3D motion capture system for measurement feedback. Since these measurements were very precise and relatively fast, we could by-pass the onboard estimation problem and focus only on the control problem. This, in fact, worked against us for two major reasons: (1) as described before, the infrared light from the 3D motion capture system interfered with inter-communication; and (2) measurement information (or control information) needed to be transmitted to the vehicle wirelessly for control purposes, which at the time of development (using WiFi) generally incurred a lot of latency and packet loss.
There was a lot that needed to be redesigned, a lot that was assumed, and there was pressure to get research publications out. In Revision 1, we tried to jump over too many hurdles at once and what we delivered was a semi-functional system — functional under optimal operating conditions, but failed to work most of the time. However we learned many things, in particular it focused our attention on parts of the design that we overlooked. This laid the ground work for Revision 2.
在二號修訂版，我們重新設計的機殼以及提供推力的單元（螺旋槳和飛行電機）。一切從零開始，但保留的大部分電力和電子控制裝置。使用了一些製造技術上的最新研究，機殼在這個階段開始使用 3D 列印的技術，使我們能夠以很少的製作限制來進行設計，同時擁有相對快速的應變時間。第一個因素非常重要，這使得數個元件可以緊密的整合在一個單位內。第二個因素使我們能夠快速測試設計，不斷地重複這個流程是免不了的。
In Revision 2, we redesigned the chassis and thrust generation unit (i.e. propeller and flight motor) from scratch, but kept most of the power and control electronics the same. Using some of the most recent advances in manufacturing technology, the chassis was 3D printed this time around, enabling us to design with very little fabrication constraints and has a relatively quick turn-around time. The first factor was very important because of the number of tightly integrated components held together within a single unit. The second factor enabled us to quickly test a design and re-iterate as necessary.
This time around, we stepped through each phase of the design systematically. The new flight motor and propeller was tested to ensure that it produced a sufficient amount of thrust and produced little vibration within the chassis, which we tested using the rate-gyroscope sensors from Revision 1. Using two units and electronics from Revision 1, we tested the closed-loop behaviour around a single axis of rotation by mounting the two units on a horizontal pivot. This alone required a few iterations of the chassis, which in the end we managed to get right.
Ignoring the intercommunication problem, we ploughed ahead and constructed six complete units for flight. In this revision, we demonstrated coordinated flight for a variety of configurations. The flight controller was computed ahead of time and sent wirelessly to each unit prior to flight.
The Distributed Flight Array: Outdoor Flight Experiments
Knowing that the chassis and thrust generation unit was sound, we then went ahead and integrated driving capabilities and intercommunication into the units. In terms of the latter, we redesigned the intercommunication scheme, employing a hard-wired interface instead of an infrared wireless link and utilized an electrical bus to clean up the mess of communication lines we had in Revision 1. A detailed description is given in the next section.
Designed from the ground upEach unit uses a single 32-bit 72 MHz microcontroller to interface with all of the onboard sensors, actuators, and communication peripherals. The same microcontroller is also used for performing all of the computation necessary for estimation and control — there is no computation that is performed offboard. An interchangeable wireless module (either WiFi or proprietary frequency hopping spread spectrum) allows us to communicate with each unit (e.g. telemetry and user commands); in the case where external sensors are used (e.g. 3D motion capture system), the data can be sent to the units over this wireless link.
Components of the DFA.
Each unit uses a single 32-bit 72 MHz microcontroller to interface with
all of the onboard sensors, actuators, and communication peripherals
Standard on most aerial vehicles is a 3-axis rate-gyroscope, which is used for measuring body angular velocities, as well as estimating the attitude of the vehicle in flight. An infrared distance measurement sensor is used for measuring the distance of a unit to the ground. Not only is this used for estimating the altitude of the vehicle, but if units share their distance measurements with one another they can also estimate the vehicle's tilt when flying over a flat surface.
We have designed each unit with magnetic interfaces, located along each of its six sides. This allows a unit to passively self-align with its connected peers. The connection strength, however, is in fact not very strong. This was intentional, as it clearly demonstrates the need for cooperation between individual units in order to achieve flight — without it, the vehicle would simple rip itself apart before take-off. To successfully accomplish this, the flight control strategy must minimize the shear forces occuring between interconnected units during flight.
