Well Windlass

Well Windlass: From learning the meaning of the word to building it

When we were asked to make windlasses on Friday, February 5th, I didn't even know what the word meant until I saw pictures. Making an unfamiliar machine made the brainstorming processes a little more challenging than that of the bottle opener. We had to use more imagination than prior experience with the machine. But this also left us with a lot of room for creativity and exploration.

Limitations, requirements, and tips to keep in mind:

The requirements and limitations we kept in mind throughout the design and building process were:

• Don't exceed a total of 500 cm² acetal sheet;
• Use up to 50 cm long acetal rod (thickness = 6.37 mm);
• Use up to 120 cm long string;
• Make sure the windlass can stand over a 12 cm gap between two tables: "the well";
• Build the crank such that it is not right above the well;
• Make sure the final structure doesn't wobble, bend or break as it lifts 1 litter of water in under 45 seconds.
• The windlass should be able to lift the water bottle at least 10 cm above the tables' top surface. 

General guidelines we outlined before brainstorming designs:

• Triangles and arches are better supporting structures than rectangles. 
• The farther apart the weight is suspended from the supports connecting it to the two tables, the more our beam bends. So keep the side of the windlass across the width of the well as close as possible to 12 cm without it falling through. 
• That said, we need a stable base and, if possible, a good grip on the table.
• To lift the water in as small time as possible, wrap the string on a wider frame that lifts more string with one rotation. Here, we figured wrapping the string around the circumference of the acetal rod would lift the bottle extremely slowly. 
  

Figure 1: If the rod on the left (a) is half as wide as the rod on the right (b), the same length of string can be wrapped around (a) twice as many times as (b).

Brainstorming possible designs:

My partner, Jiaming, and I started drew some possible designs on paper. We briefly entertained the idea of using a pulley system to minimize the effort needed to lift the weight. However, given we would only be lifting 1 kg  and that we have a limited length of string to use, we went with a more traditional windlass with two bases standing on either side of the well, and a center rotating with a string to lift
the water.

Figure 2: Very briefly considered pulley systems 

    

Figure 3: General outline of chosen windlass type and its components

Once we agreed on the general structure of the windlass, we focused on individual components like the base and stand, the cross-beam, the rotating center that wraps the string, the handle, and the different joints connecting these individual components.

Vertical supports and bases:
We designed triangular supports for support but varied their specific dimensions and bases to create several designs.

First, we concentrated on the base. We brainstormed some designs that would "clamp" the support with the table, and others with flat feet to prevent the vertical structure from tilting to any side. 

Figure 4: Types of bases brainstormed and their respective drawbacks

After trying a cardboard model of the "clamp" we designed and seeing that the support is too thin to hold 1 kg of load, we changed our design to look like the following triangular supports with small triangular bases.

Figure 5: Left: Triangular base that clicks with the bottom of the vertical support (center); Right: A close-up picture of the tight fit that connects the base with the vertical support

Later, we further modified our base to run across the well and connect the two supports. That way, the bottom is less likely to wobble or collapse inwards was we lift the weight.

Figure 6: Base across the well that clicks to both vertical supports

Our vertical support also went from being a triangular slab to a frame with a vertical at the center and three sides (each 2 cm wide) of an equilateral triangle. This saved us material while keeping the structure sturdy. 

Figure 7: Modified design of vertical support to conserve material

Rotating Center/Windlass and rotating axis:

Since stacking rods or building boxes to make the rotating center thicker would consume too much material, we decided to arrange four rods separated by a rigid circle to form a quasi cylindrical shape.

Figure 8: (Circular) rigid frames for cylindrical rotating center

We originally considered cutting out parts of the circle except for the rectangular lines that connect the rods with the center of the circle. However, this would have applied too much force on thin pieces of rod with the risk of breaking. So we chose stability over conservation of material. Instead we made the circles' radii smaller.

For our rotating axis, we have considered the cylindrical rod, a rectangular cutout of delrin sheet, and piano wire that would loosely attach the rotating piece with the support.

We abandoned the idea of using piano wire because it is too weak to carry 1 N of weight. Also, piano wire could only be used as an attachment, not as a functional part of the design.

We made a model that uses the cylindrical rod and realized that the rod slips from the circular hole that connects it to the circles carrying the weight of the water. While it could easily turn the circles and wrap the string without mass attached, the friction is not strong enough to lift the mass. 

