MODULE M6 · 10.0 HOURS

Wiring and Building Safe Power Isolation

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LEARNING OBJECTIVES

Module objectives

  1. Understand how to configure independent 12 V power branches for actuator driving.
  2. Learn the role and selection principles of ATOF fuses for overcurrent protection.
  3. Master safe power management and physical disconnection protocols.
  4. Configure safe voltage divider circuits for OpenCR controllers and FSR sensors.

Principles of Safe Wiring and Power Isolation

The 5-finger robotic hand system uses multiple high-torque actuators, so efficient and safe power distribution is essential. This project uses 11 power adapters to separately arrange actuators in units of 4/4/3, which distributes current load per branch and increases power stability [S15].

1. Ensuring Power Independence

The positive (+) output of each adapter must be maintained as an independent branch, and the act of arbitrarily joining or bundling them is strictly prohibited. Design to accommodate peak current (2.3 A per 1 XM430-W350-T actuator) within the rated output current (11.5 A) of the adapters specified in [S15] [S11]. The sum of peak currents for units of 4 branches is 9.2 A, which is within the allowable continuous output range of the adapters.

2. Overcurrent Protection (Protection Coordination)

Place an 10 A ATOF fuse per branch to protect the system from overcurrent in case of wiring or actuator error [S25]. Comparing fuse and load/power ratings alone does not guarantee safety or operating sequences. Review the fuse manufacturer’s time-current curves and power supply OCP characteristics together to verify protection coordination. However, fuse selection must refer to the ‘Time-Current Curve’ provided by the manufacturer; low load current does not guarantee safety [S25].

3. Control Circuit Isolation

We increase reproducibility by eliminating complex external bridge circuits using an OpenCR control board with a built-in DYNAMIXEL port [S13]. FSR force sensors use a divider circuit supplied from the 3.3 V sensor rail to convert voltage for ADC input and must be electrically isolated from the 12 V actuator power [S13].

4. Work Safety Rules

Since the bench prototype is not a certified machine safety system, you must physically disconnect the 3 power adapters before maintenance or modification, and measure and verify that residual voltage of each branch is less than 1 V using the multimeter DC voltage mode [S7].

WORKED EXAMPLES

Worked examples

  1. In case of abnormal heat, odor, or smoke, do not approach; cut the power supply to the 3 adapters via a pre-designated building panel breaker outside the hazard zone or a certified upstream master disconnect and evacuate. If no upstream disconnect is available outside the hazard zone, do not energize the system. Torque release is not a substitute for power disconnection. Maintenance/access must only be performed after planned stops, physical disconnection, and verifying the de-energized state by measurement [S11] [S25]
  2. Example 2: FSR ADC circuit voltage - Connect 10 kΩ divider resistors and FSR 402 using OpenCR's 3.3 V sensor rail [S13, S26]. The sensor signal voltage must be within the 0~3.3 V range, and this circuit must be physically/electrically isolated from the 12 V actuator power circuit.

LAB PROTOCOL

Power Branch Harness Fabrication and Safety Inspection

  1. 1

    Solder ATO in-line fuse holders to each adapter output line and insert 10 A ATOF fuses [S24, S25].

  2. 2

    Fabricate actuator and sensor connection harnesses using Molex Micro-Fit 3.0 connectors [S14].

  3. 3

    Distribute and wire the OpenCR board and each actuator into 3 branches and connect to each power adapter [S13].

  4. 4

    Verify insulation state of each adapter output terminal using multimeter resistance mode before applying power.

  5. 5

    Verify that each branch is 12 V in voltage mode after applying power, and always remove 3 adapters when disconnecting.

Safety check
  • Physically disconnect 3 power adapters before maintenance.
  • Replace parts after verifying residual voltage is less than 1 V using a multimeter.
  • Do not place hands inside operating range while power is applied.
  • Insulate all connection points and wear goggles when soldering.

Lab deliverables

  • Photos of fabricated power branch harness
  • Voltage measurement records per branch
  • Wiring diagram review confirmation

ASSIGNMENT

Safety Wiring Design Report

Deliverables

Rubric

  • Was power independence and isolation principle followed?
  • Were fuse and connector ratings appropriately selected for the load?
  • Does the power disconnection and residual voltage verification protocol follow safety guidelines?

KNOWLEDGE CHECK

Knowledge check

1Is it permissible to connect the 12 V output (+) of each power adapter in parallel?
2What is the most prioritized safety measure before robotic hand maintenance?
3Which power rail should be used for FSR force sensor ADC circuit?

FIELD CHECK

Completion criteria

  • Configuration of 3 independent branch harness and fuse installation completed
  • Voltage measured as 12 V at no-load per branch
  • Recorded that residual voltage of all measurement nodes is less than 1 V after physical power disconnection
  • Submission and passing of wiring safety design report

MODULE SOURCES

Module sources

  1. Micro-Fit 3.0 Connector Family Specificationcontent.molex.com · datasheet
  2. ATO AFH Series In-Line Fuse Holderlittelfuse.com · datasheet
  3. ATOF 287 Series 10 A Blade Fuselittelfuse.com · datasheet
  4. 1910.212 - General requirements for all machines ...osha.gov · standard
  5. GST160A12-R7B Enclosed Desktop Power Adaptermeanwell.com · datasheet
  6. XM430-W350 e-Manualemanual.robotis.com · datasheet
  7. OpenCR 1.0emanual.robotis.com · technical_documentation
  8. 10K Ohm 5 Percent 1/4W Through-Hole Resistorsadafruit.com · technical_documentation