SOW.pdf

Statement of Work Robotic Platform for Autonomous Robotic Construction Hardware Development and Delivery

A. Objective/Requirements

Background/History of Requirement: NASA Ames is conducting a research program involving robotic modular structural assembly for use in mission support applications as part of the Space Technology Mission Directorate (STMD) Live Domain, Surface Structures and Construction Capability (implemented by the Game Changing Development (GCD) program). Key to this research is the use of hundreds of robotic agents with high manufacturing production quality. NASA previously demonstrated initial prototypes of the inchworm style construction robot for transport and placing of structural components. Advancement in this technology leads to investigations regarding the possibility of high-volume production of modular construction robots with integrated control, communication, and sensor protocols. Coordinated part design refinement and target production of one prototype unit is to be included in this contract. The new process and parts will be used to extend research capabilities and contribute to novel advanced materials and manufacturing technology research.

B. Description of item(s) to be purchased The item to be purchased is a modular, lightweight inchworm style robotic platform for robotic construction testing and demonstrations.

C. Characteristics, Scope, and Specs

a) Design of Robotic Platform: The robot must meet the geometric specifications described in https://ntrs.nasa.gov/api/citations/20230011353/downloads/IEEE_IROS_2023_SOLLE_Final.pdf with minor modifications in performance specifications and avionics as detailed below:

a. The robot components have a modular design, and subassembly designs are reused throughout the robot design.

b. The robot can take a step or grab a structural unit within 3.0 cm (in x and y) and 1.34 cm (in

z) from the ideal position.

c. The robot can place the structural unit into the correct grid position within ±1.78 cm (in x, y, and z) and ± 3° from the ideal position.

d. The total mass of the robot does not exceed 10 kg.

e. The robot is a 5 degree of freedom bipedal inchworm robot with locking foot and cargo grippers.

f. The robot has three main actuators and two yaw stage actuators to provide in-plane rotation.

g. The robot transports structural units from a depot to the intended placement location.

h. The robot navigates a 3D grid while carrying a structural unit.

i. The robot unloads a structural unit from the cargo gripper of another robotic agent.

j. The robot locomotes across and manipulates a cuboctahedron structural unit with a pitch length of 0.3048 m and mass of at least 380 g.

k. Leg Length and Shape Design

i. Link lengths are designed such that SOLL-E can effectively walk up and down single voxel steps and move between orthogonal planes.

ii. For u=304.8mm voxel length the leg length must be (√5/2)u with rotational hinges u/2 from the attached voxel face.

iii. The link length may be maintained with offset and/or a bend to compensate for the nonzero characteristic diameter of the leg.

l. Joint Torque Requirements and Module Design

i. Minimum primary joint holding torque: 21.1 Nm.

ii. Minimum primary joint transient torque: 28Nm for 3 seconds.

iii. Minimum Range of Motion

1. YawA θA: −180◦ to 180◦

2. Joint1 θ1: −55◦ to 135◦

3. Joint2 θ2: −128◦ to 35◦

4. Joint3 θ3: −58◦ to 132◦

5. YawB θB: −180◦ to 180◦

iv. Primary actuators must utilize low gear ratio to be safely back-driveable when not powered, such as large gap radius brushless motors with small gear ratio transmission, to provide sufficient performance from standstill (low RPM) while also providing margin for control authority over dynamic effects.

v. Each leg has a foot mechanism (GripA and GripB) which align and attach the robot to the voxel structure, to connect and disconnect legs for motion along voxel surfaces.

vi. The voxelholding “backpack” (GripC) uses a mechanism that can grip and ungrip to pick-up and drop-off voxels.

vii. The ankle modules allow rotation in both pitch and yaw directions.

1. For yaw movement, range of motion must be at least ±360◦ from the initial configuration.

2. For pitch movement two legs from each ankle module meet at a knee module

(Joint2) that provides a single degree of freedom in the pitch direction and has an identical mechanism to the pitch movement of the ankle modules (Joint1 and Joint3).

b) Avionics

a. All joints in the system must be integrated with a complete power bus and control stack that includes EMI protection. This may include separate or integrated components: a main computing system, interface and isolation systems, actuator drive systems, power management and distribution systems, fault monitoring

b. Avionics and power electronics are integrated into the robot design.

c. The robot is battery powered.