Also located on each of its six sides are three gold push-pins. Together with the magnets, this interface behaves similarly to the Apple MagSafe power connector, except that this interface is used to provide a means for hard-wire communication between neighbouring peers. With this, we developed our own network layer to handle inter-unit communication, as well as algorithms for routing packets, time synchronization, information fusion, etc. on a resource limited embedded system. Units are also able to communicate with one another in plane at a distance using infrared wireless transceivers, which is primarily employed for self-assembly purposes.
Distributed Flight Array: Self-assembly.
每個單元搭配三個全方位轉輪，使它在地面上的移動具有高度的機動性，並能在群聚的狀態下一起移動。使用 3D 印表機技術來列印全方位轉輪，一體成型的優點讓它不需要裝配任何的元件。
Each unit is equipped with three omni-directional wheels, allowing it to move on the ground with a high degree of maneuverability and to be able to move when assembled together. One of the nice things about using 3D printer technology is that the omni-wheels could be printed as a single piece, without having to assemble any components.
Positioned at its centre is a fixed-pitch propeller, capable of generating enough thrust to lift a single unit off the ground. All units are physically identical except for the handedness of its propeller. Some are clockwise and some are counterclockwise — this is needed in order to cancel out the aerodynamic torques in flight. Finally, a high energy-density Lithium-Ion Polymer battery is used to power all the electronics and actuators contained onboard.
Coordinated flight The units can move around on the ground, self-assemble, generate an adhoc mesh network in order to communicate with one another, but the most striking feature of the Distributed Flight Array is its ability to fly in an unlimited number of configurations.
The Distributed Flight Array: Indoor Flight Experiments
Recall that the units are being held weakly together with magnets. Thus, each unit is generating the appropriate control effort necessary to keep the vehicle in flight while minimizing the shear forces between individual units. What is most surprising is that the units themselves do not necessarily need to communicate with one another during flight.
The only information that a unit needs for flight is its local sensor data and its position with respect to the vehicle's centre of mass. This can be computed if each unit knows the physical configuration of the vehicle. In order for a unit to determine this on its own, each unit can work out its relation to neighbouring units by sharing appropriate information. By forwarding this information around the network, each unit can arrive at the physical configuration of the vehicle, much like how one might establish his/her family tree.
Assuming a rigid body for the vehicle, which was taken into account when designing the chassis, local sensor information provides a unit with a rough estimate of the vehicle's tilt and altitude. And knowing its position with respect to the centre of mass, it's straightforward to work out the appropriate control effort needed to counter-act any disturbances. We avoided using a linear quadratic regulator or other optimal control strategies in favour of something much more straightforward, and as it turns out the method is also scalable. We employ a cascaded parameterized controller, consisting of tuning parameter that are physically intuitive (i.e. closed-loop natural frequency and damping ratio) for each degree of freedom.
Now, it wouldn't be reasonable to hand-tune the controller for each and every configuration. We instead developed a means for automatically computing the tuning parameters for any flight-feasible configuration of the vehicle that would result in best flight performance. In carefullly analyzing the parameters obtained for a variety of configurations, we then developed a scalable method for mapping the configuration of a vehicle to its approximated optimal control tuning parameters.
Rewards and reality
A lot challenges, a lot of frustration, but also a lot of reward. What started as an idea is now a reality. Although we have not necessarily shown it to reenact the Concept Animation shown above, it is certainly capable of performing each of those tasks. What we have here is a piece that suitably demonstrates cooperative behaviour.
The success of this project would not have been made possible without support from the Swiss National Science Foundation, as well as the countless number of hours spent by students and technical staff — they all deserve as much credit. The Distributed Flight Array is currently being used at the Institute for Dynamic Systems and Control at ETH Zurich as a modular robotics platform for investigating algorithms in distributed estimation and control. Updates regarding the project's status and a list of those involved with the project can be found on itshome page.
Who's Currently Involved: Raffaello D'Andrea, Maximilian Kriegleder, Igor Thommen, and Marc A. Corzillius
