Contents

About PWM Mode

In PWM Mode, the Moto Module drives a motor or other high-current device with variable speed in positive and negative directions.  This type of speed control is open-loop; that is, no feedback from the driven device is fed back into the control system.  This mode is useful for testing out a new motor or H-Bridge. 

The Moto 1.0 Application in PWM Mode

You can manipulate four variables in PWM Mode:

Set Point

This mode affects the duty cycle of the PWM signal, which effectively varies the voltage to the motor and varies the speed.  The duty cycle is set using the throttle slider.  The center point of the slider is neutral.  Sliding the set point above the center point moves the motor in one direction; sliding it below the center point moves the motor the other direction.  The stop button returns the throttle to the neutral position and stops the motor. 

PWM Rail

This setting can vary between 0 and 32767 and puts a limit on the maximum PWM output allowed.  You can use this value to:

• Set a maximum speed
• "Window" the PWM output voltage to keep it within your motor's ratings

The default for this value is no limit or 32767 (the PWM maximum). 

PWM Frequency

This value represents the PWM frequency in Hz.  The default is 39,062 Hz, which is a reasonable starting point.  To get maximum efficiency from your system, we recommend a frequency above 20 kHz.  This value is out of the audible range (for humans) so it also provides quiet motor operation.  When entering a new PWM frequency, you may not get the exact value you entered.  The controller generates a fixed number of different PWM frequencies and the program must select a frequency that is the closest match. 

Invert Output

Checking this box inverts the PWM output signal.  This reverses the motor direction.  You may want to reverse a motor when using two motors on a differential-drive robot so that positive PWM values mean forward motion for both motors. 

The basic logic flow of the PWM Mode of operation.

Related Links:

Concepts: Description of Pulse Width Modulation (PWM)