I am not getting the desired dc motor speed characteristics.

I have implemented this PWM control circuitry using 555 timer to control the speed of the dc motor. Usually when you vary the 100k pot, the duty cycle changes, due to which the steady state speed limit also changes, but that is not happening in my case. I am attaching the Simulink model below. Please assist me in this and tell me what I need to do to get the desired speed characteristics.

[Patrica]

I faced a similar issue during one of my DC motor control projects! It turned out the PWM signal from the 555 timer wasn’t properly tuned, and the pot was either not calibrated correctly or had some drift. Make sure to double-check your Simulink model settings and real-world parameters to ensure they align perfectly.

If you’re pressed for time or need expert guidance, you can try reaching out to MATLAB Assignment Experts. They’ve got specialists who helped me with a similar project, and they offer great support for both hardware and Simulink-based models. Plus, with the MAEFALL2024 promo, you can get 20% off—might be worth a shot to save some time this semester!

Answer 1

[Vinay]

Hi Anant,

The constant voltage across the DC motor is due to the MOSFET drain voltage reaching saturation, resulting in a constant motor speed. The issue can be resolved by connecting the PWM signal directly to the DC motor.By adjusting the duty cycle, the average value of the signal changes, which in turn affects the motor speed.

Kindly refer to the below documentation of “DC motor” for more details:

https://in.mathworks.com/help/releases/R2024a/rtw/freedomboard/ref/dcmotor.html?searchHighlight=dc%20motor&s_tid=doc_srchtitle

I hope this helps!

[Anant]

Hi Vinay, I tried doing what you said, I did not completely get what you meant by connecting the output pwm signal directly to the DC motor. If possible can you change this model accordingly that you said and upload here? Thank you

[Vinay]

Hii Anant, The following model can be used to connect the PWM output to the DC motor.