Scuba divers are taught to control their depth to avoid rapid ascents and descents, which could result in serious injuries such as gas embolisms and barotrauma. However, many underwater tasks necessitate lateral control, maintaining distance between subsea structures such as coral reefs, submerged drilling instrumentation, or unexploded ordnance. In this work, we discuss a first-of-its-kind wearable robotic solution providing thruster-actuated directional guidance to a diver, as distinct from prior propulsive-assistance exoskeletons. We introduce ``Robotic Assisted Diver Movement in Confined Spaces'' (RADMCS), a wearable robot that assists divers in maintaining a fixed distance from subsea structures by leveraging perception techniques in monocular depth estimation and force-feedback from submersible thrusters to provide haptic feedback. Its small and compact form factor creates a foundational platform that could be expanded to include more sophisticated control and navigation behaviors. We present results from Institutional Review Board (IRB) in-water studies with eight human scuba diver participants on threshold sensitivity tests in both a closed-water swimming facility and ocean environments; distance-maintaining experiments in a closed-water facility; and form, fit, and function testing in the ocean. We demonstrate that relatively low thrust values (10 percent of maximum) allow robotic direction of a human's movement using the physical sensation of the robot's guidance.
Figures & tables
Figure 1: The Robotic Assisted Diver Movement in Confined Spaces (RADMCS) wearable robot during a field experiment. The diver wears RADMCS on their back, enabling haptic feedback from the robot to the human through a series of thruster movements. If the difference δ between the setpoint distance d and the actual distance of the diver to the coral reef wall d′ is greater than zero, the robot indicates that the diver should yaw toward the wall, otherwise yaw away from the wall. The diver responds to the feedback, swimming in the direction indicated by the robot’s thrusters, which creates a pathway to complex navigation and maneuvering for safe navigation along coral walls or confined spaces.
Figure 2: Assembled RADMCS robotic system features with descriptions of parts.
Figure 3: Thruster configurations. The left image column shows the transverse thruster configuration that directs force perpendicular to the robot’s body, in the x^ -direction. The right image column shows the longitudinal thruster configuration that directs force along the length of the robot’s body, in the y^ -direction. The thrusters are labeled and referred to as shown in the figure for all future analysis.
Movement
Longitudinal/Transverse
Turn left (yaw CCW about z^ )
T1 reverse and T2 forward
Turn right (yaw CW about z^ )
T1 forward and T2 reverse
Table 1: Directional movement mapping of the haptic feedback from robot to human. In both the longitudinal and transverse thrust configurations the movement instruction is the same.
Event/participant
P1
P2
P3
P4
P5
P6
P7
P8
TS closed-water 225 mm longitudinal/transverse
✓
✓
TS closed-water 325 mm transverse
✓
✓
Single-sided distance-maintaining
✓
✓
✓
✓
✓
✓
✓
TS open-water 325 mm longitudinal/transverse
✓
✓
Open-water form, fit, & function
✓
Table 2: Participant list and the specific portions of the study they were involved in. Participants are coded from P1–P8. Threshold sensitivity testing is abbreviated as (TS).
Figure 4: Still frames collected during the closed-water TS test for the 225 mm transverse thruster configuration. During the “ascending” portion of the test, the thruster force-feedback increases in intensity, rotating the diver in the figure.
Figure 5: TS for ( M=2 ) participants P1 and P2 for CW and CCW rotations in both the 225 mm longitudinal and transverse thruster configurations in the closed-water environment. The gold solid curve shows the manufacturer-provided thrust–PWM calibration [ 27 ] . The inset illustrates the thruster orientations and resulting force directions used to generate rotational motion.
Figure 6: Simulated distance-maintaining experimental setup in the closed-water swimming facility. A tarp with Kalibr AprilGrids was affixed to the side of the pool. The currents produced from circulation jets created an imperfect surface leading to curvature and distortions in the images. These curvatures along with facets of the camera (including continual autofocus) had downstream effects on the quality of the control algorithm, since the feedback signal is the distance between the robot’s cameras and the wall.
Figure 7: Still frames collected during the open-water ocean TS test for the 325 mm transverse and longitudinal thruster configurations. During the “descending” portion of the test, the thruster force-feedback decreases in intensity, rotating the diver in the figure until they stop moving.
Figure 8: Simulated distance-maintaining experiment showing the correct turn directions based on distance for participant P2. The top plot shows the PWM curves for T1 and T2 . The bottom plot shows the distance to the target for both the raw data and the filtered distance data. The red line shows the participant’s end time for the trials, taking 89.89 s to complete the wall distance. The green region and accompanying aerial perspective show the left turn. The diver responds, turning left. The yellow region shows a right turn, and the diver moves away from the wall.
Figure 9: Simulated distance-maintaining experiment showing the correct turn directions based on distance for participant P2.
Figure 10: Simulated distance-maintaining experiment showing the correct turn directions based on distance for participant P8. The top plot shows the PWM curves for T1 and T2 . The bottom plot shows the distance to the target for both the raw data and the filtered distance data. The red line shows the participant’s end time for the trials, taking 43.28 s to complete the wall distance. The green region and accompanying aerial perspective show the left turn. Unfortunately, because the robot lost the distance estimation at approximately t=12 s of run time and never recovered distance, the filtered distance to target control signal never updated, leaving the robot in a high turn left thrust state for the duration of the data run.
Figure 11: TS for ( M=2 ) participants P1 and P3 for CW and CCW rotations in both the 325 mm longitudinal and transverse thruster configurations in the ocean environment.
Figure 12: Still frames from the form, fit, and function qualitative test in the ocean environment.