Torso Specification

Overview

The torso serves as the structural foundation and central hub of the robot, housing critical electronic components, providing mounting points for arms and head, and connecting to the mobility base. It must balance structural rigidity with accessibility for maintenance while keeping weight reasonable for the overall design.

Functional Requirements

Structural

  • Load Bearing: Support head assembly (2-3 kg) and both arms (2-4 kg total)
  • Rigidity: Minimal flex under operational loads (less than 2mm deflection)
  • Attachment Points: Standardized mounting for arms, head, and legs
  • Dimensions: Proportional to overall robot height (typically 35-45 cm height)

Electronic Housing

  • Main Computer: Raspberry Pi, small PC, or laptop motherboard
  • Motor Controllers: Servo driver boards, H-bridges for DC motors
  • Power Distribution: Battery packs, voltage regulators, fuse/circuit protection
  • Connectivity: USB hubs, WiFi router, Ethernet connections
  • Cooling: Ventilation for heat-generating components

Cable Management

  • Routing Channels: Organized dedicated paths for power and signal cables
  • Service Loops: Slack for articulating joints (arms, head)
  • Strain Relief: Secured cables prevent pulling on connections
  • Accessibility: Easy access for maintenance without full disassembly

Design Approaches

Box Frame Construction

A rectangular frame provides maximum internal volume and simple construction:

Advantages

  • Easy to build with basic tools (saw, drill, screwdriver)
  • Efficient use of materials (minimal waste)
  • Simple panel attachment (flat surfaces)
  • Large internal volume for components
  • Stackable design allows modular assembly

Construction Materials

  • Frame: Aluminum angle (25mm x 25mm) or wood (pine 2x2)
  • Panels: Plywood (6-12mm), acrylic sheet, or recycled sheet metal
  • Fasteners: M4 or M5 machine screws with nuts
  • Corner Bracing: L-brackets

Skeletal Frame

A minimal framework with components exposed or lightly covered:

Advantages

  • Lightest weight option
  • Maximum airflow for cooling
  • Easy access to all components
  • Maker aesthetic shows internal workings

Considerations

  • Less protection for electronics from impacts
  • More cable management required
  • Dust and debris access to components

Recommended Dimensions

Measurement Box Design Cylindrical Design Notes
Height 35-45 cm 40-50 cm Approximately 1/3 of total robot height
Width (shoulders) 25-35 cm 15-20 cm diameter Wider for arm mounting
Depth 15-25 cm 15-20 cm diameter Enough for largest component
Weight (empty) 1.5-3 kg 1-2 kg Without electronics or batteries
Internal Volume 15-25 liters 10-15 liters Available space for components

Component Layout

Upper Section (Shoulder Area)

  • Shoulder Motors: Mounted at top corners for arm attachment
  • Neck Mount: Central mounting point for head rotation
  • Cable Exit Points: Grommets or bushings for arm and head wiring

Middle Section

  • Main Computer: Raspberry Pi, NUC, or laptop motherboard
  • Servo Controllers: Dedicated boards or Arduino for PWM generation
  • USB Hub: Central connection point for peripherals
  • Cooling Fan: 80-120mm fan for active airflow

Lower Section

  • Battery Packs: Lowest position for optimal center of gravity
  • Power Distribution: Main switch, voltage regulators, fuse blocks
  • Heavy Components: Batteries, large capacitors
  • Base Mounting: Connection to leg assembly
Note: Place heavy components (batteries, motors) low in the torso when possible to lower the center of gravity and improve stability.

Access Panel Design

Panel Locations

Multiple access points enable maintenance without complete disassembly:

  • Front Panel: Access to computer, USB ports, main electronics
  • Back Panel: Battery access, power distribution

Fastening Methods

  • Thumb Screws: Tool-free removal for frequent access
  • Quick-Release Clips: Snap-on panels for rapid opening
  • Hinges: Permanent attachment, panels swing open

Power System Integration

Battery Configuration

  • Logic Power (5V): USB battery pack (10,000+ mAh) for Raspberry Pi, Arduino
  • Servo Power (6V): NiMH or LiPo packs, 3000+ mAh capacity
  • Motor Power (12V): Sealed lead-acid or LiPo for drive motors
  • Isolation: Separate power supplies prevent servo noise affecting logic

