PWM Details

From Ed's Mediawiki
Jump to: navigation, search

The pulse width modulation (PWM) control signals used with FIRST motor controllers conform to the standards of Radio Control systems. The signal is a repeating positive pulse running at about 58 pulses per second and varying in width. The motor controller measures the pulse width and applies power to the motor according to the following specifications:

  • 1.0 millisecond pulse = full speed reverse
  • 1.5 millisecond pulse = neutral = no power to the motor. With Victor and Jaguar controllers, the controller can be set with a jumper to short out the motor in the neutral state, which causes magnetic braking.
  • 2.0 millisecond pulse = full speed forward
  • In between values vary motor speed. Examples:
    • 1.25 millisecond = half speed reverse
    • 1.55 millisecond = one tenth speed forward
    • exception: within 3-10% of the neutral value, the controller is in neutral. This is called the "dead band" and how wide it is depends on the controller. For example, the Victor 884 has a minimum speed of 3%, while the Victor 883 has a minimum speed of 10%