6-Axis Robot Arm Controller

Firmware for a 6-servo robot arm on an STM32 Blackpill, plus a PyQt6 desktop app that controls it over USB.

Role: Sole developer
MCU: STM32F411CE
Software: C++ (STM32duino), Python
Source: GitHub ↗

04.1Summary

I wrote firmware and a desktop app to control a six-servo robot arm from a computer. The STM32 shows up as a virtual serial port over USB-CDC, so no separate USB-UART converter is needed.

The command set is deliberately plain text: the same commands can be sent from the GUI or from a serial terminal such as screen. That makes it easy to test the hardware independently of the GUI.

04.2Block diagram

04.33D model

Perspective: 3D model of the arm with joint angles. — Fig. 1Perspective — 3D model of the arm with joint angles.

Side view: Arm in upright pose. — Fig. 2Side view — Arm in upright pose.

04.4Hardware

MCU	STM32 Blackpill F411CE
Actuators	6 × PWM servo
PWM	50 Hz (20 ms), 16-bit resolution; 0° = 1000 µs, 90° = 1500 µs, 180° = 2000 µs
Timers	TIM1 CH1–3 (PA8, PA9, PA10) · TIM4 CH1–3 (PB6, PB7, PB8)
Power	Separate 5 V / 10 A supply for the servos; the STM32 is powered from USB
Comms	USB-CDC, 115200 baud

duty = (pulse_us × 65535) / 20000

  0° → (1000 × 65535) / 20000 = 3277
 90° → (1500 × 65535) / 20000 = 4915
180° → (2000 × 65535) / 20000 = 6554

Common ground: if the servo supply's negative terminal is not tied to the STM32 GND, the PWM reference floats and the servos do not move. 100 µF capacitors at the servo connectors reduce voltage dips during current spikes.

04.5Software

Command	Function	Example
`S<n>:<angle>`	Move servo n to angle (n = 1–6, angle = 0–180)	`S1:90`
`ALL:<angle>`	Move all servos to one angle	`ALL:90`
`STATUS`	Report all angles	`S1:90,S2:45,…`
`RESET`	Return all servos to 90°	`RESET`

Bad commands get explicit error replies (ERROR:Angle out of range, ERROR:Servo ID out of range, etc.). The GUI has a slider and min/max limits per servo; HOME, RESET and STATUS buttons send the same commands. On macOS the GUI can be bundled into a single .app with py2app.

04.6Links

GitHubFatihAksoyEEE/RoboArm ↗