Figure 9: Model of well windlass with a cylindrical rod as an axis. Note: This picture doesn't show the four rods that pass through the circles to support the string as described above.

But, if our rotating axis had a rectangular cross-section, it wouldn't slip out of a rectangular hole as we rotate it. The question, then, was "Which rod is stronger: the cylindrical rectangular one?"

When we suspended 1 kg of mass from each beam as shown in the figure below, the rectangular beam proved to be stronger (it bent less than the cylindrical one).

Figure 10: Left: Cylindrical Delrin rod bends more than Right: Rectangular Delrin rod when 1 kg of water is suspended from each

The rectangular beam is a better option both for its greater strength and because it allows rotation without sliding. Accordingly, we adjusted the center holes on the circles we designed to rotate in the middle.

However, this meant the rod wouldn't rotate very smoothly in its junction with the two vertical supports on either side. If we make the rods rectangular, the rod wouldn't rotate at all. But if we make the holes circular the rotation would be very bumpy and uneven.

To solve this, we designed bushings of 2 cm outer diameter and a rectangular hole at the center to fit the rectangular rod. This way, the bushings would rotate with the rod but slide smoothly along the circular hole in the vertical supports that loosely fit them.

Figure 11: Top left: cross section of cylindrical rod that would pass through openings in vertical stands; Bottom left: Circular opening in vertical stand to allow rotation; Top right: Bushing with rectangular opening and circular exterior to fit rectangular rod and rotate smoothly in the stands; Bottom right: Model of opening in vertical stands that would fit the circular bushing

In our final iteration, we used two of these bushings to allow smoother rotation even as the axis slides sideways slightly. We also fit two rectangular bushings slightly bigger than these on either side of the joints to prevent them from sliding too much.


Extra support:

While we were relatively confident with the ability of our structure to support 1kg of mass, we wanted to be safe and take additional measures to make sure it wouldn't deform when lifting up the weight. For this, we came up with a range of ideas:
i) Build additional triangles that would stand on the cross -beams and support the rotating axis while allowing it to rotate.
ii) Build a cross-beam that would lock the two supports from the top and with it two "hangers" that would suspend part of the mass of the rotating axis from the top cross-beam.
In addition, build two rods that connect the sides of the vertical supports at about 11 cm above the table surface. This proved to be challenging to build and attach properly. It was also not very essential given we had three cross-beams already.
iii) Replace the (rectangular) top cross-beam with an arch and have a simpler and more aesthetically appealing structure.

Figure 12: Different designs we tried for extra support labeled according to their respective descriptions above

We saw that the arch works better in terms of conserving material as well as creating a strong enough but simple structure.


Handle:
This was one of the easier parts to design. We made two rectangular pieces, one connected to the rotatable axis and the second rectangle which sticks out for us to hold as we turn the windlass.

Since we wanted a permanent connection between the two pieces to perform as one, we used thermal press to connect them.


Final Product and Performance:
Our final well windlass incorporated the best of all the parts we designed. It uses well under the limit of Delrine we were allowed to use. It wobbles slightly when lifting water due to the low friction with the table. However, when held with hand from the same side as the rotating handle, it is reasonably stable. We were able to lift the 1 litter water in under 10 seconds several times using our final product.

Areas of Parts in Final Iteration

Part (amount)	Area (cm2)
Triangular vertical supports (2)	235
Circles above well (2)	22
Bottom cross-beams (2)	64
Arch	20
Handle	25
Rectangular rotating axis	14
Bushings	33
Total	413

Note: The above areas are those of Delrin pieces cut out of 3/16’’ sheets.

We also used 28 cm of our Delrin rod and the entire 120 cm string we were allowed to utilize.

Figure 13: Final working iteration of windlass: Top left: Top view; Top right: Front view for user accessing the handle; Bottom: Side view

Figure 14: Evolution of our well windlass from earliest to latest (left to right)

What would I change/improve:

I would replace the handle with the cylindrical delrin rod for a more comfortable grip.
I would also attach the support and base with the table (with a clamp, for example) for better stability. This could also be solved by adding more mass to the supports.
And if I was to mass manufacture this windlass, I would use more 3 dimensional parts to replace the small parts put together like a puzzle, for ease of manufacturing. For example, I would use a 3-D printer to make one whole piece of cylinder rather than four rods arranged to resemble one or a one-piece handle rather than two pieces put together.



Thank you for your time.

Best,
Meba


Archives: Among the many many photos we took to document this process: