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• Applications

  New Dexterity • 07/05/2020 at 17:06 • 0 comments

  As discussed, the developed platform has a cost of 90 USD. If we include also the recommended balloon type (4 USD) and the initial filling cost (16.5 USD), the total cost of the airship comes to 110.5 USD. This is comparable to alternative indoor blimp kits, such as the Blimpduino 2.0 [15], which costs 90 USD. The Blimpduino kit, however, features a simple microcontroller that is less flexible than the single-board computer integrated into the proposed platform. Considering also the camera module, the open-source gondola design, the ROS compatibility, and the sample closed-loop control scheme, the proposed platform is much better suited for research and education purposes.

  Concerning educational use, the platform can be easily incorporated into science and engineering courses on the secondary or tertiary level. For a mechanically-oriented curriculum, the students can work on gondola design and weight optimisation, developing their CAD and rapid prototyping skills. The airship is also ideal for control courses, where the students can develop and apply controllers that range from basic PID to complex, model-based control. An advantage of using a single-board computer as the core control component is also that the code is not limited to a single programming language, since the airship can be controlled through the provided ROS interface, C/C++ or Python. Combining the above with assembly, wiring, and optional circuit design for motor drivers, the platform can be used as a complete mechatronics project that encompasses mechanics, electronics, and control.

  For research, the small LTA platform is interesting in terms of controller development, as it is susceptible to drafts and ventilation that make reliable control difficult. Another opportunity is also in guidance and indoor exploration, where the challenge is to effectively utilise the limited computational power and simple RGB input to interpret its surroundings. Indoor exploration and navigation can be further examined in terms of micro-airship fleets. Such studies can build on [31], where the authors simulated the flight paths and collisions of several miniature airships with a similar shape and envelope type as those chosen in this work. Due to its safety and quiet operation, the platform can also be used in human-robot interaction studies. As the payload is limited, the challenge is to design a lightweight interface that can still effectively convey information and engage the user.

  References

  [31] B. Troub, B. DePineuil and C. Montalvo, "Simulation analysis of a collision-tolerant micro-airship fleet", Int. J. Micro Air Vehicles, vol. 9, no. 4, pp. 297-305, Dec. 2017.

• Results

  New Dexterity • 07/05/2020 at 17:04 • 0 comments

  A. Envelope

  From the raw balloon lift measurements (Figure 7), it is visible that the untreated latex balloons lost their lifting ability in a matter of days, while others were deflating linearly at a much slower rate. A more direct material comparison was possible through determining the helium flux through the balloon membranes. To accommodate the experimental data, the helium flux equation was converted into an approximate, discrete form:

  where Δ Q was computed from the daily lift loss and Δ t was the time between measurements. The amount of gas escaping Q was defined as the volume of helium at standard temperature and pressure (STP), according to IUPAC which defines them as T S T P = 273.15 K and p S T P = 10 5 P a [30]. Assuming that helium behaves like an ideal gas, the actual escaped gas volume V a can be converted into V S T P according to the ideal gas law:

  Because the balloons were kept in a laboratory environment at sea level, the actual pressure and temperature were assumed constant at pa = 101.325 kPa and Ta = 293.15 K Assuming the pressure difference on the balloon membrane was negligible, the helium lifting capacity lHe in the laboratory environment was computed as:

  where m is the lifted mass and Va is the helium volume at laboratory conditions. The lHe for the used balloon grade helium was experimentally determined to be 0.95 kg/m3  from the latex balloon volumes, lifts and masses. Combining the above, the daily helium escape flux through the balloon membranes was computed (Figure 8).

  Examining the obtained results, it is immediately visible that untreated latex is the least appropriate for an airship application. The helium was lost through the porous material in a matter of days and latex itself ages with time and UV exposure. Latex treated with UHF exhibits substantially better helium retention properties, comparable to those of the Bubble and Microfoil balloon materials. However, even UHF treated latex is subject to aging and easily bursts on impact with a rough surface. The Bubble and Microfoil balloons performed equally well in terms of helium retention, although an issue with Bubble balloons is their availability in terms of different sizes. For the experiments, the largest available Bubble size was selected and it could only lift 40 g at maximum inflation. While this might be enough for an optimised solution, it did not suffice in the prototyping stage. The helium escape flux measurements were averaged over the experiment period and collected in Table 1, where values for untreated latex balloons were merged. The table also presents the daily and yearly helium losses through the membrane of a spherical balloon that has a diameter of 60 cm corresponding to a surface of A = 1.13 m 2 . The flux values in the first row present the helium loss per day and per square meter, while the daily and yearly rates demonstrate the actual helium loss through the balloon membrane. Using approximate retail balloon gas costs, the yearly expenses of compensating the lost helium were computed (note that the yearly costs do not include the initial cost of filling the balloon, which is 16.5 USD). Examining these yearly cost projections, it is evident that helium related maintenance of an indoor airship is cheap, given an appropriate choice of envelope material. Such platforms are thus feasible from an environmental and financial standpoint.

