User Manual

Safety Precautions

To ensure safe and proper use of the RTMA, the following guidelines should be adhered to throughout the assembly, testing, and storage process: 

Strain and Pinch Hazards During Operation:

• Exercise caution when applying downward and rotational force via the handle to avoid strain injuries to the wrist, arms, and shoulders.

• The handle height is designed based on average human elbow height to reduce ergonomic stress during use.

• Grip tape is applied to the handle to prevent overheating from sunlight, improve grip, and reduce risk of blisters or hand injuries.

Mechanical Safety Risks:

• Be aware of pinch points between moving parts when operating the apparatus.

• Avoid contact with exposed fasteners or potential sharp edges; although edges have been rounded, remain cautious of hand placement.

• Electrical tape has been applied to the exposed ends of stainless steel wiring securing the stakes and pins to minimize the risk of cuts or scratches.

Electronic and Environmental Safety:

• Protect the apparatus electronics from water and sand exposure, which could compromise electronics.

• The electronics are housed in sealed enclosures with sealed wire pass throughs and selectively potted sensor terminals for added protection.

• Strain relief has been implemented at critical wiring points to reduce wear and prevent disconnection.

• The system is rated to operate for approximately 60 hours when fully charged

Assembly Instructions

Steps

1.  Assemble Full Tripod Leg Assembly

Figure D.1: Component breakdown of steps 1a - 1e

1. Insert the bottom of the Tripod Leg Assembly into one (1) Sand Foot, aligning the pinhole of the foot and leg. 

2. Insert one (1) Detent Pin through the hole Sand Foot pinhole

3. Align the Bottom Support of the Tripod Leg Assembly with the horizontal holes in the Bottom Flat Brackets (see Figure D.1). 

4. Use two (2) Spade-Head Thumb Screws and two (2) Wing Nuts to secure the Bottom Hub Support to the main Tripod Leg, one for each hole.

5. Repeat steps 1a - 1d until three (3) Tripod Legs are fully assembled.

2. Assemble Full Apparatus Frame 

Figure D.2: Component breakdown of steps 2a - 2c

1. Align one (1) Tripod Leg Assembly with the Lower Bushing Hub and Top Hub Support (see Figure D.2). 

2. Use four (4) Spade-Head Thumb Screw and four (4) Wing Nuts to secure the Tripod Leg Assembly, one for each hole.

3. Repeat Steps 2a and 2b until all three (3) Tripod Leg Assemblies are secured to the Upper Bushing Hub and Lower Bushing Hub.

3. Assemble Full Intruder Bar Assembly

Figure D.3: Component breakdown of steps 3a - 3c

1. Insert the Lower Intruder Bar Assembly through the bushing in the Lower Bushing Hub.

2. Align the Lower Intruder Bar Assembly with the Lower Torque Sensor Coupler (see Figure D.3). Ensure that the flat facets on the Lower Intruder Bar Assembly align with the set screws on the Lower Torque Sensor Coupler.

3. Firmly tighten the two (2) Cup-Point Set Screws on the Lower Torque Sensor Coupler.

2. Final Check

   1. Ensure that all screw joints on the RTMA are properly secured.

   2. Ensure that all set screws are secured and the Intruder Bars are rigidly connected to the Torque Sensor Couplers.

3. Disassembly & Storage

   1. For disassembly, follow steps 1-3 order and remove/detach components instead of assembling.

The pins and stakes are fixed to the main leg, while the removed wing nuts and screws from the bottom hub support can be re-secured after being collapsed or attached to the clear holster mounted on the electronics box. The stake hammer can be stored in the drawstring bag 

Testing Instructions

Setup

The Resistive Torque Measurement Apparatus is designed to undergo repeated tests of a single intruder geometry at various locations of a testing site. Should a different intruder geometry be desired for a testing cycle, they may be made and installed. The parameters of the intruder geometry may be varied based on the user's desired shape and size, with the exception of a center universal mounting geometry as seen in Figure D.5. The thickness of this center mounting point may be at most 3.175 mm (0.125 in) such that it may fit within the slot at the bottom of the intruder shaft.

Figure D.4: Design of intruder universal mounting point

Secure the intruder to the intruder shaft using 2 (two) 8-32 thread size 19.05 mm (0.75 in) length bolts and 8-32 Nylon-Insert Locknuts. Changes in intruder should only be done prior to arriving at the testing site or in a clean area to prevent ingress of granular media into bolt threads. 

Prior to field testing, install the BLESerial nRF52 (preferred) or Adafruit Bluefruit Connect app on your mobile device.

