ME112: Remi (Jumping Robot)

What: A jumping robot for ME112: Mechanical Systems Design. The goal was to create a robot using a given motor that jumped as high as possible. Our robot jumped 7.75 feet on the final test, 18 inches higher than the next best robot and more than double the class average.

My role: I worked on this project with a team of five, and I focused particularly on the the mechanical design of the links and the design and component choice of the electrical system. I became a Course Assistant for this class the next year (2019-20).

When: Winter 2019

Exerpt from the Report

We designed Remi the jumping robot with the goal of creating a simple and powerful structure while minimizing weight and frictional losses. The configuration of the six links reduces potential moments and degrees of freedom. The symmetric diamond shape loads all of the links in axial compression and therefore avoids in-plane bending moments, while the geared link ends further reduce Remi’s movement to one degree of freedom. The joints were machined to be press-fit on the steel shafts and have nylon washers that hold ball bearings in place to constrain out-of-plane motion and reduce buckling––an issue that we ran into while testing. This ultimately limits the spring constant we use to k = 2200 N/m. The design additionally concentrates mass on the top of the structure to maximize the initial upward momentum after release and before the base leaves the ground. The link material is acrylic so they could withstand high axial and bending loads, the lower links are slightly thicker to reduce out-of-plane buckling, and the bases and fences are made out of basswood to minimize mass.

We conducted an initial thermal analysis to find that the motor, running at nominal parameters, would reach a steady state temperature of about 200˚C. This was assumed to be an upper limit for motor temperature. A thermal Matlab model showed that the motor could handle much higher voltages than the nominal parameters suggest. We also confirmed that overheating would not be a mode of failure through empirical testing on a power supply.

Remi’s release mechanism employs the use of Nickel Chromium (Nichrome) wire. The fishing wire that pulls the motor component down is connected to both sides of the gearbox shaft and is tensioned by a shaft secured to the base. Once the system fully compresses, the geometry completes a circuit that heats a loop of Nichrome wire, melting the fishing wire near the gearbox shaft. We chose this release mechanism because it does not cause any frictional losses and it allows us to operate the motor close to its peak power for the duration of the pull-down.