Makenna Kuzyk, Jana Gebara, Jade Belisle
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Canada has a strong presence in space robotics, and Mission SpaceWalker (MSW) is a group of ambitious young women who are leaning into Canadian robotics excellence through their investigation of how electroadhesive (EA) robots behave in reduced gravity, all while introducing a new testing procedure for rovers and adhesive space robotics. As an undergraduate student team at the University of Alberta, MSW has been chosen to fly their payload as part of the Canadian Reduced Gravity Experiment Challenge (CAN-RGX) organized by Students for the Exploration and Development of Space Canada (SEDS-Canada), the National Research Council of Canada, and the Canadian Space Agency. The annual competition is open nationwide to university students, soliciting participating groups to create a payload to be tested onboard a parabolic flight. The experiment will consist of an automated system contained within a Pelican case, featuring a mechanical design that will obtain footage of two robots on conductive and nonconductive surfaces. It will log data from onboard sensors to provide insight into the performance of the EA pads on both surfaces. The payload is expected to be flown on a parabolic flight during the CAN-RGX campaign in the 2023 calendar year.
During this Artemis age, 14 women aim to contribute to the Canadian space robotic legacy through their MSW team. The purpose of MSW’s experiment is to investigate EA performance in a microgravity setting on both conductive and nonconductive surfaces while verifying the performance of their experimental setup. On Earth, gravity produces the normal force required to move without slip. In a microgravity environment or situations where gravity’s force is orders of magnitude smaller than on Earth, an alternate adhering force must be present to create the required traction. MSW proposes EA due to its reusability and simplistic design.
EA technology could be implemented in various situations, such as untethered robots outside space stations, allowing maneuverability and the maintenance of hard to reach areas, or in meteorite exploration and mining missions, allowing the anchoring of equipment to the surfaces. This technology utilizes two oppositely charged electrodes with extremely low current and high voltage (HV) to polarize a surface. They are, in essence, large capacitors, which can be attached to the surface of bodies to induce adhesion. According to an article by Guo et al. (2017) on soft robotics, EA does not rely on smooth and clean surfaces to be able to adhere, and it allows robots to adhere to both insulating and conductive materials. EA is undergoing further research to optimize the technology, as there are many potential manufacturing processes. The team is experimenting with materials, manufacturing techniques, manufacturing processes, and electrode spacing to supplement this ongoing research. The group intends on thorough testing to ensure that EA is reliable in high-risk environments and safe for human interaction. An aspect of this project is to verify that HVs between 5 and 7.5 kV are suitable for environments such as the inside of a space station.
Integrating EA with robotics is relatively new, and its current applications span from conveyor belts to the delicate handling of objects with grippers. Robot weight can be a limiting constraint when testing climbing robots in Earth’s 1g conditions, which is less of a concern in reduced gravity conditions, such as low Earth orbit and beyond. Spenko’s (2021) timeline of technology spans the evolution of EA grippers, suspension, and anchors. EA wheels and climbing robots have yet to be tested in a microgravity environment. With successful parabolic flight data, MSW should be able to help characterize EA when deployed in a microgravity setting compared to Earth’s 1g environment. These comparisons can aid in the understanding of how EA robots can be improved both on Earth and in space through understanding how gravity and weight influence their effectiveness.
MSW’s testing procedure will also be able to provide meaningful data for future experiments relating to both EAs and robotic wheels. Past experiments, such as the NASA gecko-adhesive robotics parabolic flight (Parness et al., 2015), were neither contained nor automated due to minimal constraints placed on the experiments. To abide by the rules of the CAN-RGX competition put in place to limit hazards and increase size efficiency, MSW’s experiment will be automated within a Pelican case of approximately 0.91 × 0.91 × 0.91 m. This testing method would be beneficial to future tests in situations where experiments are constrained to smaller lab spaces, such as on space stations, where optimization and efficient use of resources is critical. An automated testing setup will also demonstrate a decreased reliance on human intervention during the experiment, a notable intention of autonomous robotics.
