Compressed Air Motor
Project Background
At Clarkson University all mechanical engineering students are required to do a senior design project. Our professor proposed seven different projects to the class for the design project. Of the seven projects, the most challenging was the compressed air motor. Only the top students were considered for this project. It was my top choice. I was fortunate to be selected to the compressed air motor team.
Specifications and Design
Professor Kane, our team advisor, gave our team a vague list of specifications for the motor. Initially he told us that the motor had to be small enough to mount on a tricycle and be capable of operating at 450psig. Immediately, some of my teammates and I expressed our concern for running a motor with compressed air at 450psig. We believed that running the motor at such a high pressure could be dangerous. Although the project guidelines were not revised, we moved forward with our design for a motor that could withstand 450psig.
After agreeing on an overall design concept for the motor, we divided the responsibility of every subsystem design among the team members. I was in charge of designing the valves, yoke assembly and a mounting plate for the motor. Due to limitations on the number of available machinists, we quickly realized that we needed to buy off-the-shelf valves and modify them. After extensive research, I sourced a compact push button valve (see left) that exceeded the pressure ratings of the project at 800psig.
Analysis and Assembly
Once the team had confirmed the valve, I proceeded to start designing the yoke. From the preliminary drawings of the motor and the piston specifications, I performed an analysis to determine the forces acting on the yoke. From the shear and moment diagram, it was clear that the greatest stresses occurred at the center of the yoke. Since the yoke is linearly reciprocating on the motor, the mass had to be minimized in order to reduce vibrational effects. Using material properties for 6066-T6 Aluminum I was able to determine that a 3/4 inch thickness would result in a 3.2 factor of safety against yielding. This led to a design concept that was 7/8 inch at the yoke center and 5/8 inch thick on the sides.
Yoke Sketch: Top View
I performed another analysis on the yoke pins that connected to the crank arms on either side. From the analysis, I was able to determine that an alloy steel dowel pin would not yield when subjected to the calculated forces. Since the crank arm would rotate a maximum of 28 degrees about the yoke pin, I chose to use an oiled bronze sleeve bearing that could tolerate the subjected load.
Yoke Sketch: Front View
In order to improve the structural rigidity of the slider rod mounts, I had each mount protrude from a common base. However, due to the geometrical constraints between the cylinder and the end of the piston rod, I designed the base of the slider rod mount to go underneath the center of the yoke.
Machined Freestanding Yoke Assembly
Testing and Implementation
Once the design concept for the yoke and its components was finalized, everything was redrawn on a master layout to confirm alignment with other subsystems. Each team member created CAD models of their parts and an overall assembly was created using Solid Edge. In addition, individual dimensioned drawings with tolerances were created for every component that needed to be machined. In order to keep track of every part, we created a part numbering system for the motor.
CAD Motor Assembly Model
After all the parts were machined, we assembled the motor, hooked it up to the shop air then slowly increased air pressure. After an initial run and some fine-tuning our motor performed just as was expected.
Finished Motor
Compressed Air Motor Operating at 100psig
Compressed Air Motor Connected to Steel Band Flywheel
Rope Climbing Device
My favorite course at Clarkson University was Intro to Engineering Design. I love design challenges so this course was right up my alley. Every semester Professor Steve Yurgartis would come up with a design challenge for the class. Our grade was weighted based on the average performance of each student’s device. This instilled a sense of competition and cooperation in the class. On the day of the demonstration, each student was given two attempts for their device to climb the rope. Each of the attempts was measured and averaged together to result in a final score for the device.
The Challenge
“Design, build and demonstrate a device to travel as far up an inclined rope as possible, as shown in Figure 1. All of the energy to power the device must be stored in two or fewer #32 rubber bands, provided. The entire device must start between vertical planes defined by the starting marks, as shown in Figure 1. In the ready to operate condition the device must be touching only the rope. Operation of the device must be initiated by a single handed release. Once the device is set into motion no operator input is permitted. The device must travel as a single unit. It must be capable of repeat performances. Construction materials are strictly limited to the list below.” (Professor Yurgartis)
Permissible Construction Material List
Figure 1: Inclined Rope (all unit inches)
My Designs
Design 1: Rope Car
Design 2: Spinning Wheels
Design 3: Traction Wheel
Design Evaluation
In order to numerically compare each design alternative, I created a weighted objectives table. I built a prototype of the Traction Wheel design after it scored the highest in the table. The prototype was put through numerous tests before the day of the demonstration. On the day of the demonstration, my Traction Wheel device achieved a respectable climbing height of 57 inches on the first attempt and 55 inches on the second, raising the overall average of the class.
Weighted Objectives Table
Traction Wheel Device
Click here to download my design reportPowder Containment Solution
The Challenge
In the summer of 2013 I interned as an industrial engineer at Shapeways, a provider of 3D-printing services. One of my first assignments was to solve a problem in the transfer system of the nylon polymer printing media. As it was configured, a large amount of media would escape into the air before entering the drum, creating not only a health hazard but a loss of material. I designed a transfer system that moved the printing media from the media mixer to the storage drums.
The Solution
Utilizing an extra section of clear coiled ducting from another project, I attached the ducting to the mixer gate and fastened it with zip-ties. I cut a hole the size of the duct in the lid from one of the drums. The duct was then threaded into the drum lid creating a tight seal.
Powder Mixer Filling A Drum
Replacing Drum Under Powder Mixer
My solution for the powder mixer worked perfectly. The coiled duct attached to the drum lid would press against the lip of the drum in order to create a tight seal. Although the savings were small in terms of the overall manufacturing cost, my solution helped Shapeways realize its strategic objective to be a low-cost producer without sacrificing material. Most importantly, it made our work environment safer.
Downdraft Table
The Challenge
While working at the 3D printing company, Shapeways, I noticed that there was a major bottleneck in the post-production process. When 3D printed parts leave the 3D printer they are extracted from the large cake of excess printing media that initially surrounds them. The parts are then batched together and sand-blasted. Once the sand-blasting is complete, the parts are individually blown with hard or soft air by an employee on a downdraft table in order to contain the powder blow-off.
The employee would hold the part in one hand and an air gun in the other. This was extremely inefficient because the employees would need to constantly switch between high-pressure and high-volume air guns.
The Solution
My coworker and I designed a system to replace the hand-held air guns with two air nozzles mounted on either side of the downdraft table. In addition, I attached two foot-pedal control valves to the air nozzles. Using the system, the employee would hold the part with both hands and easily move it between the hard and soft air.
This dramatically sped up the air cleaning step in the post-production process thereby increasing throughput. Our sole downdraft table, as efficient as it was with our new system, could not keep up with our production demands. The lead time on a new downdraft table was three weeks. I was charged with developing an immediate solution. I built the following downdraft table out of a shipping crate, a traffic cone and a shop vacuum, all of which I found in the factory.
Downdraft Table Sketch
The makeshift downdraft table was nick-named the “Draft 3000” and increased our production capability by 50%.