Fast actuating pistons?

Does anybody have any advice to speed up pneumatic piston actuation (in one direction), or if there are quick exhaust valves or fast pistons available? We are trying to build a Robonaut-like catapult, but the pistons we are using to pull down and lock are two slow actuating upwards, even with springs assisting.

1 Like

There is a section of our advanced pneumatics guide dedicated to this - Spectrum Advanced Pneumatics Guide - Google Docs

7 Likes

you might want to see if you can figure out a way to have them actuate a lever, in a way that makes it move suddenly. We used something like this in 2008 and 2014 The two bars along the top, just above the cylinders, are the “arms”.

5 Likes

I have seen one approach that held promise. It involves using a separate cylinder to create a vacuum to draw air out of the exhaust port of the shooting cylinder when launching. Also use levers that make the ball move faster than the cylinder itself.
Alternatively use the pneumatics to cock the spring. But disengage the cylinder for firing.
Caffel, FRC 423

First off they’re cylinders not pistons :slight_smile:

What size cylinders are you using? Only real speed you will get is from a 3/4" cylinder and if you leave the exhaust port off and retract with something else it will move very fast.
If you want more power than one can provide use more cylinders instead of larger ones.

2 Likes

1986 ran a pneumatic catapult in 2016. Ran double cylinders that actuated simultaneously and pushed on a point closer to the fulcrum of the lever.

3 Likes

Another arrangement to get more speed from cylinders is to multiply the effective speed by connecting two cylinders butt-to-butt or side-by-side with the rods/clevis in opposite directions, each one with its own valve. Same force with twice the air throughput and end speed, without breaking the valve rules. Different approach but same principle as Alpha’s comment (parallel vs. series), more valves contributing to the motion.

2 Likes

Short BIG plumbing, ideally valve screwed to the cylinder, air tank screwed to the valve, and diaphragm valve… and not a normal frc tank; bigger fittings. Oversize air ports on the cylinder.

Look up the valves used to back-blast air filters :smile:

There are strict rules about the CV size and port size of the valves.

1 Like

How do you do the vaccuum? Can you explain the setup?

Mount two cylinders against each other so that one rod pushes the other. Run a tube to the vacuum side of cylinder two. Attach a solenoid from that port to the exhaust port of the primary launching cylinder. This has the potential to double the force of the launching cylinder.
Aside from that, don’t hesitate to use parallel solenoid valves and tubing but boring out the ports is illegal and would serve to introduce swarf into the cylinders

What about R814?

We’ve used most of the tricks in this thread, as well as one more, 2 from:

Right you are, no more parallel solenoids. Still might help to have parallel tubing though.

That was useful feature for your launcher, it was nice having the variety of distance shots.

Some features we’ve used in 2014 & 2016 were 1) having some dead volume in the cylinder to start by not fully retracting. 2) Instead of quick exhaust valve just let it gravity return with totally open retract side ports. 3) Momentarily holding the cylinders in place with an electromagnet. 4) Some flex in the catapult seemed to be helpful, I think some can do this with a single long arm (but in 2014 they tried to make this PVC hoop from aluminum and it was less effective because of the extra stored energy in the flex of the PVC).

1 Like

I think you’ll find 1) and 2) in the photo I posted above, if you look closely

1 Like

In our 2014 catapult, we used what I thought was a neat trick. The main cylinder was pretty big, but was mounted such that, when it was in its base, lowest position, it pointed down (just a few degrees). So, when we started a shot, we would charge the main piston to full pressure, and the catapult arm would be pushed down into the robot (ie not shoot).

Then a short time later, we would fire a “kicker” piston, which actually triggered the shot. This was a tiny piston which would just push the catapult arm up 1-2 inches, enough to be over the hump, and the arm would fire with the full force of the big piston.

4 Likes

Were you using an over center mechanism where the kicker piston pushes it from the locked position to the unlocked position?

http://www.mjvail.com/destaco/intropage3.html

I was not heavily involved with the team back then, so I had to check.

I don’t think the setup we had fits that mechanism description. The piston was actually mounted through the center of the catapult arm. At rest, the arm was in a position such that the piston point down at a few degrees; when pressurized, it actively pushed the catapult down into the robot. We then had a small “kicker” piston with a few inch stroke which was mounted close to vertical. To actually fire, that kicker piston pushed the catapult arm above the horizontal line, and now the big piston was forcing the arm up, shooting.

One other detail, which I did not know about. We had a large storage tank (at “low” pressure) between the control solenoid and the catapult piston. So, just before firing, we charge the tank and big piston with 60PSI, and then fire the kicker. The big cylinder is fed air from the low pressure tank as fast as the hoses allow.

I am pretty sure you are describing an over-center mechanism. When in the “rest” position, the main cylinder pushes but cannot cause the mechanism to extend due to mechanical limits. It is often used to constrain a powerful mechanism then release it using a relatively small force i.e. your kicker. More teams should use mechanisms like this.