EA technology is potentially revolutionary for robotics, as an IEEE ICRA paper claims it is adaptable, gentle, flexible, and simple and has an ultralow energy consumption (Diller et al., 2016). Adhesion is achieved by an electrostatic effect between an EA pad and a substrate. EA creates attraction to a surface through polarizing a surface, which is achieved from two oppositely charged electrodes creating electric fields. A dielectric material encases the electrodes to avoid bridging or sparking of the pads. EA pads are ideal for space due to their low power consumption and ability to operate in a vacuum. According to a 2017 study on EA devices, EA pads should work on both conductive and nonconductive substrates. Guo et al. (2017) explain that, when the substrate is conductive, EA forces are produced by electrostatic induction, whereas, in insulating substrates, the EA forces are from electric polarization.
MSW’s pads are designed and manufactured in house, and a variety of methods have been attempted to make them, including silicone spray, conductive fabric, and silicon casting. However, the procedure that has proven most successful for the team is that of aluminum electrodes cut from an aluminum sheet and heat-pressed between two sheets of polyurethane. This manufacturing technique was the quickest to produce and was able to limit the air gaps between pad layers without compromising the electrode. The comb pattern and gap sizes between the electrodes were experimentally determined to eliminate sparking. A supply voltage of up to 7.5 kV was chosen, as testing (shown in the “HV Withstand Voltage Testing” section) revealed that this limit prevents sparking and reduces breakdown of the electrodes.
The experiment features two robots to demonstrate EA on both a conductive and a nonconductive (or insulating) surface during a microgravity flight. Sensors used to characterize and control the motion and gravitational forces (g-forces) experienced by the robots include ultrasonic sensors, limit switches, and an accelerometer. Video footage during the experiment will be collected by various cameras for proof-of-concept visuals and postflight analysis. The mission objectives can be found in the following section, and the information given here will aid in the contextual understanding of the success criteria.
There will be two robots operating on two different substrates set within a frame, depicted in Fig. 1. The top robot operates on an aluminum surface, and the bottom robot is on a high-impact acrylic surface. These two materials were chosen to test the capabilities of our EA pads on a conductive and nonconductive surface. In future experiments, MSW hopes to test a variety of surfaces with aberrations introduced, such as dust and roughness. Fig. 1 also displays an aluminum rail running the length of the substrate that will engage with a claw on the robot in the event that adhesion fails. There is an offset of 5 mm between the claw and the rail to effectively simulate microgravity and not induce forces on the robot unless detachment occurs. Jamming is mitigated by the size of the robot and clearance between the rail. The claw was designed to enable the robot to recontact the substrate during the regular gravity portion of flight if misalignment or complete detachment occurs during a parabola. A Pelican case will contain the whole experiment to limit hazards during the flight, with wires for computer control and power running out the side control panel. A computer will be mounted to the top of the case for control and surveillance of the experiment during the flight.
Fig 1 (a) The robot placement in the frame structure. (b) The top robot placement. The stacked design for the two robots is depicted in (a), while the overall position of an individual robot on its level is shown in (b). Not included in the pictures are the wires that connect each robot to the plane’s power.
Using SOLIDWORKS, the chassis was modeled with custom mounts and compartments for the electronics. The robot assembly and a labeled view can be seen in Fig. 2.
Fig 2 (a) The assembled robot. (b) The labeled robot CAD.
The EA pads will be attached to the wheels of the robot, which are in the final design stage. This attachment method will involve the use of friction and tension to ensure that slippage off the wheel does not occur. The mobility with the wheel allows it to be easily attached and provide the forward driving force against a substrate in microgravity where normal forces are not present.
In normal operation mode, the robots are programmed to move back and forth using the limit switches placed on the front and back of the robot; when the limit switch comes in contact with the casing at the end of its traverse, the robot will reverse the motor direction. MSW selected limit switches to trigger the robot to change direction, as they are simple to implement, and their response to a trigger occurs in a reliable manner. Ultrasonic sensor data indicate the distance from the casing wall, and the accelerometer validates this distance while also indicating the g-forces experienced by the robot. Ultrasonic sensors were chosen, as they are relatively cheap when compared to alternative distance measurement sensors and are accurate to 2 mm. This is sufficient for the requirements of the experiment, as only the overall change in distance is required to verify the movement of the robot compared to the wall. In the event that a robot detaches from the substrate, the ultrasonic sensor and accelerometer will display no change.
