MOTOR RETAINERS

The motor retainer plays a critical structural role within the rocket's power section. Its primary purpose is twofold: to center the motor concentrically within the rocket body and to support it axially from the bottom during launch and separation. This component is particularly essential due to the "snatch force" experienced at separation, when the payload and power sections decouple and the motor absorb the reactive force without compromising alignment or structure.

Each retainer is designed in Onshape and manufactured from 6061 aluminum, chosen for its strong strength-to-weight ratio, corrosion resistance, and machineability. Throughout the 2023, 2024, and 2025 iterations, the design underwent meaningful evolution. While all retainers fulfilled the same structural purpose, the 2025 geometry differed significantly due to our team’s decision to manufacture our own solid rocket motor—requiring a new interface diameter and altered load paths.

To minimize mass while preserving mechanical integrity, each year's retainer design prioritized weight reduction. The 2023 version, weighing 0.551 lbs, featured large pockets while maintaining a factor of safety (FoS) of 7.0. In 2024, refinement of material distribution and mounting features dropped the weight to 0.488 lbs with an FoS of 5.2. The most aggressive design emerged in 2025: a minimalized ring geometry that reduced mass to just 0.338 lbs while still maintaining a safe FoS of 2.7.

All designs were validated using FEA. The maximum force applied to each design was calculated using the following equation:

This relationship captures the proportional force experienced by the power section relative to the entire vehicle mass during rapid separation. Since both the mass ratios and separation systems changed across years—CO₂ cartridges in 2023 and 2024, and a black powder charge in 2025—the applied snatch forces varied accordingly, and each year's FEA analysis used updated values. These snatch forces were pulled from the OpenRocket simulations.