Topic 2: Hardware Reliability, Power Systems & Servos

Topic 2 focuses on making your robot’s mechanical and electrical subsystems robust enough for extended, real-world use. You will move from reading motor and battery datasheets to designing maintenance schedules, derating strategies, and protective circuits that keep robots running safely.

2.1 Module A — Motor Types & Torque Curves

Motor and Actuator Types in Humanoids

You will review:

• BLDC (Brushless DC) motors used with gear reductions in joints.
• Servo actuators that integrate motor, encoder, driver, and sometimes gearing.
• Harmonic-drive actuators that provide high torque and zero backlash but have specific lubrication and lifetime characteristics.

For each, you will learn to interpret:

• Rated torque vs peak torque
• Rated speed vs no-load speed
• Thermal limits and recommended duty cycles

Reading and Using Torque–Speed Curves

Torque–speed curves link actuator capabilities to your robot’s tasks:

• Lifting an object from a shelf vs carrying a load across a warehouse.
• Climbing a ramp vs walking on level ground.

You will:

• Use torque–speed curves to check whether joints can execute desired motions without repeated overcurrent events.
• Design motion profiles (accelerations, decelerations) that stay within continuous operating regions.
• Understand why operating near peak torque for long periods dramatically shortens actuator life.

Stall Detection, Overheating Protection, and Derating

Topic 2 emphasizes protection mechanisms:

• How to detect stalls from current sensors, encoder feedback, or motor velocity estimates.
• How to set software limits that reduce torque output or pause motion when temperature or current thresholds are exceeded.
• How to apply derating (e.g., treating a motor as if it were smaller than spec) to increase reliability and lifetime.

You will design:

• Basic actuator health monitors that run continuously and trigger warnings or safe states.

2.2 Module B — Power Delivery & Battery Concerns

Battery Chemistry, Packs, and Safety

You will compare:

• Li-ion vs LiPo chemistries and what they imply for:
  • Energy density
  • Peak current delivery
  • Mechanical robustness and puncture risk
  • Thermal runaway and fire risk

You will learn:

• How pack design (cell count, series/parallel configuration, BMS choice) impacts runtime and peak power.
• How to interpret datasheets for maximum continuous and burst discharge currents.

Discharge Curves, Mission Planning, and Duty Cycles

Battery discharge curves show:

• How voltage drops over time at different loads.
• How usable capacity changes with temperature and age.

You will:

• Connect discharge curves to mission planning (e.g., maximum safe task duration before requiring a recharge or swap).
• Design low-battery thresholds that provide enough time for the robot to reach a safe posture or dock.

Power Distribution, Protection, and Emergency Shut-Off

Power delivery must be designed for fault tolerance and safety:

• Fuses or circuit breakers on major branches.
• Proper wire sizing to avoid overheating.
• Use of contactors or relays for hard power cut-off.

You will:

• Design an emergency stop (E-stop) chain that:
  • Cuts power to actuators quickly.
  • Leaves compute and logging alive where appropriate.
  • Can be activated from hardware buttons, software, or external safety systems.
• Map out the difference between a controlled stop and a hard stop, and when each is appropriate.

2.3 Module C — Wear-Out & Maintenance Cycles

Servo Evaluation and Inspection Schedules

Just as industrial machinery has inspection intervals, so should your robot:

• Periodic checks of joint backlash and unusual noises.
• Visual inspection of connectors, cables, and harnesses.
• Checking for loose fasteners or mounting hardware.

You will:

• Draft a servo evaluation schedule specifying:
  • Inspection intervals (hours of operation or calendar time).
  • Measurable acceptance criteria (e.g., maximum allowable backlash).
  • Actions to take when components fall outside spec.

Thermal Monitoring and Lubrication

Heat is a primary enemy of actuator longevity:

• Prolonged operation near thermal limits accelerates wear.
• Poor lubrication increases friction, which in turn raises current and temperature.

You will:

• Decide where to place temperature sensors (motors, drivers, gearboxes).
• Set warning and shutdown thresholds in software.
• Understand vendor recommendations for lubrication intervals and products (especially for harmonic drives).

Predictive Failure Detection with Telemetry

Finally, you will use telemetry to predict failures before they cause downtime:

• Track current draw and torque commands for similar motions over time.
• Watch for increasing temperatures or slower-than-expected movements.
• Log encoder errors, communication retries, or controller resets.

You will:

• Define a minimal set of health metrics to record for each joint and actuator.
• Sketch simple rules or models (e.g., thresholds, trend analysis) to flag components that need attention before they fail.