Planetary Gearset
This project was completed for my Mechanical Design course at school. I designed all parts in CAD, ran CAM simulations and milled the gears, laser-cut the acrylic, and assembled it all.
Planetary gearsets have some very interesting applications, especially within the automotive industry. Many hybrid vehicles use them for alternating power transmission between the motor generators and the internal combustion engine. Their advantage is the ability to change gear ratios simply by holding different gears fixed, rather than having to physically move the gears within a transmission.
Design
A surprising amount of effort went into creating the gears! This was the first time in CAD that I have ever used parametric equations, and other complex mathematics, to define shapes. Up to this point, my personal projects involving gears had always borrowed them from the built-in SolidWorks toolbox.
There are many important parts to designing a gear, such as the diametral pitch (or module, if working with metric gears), the pitch circle, the base diameter, the pressure angle, and the involute shape. Below is a sketch within SolidWorks showing some of these things that define the gear's geometry:
1) The second-smallest circle is the base diameter of the gear, which defines where the involute curves begin.
2) The involute curves govern the contact surface geometry on each tooth. They are designed to reduce friction to transmit power as efficiently as possible.
3) The second-largest circle represents the pitch diameter. The distance between the pitch diameter and the top of the gear is the addendum (which basically determines the height of the teeth past the pitch).
The involute curves were defined by these parametric equations:
After designing it in SolidWorks, I milled the gears out of HDPE and laser-cut the acrylic. I was very happy that I defined the gears with the correct tolerances, so that the final result (pictured above) meshed together very well. The model now sits on my work desk!