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DRV8849: Driving a motor using DRV8849 with microstepping of 1/128.

Rohit Bhadauria
Prodigy 80 points
Part Number: DRV8849

Tool/software:

Hi,
i am using the stm32 controller to generate PWM pulse for rotating the motor with 0.9 degree per step with microstepping of 1/128. i am checking the pulse frequency as per calculation as 102400 Hz to rotate the motor , but at driver input i am getting the 800 Hz as frequency.

what i am understanding is that earlier to rotate the motor to 0.9 degree it was taking 800 Hz. now it is taking the 800 Hz to run the 0.9/128 Degree motor. so am i write or doing something wrong and should get the output as 102400 Hz at driver input. one more thing that i am getting the microstepping reflected at motor.

  

  • 0
    TI__Mastermind 44615 points

    Hi Rohit,

    Thanks for your question.

    Rohit Bhadauria said:
    PWM pulse for rotating the motor with 0.9 degree per step with microstepping of 1/128. i am checking the pulse frequency as per calculation as 102400 Hz to rotate the motor , but at driver input i am getting the 800 Hz as frequency.

    Step input frequency is based on the motor speed. A 0.9 ° stepper needs 400 pulses for 1 rev. with full-steps or 128 * 400 = 51200 steps for 1 rev. of the motor. Now, for example you want the motor to spin at 1 rev. /s speed the step input frequency must be 51200 Hz. So, 102400 Hz step frequency will drive the motor at 2 rev. /s or 120 RPM. 

    If you are getting 800 Hz at the driver STEP input it is an issue with the MCU setting in your firmware. This would run the motor very slow, If you need 120 RPM with 1/128 step setting in the DRV8849, you must input 102.4 kHz to the STEP input. 

    Rohit Bhadauria said:
    what i am understanding is that earlier to rotate the motor to 0.9 degree it was taking 800 Hz.

    If you want to move the motor by 0.9 ° in position you must input 128 pulses when the driver is set for 128 microsteps mode. The number pulses is important. The frequency determines the speed at which this position is achieved. The position result will be the same for number of pulses = 128 regardless of its frequency. Thank you.

    Regards, Murugavel