Well Windlass
The Well Windlass project pushed my partner (Drew) and I to create a windlass from 500 cm2 of Delrin plastic, 50 cm of Delrin rod and 120 cm of string. The bottle had to be capable of lifting a 1 kg bottle within a time frame of 30-45 secs.
A visual summary of the process: Image of our mock-ups and solid works drawings
When we first began brainstorming, it was clear that we wanted to create a wheel of some sort that would help assist in lifting the weight. Initially, we wanted to design a gear structure of some sort, however, decided on using disks to roll up our bottle.
To reduce the stress applied to the rod when lifting the weight, we decided on dividing the rod into three segments. The rod pieces would then be placed in a triangular manner around the disks. This design element not only decreases the stress applied on a single rod (when compared to the three rods), but also increases the string’s rotational circumference; in turn, reducing the amount of time taken to lift the bottle.
The bottle had to be lifted at least 10 cm above the table between a 12 cm gap. Keeping these project restrictions in mind, we created a stand for the rolling disks of 17 cm in height. Additionally, we accounted for the rods to maintain a length of 15cm or more to, therefore, allow the stands to run across the table gap of 12 cm.
The stand itself would have a semicircular cut of similar radius to that of the disks to connect them to the stands. Furthermore, these cuts would have complementary semicircular supports (as shown below) on either sided of the disks, as to prevent the disk from slipping when rotating the handle to lift the weight.
To maintain the stands upright position we planned on adding triangular supports (as pictured below) to their base. However, we found that this set up caused the stands to slide away and collapse, as the disk and rod system pushed down on them. Hence, we iterated our design to add rods to connect the stands to one another across the table gap.
Windlass with triangular supports
Windlass structure after iteration and addition of rods
Below is our final windlass design. When connecting each of the parts together, we came across several challenges when it came to press fitting. It was hard to understand the amount of uncertainty to account for when producing parts on solids works. Often the measurements on the computer program did not identically match the laser cuts. Therefore, we used the aid of piano wire and heat staking to bring our windlass together.
Brief engineering analysis:
When considering the physics behind the windlass, Drew and I specifically analyzed the torque required in rolling the disks and lifting the bottle off the ground. Torque is defined by the product of force and distance, therefore a higher torque can be created by either increasing the distance from the applied force or the magnitude of the applied force.
Ideally, one would not want to have to place a great amount of force to lift up the bottle; therefore we chose to manipulate the distance of the handle from the center of the disk. By having the handle being the furthest distance from the center, a consumer using the windlass would not have to apply a great amount of force to provide the needed torque to lift the bottle. (It is important to note that the force applied is perpendicular to the distance from the center of the disk, therefore sin(theta) = sin90= 1 in relation to the equation of torque.)
Additionally, we chose to use the thickest Delrin plastic for the stands. This provided a strong support capable of providing the normal force required to balance the force needed in lifting the bottle. Overall, these considerations helped us make a relatively stable windlass structure.
Reflection on Design process:
Despite the features for support on our stand the structure would move at times when attempting to lift the bottle, upon revision hooks could be added to the base of the stands to prevent the structure from moving greatly. This would also prevent the structure from falling between the table gaps and allow for an easier rotary motion when using the handle. Moreover, the addition and use of triangles can help further stabilize the windlass structure.
Had we had more time, we would have liked to further divide and increase the number of rods attached to the disk. This would have allowed us to decrease the overall length of the rod-disk system to help create a more triangular like structure. Notably, the addition of more rods would help decrease the stress placed on each rod by the weight, as well as decrease the time required to lift the bottle. The figure below shows the proposed changes we would have made to our windlass.
Accounting of material usage for the final prototype:
Overall we used 483cm2 of Delrin plastic to created our Windlass.
I really liked the wheel you two used to wind up the string. That was super clever and a great way to be able to carry more weight. I also really like how you write your blogs, they’re so nicely formatted! Very clear and concise.
Your design was very unique, and it’s definitely got potential for some interesting applications. Congrats on a successful windlass and a well-written blog!