For those who do not know, a well windlass is a mechanism used to crank a bucket out of a well instead of pulling the rope up manually. This makes it easier for the operator to retrieve more water with less effort.
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| Image from http://upload.wikimedia.org/wikipedia/commons/1/1e/Ramelli_windlass_well.jpg |
For this project, my partner Christina and I were challenged to construct our own well windlass while simultaneously applying our new knowledge of fastening and attaching as well as our previous experience with cantilevers and beams. The deflection equation,
(F(L^3))/(3EI)
Where F = the applied force, L = the length of the lever, E = Young's Modulus (or the ratio of stress to strain aka stiffness) and I = the moment of inertia (the lever's stiffness of its cross sectional area). In addition, we were given specifications that we had to work within in order for our windlass to be considered successful:
1.) We only had 500^2 cm of Delrin, 50cm of Delrin rod and 120 cm of string to use
2.) Our windlass had to span a gap of 12 cm and be able to lift the top 10cm of the bottle above the gap
3.) The windlass had to support the load of a 1 liter bottle of water without wobbling or breaking
4.) The crank to wind up the string could not be over the gap
We started by brainstorming. The Delrin rod was too flimsy to support the water bottle on its own, so we decided to support the entire windlass with two large bases connected at intervals by cut pieces of rod. The shorter the rod was, the less it bent. This was due to the lever arm length affecting the applied torque. Once we shortened the arm, we lessened the torque and made the rod more effective.
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| Not the sturdiest of rods... |
We wanted something that would utilize the strength of the Delrin sheets...
But that would also carry the string away from the gap, like a crank and pulley system...
Additionally, it had to account for all the forces applied to it, such as gravity, tension, and friction. It had to have wide 'feet' to keep it well balanced...
Finally, the pulleys and crank had to be easy to use and apply, and since we could only cut out pieces, the pulleys had to consist of one small circle between two large ones.
This design would utilize the strengths of both the rod and the 3/16 in Delrin: the Delrin would act as a support while the rods transferred the string away from over the gap to the crank. The pulleys would help take some of the force from the bottle off the crank and make it easier to turn. Additionally, they would also be able to spin freely if the friction between the them and the string proved too great once the bottle was lifted.
Without extra support, the two connected bases would have been unstable and probably fallen over if the right force was applied in the wrong way. We designed two identical feet and fit them to the bottom of the bases on either side of the gap. We used press fits for their simplicity and so that we could disassemble the product if we needed to once more parts were cut and ready to be connected.
After our brainstorming session, we made a foam demo of our model...
Once we were happy with our design, we began to build the various pieces into Solidworks. Whereas the bottle opener only required on part file, the windlass was made of several different pieces, and required multiple. It was tricky keeping our files organized, both on the desktop and within the group Dropbox file. We eventually resorted to naming our files by our first names to help differentiate them.
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| The stabilizing foot |
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| The loose and tight bushing |
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| The pulley pieces |
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| The base |
Partway through designing the various pieces, we realized that the Delrin rod would never work as a sufficient crank and spindle for the rope. The rod was circular, with no distinguishing features that could give the rope the friction it would need to wind around it.
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| Well, THAT'S not going to hold it... |
We had to pause and redesign a crank and spindle that would work for us, using Delrin sheet.
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| The second crank iteration |
Eventually, we came up with the idea to use Delrin in place of the third pulley. The Delrin would be rectangular in shape with two smaller rectangles erupting from its ends. A hole through its center would allow the rope to be fastened tightly to it, and therefore provide the force needed to keep it in place. The small extremities would be filed down to fit into circular holes. This would also make it easier for them to spin. Finally, using a press fit, the handle would be attached. We measured to make sure it would not be so long that it would touch the ground on each turn.
Besides the crank and handle, several other pieces underwent mild modifications in Solidworks (see above pictures). The bases went from a multi-part design, to two single arches with an area for the crank. This edit saved material and helped make the windlass more sturdy. The arch design strengthened the bridge over the gap, ensuring that the water bottle would not break it once the crank began to lift the bottle.
