This document introduces the different choice we needed to do regarding the flight computer and the sensors that we will use in Ather Speer
We decide to build a custom PCB with only sensor and no breakout as the other fc are made in the ERT.
High customizability
We can use more sensor for redundency
Cheapest method
The hardest method to integrate and test
It needs more time to build
We decide to build a custom PCB but we integrate the sensors with breakout modules.
Moderate customizability
Method easier then the previous
The breakout usually have filters integrated to the module
It cost more then the fully customize FC
Only one sensor used to minimize the cost
We decided to go for the fully customize FC so that we will learn more and we will have redundency sensors.
Only 2 wires needed (SDA, SCL)
Every device can be connected with the same 2 SDA and SCL wires
Max speed around 100 Kbit/s (standard mode)
Every devices must have a different adress
Max speed around 60 Mbit/s
Easy to set up
4 wires need (MOSI, MISO, CLK, CS)
Each device need a new CS connected to the main board
We still need to figured it out
Widely used by the ERT
Lot of pins
SD card reader integrated
1 Mo of RAM
Test need to be done to know if the gyroscopic sensors still works at high accelerations
The code must detect when the range of the IMU is exceed and switch to the other accelerometer
Less known
SD card reader integrated
520 Ko of RAM
We decided to choose the teensy 4.1 as it is well know in the ERT.
It was the only choice in our mind because it is used in the ERT for will and is highly used for various model rocket projects.
We use an IMU to measure the angular displacement and the acceleration at low acceleration, but the rocket need to reach mach 1.2 so we will have a high acceleration and the IMU wont work at that range so we use a high range accelerometer when we exceed the range of the IMU.
The IMU sensor selected has already been used in the ERT
Method use in the ERT in the past and in other model rocket projects
Test need to be done to know if the gyroscopic sensors still works at high accelerations
The code must detect when the range of the IMU is exceed and switch to the other accelerometer
We only use one gyroscopic and one accelerometer sensor.
The high range accelerometer is less precise than the IMU with a lower range
We decided to go for the IMU + high range accelerometer so that we use existing method which we know that will work.
We use only one sensor and we get the difference of pressure between the nose and the static pressure.
Easy to find module
We can use have some redundancy without loosing to much space
To compute the velocity with the pressure, we need to divide pressure at the nose cone by the static pressure, so there will be approximation
We use two sensors to get the quotient of the pressure at the nose cone and the static pressure.
Easier calculation to get the velocity
We can use have some redundancy without loosing to much space
we need less tubing in the nose cone
Take more place in the PCB
We need 2 module to compute the quotient of the pressures
We decided to use two static pressure sensor to simplify the computation and the design of the tubing inside the nose cone.
We can measure easily the temperature where we want
Easy to integrate
Use of a TMP1075DSG mounted on the board to measure the temperature.
Easy to integrate
Use only I2C communication
As their is no disadvantage to use both methods we will use all three methods to get temperature in differents region of the rocket.
We decided to use the most commonly module used in the ERT, the Lora rfm95
Module used by Firehorn I avionic but not necessarily a good gps breakout
Antenna built in
Can be use either in SPI or I2C
Only exists in breakout format
U block GPS already used by Icarus
Antenna built in
We can only use I2C in high speed mode (320 Kbits/s)
We want to try using the U block GPS because Firehorn had issues with their GPS module.