Wheeeee... I think you're out of luck for PWM output on that PLC. The digital outputs on that are relays, which aren't likely to switch quickly enough. And are likely to die a sudden death if you convince them to switch quickly enough. You'll definitely need to find some sort of analog->PWM converter, or find yourself a different controller.
If you have access to some FRC hardware, you might try the
RobotOpen Arduino Shield. You'll need an FRC digital sidecar, power distribution board, and a few other things, but it's a heck of a lot more likely to work and work well FRC speed controllers and electronics.