Meco Transmission

Meco Transmission

Transmission components handle power transfer between machinery components. They model rotating shafts and gears that connect pumps, turbines, and other rotating equipment in rocket engine systems.

Overview

The Meco Rocket Simulator supports 2 transmission component types:

Component Type	Purpose	Key Parameters	Connections
Shaft	Primary rotating element	Rotor inertia properties	Machinery, Gears
Gear	Speed/torque conversion	Teeth count, gear ratios	Other Gears

Shaft

Overview

• Type: Shaft
• Purpose: Primary rotating shaft that connects machinery and provides rotational inertia
• Modeling: Rotational dynamics with inertial properties

Parameters

• Basic Parameters:
  • name - Component name (string)
  • rotorLength - Shaft length in meters (double)
  • rotorRadius - Shaft radius in meters (double)
  • rotorDensity - Material density in kg/m³ (double)

• Connection Parameters:
  • gears - Array of connected gear names (array of strings)

Design Guidelines

Material Properties

• Steel Shafts: 7850 kg/m³ density, high strength
• Titanium Shafts: 4500 kg/m³ density, lighter weight
• Aluminum Shafts: 2700 kg/m³ density, lowest weight but limited strength

Sizing Considerations

• Length: Physical distance between connected components
• Radius: Sized for torque transmission and critical speed avoidance
• Inertia: Affects transient response and system stability

Critical Speed

Avoid operating near shaft critical speeds:

• First Critical: Typically avoid 70% of critical speed
• Flexible Shaft: Consider multiple critical speeds for long shafts
• Rigid Shaft: Operate well below first critical speed

Example JSON

{
  "name": "LOX Transmission",
  "category": 4,
  "type": "Shaft",
  "rotorLength": 0.5,
  "rotorRadius": 0.03,
  "rotorDensity": 7850,
  "gears": ["Reduction Gear", "Output Gear"]
}

Gear

Overview

• Type: Gear
• Purpose: Speed and torque conversion between rotating components
• Modeling: Gear ratios, inertial properties, and mechanical connections

Parameters

• Basic Parameters:
  • name - Component name (string)
  • teeth - Number of teeth (integer)
  • rotorLength - Gear face width in meters (double)
  • module - Gear module in meters (double)
  • rotorDensity - Material density in kg/m³ (double)

• Connection Parameters:
  • gears - Array of connected gear names (array of strings)

Design Guidelines

Gear Ratios

Gear ratio between two gears = Teeth₂ / Teeth₁

• Speed Increase: Ratio > 1 (more teeth on driven gear)
• Speed Reduction: Ratio < 1 (fewer teeth on driven gear)
• Typical Ratios: 2:1 to 10:1 for single stage

Module Selection

Module defines gear tooth size:

• Fine Pitch: 0.001-0.003 m module for high-speed applications
• Medium Pitch: 0.003-0.008 m module for general applications
• Coarse Pitch: 0.008-0.020 m module for high-torque applications

Gear Sizing

• Pitch Diameter: teeth × module
• Face Width: Affects load capacity and gear life
• Material: Steel for strength, consider weight for aerospace applications

Example JSON

{
  "name": "Reduction Gear",
  "category": 4,
  "type": "Gear",
  "teeth": 48,
  "rotorLength": 0.025,
  "module": 0.004,
  "rotorDensity": 7850,
  "gears": ["Output Gear"]
}

Transmission System Design

Single Shaft Systems

Direct connection between pump and turbine:

• Advantages: Simple, reliable, minimal losses
• Disadvantages: Fixed speed ratio, limited optimization
• Applications: Gas generator cycles, simple configurations

Geared Systems

Multiple shafts connected through gears:

• Advantages: Speed optimization, multiple power take-offs
• Disadvantages: Complexity, additional losses, weight
• Applications: Staged combustion cycles, auxiliary drives

Speed Optimization

1. Pump Speed: Optimize for flow and head requirements
2. Turbine Speed: Optimize for gas flow and efficiency
3. Gear Ratio: Match pump and turbine optimal speeds

Inertial Effects

1. System Inertia: Sum of all rotating component inertias
2. Transient Response: Higher inertia slows acceleration/deceleration
3. Stability: Affects control system design and governor response

Connection Hierarchy

Shaft Connections

Shafts connect to:

1. Machinery components (pumps, turbines)
2. Gears for speed/torque conversion
3. Other transmission components

Gear Connections

Gears connect to:

1. Other Gears for multi-stage reduction/multiplication
2. Must ultimately connect to a Shaft for machinery attachment

Connection Rules

1. All machinery must connect to a shaft
2. Gears can connect to other gears or shafts
3. Connection topology must form valid mechanical system
4. Avoid circular dependencies in gear trains

Performance Considerations

Efficiency

• Shaft Bearings: 99-99.5% efficiency per bearing set
• Gear Meshes: 96-99% efficiency per mesh
• System Efficiency: Product of all component efficiencies

Losses

• Bearing Friction: Function of speed and load
• Gear Mesh Losses: Sliding friction and churning
• Windage: Air resistance at high speeds
• Oil Churning: Viscous losses in lubrication system

Reliability

• Fatigue Life: Consider stress cycles and material limits
• Lubrication: Essential for bearing and gear life
• Contamination: Protect from propellant and combustion products
• Thermal Effects: Account for temperature variations

Common Configurations

Direct Drive

Turbine → Shaft → Pump

• Simple, reliable configuration
• Fixed speed ratio
• Used in gas generator cycles

Single Reduction

Turbine → Shaft → Gear → Gear → Shaft → Pump

• Allows speed optimization
• Single gear reduction stage
• Common in rocket applications

Multiple Shaft

Turbine₁ → Shaft₁ → Gear₁ ↘
                           → Main Gear → Main Shaft → Main Pump
Turbine₂ → Shaft₂ → Gear₂ ↗

• Multiple power sources
• Complex but flexible
• Used in staged combustion cycles

Design Process

1. Power Requirements: Determine pump power needs
2. Speed Requirements: Optimize pump and turbine speeds
3. Gear Ratios: Calculate required speed ratios
4. Shaft Sizing: Size for torque and critical speeds
5. Gear Sizing: Size for torque capacity and life
6. Integration: Verify mechanical packaging and connections

See Also

• Main Components Overview
• Machinery Components
• Control Parameters
• Mechanical Design Reference
• Gear Design Guidelines
• Shaft Critical Speed Analysis