3-position pistons

So our team was looking into having pneumatics with multiple positions for our a acquiring mechanism. We need to have 3 positions and are weighing two options. We can either use 2 pistons attached in line or get a 3 position piston like This Have any teams used them? Are they any good?

No, I haven’t used the 3-stop model, but we have always done well with Bimba products. We made a 3-stop pneumatic setup for our Ultimate Ascent climber. The solution we came up with was remarkably light – we used two equivalent double acting cylinders with double-end (X) mounts, and placed them side by side but pointing in opposite directions. We then cut two flat plates with two holes in each, placed them over the ends, and tightened down the four nuts. The picture attached shows about what it looked like. Because we didn’t want our hook to rotate, we used a hex shaft on the free end cylinder and made a “cage” of angle aluminum to keep the free cylinder in the desired line; if you’re not worried about the rotation, this could probably do it for you.

i have never used a 3 position cylinder but i have combined two together and there bottoms which would give you a total of four positions, (up up) (up down) (down up) (down down) assuming there different lengths if there the same length you would get three positions (up up) (up down) (down down) at that point its just a matter of finding the sizes you need

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.

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

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.

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:

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_Main_Robot/blob/master/src/org/team2168/commands/tusks/TusksShortShotPosition.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.

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.

We are attempting something similar. We looked at these options, but then we realized that a two cylinders, each controlling one end of our mechanism, gives us three positions if we don’t mind the middle position “opening” being off-center. This seemed okay because it will only carry the weight of one object in its middle position (you don’t stack anything on top of it anyway.) Not sure how it will work out, but that’s what our solution is so far.

The reason we arranged the pistons next to each other as shown in post #2 was that we were looking for a package with an extended length more than twice the compressed length; I haven’t seen any integrated 3-position cylinders which do that. If you do combine cylinders and do not have this restriction, they can be back-to-back, tip-to-tip, or tip-to-back.