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• Methods

  New Dexterity • 06/29/2020 at 07:54 • 0 comments

  The lifting gas chosen for the proposed robotic airship platform is helium as it is safe and provides high lifting capacity. An alternative with comparable buoyancy is hydrogen, which was immediately discarded due to its high flammability characteristics. Hot air was also considered, but its lifting potential is significantly lower than that of the above gases. In addition, the heating element would pose a safety risk, especially for indoor use. Other lifting gas choices are either toxic, flammable or offer minimal buoyancy, making them inappropriate for this application.

  A. Envelope Material

  Before designing the gondola, a number of envelope material candidates were examined with respect to their helium permeability and mechanical properties. To ensure a low cost platform, the envelope was chosen from the following set of commercially available balloons (see Figure 2):

  • Qualatex untreated round 41 cm (16 inch) latex balloon
  • Qualatex untreated round 61 cm (24 inch) latex balloon
  • Qualatex round 61 cm (24 inch) latex balloon treated with Ultra Hi-Float (UHF) [25]
  • Qualatex 61 cm (24 inch) clear Bubble balloon (layered membrane including a high barrier layer of ethylene vinyl alcohol copolymer)
  • Qualatex round 91 cm (36 inch) Microfoil (metallised PET) balloon

                                                                             

  Evaluated balloons, from left to right: Qualatex untreated round 41 cm latex balloon, Qualatex untreated round 61 cm latex balloon, Qualatex round 61 cm latex balloon treated with UHF, Qualatex round 61 cm Bubble balloon and Qualatex round 91 cm Microfoil balloon.

  To evaluate their helium permeability, the balloons’ lifting capacities, along with their surfaces, were measured daily over the course of 16 days. Because of their elastic properties, the surfaces of latex and Bubble balloons were determined through their circumferences. The Microfoil balloon surface was measured before inflation as the material does not stretch. After collection, the helium escape rate was computed as the flux through the balloon envelope, given by:

  where J is the gas flux, Q is the amount of gas escaping, t is time and A is the envelope surface. The obtained helium escape rates were then averaged and used in a feasibility study projecting expected helium losses through the membrane of an ideal spherical balloon. The approximate cost of helium used in the study was based on commercially available balloon gas tanks.

  The mechanical properties of latex, Bubble and Microfoil materials were examined in terms of membrane thickness in the inflated state, membrane area density in the inflated state, membrane tensile strength, and membrane elongation characteristics. Material samples for latex were taken from the Qualatex untreated round 61 cm balloon. For the Microfoil balloon, thickness was measured in the uninflated state because the material stretching is negligible during inflation. As the latex and Bubble balloons stretch during inflation, their inflated membrane thickness ti was estimated by assuming constant density of the material:

  where tu is the uninflated membrane thickness, Au is the uninflated balloon surface, and Ai is the inflated balloon surface. The area density for all balloons was computed from the uninflated balloon mass and...

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• Related Work

  New Dexterity • 06/29/2020 at 07:46 • 0 comments

  With the spread of intelligent robotic agents, numerous robotic platforms have been developed and disseminated in an open-source manner to allow replication by others in robotics education and research [7], [8]. Even though considerable progress has already been made in the field, most of the related work has focused on ground-based, stationary, or humanlike robotic devices [7], [9]–[10][11]. While they are certainly a reasonable choice in many educational and research scenarios, such robots are often heavy, expensive, hard to replicate, or have limited mobility.

  Such limitations can be overcome by indoor aerial platforms, which have in the recent years received a lot of attention. The most popular choice of such systems are quadrotors that have been developed as fully autonomous indoor, aerial robotic platforms [12]–[13][14]. Other studies have focused on indoor robotic airships. Skye [5] is a spherical omnidirectional blimp actuated by 4 rotors and equipped with a high resolution camera unit. It was intended for entertainment and interaction in large indoor and outdoor venues as the platform itself is quite large, with a diameter of 2.7 m. Another entertainment-oriented indoor airship platform is the Blimpduino [15], which features an Arduino-based control board that allows communication and basic control through a mobile app. The blimpduino came at a very affordable price of 90 USD, although it is not available for purchase anymore at the time of writing. A notable example of an autonomous indoor blimp is also the GT-MAB [16], one of the smallest autonomous indoor LTA platforms designed for human-robot interaction and autonomy studies. In [17], the GT-MAB was demonstrated in a human following and gesture recognition scheme, paving the road for flying airship companions.

