Group Members: Spencer Lehr, Alexander Copeland, Matthew McGinn
How our project works
Originally, we all agreed that we should make a device that takes as straight of a route to the weight as possible. We decided this route because we wanted to go for the lightest possible design, and also the most effective. We knew that in order to do this, we would need to bend the flat pieces of aluminum in order to make the moment of inertia higher, therefore deflecting less. We also knew that we needed a minimalist approach to our lifting device and base. For our lifting device, we first looked at the box of the servo and found the max torque that the servo could produce. From there, we calculated, using geometry, the max length we could use for the arm. With this calculation, we found that we could use just a simple arm lift device, instead of a needing a huge truss or counterweighted system. We also decided to go with a free flowing base instead of a square plat base. This reduced the weight drastically and also gave us more adjustability. In the end, we were able to use these characteristics to make our project lift a 1-lb weight a height of 2 inches.
A few of the glaring, initial problems were that our model leaned on the course’s wooden wall for support and was only able to lift the weight 2 inches or more if the weight was preloaded onto our model’s lever arm. When we tried to fix the latter problem, we found that rigid beam deflection was an additional problem that needed to be fixed. The deflection was caused by the force exerted of the servo attempting to lift the 1-lb weight 2 inches. Rather than lift the weight once power was added to the servo, our main T-beam would deflect downwards for a few seconds and then start to lift the 1-lb weight, reducing the maximum lifting height to approximately 1.25 inches.
In order to fix our three major problems, we added beams, either in tension or compression, at various points. We solved the issue of deflection by adding a beam, in compression, from the base of our structure to a point roughly 1/3 of the length down the main T-beam. The force, and resulting moment, from the beam in compression on the T-beam counteracted the moment from the servo lifting the 1-lb weight. We addressed the problem of our structure using the wooden wall of the playing field for support by adding another beam in compression. The beam in compression was able to ‘push’ our structure away from the wooden wall and simultaneously maintain the same level of support on the structure that the wooden wall provided. The concept worked because, similarly to the previous problem, the added beam in compression provided a resultant force on our structure that acted in the same direction and similar in magnitude to the force provided by the wooden wall, which had previously provided support. Our final problem was to prevent preloading the 1-lb weight in our structure. Because we were able to fix the problem of beam deflection when our lever arm was not in contact with the weight before lifting, we had to simply adjust the lever arm to be located below the 1-lb weight initially. Solving this problem called for a beam in tension acting on our main T-beam. The result was a force that ‘pulled’ the main T-beam downward and prevented the lever arm from being pre-loaded with the 1-lb weight. An additional change we made was to change the aluminum strips in the base of our previous model to more rigid beams, not out of necessity for the project, but in order to add durability and stability to our project. In the end, the changes we made not only allowed the newer version of our project to work, but added a layer of durability to our project that our previous version did not have.
Interesting and Unique Characteristics
· Lightest project – weighed in at 6.5 oz
· Very Sturdy – Minimal deflection
· Minimal use of fasteners – Only put few fasteners along beam and only at certain junctions in order to decrease weight
· Long T-Beam – The use of a T-beam resisted deflection in the y as well as x direction. A beam running down the middle of the T-beam helped to significantly decrease the deflection in the y direction in order to acquire the desired lift height of 2 inches.
· Claw foot base – This base allowed us to drop significant weight, while still allowing for a strong a sturdy base.
· Highly Adjustable – No fixed base allowed us to move the structure in order to put the lift arm at optimal placement
· Adjustable Lift Arm – Used just the grooves in the servo in order to allow for the lift arm to be removed and placed so that the arm starts directly under the weight