Well Windlass: The initial design

The well windlass has been a long saga, and we will finally display our design on Wednesday.
It started with the assignment and constraints: The device must lift a bottle out of a 12cm gap between tables, raising the top 10cm above the table, using only 500 square cm of Delrin and 50cm of rod.
First, my partner Julie and I individually brainstormed possibilities.

First page of planning sketches

Second page of planning sketches

We brought our ideas together in a meeting. We decided that a design with a triangular profile, while it seemed strong, would be too difficult with our attaching methods, which work at right angles. Instead, we chose the last design shown on the second page of notes: an arch-like design that would place two sheets vertically, so that the force of the bucket would be pushing parallel to the sheets of Delrin instead of perpendicular, allowing them to support more weight. We wanted a crank attached to a Delrin rod on which the string would wind, as well as a ratcheting gear to hold the bucket if you stopped cranking in the middle of raising the bucket. After our meeting, I sketched the parts we would need on graph paper, as shown below.

Sketch of parts, 1 square = 1cm

In sketching the parts, I used a scale of 1 square = 1cm to make sure that all the parts would fit within 500 square cm. In the end, I could fit everything in a rectangle 19 x 26 cm, or 494 square cm - barely fitting! Due to the constraints, the width of the "bridge" could only be 18cm, which, if the feet of the bridge are 2cm wide, leaves only 1cm between the feet of the bridge and the edge of the well. Also, the height to the rod is only 11.5 cm. We decided on a width of 6cm between the two bridge pieces, trying to keep it narrow so that the rod would not bend under the weight of the bucket. 

With these worries in mind, we constructed a cardboard model using the dimensions in the drawing. The model seemed quite stable (for being held together with tape) and gave us a good idea of the size of the device. The crank arm and the ratchet gear were especially hard to make out of cardboard and didn't really add anything to our understanding of the device. 

Cardboard model of the windlass

Julie suggested using two cranks and rods, to disperse the weight of the bucket and prevent the rod from bending. However, we abandoned this idea because it would take a lot of force to raise the bucket  high enough between two rods (to have 10cm of clearance above the table in our design, the bottle has to get within 1.5cm of the level of the rod(s)), and when the bottle is close to the rods, pulling from two places would require a lot of tension for a relatively small vertical force on the bottle. Therefore, we returned to the idea of having one crank in the center of the "bridge." When we tested the strength of the Delrin rod, we determined that a 6cm length would be stiff enough to hold the bottle without bending, which alleviated our fears. 

We also abandoned the idea of having a ratchet to hold the bottle up, since it seemed much to complicated to achieve in the time we had available and would not significantly improve our overall design. 

We then got our design approved and proceeded into SolidWorks!