The device has a 60+ hour battery life. To charge the device, remove the M3 bolts securing the front acrylic plate of the electronics box. Take care not to remove any wires accidentally while removing this plate. Consult the wiring diagram in case of accidental unplugging. Unplug the USB connection between the power distribution board and remove the Anker 325 power bank. The Anker 325 power bank can be charged with any standard USB-C cable. After charging, reconnect the USB connection to the power distribution board and resecure the front acrylic plate.

Field Testing

Figure D.5: Simplified Sequence of Operation of the RTMA

Tools Needed For Testing:

• 3/32” Allen Key

• Hammer

1. Initializing the RTMA

   1. Check that the RTMA Mode Switch is in Setup (S) mode.

   2. Power on the RTMA.

   3. Connect to the device via the BLESerial nRF52 (preferred) or Adafruit Bluefruit Connect app on your mobile device.

2. Placing the RTMA

   1. Place the RTMA at your desired test location. Users should be able to walk completely around the RTMA unimpeded. If partial water submersion is desired:

      1. The height of the water should not exceed the top of the sand foot if in wave conditions.

      2. The height of the water should not exceed the bottom of the lower bushing hub in stagnant conditions.

   2. Ensure that the torque sensor cable is not tangled around the apparatus frame or intruder.

   3. On each sand foot, insert the two stakes into the corner holes. Use a hammer if necessary to secure the stakes.

   4. Insert the soil moisture sensor into the sand.

3. Adjusting the penetration depth

   1. Choose a desired penetration height. Adjust the dial on the switchboard to this desired height.

   2. Loosen the two set screws on the depth locking collar using the 3/32 “ Allen Key. 

   3. Adjust the depth locking collar to the desired height marker. Markers are in  2.54 cm (1 inch) increments, with the lowest marker being 0 and highest being 25.4 cm (10 inches). The top face of the depth locking collar should be aligned with your desired marker. 

   4. Tighten the two set screws at the desired marker using the 3/32 “ Allen Key. .

   5. Using both hands, push the intruder handle into the sand. If necessary, adjust the bottom dog clutch attached to the pulley system to align with the top dog clutch and depth locking collar. 

      1. WARNING: Penetration of the intruder into the sand may take large amounts of force. Take care to apply the force evenly onto the handle in a vertical fashion to avoid bending. Take breaks if necessary to avoid strain/injury.

4. Conducting a test

   1. Have User 1 firmly grasp both sides of the intruder handle. Have User 2, while monitoring the LCD screen and Bluetooth app monitor on their mobile device, toggle the device into Collection (C) mode. 

   2. User 1 should walk around the entire apparatus frame while grasping the handle. Speed and amount of rotations can be varied or maintained consistent depending on desired testing conditions. User 2 should monitor the LCD screen for Torque Limit warnings. Stop testing if the torque is exceeding 65 Nm. 

5. Ending a test

   1. Have User 2 toggle the device into Setup (S) mode. On the Bluetooth app monitor console, type “L” to verify that a new test data CSV file with the timestamp was made. Type “S” to view the test data CSV file. 

   2. Loosen the two set screws on the depth locking collar. Using both hands, pull the intruder out of the sand using the 8/32” allen key.

   3. Rotate the intruder handle counterclockwise until the torque sensor cable is completely unwrapped. 

   4. Remove the stakes from each foot and remove the soil moisture sensor from the sand. 

   5. Move to a new testing location if desired and repeat steps 2-5, or disassemble the apparatus. 

Data Transfer

To transfer data collected by the RTMA after testing, the SD card inserted into the Arduino Mega2560 REV3 must be removed and inserted into a separate device. To remove the SD card, remove the M3 screws securing the front acrylic plate on the electronics box. With the power off and taking care not to accidentally unplug any wire connections, remove the SD card from its slot. Open the SD card on a separate device and copy the data. The data may be deleted from the SD card afterwards using the separate device, or by typing “C” into the console of the Bluetooth monitor during regular operation of the RTMA. The SD card must be reinserted for the RTMA to initialize properly. 

Data Analysis

To perform analysis on data from the RTMA, first extract the desired CSV “Test Summary” files from the onboard SD card. The title of each test file has the format “YYMMDD_HHMMSS.csv”, encoding the time and date of the test for identification purposes. CSV files are formatted with a header including the file metadata (date/time of test) and environmental data measured during the test (GPS coordinates, temperature, etc.). Environmental data are included as human-readable outputs. Following this, three columns are generated measuring time (ms), angle (deg), and torque (Nm) measured at 50 Hz. 

To generate visualizations of these data, utilize the MATLAB function. Use the function with the command ‘analyzeRTMA(‘FILENAME.csv’) in MATLAB.