Custom 2S ESC (~1/10) with I2C, TCS, ABS and more!
RaceESC is a compact, lightweight, 40A capable esc with an I2C connector for other projects (telemetry, etc). Will run a version of AM32 with a custom TCS and ABS algorithm.
Waiting on a reviewer. We'll let you know as soon as there's a decision.
hey - this is amazing but can i get a cost breakdown? 420 seems incredibly high, but this is a v cool project!
Github repo for the project is live, put together some documentation for the esc, an collated files and wiring diagrams.
Layout final and enclosure cad
layout 3 Version 2, completely rerouted it made it better, its still tight though
Finished version 1 of the layout, apart from some minor quirks.
Added a charge pump fromt the regulated 5V to double the voltage to regulated 10V, for the gate driver.
I dont like this layout. It sucks. Areas to improve:
Finished routing the board on 4 layers, I put the high side FETs on the top, and low side fets on the bottom to keep the board compact, optimised the layout of my buck converter to reduce EMI, by reducing loop area, and used a logic one side, power on the other design. I want to change some things with the board, especially the boost converter, which is way overkill at 10V/2A… I only need to supply the gate driver with like 10V/20mA.
Mostly finished the schematic! Things added:
Gate driver:
Allows MCU to drive mosfet gates at high currents (like 1.2A), which the MCU pins cannot source. Also allows the use of bootstrap capacitors which I can use to switch the high side FETs. I went with relatively large bootstrap capacitors as this is a relatively low frequency ESC.
Mosfets:
6 High currrent 3.3x3.3mm N-MOSFETs arranged in a half bridge fo the ESC. As this esc connects to a separate board with current sensors already on it, The power layer does not include any current shunts
MCU:
To read Back EMF from the motor, manage signals and control the mosfets, you need a microcontroller. For this ESC I went with the ARTERY AT32F421 because it is cheap and adequite for this application. I had to break out the debug pins (GND, NRST, SWDIO, SWCLK), add decoupling capacitors and pull up/down resistors. The AT32 is also useful because it has a comparator (compares two voltages and outputs 1 if one is higher and 0 if the other is higher) in it which I can use to read the motor Back EMF really quickly.
Feedback network: Splits the phase voltage (voltage on the wire of the floating (unpowered) phase of the motor) using a voltage divider, so that the MCU can read it. 3 resistors for each phase + 1 feedforward cap for high frequency noise.
Connectors:
The board has a 5 pin JST SH connector which carries 5V, GND, SCL, SDA and GPIO (broken out I/O pin from the control pcb). This allows the master board (the telemetry/control board for the car) to control the esc and link the ESC MCU to the master boards sensors (EG the IMU for traction control).
3.3V regulator and indicators:
3.3V LDO drawing power from the buck output to feed the MCU. 2 generic indicator LEDs, one connected directly to an MCU pin, one to GPIO pin on the interface connector, which could be used to indicate a complete connection between the telemetry board and the esc.
Power capacitors: For bulk capacitance (for large voltage spikes), two low-esr polymer 220uF capacitors were used. Each MOSFET gate also gets a 4.7uF and 100nF capacitor to smooth out voltage spikes caused by sudden changes in current caused by the FET switching on.
Now comes the fun part: ROUTING!!
Boost converter desigh headache, lapse isnt working. WHY ARE BOOST CONVERTERS SO COMPLICATED?? Spent a solid 2-3 hours trying to wrap my head around the “right half plane zero”, Finally understood it enough to finish the schematic, (this devlog actually too 7 hours). The bit that was the hardest was the small RC (resistor capacitor) network connected to the COMP pin, which allows the chip to dampen oscillations on the voltage feedback loop. It required complex numbers which I have NEVER used before so this was scary. The purpose of the buck converter is to supply 10V to drive the mosfet gates, which will help efficiency (lower RDS on), and make sure the UVLO on the gate driver chip doesnt trip and shut off the motor if the battery voltage dips below it (eg under heavy load voltage drips). The boost converter should be capable of 10V/2A, which is overkill for the gate driver so I might look at compacting it in the future
Turns out the MPS2315 isnt available on JLC assembly, so I have to choose a new buck converter. Chose this TPS54302 Buck converter from TI and the documentation for it was really really good. Turns out the schematic for this also has less parts and has the added bonus of zero (or very little) dropout (dropout is the minimum input voltage to still output 5V). The buck will still be able to provide 5V/3A as a BEC - not bad. Used a 22uF input capacitor and 2x 22uF output capacitors. The input pin “EN” lets me set a UVLO (under voltage lock out), where the chip will turn off if the input goes below a certain voltage (EN takes input from a voltage divider). The chip has internal weak resistors for EN, so the standard UVLO is ~4.4V, which is perfect, which is why I left EN as no connect.
