Power Subsystem - Carleton-SRCL/SPOT GitHub Wiki
The power system is responsible for delivering 5 V and 12 V to the various on-board components. A 24 V, 10 Ah battery supplies power, in parallel, to a 5 V and a 12 V voltage regulator. The 5 V regulator has a throughput of 30 W, which is used to power the on-board computers, cameras, and other sensors. The 12 V regulator can output 350 W of power, which is used to drive the solenoid valves, reaction wheel, robotic arm, and any future 12 V components. Push terminals are installed for each voltage level, such that adding a new component requiring power is a trivial task. Cables are run to the upper and lower decks that provide 12 V and 5 V of power, so that any component on any deck can access power. The components used in the power subsystem are listed in the Table below.
| Name | Manufacturer (Supplier) | Part Number | Use |
|---|---|---|---|
| Battery | Hui Electronics (aliexpress.com) | BCC-Shenzen-24V-10Ah | Onboard |
| Battery Charger | Hui Electronics (aliexpress.com) | XVE-2940200 | On bench |
| Battery Charger Plug | Switchcraft Inc. (Digikey) | SC1381-ND SC1382-ND |
Installed on battery chargers |
| Control Panel Jack | Switchcraft Inc. (Digikey) | SC1390-ND | Onboard |
| Battery Jack | Tensility International Corp (Digikey) | 839-1144-ND | Onboard |
| Battery Plug | MPD (Digikey) | 172-4204-ND | Onboard |
| Power Switch | E-Switch (Digikey) | EG1515-ND | Onboard |
| 12 VDC Regulator | CUI Inc (Digikey) | VHB350W-Q24-S12 (obsolete) VHB350-D24-S12 |
Onboard |
| 5 VDC Regulator | CUI Inc (Digikey) | PYB30-Q24-S5 (obsolete) | Onboard |
| Push Terminals | TE Connectivity (Digikey) | A104596-ND A104586-ND |
Onboard |
| Arduino Pro Mini (5V/16MHz) | SparkFun Electronics (Digikey) | 1568-1055-ND | Onboard |
| Breakaway Male Header Pins | Molex (Digikey) | WM50017-36-ND | Onboard |
| Protoboard (100mm x 75mm) | DFRobot (DigiKey) | 1738-1005-ND | Onboard |
| Protoboard (78mm x 58mm) | DFRobot (DigiKey) | 1738-1001-ND | Onboard |
| Micro USB Cable, Plug Up | CNC Tech (Digikey) | 1175-1694-ND | No longer used (power to RP3s) |
| TTL-232R FTDI Cable, 5V | FTDI Ltd (Digikey) | 768-1029-ND | Yes, to program Arduino Pro Minis |
The following Figure shows the main components how they are installed on the avionics deck of the spacecraft platforms.
A control panel was designed that has a main power switch, as well as status LEDs. An Arduino Mini microcontroller is installed on the control panel and provides some basic functionality to the platform. It acts as a battery monitoring computer. It does this by measuring the voltage across a voltage divider on the 24 V battery line, such that the battery voltage is scaled to a range readable by the Arduino Mini. When the battery voltage drops below 23.8 V, a yellow light on the control panel is illuminated, signaling to the operator that the battery needs to be charged shortly. A charging port is incorporated into the control panel, such that no disassembly is required to charge the battery. If the operator does not charge the battery as it continues to drain, the Arduino Mini will trigger the emergency stop and repeatedly flash the low battery LED when the battery voltage drops below 23.3 V. This is for safety, as when the battery voltage drops too far, the battery circuitry cuts power suddenly. By triggering the emergency stop, all non-critical components are safely stopped. A schematic of the power system is shown in the Figure below.
An updated version of the power system is given below with the following changes:
- includes specifics on the circuitry for the Control Panel
- corrects direction of MOSFET from previous version
- updated with Jetson Xavier NX as main computer, with relevant GPIOs highlighted (as of Jan 2024)
- updated GPIO resistors to represent current configuration (1k Ohm instead of 10k Ohm)
- modified 22k Ohm pulldown resistor for thruster GPIOs to span GND instead of the e-stop MOSFET drain
The power subsystem is significantly overdesigned, due to the overall platform design changing so rapidly after the power subsystem was purchased. This is convenient for the operator, as the batteries last a very long time between charges. Also, there is a lot of additional capacity for future components to be added.
The GPIO pins that actuate the thrusters are specified in the "pwm_scripy.py" file. These are the pins specified in the most recent (Jan 2024) electrical diagram using the Jetson Xavier as the main computer.
The image below gives the circuit for the electromagnet on BLACK, which is powered by the 12 V line. The white wire connects the onboard computer to the gate of the MOSFET and sits at a +3.3 V potential to turn the magnet on.
In the most recent version of this circuit with the Jetson Xavier as the main computer, the 470 kOhm resistors were replaced with 1 kOhm resistors. This ensures the magnet operates at full strength.
Below are images of the front and back of BLUE's control panel, for reference, of how the electrical schematic was implemented. The circular hole leaves room for the battery charging jack, and the rectangular hole leaves room for the rocker switch. A model of the breadboard used on the bottom deck for power the solenoids using MOSFETs is also provided below.
