MSXII Electrical System
- Titus Chow
Goals
- Increase consistency between boards
- Improve ease of debugging (hardware and software)
- Reduce board complexity and cost
- Reduce off-board components
- Better LV granularity
- Add features to make the car more practical
Background and strategic fit
MSXI's electrical system had issues with inconsistency between boards. In addition, many of our circuits were over-complicated, off-board, or unused. This made it difficult to actually manufacture and test our systems, delaying the system bring-up until within 48 hours of the race. Moving towards a system with more shared parts and reduced board complexity will ease inventory management and debugging.
We also had issues with the supplementary battery being drained. In retrospect, this is because we were powering too many things through the powerpath interface when we should've been running them through the DC-DC directly.
In addition, in our move to make a more practical car, we would like to add a dashboard.
Assumptions
- Every board will require a shared set of components - MCU, CAN, 12v to 3.3v, debug LEDs, SWD, serial output (for debugging)
- Most of our boards can be simplified or broken up into multiple boards
- We can consider the electrical system as 4 main subsystems - power management, battery management, driver controls, and telemetry
Requirements
| # | Title | User Story | Importance | Notes |
|---|---|---|---|---|
| 1 | Standardize common components | To ease inventory management, we want to standardize on a common component size. In addition, we should design a common set of blocks that can be used across multiple boards. | ||
| 2 | Reduce off-board components | We shouldn't need to plug in and unplug 30 different things to work on the electrical system. If we can move more components directly onto the PCBs, this will make manufacturing and maintenance much easier. | Themis and the PJB are two examples of this problem. Plutus also has many off-board connectors. | |
| 3 | Isolate system responsibilities | We need to minimize unnecessary interaction between systems as much as possible. It doesn't make sense for press the horn from the driver controls and have the power management system actually honk the horn. This is will also reduce off-board connections. | ||
| 4 | Determine power requirements | We need to determine what needs to be on and what can be turned off at certain times. We also need to consider current draw through our connectors and how to prevent ground loops. |
Questions
Below is a list of questions to be addressed as a result of this requirements document:
| Question | Outcome |
|---|---|
| How will the killswitch be handled? | |
| What component size are we deciding on? How will we enforce it? | |
| How can we move more off-board components onto PCBs? | |
| What will our electrical network look like? How will CAN be handled? |