Challenge:
Team of 6: design and build a pedal-powered walking vehicle to be used in a jousting contest.
Skills:
Solidworks, FEA, Motion Analysis, Machining, Linkage Design, Differential Power Transmission, Project Management
Individual Contribution:
Project manager, designed linkage legs, chassis, and rider interaction
Make it RIDEABLE. And PEDAL POWERED. It also needs LEGS. No rolling allowed. It has to TURN.
Oh and by the way...
You're going to JOUST on it.
For the final project of Engs 146, our group of 6 designed, verified, and fabricated a 12-legged, differential/pedal-powered, forward-steering rideable horse-beast. The overall goal of the project was simple: make a rideable walking vehicle capable of forward movement and able to execute a 90 degree turn. However, the scale of the beast introduced design challenges that we had never met before: namely high load bearing capability and monumental assembly coordination. This was the second year of the walking beast challenge, and the previous year's beasts largely failed; most broke during competition. We had the opportunity to learn from the previous year's mistakes and create something truly spectacular.
Long before fabrication began, we conducted a detailed exploration of possible movement strategies. Assuming that we would develop a leg set that could function as a smooth wheel, we first tried to determine how we would arrange the leg sets on the beast. Our primary criterion was that, during a turn, each leg set must trace a path concentric to the other leg sets' paths, as shown in the above center panel. This would prevent the leg sets from slipping with respect to one another and minimize the lateral torsion that each leg would experience. We settled on a tricycle system with the back two leg sets powered, separated by a differential, and the front leg set on a swivel.
After deciding on our tricycle layout, we had to optimize the foot path to have a smooth ride. I took full responsibility for this phase of the design, going through multiple iterations of a four bar linkage. The important parameters were lift height, to raise above bumps, levelness of ground contact, and length of stride. We also wanted to minimize the length of the members to avoid buckling. We settled on a design with a slight rocker, shown below far right, to lengthen the stride to 93 degrees of near-flat travel. This allowed us to combine 4 legs, each offset by 90 degrees, to create a leg set with near-flat ground travel at all points during the rotation of the crank shaft.
Our next challenge was to incorporate the linkage legs into a chassis capable of supporting a rider and executing turns. While two members of the group split off to design the planar-gear differential, I led the design of the modules for the linkage legs and the chassis assembly. Three identical linkage leg sets come together on a bicycle frame to form the chassis. The beast is steered by "reins" attached to the existing headset of the bike, and a bicycle seat was welded to the back of the chassis for rider comfort.
The entire assembly is fully functional and moveable in Solidworks. I ran Motion Analyses and Finite Element Analyses to validate the designs before committing to construction. The design is modular, allowing for easy assembly and repair.
a single linkage set
full-scale indoor test
completed rear linkage sets
competition day: the joust
Our completed horse-beast was a total success. It walked, turned, and jousted with strength and grace. I could not be prouder of the team or the finished horse. Today, it stands on display in the atrium of the Thayer School of Engineering as an example for future classes.