DynamixelCtrl ACTIVE
About
A small interface board that bridges an ordinary full-duplex UART to the half-duplex TTL bus of Dynamixel servos. Robotis' AX series talks on a single wire, which no Raspberry Pi or Arduino serial port drives natively; the commercial adapters that do are priced out of proportion to what they contain. The board was built because an experiment needed it.
The bus direction is switched by a 74LS245 octal transceiver driven from a dedicated DIR line, with 2N7000 MOSFETs handling level translation between 3.3 V and 5 V logic. Four headers carry the whole interface: Raspberry Pi, Arduino, the Dynamixel daisy chain, and a separate 12 V input so servo power never shares the logic rail. Designed in KiCad, with gerbers and a FlatCAM project for in-house isolation milling.
On the software side, a standalone Protocol 1.0 driver — no vendor library — exercises the board through the four modes of an AX-18A: joint-mode positioning at low and full speed, continuous wheel rotation, and torque control down to free-wheeling. Validated at 1 Mbaud on an Arduino Mega.
The bus direction is switched by a 74LS245 octal transceiver driven from a dedicated DIR line, with 2N7000 MOSFETs handling level translation between 3.3 V and 5 V logic. Four headers carry the whole interface: Raspberry Pi, Arduino, the Dynamixel daisy chain, and a separate 12 V input so servo power never shares the logic rail. Designed in KiCad, with gerbers and a FlatCAM project for in-house isolation milling.
On the software side, a standalone Protocol 1.0 driver — no vendor library — exercises the board through the four modes of an AX-18A: joint-mode positioning at low and full speed, continuous wheel rotation, and torque control down to free-wheeling. Validated at 1 Mbaud on an Arduino Mega.