(Pics and Vids uploaded later)
The midterm assignment is to create a physical working model from Mechanical Models books. I chose the Roller-Gearing Mechanism for my project, because I love the way a small plate drives a bigger one with contact of rollers located on its circumference. Also, roller gearing is a great way of gearing solutions, because it reduces friction and requires less lubrication than ordinary gears. The math behind this mechanism is the rule of hypocycloids — If a small circle is rolled around the inside of a circle exactly twice as large in diameter, any point on the small circle will trace a straight line, which will be a radius line of the large circle.
There are 3 stages of this project: 2-D Drawings, Low/Mid Fidelity Prototypes and Final Working Model.
2D-Drawings:
I made a couple of changes to my previous 2d drawings for laser cutting.
- Added extrusion on the bottom of the back plate so it could be plugged into the base plate.
- Merged paths for the rail on the large disk so it would be easier to etch with a laser cutter.
Original File:
Updated File:
Low Fidelity Prototype
I built a low fidelity prototype that almost worked with cardboard, foam and 3 K-nex rollers. Picture here
Working Model
The first time when I tried to cut pieces with laser cutter, it did not cut through the material even after I tested for speed and power, reason being that the wood board was bent so the laser emitter could’t focus the beam due to discrepancy on the z-axis, ending up wasting a lot of material.
After cutting pieces, I doubled the thickness of the pieces by adhering same pieces together. It was hard to double the rollers due to excessive glue, and I managed to apply wood glue with a toothpick.
The next problem is the dimension of dowels. The dowel dimensions I created for my model were 3/16” and 5/16” as indicated in the book, while in OEDK there are only dowels of 1/8” 1/4” and 1/2”. I first tried to apply tape on 1/4” dowel, and it fitted in the 5/16” hole. However, considering durability and smoothness issues I bought some 3/16” and 5/16” dowels from Amazon.
After determining appropriate position of each element, I glued and clamped the model with all the moving parts on their right position, and it worked very smooth. The trick is leaving some space on the axial direction between the rollers and the main disk, so the friction is almost negligible.
This is what the model looks like:
This is a short video showing how it works:
