ESP32 processors should make excellent controllers for Dynamixel servos.
Each ESP32 has three UARTs, but one is often used for debugging and data upload.
Timing constraints for RS-486 and servo control often require careful code.
The dynamixel C library has a wide variety of flaws. Beyond being strictly non-functional in its Linux port as of 1/5/21, it allocates and frees memory frequently.
Thus, let us create a C library which is efficient and can be used with the ESP-IDF RTOS for high efficieny.
This library uses 3 pins per output, because most RS486 chipsets require an enable pin.
The pins are configured in:
dynamixel-idf/components/DynamixelSDK-c/include/port_handler_esp_idf.h
The goal is fast response time. We have to level-shift between 5v and 3.3v quickly, experimentation shows the Adafruit implementation of the BSS138 to be sufficient for 4Mhz transport. https://www.adafruit.com/product/757 - note that in this implementation, the "OE" output enable must be left to float.
For the 486 converter, we are using the TI 486 chip: https://www.ti.com/lit/ds/symlink/sn65hvd485e.pdf
The more expensive TI chip - https://www.ti.com/lit/ds/symlink/sn75lbc176.pdf - did not function, so we simply swapped it out.