3-position pistons

[Andrew Schreiber]

Originally Posted by JesseK

We're considering a 3-position for one of our new grabber ideas, but can't quite figure out how to hook them up. Anyone have thoughts?

The 3-position is more desirable, IMO, for cost, weight and simplicity reasons.

I've attached how we hooked one up for testing last year.

[who716]

i have trouble seeing that a 3 position can get you as much distance as two cylinders im sure there is a much smaller restriction with the three point, we have to spread 16 inches so at that points a 10 in long cylinder and a 6 inch long cylinder is a better option

[JamesCH95]

In 2010 we used two pairs of cylinders connected shaft-to-shaft to deploy a deflector. It worked quite well. We connected them with the shank of a rod-end (we cut the spherical bearing off), with one cylinder shaft threaded in from each end.

[otherguy]

We used them all season long last year. We had a catapult ball shooter. The cradle that held the ball had an arced "tusk" that could be moved to three different position to affect our release angle.

Our source code (with ascii art) is available here:
https://github.com/Team2168/FRC2014_...ems/Tusks.java

Note that the way these components work is there are two rods which are not coupled to one another. The middle port on the actuator extends the external rod, and retracts the internal rod. As a result, if you're trying to move the actuator to the intermediate position, you'll need to sequence the move, otherwise you may not allot enough time for pressure to vent to atmosphere. It's hard to explain in words...
You can see how we implemented this sequencing here: https://github.com/Team2168/FRC2014_...tPosition.java

Our plumbing was also a little more complicated than normal for these. As we used two double solenoids, so it required a check valve to be installed in line. If you need a pneumatic schematic, PM me (as I won't see requests in this thread) and I'll document what we did on our robot from last year.

[Kevin Sevcik]

I would recommend that you pay careful attention to Bimba's dimension drawing on those 3-position cylinders. If you want the positions at something like 16", 14", 0", then the whole mechanism gets extremely long. My example there ends up a minimum of 30" long, unextended. As you can imagine, that's also going to consume a LOT more air, since you're basically pumping the a 14" stroke and then a 16" stroke. Back-to-back or side-by-side cylinders are a lot more air efficient if your application can work with them instead. With back-to-back cylinders, you can actually get 4 positions instead of 3.