Power system for self-driving RC model - Page 1
Forum section: electronics / projects

author: AndBondStyle
author_rank: Newbie
timestamp: June 23, 2024, 07:10:42 pm
content: I'm working on designing a power system for a prototype RC car with self-driving capabilities. Currently it consists of a 6S li-po battery and a number of generic XL4015E dc-dc converter modules, supplying various voltages for different components. Those components include:1. ODrive v3.6 (BLDC driver) — has integrated converter, so connects to the battery directly2. x2 Servo motors — 8.4V nominal3. Teensy 4.0 and miscellaneous sensors — 5V with internal LDO to 3.3V4. Jetson Orin NX — accepts 9-19V, currently runs at 12VWith new revision of hardware I want to support some new features:1. Hot swappable battery — ability to quickly swap the main battery without going offline (i.e. rebooting the jetson and all the electronics). That means there should be some hard-mouted small reserve battery (or super capacitor bank?) or that the car should use two identical batteries which can be swapped sequentially. The last option I want to avoid, because there is not much free space available.2. Park mode — in order to do some debugging, software/firmware updates, captured data downloads etc. without powering from the battery, I want an ability to power the system from an external PSU (i.e. 19V notebook power brick or even USB PD 20V input). In this mode, all the electronics should be online, excluding the BLDC motor (it requires too high currents to operate).3. Monitoring — while not being a must-have feature, it’s always nice to have an ability to monitor voltages and currents for different power rails (for the battery itself, servo motors and jetson at least)4. Standby — currently there is no way to completely power off the system without unplugging the battery. Also there’s no BMS for the battery, so if left plugged in and unattended, it drains itself to death (already happened once). In the new version I want to implement some sort of power button. It can be a simple relay switch, which I don’t quite like, because there are some large current spikes when connecting the battery because of BLDC driver capacitor bank. Maybe it can be solved with a solid state relay of some sort? Also I was wondering if it’s possible to use the BMS for this purpose: it usually contains an array of mosfets, and it should be possible to force the BMS controller into “off” state. While browsing some datasheets for BMS controllers, I found that some of them have an option to connect in series (i.e. if you want to support 10S battery, you can daisy-chain two 5S controllers), so it should be possible to use that daisy-chain pins to force off state.Here is the overall system diagram draft I sketched so far. For now, please ignore the “EN logic power” and “EN motor power” blocks — those was some plans of integrating a killswitch (a physical button or RF receiver that can immobilize the robot in case of a critical failure or loss of control). Also, this diagram does not include the reserve power source to implement hot-swappable battery. Initially I was planning to use “AUX power input” for that purpose (i.e. a decent USB PD power bank), but an integrated solution feels more convenient.And here are my current questions:1. Can you recommend some modern DC-DC buck converter ICs? Ideally, I want to choose the same IC for all buck converters. Also, maybe some ICs have internal current monitoring and an easy interface with MCU (or maybe it’s not worth it, and it’s better to have an external current sensors)?2. What do you recommend to implement the “power mux” block? The “AUX power input” should always take priority over battery, but the battery should not be charging from it. Also, the battery voltage and aux input voltage can be different, and I’m not quite sure how to deal with transients that can occur when switching the power source.3. What do you recommend to implement a proper standby (shut off) mode? Should I use a simple contact relay or solid state relay (or a mosfet array)? Is my idea of forcing the BMS to shut off feasible?4. Any overall suggestions and criticism are always welcome. I feel like this project is on the edge of my current skills, and maybe I’m over-engeneering stuff, so I want to get all possible advice I can get. Therefore, thank you a lot for your time helping me.

author: kevin.gibbs
author_rank: Regular Contributor
timestamp: February 12, 2025, 12:37:54 pm
content: Question 2: I think your voltage stabilizers should be able to handle the transients. During the changeover, the current consumption should be low—after all, the motors are not running at that time.For the replacement battery, I suggest making additional terminals. First, you connect the second battery and then switch to power from it. Even with the motors, your current consumption is not so high—switching can be organized on MOSFETs. Just don't forget to consider protection against both batteries' parallel connection.