ARCSnake

I focused on enhancing the screw block of our robot by increasing its power output by 40%. This involved several key improvements, starting with increasing the torque ratio and aligning the belt drive. I developed a test plan and built a testbed to validate these changes on prototypes, ensuring that the adjustments led to the desired improvements in performance. As a result, the peak tangential force of the screw block increased from 40.0 N to 75.9 N at commanded speeds of 10 rad/s and 50 rad/s, with the resultant torque ranging from 3.60 to 6.83 Nm. Despite the motor's max torque output of 1.5 Nm and the 7:1 gear ratio of the screw drive train, I aimed for an ideal torque output of 10.5 Nm, achieving an efficiency of 66.67%.

In the process, I integrated hardware and mechanical design to complete a cross-functional robot capable of underwater testing. During testing, it became clear that the screw motor's torque output was a limiting factor, especially when operating in sand, where a higher torque was needed due to the increased shear force required to penetrate the terrain. The goal is to improve efficiency to allow the screw block to perform more efficiently across different locomotion modes, including swimming, wheeling, and screwing through various terrains.

Motivation:

Screw-based locomotion is a robust method of locomotion across a wide range of media including water, sand, and gravel. A challenge with screws is their significant number of impactful design parameters that affect locomotion performance in varying environments. One crucial parameter is the angle of attack, also referred to as the lead angle. The angle of attack has a significant impact on the screw’s performance as it creates a trade-off between efficiency and forward velocity. This trend is consistent across various types of media. In this work, we present the Novel Actuating Screw Unit (NASU). It is the first screw-based propulsion design that enables the reconfiguration of the angle of attack dynamically for optimized locomotion across multiple media. The design is inspired by the kresling unit, which is a widespread mechanism in origami robotics, and the angle of attack is adjusted with a linear actuator, while the entire unit is spun on its axis as an archimedean screw. NASU is integrated onto a mobile test-bed and experiments are conducted in a large variety of media including gravel, grass, and sand. Our experiments show the proposed design is a promising direction for reconfigurable screws by allowing control to optimize for efficiency or velocity.

My Contribution:

I developed the first Archimedes screw-based propulsion system that allows for reconfiguration of the angle of attack, optimizing locomotion across various media such as sand, gravel, dirt, grass, and water. This innovation was driven by the need to adapt the robot’s performance characteristics depending on the environment. By enabling adjustments to the screw pitch, a critical parameter affecting mechanical advantage, I designed a system that allows for significant changes in output, enhancing the robot's versatility. The design incorporated a 2-DOF joint that allows the blades to pivot, thus optimizing the angle of attack between 10-35 degrees. I used lightweight materials like 3D-printed Onyx and laser-cut acrylic to balance strength and manufacturability. Through FEA analysis, I ensured the system’s structural integrity under stress, confirming that deformation and stress levels were within acceptable limits. This adjustable screw unit has proven to improve multi-domain locomotion, effectively allowing the robot to switch between high torque for screwing through terrain and high speed for swimming or wheeling, making it adaptable to different operational demands. 

Project Overview:

To understand and test ARCSnake's abilities, a specialized teleoperation device was developed to intuitively control the complex, hyper-redundant system. We coin this device Voodoo Doll because it is a scaled-down model of the actual ARCSnake and gives a one-to-one kinematic mapping between the operator’s device and ARCSnake’s U-Joints. Each U-Joint on the Voodoo Doll has two magnetic encoders to measure the operator’s command inputs. The values are continuously read and sent as set points to the corresponding U-Joints on ARCSnake with negligible delay.

My Contribution:

I designed universal joints with lockable positions for ARCSnake V2, using magnetic encoders to track the configuration of a voodoo doll, enabling teleoperated control of the robot's joint positions. This innovation addressed challenges with the original voodoo doll controller, such as the need for two people to operate it and difficulties in performing complex 3D motions. I implemented features that allowed one person to control the system more easily, introduced the ability to lock and unlock positions for more precise control, and ensured that the design was scalable to the actual robot. The final design made complex movements like navigating stairs more manageable while maintaining safety and ease of use. 

Motivation:

Robots “in-the-wild” encounter and must traverse widely varying terrain, ranging from solid ground to granular materials like sand to full liquids. Numerous approaches exist, including wheeled and legged robots, each excelling in specific domains. Screw-based locomotion is a promising approach for multi-domain mobility, leveraged in exploratory robotic designs, including amphibious vehicles and snake robotics. However, unlike other forms of locomotion, there is limited exploration of the models, parameter effects, and efficiency for multi-terrain Archimedes screw locomotion. In this work, we present work towards this missing component in understanding screw-based locomotion: comprehensive experimental results and performance analysis across different media. To collect this data, we designed a mobile test bed for indoor and outdoor experimentation. Beyond quantitatively showing the multi-domain mobility of screw-based locomotion, we envision future researchers and engineers using the presented results to design effective screw-based locomotion systems.

My Contribution:

I engineered and assembled a specialized testbed to facilitate precise measurement at the screw sub-unit level using a 6-DOF force-torque sensor. This testbed, designed for constrained axial movement, was constructed using 80/20 materials for easy assembly and quick adjustments. I conducted structural performance analysis through SolidWorks FEA, focusing on minimizing displacement to ensure accurate data collection. The testbed incorporated a motor from ARCSnake, chosen for its lightweight and compatibility, allowing axial movement while restricting other directions. The design allowed for easy swapping of configurations and was mobile enough for testing across different environments. Data collected on campus revealed that smaller particle materials like sand and gravel generated less resistance than solid media such as grass and dirt, confirming expected robot performance trends.