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https://www.thingiverse.com/thing:2517464
Main Gear Box, Helicopter driven by 2-Engines by konchan77 is licensed under the Creative Commons - Attribution - Non-Commercial license.
http://creativecommons.org/licenses/by-nc/3.0/

# Summary

Main Gear Box, Helicopter driven by 2-Engines

Main Gear Box (MGB) for Helicopter driven by 2-Engines has complicated gear train in inside.
To understand this mechanism, I designed the internal visible model.
There are many different designs for each actual helicopter, therefore this model is just a sample.

The features of MGB are;
 1. 2-Engine Inputs
 2. 1-Tail Take-Off Output (moved to the opposite side to clarify→See "Update")
 3. 3-Stage Reduction (including 1- Planetary Gear) and 2-Stage Reduction + 1-Stage Increase
 Note: (1) Gear types used in this model are changed due to ease designing and printing. 
             Bevel Gear → Spur Gear + Face Gear, Helical Gear → Spur Gear
       (2) Clutch and Accessary drives are omitted at this time.

Download files includes;
-files: STL Files
-images: Parts Breakdown and Sub-assy photos for assembly Aid.
-Excel File: Parts List with related hardware

Purchase Parts Information;
-Bearings; No metal Ball/Roller Bearing is used. Then some grease for plastic is recommended for lubrication. 

-ABS Tube 
   See Parts List

-Screws and etc.
   Micro screws M1.4x3.5L -  5 ea  - Direct screw-in to 1 mm diameter hole (No nut), 
   Screws M2 x 6L -  20 ea, See Parts List
   Screw M2 x 25L and Nut+ Some tube for Turning Handle (Optional)
 
Printing parameters recommended (0.4mm Nozzle is used)
- Gears: 0.2mm Layer Height, 100% infill
- Bodies: 0.2mm Layer Height, 40% above infill (for threads)  
  Raft and Support: Depending on your experience

Assembly Points
- Standard Skill (such as Drilling, Tapping, Filing, Tightening, Painting and Gluing etc.) is needed and perseverance too.
- For gears: Deburring (removing the sharp edges etc.) is very important for smooth rotation.
- If you do not give up to finish the gear teeth, then you can get the smooth rotational MGB model.
- Good luck!!

Total Net Print Time: Approx.  28HR
- (Estimated as case of PLA, 0.4mm Nozzle, 0.2mm Layer Height, 40% infill and No raft and support)
  Note: When at actual print, each parameter should be adjusted by your experience.

Update (Sep.15,2017)
New file (Body-Mid901.stl) and related photos are added to return "Tail Take-Off Output"  at the same position.


# Print Settings

Printer: idbox
Rafts: Doesn't Matter
Supports: Yes
Resolution: See Above
Infill: See Above

# Post-Printing

## See Above


# How I Designed This

## See above.  123d design and fusion360 are used.