d. Fault states must be implemented with automatic and manual triggers:

i. Stop: When the stop command is sent from the server

ii. Gripper over-current: When the current draw of gripper servo exceeds nominal operational level

iii. Yaw motor over-current: When the current draw of yaw DC motor exceeds nominal operational level

iv. Yaw motor out of range: When the command value for yaw DC motor exceeds nominal operational value

v. Joint 1/2/3 motor response timeout: When the Joint 1/2/3 motor does not receive feedback from the external motor driver within the expected time frame

vi. Joint 1/2/3 motor target mismatch: When the Joint 1/2/3 motor does not return the commanded target within the expected time frame

vii. Joint 1/2/3 Absolute encoder mismatch: When the discrepancy between absolute joint and incremental shaft encoders for Joint 1/2/3 exceed an allowable threshold

viii. Synchronization fault: When the board synchronization is indeterminate

e. Each robot communicates independently using WiFi.

f. Power monitoring is integrated to manage and monitor battery health and power consumption.

g. The robot is able to report its status including: battery voltage, actuator current, actuator torque, and actuator position.

h. It must be possible to execute synchronized motion of any set of actuators on the robot.

i. Standby, operational, and safed modes that are automatically or manually triggered depending on the condition. These three modes of operation allow for robot initialization, operations, and fault recovery.

i. Standby mode is the default startup mode and allows for initialization and calibration of robot parameters as well as minimal power consumption. Once initial calibration has been completed, the robot can be commanded to enter operational mode.

ii. In operational mode, the robot is fully powered and can receive individual commands that contain the target angle for each joint or execute macro commands that move multiple joints with pre-stored trajectory motions. Every 25 ms or less, the controller board controls each actuator and processes current state (including position and power consumption). The robot can receive a command to enter back into standby mode in order to disable torque on the BLDC motors.

iii. Safed mode is triggered when the robot receives a stop command from the base station or an internal system fault is triggered. In this mode, all motors are halted in their current position to prevent collisions with the structure. The system faults are designed to prevent damage to the robot and structure from errors in planning, communications, hardware, or operations.

j. Pre-planned Trajectories: The transitions of the SOLL-E robot between different configurations are defined by trajectories. Three different types of trajectories are used for carrying out needed operations: locomotion, grab, and placement trajectories.

i. Key Configurations: The “stand” configuration indicates the grippers are on x-axis or y-axis adjacent voxels, but can be separated in the z-axis one unit up or down. The “step” configuration indicates a space of 1u in the x-axis or y-axis with the same convention for the z-axis. The “balance” configuration is added to allow the robot to balance with one foot on a single voxel. This configuration minimizes main joint holding torques when the robot performs a yaw motion.

1. The robot achieves all poses needed for locomotion across the lattice surface including:

a. StandDown

b. Stand

c. StandUp

d. StepDown

e. Step

f. StepUp

g. BishopDown

h. Bishop

i. BishopUp

j. Balance

ii. Grab trajectories utilize two robots. One carries a voxel from the base station to a build front, then hands it off to another, which places it at the build location. There are seven voxel grab configurations based on the handoff position of the transporting robot.

1. The robot achieves all poses needed for unloading a structural unit from another robotic agent including:

a. StepGrab_fromCargoStand

b. StepGrab_fromCargoStep

c. StepGrab_fromCargoOrthoLeft

d. StepGrab_fromCargoOrthoRight

e. StepGrabDn_fromCargoStand

f. StepGrabDn_fromCargoStandUp

g. StepGrabDn_fromCargoStep

iii. Placement: For the placement trajectories, three approach directions – straight, CW, and CCW – must be considered due to the presence of adjacent voxels.

1. The robot achieves all poses needed for placing a structural unit at the build front including:

a. Place_StandDown

b. Place_Stand

c. Place_StandUp

d. Place_Step

e. Place_StepUp

f. Place_BishopDown

g. Place_Bishop

h. Place_BishopUp

c) The actuators for the main joints have the required torque density to support the robot in the worst case (fully cantilevered) position.

d) The robot takes one unit step forward within 20 seconds.

e) Design Deliverables: 3D CAD files (native format per a standard CAD package such as Solidworks, Creo, NX, etc. and step files of geometry alone) of robot components, for research use (process analysis) by the technical POC.

1. Robotic Platform Production

a. Fabrication of one robot unit.

b. Perform initial functional testing on the unit for quality assurance.

c. Deliver the robotic hardware to the technical POC.

2. Determination of process scalability

a. Analyze volume production potential and provide a written report on expected costs of speed of production at state-of-the-art volumes.

D. Period of Performance The item shall be delivered within 4 weeks.