19.1 Project Proposal
Introduction
The idea of a jumping rabbit toy/mechanism came across within our group’s brainstorming stage and resulted in the most favorable idea in terms of complexity, challenge, and relevance to the class. It’s also an interesting branch off of what our class scope is considering the amount of dynamics involved. We know that the idea is doable from existing products and research: hopping frog toy mechanism, avian-inspired multifunctional legs (Fig 1), inspect jumping mechanism; we are also aware of the difficulties and challenges given the struggles of previous attempts in this class. Thus, we aim to limit our scope to a functional hopping mechanism that can achieve respectable airborne time before expanding its capabilities in a fully unaided dynamic environment.
Fig 1
Problem Description
To achieve a physical mechanism capable of jumping airborne, there are two main issues we need to tackle. First, the mechanism has to have a high enough theoretical energy density ceiling that allows it to reach a certain height characterized by its maximum achievable potential energy. Second, the mechanism needs to ensure its energy transfer efficiency over the entire jumping process is high enough to pass the airborne threshold. In practice, we expect many variables complicating efficiency analysis, and we will aim to construct our scope around mechanism-related factors that impact the system’s efficiency, and assume basic, ideal behaviors of numerous subsystems to simplify our model.
Proposed Mechanism
After several design iterations, we decided to implement a motor-cam-driven 4-bar mechanism to enable the controlled storage and timed release of energy in a torsion spring, which will be positioned at the joint where link L2 connects to the ground. This design draws significant inspiration from the biomechanics of animals that generate powerful force impulses to perform forward jumps. The cam profile will be specifically designed to gradually wind the torsion spring as it rotates, allowing energy to build up smoothly over time. A strategically placed drop-off point on the cam will serve as the release trigger—once reached, the cam will suddenly reduce its contact with the spring-loaded linkage, unleashing the stored energy. This release will generate a rapid impulse force that drives the leg, which is designed as an extension of the coupling link, to execute a jumping motion.
The cam will remain in continuous contact with an arm extending from the input link, ensuring synchronized movement throughout the mechanism's cycle. The cam portion of the assembly will be situated toward the front of the rabbit toy, where a compact and lightweight servo motor will drive its rotation. This design allows for both precise control of the timing and magnitude of the jump, while maintaining simplicity and minimizing weight, both essential for efficient and repeatable jumping performance.
Proposed Scope for Final Work
As stated before, we will first focus on the basic function of having the robot get airborne based on our energy/efficiency analysis. In practice, this might involve external aids to the system in areas such as weight relief and externally supported DOF constraints. Next, we will perform a more rigorous analysis that examines the impact on jumping performance due to different link configurations or ratios. Finally, we will pursue a more complex and independent system that more aligns with the full projection of a hopping bunny toy or bird toy.
Preliminary Design Ideas
The CAM system will roll up the string to prepare the actuation. This extends the extension spring near the feet and compresses the two compression springs above, storing energy before release. There is also energy stored in the spring that propagates the CAM, which, when pressure is applied, is lost, causing the CAM to roll backward, releasing the string. The two compression springs and the extension spring want to return to their natural state. As the string loses tension, the extension spring will compress, pulling the mechanism forward, and the two compression springs will extend, initiating updraft motion. This sequence of action will repeat to create a perpetual jumping motion until interfered with externally. The leg mechanism is non-grashof.