Epicyclic_gearing_with_laser_cuttera gearing system for high torque done with a laser-cutter

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README.md

Epicyclic gearing with laser-cutter

CC BY-SA charlyoleg 2013

1. Introduction

The purpose of this project is to create an open-source, efficient and cheap transmission system with a high reduction ration. A large reduction ratio allows using a lightweight small DC-motor (from 1 to 10 Watt) for automating task such as locking a door or adjusting a mirror orientation. The design files are generated with the Python library Cnc25D. The design is first tested with acryl-glass cut with the laser-cutter. If it succeeds, the design will be also manufactured with a 3D printer and then with a CNC.

2. Description

The epicyclic_gearing_with_laser_cutter design is a gearing system to decrease rotation speed and increase the torque.

3. How to regenerate the design files

  • Install FreeCAD 0.13 or newer

On Ubuntu:
$ sudo add-apt-repository ppa:freecad-maintainers/freecad-stable
$ sudo apt-get update
$ sudo apt-get install freecad

  • Install the Python package Cnc25D:

On Ubuntu:
$ sudo pip install Cnc25D -U
$ sudo pip install matplotlib -U

  • Run the script cutter_calibration.py

$ python epicyclic_gearing_with_laser_cutter.py or if you want to view the design in the FreeCAD GUI:
$ freecad epicyclic_gearing_with_laser_cutter.py

4. What is Cnc25D?

Get the source on GitHub

Read this documentation

5. Conclusion

What I have learned with the four prototypes of this project?

Prototype 1


I wanted some thing robust to test the principal of my design. I chose thick acrylglas plank (8mm). The two stage system becomes a huge cylinder (100mm diameter 120mm height). It works but with a lot of resistance. The main raison of the mechanical resistance is that the 8mm acrylglas can not be cut accurately. I have read that the laser cutter precision decreases with material thickness and increases with laser power and cutting speed.

Zsun = 19 Zplanet = 31 Zannulus = 81 Ratio per stage = 1/5.263

Prototype 2


The main goal was to increase the smoothness of the gear by solving the imprecision issue. I used only 3mm and 4mm acryglass. This requires more work as most of the gears must be done by assembling several slices in order to get the expected gear height. The assembly is done with 1mm steel rod. The assembly looks like a cylinder of 100 mm diameter and 55 mm height. The axle were first done with 8mm aluminium tube. That was a bad idea because there are too weak. After replacing the aluminium tube with steel axle, the two stage system works much smoother.

Zsun = 19 Zplanet = 31 Zannulus = 81 Ratio per stage = 1/5.263

Prototype 3


The main goal was to reduce the size of the system and in particular the diameter. For this purpose, I have reduced the number of teeth because I wanted to keep a module of 1 to keep the system solid. I have used 3 mm steel axle. It works quiet well. The main issue comes from the input and output shaft that were not really though through.

Zsun = 13 Zplanet = 19 Zannulus = 51 Ratio per stage = 1/4.923

Prototype 4


Input gearwheel with many teeth and a module of 1. Output gearwheel with few teeth and a large module. A central axle of 6 mm fixed to the holder at the two extremities. The biggest challenge is to make the sun gear that have 16 teeth and a free axle of 6 mm. There is not that much space left to put the 1 mm steel rod for the Z stability. I had to add a feature to the gear-generator to align the rod-hole just under a gear-tooth.

Zsun = 13 Zplanet = 19 Zannulus = 51 Ratio per stage = 1/4.923

Prototype 5


Five stages. The input is designed to receive an electric motor.

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Epicyclic_gearing_with_laser_cutter by charlyoleg
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