Flight procedures were developed both as a requirement for the competition and to have a thorough plan while in flight. Having clear flight procedures means that everyone aboard the flight knows what is going on at all times. Additionally, since the plane can only remain in the air for so long, there is a limited timeframe in which to conduct the experiment. Any extra time spent setting up the experiment takes away from the allotted experiment time. An efficient, practiced procedure allows the experiment to be set up in the quickest manner possible with no surprises. The flight procedures can be seen in Fig. 3, with the two researchers required by SEDS flying the payload labeled as mission specialist 1 and mission specialist 2. They will be in constant contact with the flight crew, who will indicate when microgravity conditions begin. This is when the motor power will be supplied, allowing the robot to move. Level flight will only be used if the robot or experimental materials require repositioning, which, although not expected, has procedures prepared. During level flight, specialists will identify any issues through the cameras if possible, turn off all power to the experiment using the kill switch, open the Pelican case and ground all electrical components, and then fix the misalignment or issue within the 3-min window. These procedures will be practiced prior to flight.
Fig 3 The in-flight procedures. Task blocks are colored according the personnel legend. Tasks that are vertically aligned are considered to be taking place in parallel (i.e., at the same time). Procedure template provided by SEDS.
For the robotics experiment to be deemed successful, objectives have been broken down into three detailed criteria:
Withstand voltage testing was performed to examine the voltage limits of the different manufacturing methods the team explored to create the EA pads. The success criterion of these tests is defined as the voltage reached before sparking or shorting is qualitatively observed.
Two methods of manufacturing were tested, one of which altered the electrode material. The first method involved the encapsulation of electrodes in polyurethane with differing electrode materials. Overall, thicker electrodes with larger gaps produced less sparking and shorting. The other method involved changing the dielectric used, with polyurethane being exchanged for Engage 8200 thermoplastic pellets (pad 2). The results are seen in Table 1. Pad 2’s method of manufacturing was no longer investigated for quantification due to the limitations of the design and minimal withstand voltage observed.
Table 1. The withstand voltage testing.
The results of withstand voltage testing progressed into the quantification of the EA shear forces experienced by the pads. The controlled variable within these tests was the applied voltage. Different parameters were altered to investigate the changes in the EAs. These included electrode width, electrode spacing, pad width, and pad length. These are shown on the left in Fig. 4 with a schematic of the testing set up on the right.
Fig 4 The electrode pattern details and test setup.
The setup included a 3D printed rectangle made of polylactide, placed underneath the EA pad to allow for proper positioning. The EA pad was placed on top, with a rectangular piece cut out of paperboard. This paperboard was utilized to demonstrate the point of force imbalance. Coins were used as a standardized mass and placed at the end of the pulley system to induce a force. The coins were utilized due to their precise values of mass, ability to add mass in smaller increments, and ease of layering to avoid the production of momentum given their smooth surfaces. Four separate pads were tested, with the results demonstrated in Table 2.
Table 2. The pad quantification.
Functionality testing has occurred and will continue until flight to ensure optimal performance of the EA pads since full experimental testing is not possible due to the full-gravity environment. The functionality tests are carried out with a 5-kV applied voltage from a power supply source and occur in three rounds: functional testing, quantification, and then longevity. These rounds are described as follows:
Initial functionality test results revealed the mylar electrodes’ defectiveness. This was observed through the inability to progress past round 1. The manufacturing method was then switched to use thicker aluminum sheets. The results of the initial readiness test are displayed in Table 3.
Table 3. The functionality testing of the final EA pad design.
