Pneumatic Piston Strength

Recently, we went to a nearby high school to scrimmage. We saw that their pneumatic claw is many times stronger than our own pneumatic claw. The spacing is nearly identical, and after experimenting with tube length, our claw still closes at the same strength. We just cannot figure out why the high school’s claw is so much stronger. We use double acting pistons, but only use one side (to close the claw), resulting in a double acting single acting piston. Because of this, we have rubber bands to pull the claw open.

Are there any factors that may contribute to a stronger actuation, like placement?

Wouldn’t the rubber band holding the claw open resist the closing of the claw?

just as @theEqualizer says, your problem and solution are in your own post, when a double-acting cylinder is used as a single-acting cylinder, you have to use some sort of spring return. A VEX pneumatic cylinder can develop around 12 lbs of force…you must take away the force the rubber bands are pulling against the cylinder, which can really add up. Running your cylinder as a double-acting will get you more force.

Do you have only single-acting solenoids? Then use a pair to create a double acting one. In this case, the air savings of operating your cylinders single acting is not worth it.

The reason why we run our double acting cylinders as single acting is because the single acting pistons use air to open, but we need our pistons to use air to retract. The rubber bands just act as a spring that pulls the piston open when the air is released.

This is where your loss of strength is coming from, because your air cylinders must work against the rubber bands. Switch your cylinders to double acting, and you’ll have the strength you’re looking for.

Is the double acting go to last a whole match though? i tried using them and they ran out of air on me within 30 seconds

Are you using two air tanks? Also, check for no leaks in the system. Two of our teams use pneumatic claws and they work fine for the entire match.

I’ve seen plenty of teams using a similar setup, with the double acting piston being reset with rubber bands.
Have you tried different positions for the piston?
The further from the fulcrum (claw hinge) they are, the better as this gives them more torque. Also, the closer they are to a right angle with the claw the better (this also supplies more torque)

Do you have a picture or a diagram we can see?

yes I’m using two tanks that are t’d together and i have checked multiple times and have found no leaks in the system. I have tried single acting pistons and double set up like a single none of these seem to last long enough and die after 10-12 pickups

We ran a double actuating setup, and could get about 60 reliably strong actuation pairs(open/close)

Shrink the distance from your solenoid to your piston. That space is wasted air. It sounds like that’s the issue.

I’d be very suspicious of how much air the HS team is putting in their tanks. I suspect they were pumping up to 150 or higher psi, which increases the strength significantly.

That’s very funny, since the reason why we switched to single acting was because we could only get about 15-20 actuations even at 150 psi

Does the length of the tube between solenoids and pistons affect strength? We were thinking about testing this tomorrow…

Below is a picture of our claw and piston placement:
FullSizeRender-13.jpg

We had our pistons almost literally horizontal. In addition, we had it with two regulators covered in electrical tape. How the solenoid works is it opens the tube for a set amount of time. So more tubing is wasted percentages of air.

We ran ours at 107 PSI- our pump lost 7 when undoing on average, so it worked fine.

We also found that if you can stretch the routing of your tubing from the reservoir Not overly large amounts but it helps with air capacity

Motor claw has many benefits you should explore…

We have an almost identical setup as yours, 10 - 15 cycles is way too low. I would suggest taking off the rubber bands and testing how many cycles you can get. If it is still below 25 cycles you have a problem.
The first thing I would do is check for leaks in both the open and close position.
Then check for leaks elsewhere in the tubing/ tanks.
Then check and make sure that the tubing is not kinked anywhere.
It also seems like you have an excessive amount of rubber bands, I would recommend just putting enough to allow the claw to open, this will allow you to have more cycles.
How are you closing off the other solenoid valve?

Currently, we have double acting cylinders with single acting solenoids, since we are using the top hole (is that what it’s called?) of the cylinder. We can get about 50-60 actuations, except it’s not as strong as we would like it to be. When I said 10-15 actuations, I was talking about our old design, where we used air to both close and open. The question I was asking was wether or not there was any way to make the actuations stronger. Sorry if I was unclear.

Haha, we used to have a motorized claw, but we found that pneumatics would work better for us. Thanks for the suggestion though

Pump it up to 100psi, let it sit for 3 minutes, take the pressure after that with a tire gauge or something, then post the results here. More than likely you’re just leaking a ton without knowing it.

make up some soap solution (a squirt of dishwashing soap in a cup of water). Put it in a little squirt bottle (or use a little brush) and apply it to your connections and you’ll find your leak every time.

Most often it is where a hose plugs into a fitting. carefully re-cut the hose as square as possible and reconnect it.

Next culprit is the fitting itself into the cylinder, solenoid, or air tank. Here is the proper way to install these fittings: make sure the seating surface and fitting gasket are completely clean. Screw in the fitting finger-tight, then use a metric hex key wrench inside the fitting to tighten them 1/3 turn (120°) to seat the gasket. If the gasket is damaged, they will not seal, so be careful. Thread sealant or tape is not used on this type of fitting: proper tightening of the gasket is the key.

The other problem can be pumping the tank up without losing air when you disconnect the tire chuck. There are several solutions, including adding a valve to the plumbing, or our teams use a high-quality press-on chuck with a big air tank to pressurize to 100 psi.

I don’t think we are leaking any air, we made sure of that. We just can’t understand why our claw is so much weaker than our local high schools…