  Some research has also focused on human interaction with rotorcraft, where work was mainly based on one-directional communication through gesture recognition. In [18], the authors presented an agent capable of full-pose person tracking and accepting simple gestural commands. Authors of [19] expanded this concept by developing a gesture-based interface for communicating with teams of quadrotors. In [20], the authors reversed the information flow and examined the communication of UAV intent to a human user through motion. Regarding rotorcraft, only the visual mode of interaction was considered in human robot interaction research because these platforms are generally too loud for auditory communication and too dangerous for tactile communication. LTA vehicles, on the other hand, can be silent and harmless to the user, provided that an appropriate lifting gas is chosen.

  The miniaturisation and democratisation of electronic components (access to sophisticated technology has become more accessible to more people) has allowed for progressively smaller and more low-cost designs of indoor airships, which have since become relevant for both robotics education and research. Initial studies have focused mainly on airship control and navigation, utilising the aerodynamic envelope shapes of their larger, outdoor airship counterparts. In [21], the authors presented an early indoor blimp system and studied visual servoing techniques. In [22], a dynamic airship model was developed and successfully applied in an indoor testing environment. Other examples that make use of the classic blimp envelope shapes include developments in blimp autonomy and navigation as described in [23], [24]. But all these studies have not focused on the feasibility of the robotic airship platforms, have not examined the permeability and applicability of different materials, the yearly helium losses, and the projected costs and none of these studies has proposed an open-source, platform that can be used for both robotics education and research.

  References

  [7] S. S. Srinivasa, P. Lancaster, J. Michalove, M. Schmittle,...

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• Introduction and Motivation

  New Dexterity • 06/29/2020 at 07:43 • 0 comments

  In the golden age of the giant airships, these vehicles had surpassed the fixed wing aircraft in terms of flight range, payload, and fuel efficiency. Even though the dream of filling the skies with fleets of transport and cargo ships has faded, the advantages of lighter-than-air (LTA) crafts remain. These can be applied in several fields of robotics education and research, where miniature robotic devices (both aerial and mobile) are slowly but surely making their appearance, attracting an increased interest.
  

  In terms of indoor exploration and navigation, airships offer higher mobility and looser path planning constraints when compared to ground robots. Additionally, their field of view is less obstructed and locomotion issues over different terrain and obstacles are bypassed completely. Conventional unmanned aerial vehicles (UAV) that are capable of static hovering in most cases generate lift purely through rotor thrust, which typically drains their battery in under 20 minutes. LTA vehicles, on the other hand, are able to maintain a desired altitude for significantly longer periods of time on a single battery charge [1]. In addition, airship platforms generally do not require precise collision control indoors, as their low speed and soft envelope prevent damage to themselves and their environment.

  These attributes render LTA platforms an interesting solution for various robotics education and research applications. Even though their physical interaction capabilities are limited, their higher mobility and lower cost makes them a viable alternative to static or ground-based robots in many applications involving tele-embodiment, monitoring, guidance, and entertainment [2]–[3][4][5]. Compared to rotorcraft, airships are silent and safer due to the absence of sharp, high velocity rotor blades. This allows close proximity interaction and makes them more attractive to users [6].

  Despite their promising features, the spread of indoor airship platforms is slow due to the design and control challenges they involve. The first task in LTA vehicle design is choosing an appropriate lifting gas. For indoor applications, helium is the default choice because of its non-reactive properties and high lift capabilities. Helium is non-renewable, making the choice of envelope material critical when considering environmental and financial aspects. Because of the small size of helium molecules, the gas escapes quickly through most conventional films which results in loss of lift over time. For indoor applications, the airship size is also constrained by standard corridor and doorway widths, limiting their maximum lift and weight of mechanical and electronic components. Once built, an airship is hard to control due to its slow response times and nonlinear dynamics. This imposes some very nice problems in terms of control design from an educational perspective. Small crafts are also highly susceptible to external disturbances, as drafts and air conditioning may greatly influence the airship’s behaviour.

  This project focuses on the feasibility, design, and development of an open-source, helium-based, indoor robotic airship that can be used for education and research purposes. First, it focuses on the environmental and financial feasibility of the platform with respect to the helium losses through different envelope materials. The results offer yearly helium loss and related cost estimates for a range of commercially available balloons in an indoor environment. The mechanical properties of candidate materials are also evaluated. Then, the project presents a compact gondola design and explores the effects of its placement and rotor angle positioning on flight stability. The efficiency of the final design is experimentally validated via a proof-of-concept path following exercise that proves its manoeuvring capabilities, while the airship’s motion is being tracked by a Vicon motion capture system. Finally, the platform is examined in terms of cost and...

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