DRAFT: This module has unpublished changes.

ME 112: Mechanical Systems Design

 

Characteristics of machine elements including gears, bearings, and shafts. Design for fatigue life. Electric motor fundamentals. Transmission design for maximizing output power or efficiency. Mechanism types, linkage analysis and kinematic synthesis.

 

This course was one of my favorites as an undergraduate. It stressed a balance of physical and virtual prototyping, as it is often times easier and cheaper to create computer models to mimic how the actual system would behave.

 

Because this course was happening at the same time as the Winter Olympics our midway project was to build a "bobsled rescue vehicle," which was basically a LEGO crawler that climbed up a monorail and attached to a magnet as the crawler moved below. Not only did our vehicle have to be robust and functional, but also energy efficient during the initial climb sans magnet, final ascent with magnet, and the final descent. In order to create an energy efficient machine, we first tested our motor to create power and efficiency characteristic curves. We then tested different gear ratios to determine our ideal design.

 

 

Notice the string hanging down from the side. This string attached to the magnet mass, applying a large torque to our vehicle. This was one of the most difficult problems we had to solve in our project. 

 

Besides prototyping and testing, my main job for this project was the performance analysis, where I calculated estimated power losses in all aspects of the machine from the initial electric power in to the propulsion work out. I also created an Excel model of the gear stresses to ensure that our gearbox would survive. Here is our lengthy report of the process from initial design to future directions. 

 


The final project was to design and build an animatronic duck that had to swim roughly 1 m/s. 

 

 

 

Here is the project's executive summary:


The goal of the duck project was to construct an autonomous, battery-powered animatronic duck that propels itself forward in water using bio-inspired paddling motions. The duck needed to move in a straight line without guides or a remote control, and had to have an additional biomechanical feature powered by the same motor powering the legs and feet. To tackle this project, our team decided to first write MATLAB code that would easily analyze various possible linkage mechanisms for the duck legs and feet. Based on that, our team decided to use a four-bar linkage driving mechanism attached to a pulley system that connected the integrated transmission output to the crank shaft. We then set up the two four-bar linkage mechanisms for
each leg and foot to be 180 degrees out of phase to produce a realistic and continuous paddling motion similar to that of a duck. Each duck foot was attached by a hinge at its “ankle” to mimic a duck’s flexed foot during the propulsion stroke and a pointed, flat foot during the pull backstroke. Our bio-inspired additional feature was a duck tail that swished back and forth as the duck paddled through the water, which was connected to the motor via the left rocker linkage. The drive system encompassed a Tamiya worm screw gearbox and a timing belt from the motor’s output, which attached to the crank shaft in the four-bar linkage mechanism. Our prototype met the design requirements of autonomously propelling itself in a straight line through the water, and our average speed during testing was sixteen centimeters per second. Moving forward, a future iteration of our duck would include removing the belt system, which
reduced efficiency and was the least reliable component of the system. This would also reduce the gear ratio and increase the speed. The four-bar linkage we used would be redesigned to provide a smoother trajectory to minimize any shock load experienced as the feet changed direction. We would likely use nylon or delrin to increase the duck’s durability and reduce the friction of the transmission elements, and vacuum form and reinforce our body to avoid the structural and supply chain problems we encountered when working with the pink foam.

 

 My main contributions were the MATLAB modeling as well as design and analysis of the paddling mechanisms. Please see the below document to learn more about this exciting project:

 

 

DRAFT: This module has unpublished changes.