Position control of pistons with simple solenoids

[BoilerMentor]

In 2013 1747 attempted to build a pneumatic climber. We used a fairly complex, but available set of manifold style solenoids from SMC. The climber ultimately did not work due to significant mechanical issues that were encountered, but the pneumatic end of the climber was successful. The climber was ultimately ditched after a single regional event spent playing defense the whole time and never hanging for a Frisbee shooter and a simple low bar pneumatic hang.

IIRC there was a double acting solenoid and two single acting solenoids per cylinder. The double acting valve controlled direction and the single acting valves were basically an on/off for air supply to the cylinder. What this resulted in was the ability to select a direction (extend or retract) and then either allow flow in to and out of the cylinder or cut that flow off at both ports which maintained the position of the pneumatic as long as the load on the cylinder didn't change. This wasn't instrumented with something like a string pot or linear pot, so I don't know what accuracy was, but I suspect with appropriate flow control it could be accomplished.

In hind sight, I'm wondering if this is/was legal considering the single-solenoid-output-per-cylinder rule, but maybe since they were in series it wasn't an issue. I know we had tons of questions, as you'd expect with a 5 gallon aluminum air tank on the robot.

I wish I had a video to share, but that robot, pre-Frisbee shooter, is our robot-which-shall-not-be-named.