The 28X1 can do PWMOUT but the command shares the same internal timer as the SERVO command so you can’t have both at once (28X2’s have additional timers to work around this issue). The 28 project board is not the best for speed control of the motors either. Usually you PWM the enable lines on the motor driver to control speed. On the 28 project board the enable lines are hardwired into V+. It would be a somewhat difficult process to modify the board to accomodate PWM on the motor driver enable pins.
The “standard” 28x board, using a 28x1, has “regular” output pins going to the motor driver. Even if you wanted to PWM one of the direction pins (which would work) it is simply not wired that way. The only way to get a PWM signal to any pin on the motor driver would be to physically cut traces and re-route with hand-soldered jumpers.
I have read about a way around cutting traces that requires some care. Pull the L293, carefully bend pin 1 and pin 9 (pin 1 is nearest the dimple and pin 9 is the bottom of the other side) outward about 90 degrees, replace the chip in the socket, solder a couple wires (one per pin) 4" or so was suggested, plug said wires into PWM 1 and 2 on the board.