Before we sent our files to the laser cutter, we practiced making our own bushings and press fits to ensure that our pieces would fit together perfectly. Otherwise, we might have ended up wasting a lot of material.
Our final design began to fall into place. Our bushing and press fit measurements were spot on, thanks to the margin of error information we learned during our fastening and attaching session (see fastening and attaching post). We knew that any piece that needed to fit tightly would have to either have a .5 mm added/subtracted from it in order to actually fit snuggly.
It was time to start cutting.
The initial cut went very well, but we ended up having to re-cut several bushings and parts to the handle for size reasons. The handle's notches did not reach far enough to create successful press fits and several of the tight bushings ended up being more loose than expected and did not keep the pulleys pressed tight enough.
Otherwise, we were very frugal with our material and wasted very little.
Once all the pieces were cut, we began to assemble our 2D parts into a 3D windlass. All the press fits and bushing worked perfectly.
Using only 5 inch of the provided Delrin rod, we assembled our two pulleys, attached the string, placed it over the gap....and did our official (and probably only, given how little time we had left) test run.
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| Our presentation run (not the test run, but they are essentially the same) |
We were pretty satisfied with our results...
The windlass worked better than expected. The pulleys kept the string aligned with the crank. The crank was easy to turn and never let the rope slip. The base remained mostly stationary and easily lifted and supported the weight of the bottle thanks to the double overhanging beam design, along with the arched sharp, which maximized its strength against the bottle by minimizing the affects of the two beam's moment of inertia. We could not control lever length, as the beams had to be a minimum of 12cm to span the gap, but we could control how well supported the two beams were, and made sure they would be strong enough to complete their task. All in all, we were two very happy engineers.
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| Side view with bottle |
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| Looking through it |
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| Long shot |
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| Crank handle |
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| Crank handle and spindle |
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| Feet and base |
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| Top view of pulleys |
As a final edit, we connect the handle and the piece that attached it to the spindle with a heat stake, to ensure no amount of force could cause it to fall off mid-crank. Aside from this connection, the entire windlass can be disassembled into a neat, easy to transport pile.
In total, we used 12.7 cm of rod and 273.12 cm^2 of sheet.....well under our limit for the Delin.
We had to use all of the 120cm of provided string, though, as the distance from the crank over the pulleys and down to the bottle lid barely left enough string to attach it securely. There was no way to adjust for this, so we used all of it. Because we kept our shapes basic, calculating the total Delrin used was simple. We used basic geometry equation, like the areas of a circle triangle. Our specific calculations and estimations can be seen below.
In total, we used 12.7 cm of rod and 273.12 cm^2 of sheet.....well under our limit for the Delin.
We had to use all of the 120cm of provided string, though, as the distance from the crank over the pulleys and down to the bottle lid barely left enough string to attach it securely. There was no way to adjust for this, so we used all of it. Because we kept our shapes basic, calculating the total Delrin used was simple. We used basic geometry equation, like the areas of a circle triangle. Our specific calculations and estimations can be seen below.
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| Geometry calculations |
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| Geometry calculations, again |
Even though our product worked extremely well, if we had enough time, there are still a few edits we would like to make. While we cranked the base moved slightly due to the force acting on the handle. If we could re cut the two base walls, we would add hooks to go over the lip of the gap on either side to make the windlass more stable and secure. Additionally, we would also make the spindle more like the pulleys, with a small gap in between two large buffers, so that the sting could not slip off it and become lodged between the spindle and the wall. This made the crank slightly harder to operate. As an extra edit, we could probably honeycomb our two bases, and thus use even less of the material we were given, but we did not want to compromise the strength of the bases, since they were supporting the brunt of the applied forces.
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| The demo and final product |
I guess I won't have to lift my textbooks from my bag to my desk anymore.....assuming a one liter bottle weighs about the same as a Physics book.
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