Zero Test Bench Software Stack

Author: Cristian Bicheru

For questions, feel free to reach out to [email protected].

Introduction

The hardware stack consists of a laptop and a Raspberry Pi 4B. Each device has its own software located in the appropriate directories. ZeroMQ is used to link the monitor software on the laptop to the controller software on the Pi. Onboard sensors and their settings are defined in sensors.cfg.

zerolib is a library containing code used by both the monitor and the controller.

The Engine Test Programs directory contains valve throttle profiles to be executed during a cold flow or static fire test. The format is a 4 column csv file. The first column is the time (in seconds) since the test begins, the second column holds the desired fuel valve throttle position and the third column holds the desired oxidizer valve throttle position at this timestep. The last column controls the torch ignitor state. A 1 turns the ignitor on at this timestep and a 0 turns it off. Between timesteps, the throttles are linearly interpolated based on the current time.

Testing Procedure

Once the all of the hardware is setup, an ethernet link should be established between the laptop and the Raspberry Pi. Then, the battery pack is connected to the electrical box.

At this point, an SSH link is established to the Pi. The pigpiod service is started using ./start_pigpiod.sh. Then, the controller is started with ./start_controller.sh. Once the controller software is finished initializing, the monitor should begin to show live data collected from the controller. Any warnings/errors from the Pi are shown either in the SSH console or the monitor software.

Pi Setup

To improve the reliability and performance of the Pi, it is running a custom compiled kernel with PREEMPT_RT enabled. The Pi is also overlocked to 2 GHz.

Video Feed

To establish a live camera feed, connect an android phone to the Pi via USB and run the ./start_camera.sh command. This will forward the 8080 port on the phone to 8081 on the Pi. A camera server (e.g. IP Webcam) can then be run on the phone (broadcasting on port 8080) and accessed on the laptop.