[Al Skierkiewicz]

The spikes are meant to have a steady state control voltage at the input to produce a steady state output. The solenoids are designed for a steady state input as well. By feeding them a PWM signal, they will attempt to follow the input. Mechanical marvels that they are, that varying signal may just destroy them. Either by heat generated in the movement or just the rapid banging of the parts as they try to follow the input signal. Even if they were to follow the input signal without damage, you wouldn't want to modulate your air to a piston by using this method. It would be inefficient. Although there is no specific instructions in the robot electrical manual, it is certainly implied that Spikes only are the driving device for air solenoids. Sorry.