semubot_driver

Low-level serial driver for communicating with the SemuBot STM32 wheelbase firmware.

---

Overview

semubot_driver provides the host-side interface to the STM32 firmware over serial. It handles sending velocity commands, reading wheelbase state, and serves as the serial backend for ros2_control-based stacks when needed.

Use this package for:

• Direct serial testing of firmware variants
• Onboard-control variants where the STM32 handles mixing or PID internally
• Serial backend for ros2ctrl-serial

For ros2_control-based stacks, see semubot_ros_control.

---

Serial Protocol

Host → STM32

CMD:vx,vy,wz

Field	Meaning
vx	Forward / backward
vy	Left / right (strafe)
wz	Rotation / yaw

Examples

CMD:0.20,0.00,0.00    # forward
CMD:-0.20,0.00,0.00   # backward
CMD:0.00,0.20,0.00    # left
CMD:0.00,-0.20,0.00   # right
CMD:0.00,0.00,0.20    # rotate
CMD:0.00,0.00,0.00    # stop

STM32 → Host

STATE:p1,p2,p3,v1,v2,v3

Field	Meaning
p1, p2, p3	Wheel positions
v1, v2, v3	Wheel velocities

Motor order

Index	Joint
M1	omni_ball_1_joint
M2	omni_ball_2_joint
M3	omni_ball_3_joint

---

Firmware Variants

onboard-serial

Host sends CMD:vx,vy,wz. STM32 applies the onboard open-loop mixer and drives motors directly. No PID.

onboard-serial-pid

Host sends CMD:vx,vy,wz. STM32 computes wheel velocity targets, reads encoders, runs onboard PID, and drives motors. PID runs entirely on the STM32.

ros2ctrl-serial

The semubot_ros_control hardware interface sends low-level motor commands over serial. semubot_driver acts as the communication backend. PID runs on the ROS 2 side.

/cmd_vel
    → ros2_control controller
    → SemuBotHardwareInterface
    → semubot_driver
    → STM32 → PWM

---

Usage

Direct serial testing

Open a serial terminal to the STM32 and send commands manually:

# Forward
CMD:0.10,0.00,0.00

# Expected response
STATE:p1,p2,p3,v1,v2,v3

# Stop
CMD:0.00,0.00,0.00

ros2_control mode

Run the driver node as the serial backend for the ros2_control stack:

ros2 run semubot_driver driver_node --ros-args \
  -p mode:=ros2_control \
  -p serial_port:=/dev/ttyACM0 \
  -p baud_rate:=115200

In this mode the driver forwards low-level motor commands from the hardware interface to the STM32 and returns encoder state. The STM32 does not perform mixing or PID — that is handled by the ROS 2 controller.

Do not use mode:=ros2_control for onboard PID testing. In that case the STM32 expects CMD:vx,vy,wz directly.

---

Related Packages

Package	Description
semubot_ros_control	ros2_control hardware interface and velocity controller
semubot_bringup	Top-level launch files
SemuBot-Firmware	STM32 firmware (FreeRTOS, micro-ROS)

---

License

This project is licensed under the Apache 2.0 license - see the LICENSE file for more information.