Hopper Design Project (IDEA 170)

IDEA 170, fall 2023. This task in my freshman fall was to create a biologically inspired mechanism that hops after waiting between eight seconds and a minute, built only from a predetermined kit, with design goals of my own.

I set myself the goal of making the whole frame from the kit's single aluminum plate, which pushed me toward a light, compact, space-efficient design.

Stage 1: getting off the ground

The first design was a triangular frame with two flaps that swing into the ground and push the hopper into the air. My first laser-cut prototype worked, but only jumped a couple of centimeters, so I moved to iterating.

Stage 2: component evolution

Every part went through many versions, laser cut in 1/8" MDF and checked in SolidWorks assemblies.

• Connectors: I tested where material could come out, then added vertical as well as lateral braces after a cross-braced version collapsed under the band's force. The bracing pattern, inspired by spiderwebs and tensegrity, carries through the whole hopper.
• Frame: I kept material at the interfaces, kept the outer frame thick, and hand-cut an aluminum version to gauge weight.
• Flaps: the most iterated part, because they had to be light to swing fast and strong enough to hit the ground at speed. They kept breaking at the same point, so I curved the cutouts to ease stress and added material where they failed. I also twisted the resistance bands during installation to stop them tearing.

Stage 3: how to wait

Controlled failure of MDF clips and deformed wire clips either stuck or released at once. The working timer pulls a wire through an earplug, using friction-creep to slow the release.

Results

• The finished hopper weighs 9 g, with a 7 g frame (SolidWorks estimates 6.56 g).
• The frame's volume is 10,212 mm³, which would fit in the 12,290 mm³ aluminum block. Unfortunately, Wesleyan's waterjet cutter wasn't in operation that semester, so I had to stick to MDF for the final.
• It reaches close to a meter and waits about 30 seconds.
• Stored energy was 0.598 J against 0.076 J of gravitational potential energy, an efficiency of 12.7%. Much of the flap motion happens after takeoff or is lost to impact, hinge friction, and the timer.