In-space assembly is a key capability to enable construction of large-scale structures required for sustained human presence in space. Robotic assembly is critical to reduce required crew time and risk, while modularity ensures that solutions are versatile and adaptive to complex mission concepts. NASA's Automated Reconfigurable Mission Adaptive Digital Assembly Systems (ARMADAS) project demonstrated that robots with relatively low cost, size, and degrees-of-freedom (DoFs) can be used for large-scale modular lattice structure assembly. This is possible by using the structural modules for robotic systems metrology and error mitigation. Robots with reduced complexity may lead to advantages in initial and maintenance cost, offering an alternative to large, complex, and expensive robots. In this paper, we describe the Structure Omni-directional Foldable Explorer (SOF-E), a robot with significantly lower mass and DoF compared to the previous ARMADAS robot architecture. Although SOF-E is a five DoF robot with only two or three control states per actuator, it is capable of transporting and placing structural modules by collaborating with other instances of itself. We discuss the mechanical design and architecture of SOF-E, including analysis of energy usage during each operation. Experiments demonstrate that during locomotion and module transport tasks, SOF-E requires significantly lower energy than the previous cargo transport robot architecture, the Scaling Omni-directional Lattice Locomoting Explorer (SOLL-E). The cost of transport metric is used to compare the energy efficiency of the operation.

This paper presents the design and development of a transport and placement robot that demonstrates autonomous assembly of structural building blocks. The robots are intended to serve as a critical component of automated structural assembly and maintenance systems. The Scaling Omni-directional Lattice Locomoting Explorer (SOLL-E) uses a 5-DoF bipedal inchworm locomotion architecture with locking foot and cargo grippers. The locomotion system employs large magnet gap diameter BLDC motors with moderate timing belt gearing for primary joints, and DC planetary gearmotors for turning. Foot and cargo grippers are identical, with servo-actuated locking mechanisms. Three modular controller boards are used to control these actuators in real-time, with command and telemetry data transferred between the server and each controller board via WiFi. Functionality and performance were evaluated in a ground demonstration.