Final Design

Sponsor and Overview

The sponsor of this project is SEDS UCSD, a student organization on campus that works on liquid rocketry, including self-landing rocket technologies. SEDS UCSD's Riptide vehicle is designed as a testbed for self-landing rocket controls. The goal of this project is to develop a thrust vector control module that can rotate a rocket engine to guide the sponsor’s Riptide vehicle in the desired directions.

The following requirements were established for the TVC module:

- 7° radius gimbaling from central axis
- Withstand 2000 lbf thrust force
- Use two linear actuators provided by sponsor
- Continue motion for 15 seconds
- Mount to Nephas engine and Colossus test stand

A rod-end gimbal design was used to achieve the requirements.

Why Thrust Vector Control?

SEDS UCSD is currently working on a self-landing rocket named Riptide, which will fly to 1,000 feet and land back on the ground propulsively. Using this vehicle and engine, SEDS will be competing in the Collegiate Propulsive Lander Challenge (CPLC). The first milestone of the CPLC challenge is to demonstrate an engine fire using a thrust-vector control system.

TVC systems are the main method of direction control for propulsive landing rockets.
By gimbaling the engine, the vehicle can fly towards different directions.
The final stage of the CPLC competition requires landing within a 10 meter circle designated by the competition organizers.

Description of Final Design

A design was created using rod-ends to provide clearance for engine components in the center of the gimbal.
Gimbal has 3 separate plates for manufacturability
Maximize clearance while minimizing overall length for engine clearance off the ground
7075 aluminum for strength without sacrificing weight

The team worked on the following four components to create a TVC module:

Thrust Structure: absorbs compressive forces, mounts to test stand and vehicle
Rod-End Gimbal: provides freedom of movement in two-axes
Clevis Arms: mount linear actuators to sponsor’s Nephas engine at the required angle to enable 7° of movement, designed to withstand engine vibration
Actuator Electronics: enable communication between Riptide electronics and linear actuators to draw a circle

All of the components were designed for in-house manufacturing on campus

Rod-End Gimbal

Thrust Structure

Clevis Arms

Actuator Electronics

Thrust Structure

Thrust structure with:
- Modularity to test stand and rocket
- Plumbing clearance
- Actuator mounting points
Designed for compressive forces and modular mounting
Ease of manufacturing
Modularity tested and confirmed
110% compressive static force confirmed (2200lb)

Rod-End Gimbal

Design: Three plates joined by four rod ends

Each part to be one-sided CNC operation aside from middle plate
Close fit holes for 10-32 fasteners
Clearance and lightweight, easy to assemble and take apart

ANSYS FEA results indicate 1.2 factor of safety on the gimbal design
Upper plate was constrained as a fixed support and the thrust load was applied to the lower plate
Bearings were modeled with freedom of rotation, not bonded joints

Clevis Mount

Hardware Stackup Diagram

Length of arms dictated by gimbaling angle requirement (7 degrees)
Hardware stackup to limit movement under vibration
Two parts for ease of manufacturing

Linear Actuator Electronics

20240605_184628.mp4

Required to use Ultra Motion actuators provided by SEDS:

Throw length was shorter than expected but still useable

Integration with Riptide computers:

CAN code used to draw a circle when mounted to clevis arms
- CAN bus: Riptide standard communication protocol
- Phase shifted movement of actuators in sequence with maximum speed and acceleration of hardware
XT-60 connectors used to match Riptide standards

Component Testing

20240320_155326.mp4

PLA Test

Circle successfully drawn
Hardware assembly confirmed
Clearance for plumbing confirmed

Compressive Test

Used hydraulic jacks to test compressive loading
Tested thrust structure at 2200 lbf load
Achieved 1.1 factor of safety at the limit of measurement devices

Hardware Demonstration

20240606_113805.mp4

Concerns and Future Recommendations

Remaining Concerns

Full assembly compressive load testing including gimbal and thrust structure together
Assembly with SEDS Injector
- Injector not delivered yet
- Can't test with real hardware

Recommendations

Start machining hardware earlier to get more tests in
Committing to regular fasteners from the start for ease of assembly and design finalization
Checking the specifications of the sponsor-provided materials (linear actuators) before starting the design process
More thorough design reviews with sponsor earlier on

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