Linkage Project

Design I - Project 2 Description:

"After proving yourself to be a determined engineering intern in NASA’s Mars Surface Habitat Program, your supervisor has asked you to apply your talents to designing components of the habitat’s backup airlock system. In order to prevent anyone from being stuck outside in the harsh Martian landscape (and turning into Matt Damon from The Martian) you need to design an assembly that will convert the rotary motion of the backup motor to linear motion that controls pressure in the airlock."

Restrictions:

All links must be columnar components
All links except the crank link must have a length to width ratio of at least 2:1 respectively
Links can have holes, straight slots, or both
Any hole or slot must be circular except for the crank link’s hexagonal cut-out to connect to the crank shaft
All holes and straight slots must be centered in the width of the link
Must touch only the approved connection locations: 1 at the crank shaft, 1 at the linkage shaft, and 1 hole selected as available on the mounting plates
Must connect to the crank shaft (motor driven) to the linkage shaft (carriage and rail system on the underside of the bottom plate, slides with low friction between right and left sides of rig)
Must have a 2” gap between the button presser and the button prior to test initiation (motor off, Arduino off)
Must always stay within the inner frame of the rig and never go behind the front face of the mounting plates
Material Choices: 3/16” thick acrylic, 1/4” thick acrylic, and 1/4” thick plywood

Challenge Setup

Our Design

My team did analyses on and experimented with sets of linkages of various lengths, widths, and slot/hole placements as well as the location of spacers that are used during the actual test. The first iteration was made of 3/16” thick acrylic because we predicted acrylic would be more consistent and have fewer defects than plywood meaning a lower chance for unpredictable cracking. Meanwhile, we chose the thinner acrylic to help minimize mass. The design only had 3 connection points with no slots and was based on Grashof's Law for a crank-rocker system. We ended up with a total mass of 121 g and a time of 35 seconds for this system. In our final iteration, we increased the length of the rocker and coupler to increase the time that the button was pressed. Meanwhile, the attachment point was moved down by one peg and the crank link's width was increased to lower the stress on potential failure points in the system. The final system had a total mass of 158 g and a time of 54 seconds, meaning we improved our time by 54% while staying under the maximum mass.