[timytamy]

One little tip, while it may be tempting to go with single (sprung) solenoids only (to save on channels) think about what happens in an e-stop/disabling.

If you use a single acting solenoid on a large arm or mechanism, then disabling can result in that solenoid shifting back into it's default position, and it's arm/mechanism flying back as well. This can pose a hazard :O

People expect a robot to stop moving when it's disabled, not all the pneumatics to retract.

We do however use single solenoids on internal mechanisms that are either low risk (eg shifters), or stay in one state for the majority of the time (eg latches).