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Student rocketeers modulate solid-fuel rocket motor thrust with Zynq-based NI myRIO controller + lotsa smarts

Xilinx Employee
Xilinx Employee
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Solid-fuel rocket motors are usually binary things: they’re either on or off. Once on, they burn until empty. A student design team at the University of North Carolina Charlotte decided to put some analog control into their solid-fuel rocket by modulating the motor’s thrust with a variable-geometry nozzle extension; the purpose is to use thrust modulation to achieve desired altitudes repeatable accuracy. A ceramic-sleeved metal cylinder serves as a variable nozzle extension and a high-torque servo motor controls the effective length of the extension to modulate rocket-motor thrust during the 3.69 second burn. Extending the cylinder gives the exhaust gasses a larger expansion chamber causing under expansion of the exhaust, which in turn decreases thrust and acceleration. A control loop constantly attempts to match the pre-loaded acceleration profile by adjusting the size of the expansion chamber with the objective of attaining a targeted altitude of 3100 feet.


How well did it work? Here’s the graph:




Modulated Solid-Fuel Motor Rocket trajectory.png




A Zynq-based National Instruments (NI) myRIO embedded data-acquisition system and controller operates the high-torque servo using a 50Hz closed-loop PID algorithm programmed using NI’s LabVIEW graphical system design environment. The myRIO controller operates the PID loop while taking data from many sensors including an accelerometer and 3-axis strain gauge rosettes. A second myRIO controller in the rocket’s payload section records atmospheric data including pressure, humidity, and ambient light; GPS position data; and a USB-connected video camera.


According to the student team, the use of LabVIEW and NI hardware was essential to the success of this project. With the limited space and processing speed required, the NI myRIO fulfilled all of the project needs in one package. The built-in Wi-Fi feature of the myRIO allowed the team to access the myRIO without disassembling the entire vehicle, eliminating the need for a connection port, simplifying the launch process, and saving critical space in the payload bays. The myRIO’s 64-pin connector allowed for connection of additional sensor equipment above and beyond the minimum requirements. The myRIO’s USB connector and the sheer number on both analog and digital I/O ports made for easy assembly and wiring of the entire system.


The project began in May 2013 with the development of the thrust modulation idea. From the development stage, the team designed and constructed a solid motor test stand and conducted both static and dynamic testing to verify the theory. In September 2013, construction on the half-scale rocket began, which also tested the theory statically. Construction on the full-scale vehicle began in January 2014. With the release and delivery of the first NI myRIO in late February 2014, payload subsystem construction began with the first full-scale test flight with payload in March 2014. From concept to completion, the project took eleven months with a little under two months between the release of the myRIO and the completion of the payloads.


Here’s a very short summary video showing construction, testing, and flight of the rocket:





Note: This student project was one of three highlighted at the NI Engineering Impact Awards dinner during the recent NI Week held in Austin, Texas.