CMS is the current rocket being developed by the Purdue Space Program liquids team. I have been a member of the team since 2021 and have been the teams avionics lead for the entirety of the CMS project. As lead I have my hand I every aspect of CMS avionics systems however I focus mostly on hardware and over all architecture and appointed Sagar Patil to be an avionics software lead. 

CMS avionics Architecture

The CMS avionics architecture is result of months of collaborative work by me Sagar Patil including the majority of part selection. 

*Sensor positioning and the need for sensors was collaboratively decided by the team as a whole .

Vehicle SV-2 Diagram 

*out of date - current versions have all places holder connector blocks defined 

Bang Bang Boom Box !! (b⁴)

The B⁴ is a modular hardware testing platform that I created to support full stack avionics testing, remote software unit testing, and integrated testing with other vehicle subsystems. The B⁴ uses three Drok serial addressable power supplies allowing me to dynamically change the power being provided to the avionics hardware to support different test configurations, or to simulate different conditions that the system may encounter. The main purpose being to be a flexible system to test and develop avionics hardware and software that can be easily moved to the test site or just used in a dorm room. 

To support remote software development the B⁴ has been upgraded with a Raspberry pi 4.0 and ethernet switch. The PI can control the Drok power supplies and is connected to the network switch. To allow for fully remote testing the boot select, reset pins, USB serial, and debug pins of the development boards are also connected to the GPIO of the Pi. This configuration allows for the entire avionics hardware and software stack to be deployed and tested into this box with each of the avionics boards connecting into the network as they would be under launch conditions.

the first prototype board dev - 1

While Dev-1 tried to implement almost every aspect of the avionics system, it was primarily targeted at testing the implementation of the RP2040 micro controller. While every other part of the board proved to not be successful, it taught me a lot about PCB design. The RP2040 micro controller was successfully implemented and functioned as expected.

I was solely responsible for the PCBA stack up, ethernet & processing hardware sections as well as the ADC input channels including their assembly. However as lead I had a hand in all hardware design despite the power and thermal couple measurement systems being implemented by other members of the team.

development boards 

From the lessons learned about building prototype hardware with DEV_1 I decided to make a series of test boards each focusing on one subsystem. The dimensions of the test boards optimized the cost for manufacture with jlcpcb, with each board being 100mm x 100mm 4 layer with impedance control.  

bang Bang test board

I developed the Bang-Bang Test board to be the minimal viable product required to test the Bang-Bang control loop with fluids hardware. The test board proved to be successful demonstrating the implementation of the high frequency ADC, soliod actuation circuits, and pyro technic channels. 

REV_1

REV_2

REV_3

This revision is currently undergoing exadurated testing in B⁴ to ensure reliability. TC testing is still pending an aims to validate the use of thermocouple with a high density D-sub termination.

*mostfet selection was completed by the Power Systems RE  

Ethernet test board

I made the ethernet test board to validate my ability to integrate ethernet hardware without some of the troubleshooting shortcomings of DEV_1. The main goal of the board is to prove #1 the function of the W5500 ethernet bridge passing through a high-density d-sub. #2 the ability to connect the W5500 to a COTS BotBlox network switch. #3 the ability to operate the BotBlox switch with magnetic coupling. #4 the ability to connect a magnetically coupled BotBlox port to a magnetically coupled W5500.

REV_1 

REV_2

Demonstrated W5500 magnetic isolation for connection to external ethernet devices. 

REV_3

REV_4

Demonstrated W5500 to BotBlox Switch functionality 

RP2040 Test board

This board is meant to further validate the stability of my RP2040 implementation and test maximum achievable SPI speeds in different layout conditions using SPI flash chips.

Engine modulation unit (EMU)

EMU is responsible for two flight critical operations. Operation of a bang bang system that regulates the propellant tank pressure through the actuation of solenoid valves. This control loop requires EMU to have two delta sigma ADC inputs for tank pressure transducers and solenoid actuation circuits. Its second flight critical task is the ignition of the engine and the actuation of the main pyrotechnic propellant valves. While not critical for the flight of the rocket, some of the other functions of EMU are critical to the function of the avionics package. EMU serves as a hub for the avionics system, hosting that network switch and distributing power from the power systems board to the rest of the vehicle. 

REV_1 

I made this first revision alongside the development of its subsystems and as such trace routing was not optimal and it wasted board space.

REV_2

I designed the second revision after finishing most subsystem development boards. This allowed me to create a much more compact design with far better routing. Physical mounting of the board into a full metal enclosure to protect it from FOD and prevent damage was taken into account along with the forces that the board will experience during flight from acceleration and vibration of the SMT components and wire to board connections. Some changes that address these issues is the use of vertical panel mount D-sub connections that will transfer the load of the wire harness through the metal enclosure opposed to the PCBA and the use of 2216 epoxy potting of SMT components.