Open Source SMA HDRM
A Hold-Down and Release Mechanism (HDRM) is critical for securely stowing deployables like solar panels and antennas during launch and releasing them in orbit. This project provides a fully open-source design specifically for CubeSats, lowering the barrier to entry for small satellite developers.
Overview
Commercial HDRMs are often prohibitively expensive or proprietary. This project utilizes Shape Memory Alloy (SMA) technology to create a reliable, non-explosive release actuator. The design includes complete mechanical CAD, PCB schematics, and manufacturing instructions.
Key Specifications
Actuation
Shape Memory Alloy
Preload Capability
~1500 N
Power
5V @ 2A (< 2s duration)
Mass
Lightweight Aluminum
Fabrication & Build
All parts are designed to be manufactured using standard CNC milling (Aluminum 6061 T6) and off-the-shelf components. The custom PCB is simple to manufacture with standard Gerber files provided in the repository.
- Mechanical: High-tolerance CNC milled parts for the Base, Slider, and Cover.
- Electronics: Custom PCB for driving the SMA wire.
- Assembly: Detailed step-by-step guide available in the repo.
Development & Testing
The mechanism has undergone rigorous testing to ensure reliability in vacuum environments and under launch loads. The "Blossoming" issue common in boom deployments (as seen in the Solar Sail project) is mitigated here by the robust hold-down force provided by this HDRM.
Lessons Learned: Why it wasn't flown on MOI-1
Despite the robust design, this specific iteration was not flown on the company's first satellite mission (MOI-1). The primary challenge was tolerance sensitivity in the dual-slider mechanism.
The design relied on two sliding elements which required precise tolerances to operate smoothly. While hinges with pin-and-ball interfaces can accommodate loose tolerances, the linear sliders combined with the PCB mounting holes created a stiff stack-up. Since this was the first mission, the team faced uncertainties regarding the manufacturing tolerances of the solar panels and the PCBs.
Furthermore, the solar panels ended up being significantly heavier (~2 kg) than initially estimated, complicating the ground testing equipment setup. A pin-based design with a ball-end would have likely been more forgiving of these misalignments and tolerance stacks.
Gallery
