Embedded systems · Implementation study
Closed-loop motor control in C and C++
How speed feedback, timer-driven control, and a suitable motor driver work together to regulate a motor under changing load.
What the demo shows
The rotating graphic, RPM, current, and duty cycle are scripted examples. No motor, physical feedback loop, or controller tuning is running in this page.
Proposed system flow
- 01Speed feedback
- 02Control calculation
- 03PWM and driver
- 04Motor response
01
Match the controller to the motor
A practical implementation begins with the motor type, supply, driver, load, and feedback sensor. For a brushed DC speed-control example, a microcontroller timer can produce PWM for a suitable power driver while encoder measurements estimate shaft speed. PWM specifies the fraction of each cycle that is active; duty cycle is not itself a measured RPM value. Other motor types can require different commutation and control strategies.
02
Run the feedback loop on a defined schedule
At each control interval, firmware would compare target and measured speed and update a PI or PID controller. Arm's CMSIS-DSP library provides PID primitives for floating-point and fixed-point implementations. Gains must match the selected update interval and physical plant. Output limits, integral windup handling, and startup behavior would be designed explicitly; adding a PID library alone does not establish stability.
03
Keep control independent of the dashboard
The device would enforce current limits, feedback timeouts, and fault handling locally. A web interface could request bounded setpoints and display telemetry, while the time-critical loop stays on the controller. Network loss must have a defined response. Where the machinery requires protective shutdown, that protection needs an appropriate hardware and system design independent of a browser command.
Validation plan
- Measure overshoot, settling time, steady-state error, and loop timing under representative load.
- Test startup, stall, disconnected feedback, and commanded speed limits on a controlled test bench.
- Verify the selected fault response during network loss and processor reset.
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