Canada has a heritage of space robotics, particularly at the intersection with human space exploration: Canadarm and Canadarm2 serviced the Space Shuttle and International Space Station, respectively, and Canadarm3 is envisioned to facilitate autonomous operations for the Lunar Gateway, which will be a key component of NASA’s Artemis program. MSW is hoping to continue Canada’s prevalence in the space industry by researching EA robotics. Our experiment consists of an automated robotic experiment conducted in a Pelican case, which will be flown on a parabolic flight in 2023 as part of the CAN-RGX competition hosted by SEDS-Canada. The objectives include investigating whether the testing setup for related enclosed rover and adhesive robotics experiments is feasible, the ability of an EA robot to adhere using simple EAs made of polyurethane and aluminum sheets, and the difference in adhesion in microgravity between conductive and nonconductive surfaces.
Due to constraints, such as gravity on the EA normal force, MSW’s objective is to collect evidence that this technology is well suited for microgravity conditions. Parabolic flight is an essential component to understand EA behavior since effects such as increased inertia occur when simulating weightlessness with a counterweight. Data collected from this experiment will aid in furthering academic research on EAs in space, as the trials will be run on various space materials while obtaining footage for our proof of concept. The experiment is expected to aid in the understanding of EAs and help the development of space technologies. Just as Neil Armstrong declared “one small step for man,” the intent is that the first EA robotic flight on the Falcon 20 will be one of many giant leaps for womankind in the field of space robotics.
• R. Chen et al., “Bio-inspired shape-adaptive soft robotic grippers augmented with electroadhesion functionality,” Soft Robot., vol. 6, no. 6, pp. 701–712, Dec. 2019, doi: 10.1089/soro.2018.0120.
• M. Spenko, “Making contact: A review of robotic attachment mechanisms for extraterrestrial applications,” Adv. Intell. Syst., early access, Jul. 2021, doi: 10.1002/aisy.202100063.
• A. Parness et al., “Zero gravity robotic mobility experiments with electrostatic and gecko-like adhesives aboard NASA’s zero gravity airplane,” International Astronautical Federation, Paris, France, 2015. [Online] . Available: https://web.stanford.edu/∼kalouche/docs/zero_g.pdf
• S. Diller, C. Majidi, and S. H. Collins, “A lightweight, low-power electroadhesive clutch and spring for exoskeleton actuation,” in Proc. IEEE Int. Conf. Robot. Automat. (ICRA), Stockholm, Sweden, May 2016, pp. 682–689, doi: 10.1109/ICRA.2016.7487194.
• J. Guo et al., “Experimental study of a flexible and environmentally stable electroadhesive device,” Appl. Phys. Lett., vol. 111, no. 25, Dec. 2017, Art. no. 251603, doi: 10.1063/1.4995458.
Makenna Kuzyk (mkuzyk@ualberta.ca) is an undergraduate student in engineering at the University of Alberta, Edmonton, AB T6G 1H9 Canada, and an aspiring astronaut. She has been involved in numerous space activities including Mission SpaceWalker, AlbertaSat, and Students for the Exploration and Development of Space, and she is a 2022 Zenith Pathways fellow. Outside of school, she loves writing music, playing sports, and traveling. More information can be found on her website at www.makennakuzyk.space. To stay posted on Mission SpaceWalker, follow us on Instagram or TikTok@missionspacewalker.
Jana Gebara (gebara@ualberta.ca) is an undergraduate student at the University of Alberta, Edmonton, AB T6G 1H9 Canada, currently earning a bachelor of science degree in mechanical engineering with a certificate in international learning and a certificate in sustainability. She has a strong fascination with robotic applications for extreme environments. She is the president of Space Exploration Alberta Robotics and coproject manager of Mission SpaceWalker, and she is heavily involved in educational outreach initiatives.
Jade Belisle (jbelisle@ualberta.ca) is an undergraduate student in the Department of Mechanical Engineering, University of Alberta, Edmonton, AB T6G 1H9 Canada, enrolled in the biomedical cooperative option of mechanical engineering. Passionate about space and aerospace engineering, she holds the position of mechanical colead for Mission SpaceWalker, participates in the Student Team for Alberta Rocketry Research, and has worked for AlbertaSat at the University of Alberta. She enjoys the many unexpected challenges that occur throughout a design process and the opportunity to find innovative solutions.
Digital Object Identifier 10.1109/MPOT.2023.3241423