Power Distribution

  • Main Switch: Master power cutoff, easily accessible
  • Fuses/Circuit Breakers: Protection for each power rail
  • Voltage Regulators: Step-down converters for 5V, 3.3V rails
  • Power Indicators: LEDs showing active power rails
  • Emergency Stop: Accessible button to cut all motor power

Charging Access

  • External charging ports prevent opening torso for daily charging
  • Label charging voltages and polarities clearly
  • Use standardized connectors (XT60, Anderson Powerpole)
  • Consider integrated BMS (Battery Management System) for LiPo safety

Thermal Management

Ventilation Strategy

  • Air Intake: Bottom or lower side vents with dust filters
  • Exhaust: Top or upper side vents (heat rises naturally)
  • Fan Placement: Exhaust fan at top creates negative pressure, pulls air through
  • Component Spacing: Minimum 10mm clearance around hot components

Heat Sources

  • Servo Controllers: Can reach approximately 60-80°C under load
  • Voltage Regulators: Require heatsinks for continuous operation
  • Main Computer: Raspberry Pi needs airflow, can throttle when hot
  • Batteries: LiPo packs must stay below 60°C for safety
Safety Warning: Inadequate cooling can cause component failure or, in the case of LiPo batteries, fire hazard. Always provide active cooling for enclosed electronics.

Cable Management Best Practices

Routing Principles

  • Separate Power and Signal: Keep high-current wires away from sensors and data lines
  • Secure at Intervals: Cable ties every 10-15 cm prevent sagging and tangling
  • Service Loops: Extra length at joints allows for movement
  • Labeling: Tag wires at both ends (printed labels or colored heat shrink)
  • Future Expansion: Leave spare capacity in channels for additions

Cable Types

  • Servo Wires: Pre-made 3-wire servo extensions (various lengths)
  • Power Cables: Silicone-insulated wire (14-18 AWG for high current)
  • USB Cables: Short runs, quality shielded cables to prevent data errors
  • Sensor Wires: Twisted pairs or shielded cable for noise immunity

Connectors

  • Servo Connectors: Standard 3-pin headers, polarized
  • Power: XT60, Anderson Powerpole, or barrel jacks
  • Data: USB, Ethernet, or custom pin headers with keying
  • Expansion: Spare connectors on panels for future modules

Assembly Checklist

Frame Construction

  1. Cut frame members to length
  2. Assemble frame with corner brackets
  3. Verify squareness with diagonal measurements
  4. Drill mounting holes for components
  5. Apply finish or paint if desired

Component Installation

  1. Install mounting standoffs and shelves
  2. Mount main computer and secure with anti-vibration mounts
  3. Install servo controllers and power distribution
  4. Mount batteries in lowest position
  5. Install cooling fans with airflow direction marked
  6. Add sensors, switches, and indicators

Wiring

  1. Route power cables first (largest, least flexible)
  2. Install main power switch and fuses
  3. Connect computers and controllers
  4. Route servo cables through exits to arms and head
  5. Secure all cables with ties
  6. Label connections
  7. Test continuity and polarity

Testing

  1. Power on logic systems (no servos connected)
  2. Verify voltage levels on all power rails
  3. Connect and test one servo at a time
  4. Monitor temperatures under load
  5. Check for electromagnetic interference
  6. Verify emergency stop functionality

Maintenance Considerations

Regular Maintenance

  • Weekly: Check battery charge levels, inspect visible connections
  • Monthly: Clean dust filters, verify cooling fan operation
  • Quarterly: Inspect all fasteners for tightness, check cable wear
  • Annually: Full inspection, re-apply thermal paste, replace worn components
Note: Alternatively schedule maintenance based on operational hours (e.g., every 100 hours of operation) for robots in continuous use.

Common Issues

  • Servo Jitter: Often caused by insufficient power or EMI
  • Random Resets: Check power supply capacity and connections
  • Overheating: Verify fan operation, clean vents
  • Loose Components: Use threadlocker on vibration-prone fasteners
Design Philosophy: The torso should be the most robust and reliable component of the robot. Invest time in cable management and component layout during initial build—it pays dividends during every subsequent modification and repair.