Pistons not extending fast enough?

[ttldomination]

So, I have a basic understanding of pneumatics, so I'll attempt to advise you the best I can. Warning, this is going to be a long read, so take a deep breath, and try to understand as much as you can.

The name of the game is flow rate. How do you move air as quickly as possible into the cylinders? If you move the air in quicker, the cylinder will shoot out faster.

Before I get into this, I'm going to set up an analogy for us to follow. Think of the cylinders as buckets, and the solenoids as hoses that carry water. The goal is to fill up the buckets of water as fast as you can.

Now, based on the videos, you have one solenoid hooked up to two, fairly large, cylinders. You're essentially trying to fill two big buckets with one hose. So, how do you make the system faster? How can you change up your variables (buckets and hoses) to make the system fill up faster?

Let's go through a few scenarios:
Use more hoses - Of course, if you use, say, one more hose (read: solenoid), that'll help with the flow rate, and it'll help you fire quicker. Now, I believe the rules limit you to maximum one solenoid per cylinder, so keep that in mind.

Use smaller buckets - While this may seem counter intuitive, this is also correct. Using smaller cylinders will help you fire faster. There's a tipping point between cylinder size that gets you the best speed vs. power. I'd recommend reaching out to a team to find out what they're using.

Use a larger hose - Now, this is interesting. If you use a solenoid that's rate for a faster flow rate, you can move air quicker, which will ultimately shoot the pistons out faster. FIRST doesn't impose a solenoid flow rate limit, but given a set of constraints (price, power, etc.) you may be limited on what's actually available to you.

Pool your water into a smaller bucket ahead of time - Now, this is a little bit more difficult to understand, but bare with me. Let's say you pop the solenoid and let the cylinders build pressure, but you lock down the shooter. Then, at a later point in time, you manually release the shooter (via a latch or something). Here, the cylinders are essentially acting like compression springs, but you are able to get over the flow rate problem.

That's the tip of the iceberg, and I recommend you do some more soul searching (read: researching) into your issues, your system, and which solutions would best fit your setup.

Here are some other threads that may help:
Team 842's Amazing Machine
Creating Pneumatic Launchers
This talks more about letting the solenoids fire before you release the catapult.

Let me know if this makes sense, if there are any errors, or if you need any further assistance/clarifications.
- Sunny G.

[Matt C]

This might give you some ideas, and it's the clearest picture I have of our shooter which appears to be similar in geometry to what you are attempting to accomplish. The pistons are 7" stroke, both have a small air tank on the working pressure side attached to each piston. The pistons push just short of over center (they almost line up with the hinge point on the front of the "catapult"). This puts only a slight force on the modified gate latch(not seen on the left side of the picture inside the robot, actuated by a .5" stroke piston which lets go to release the pre-pressurized shooter. The pivot is a pair of door hinges and there is a strap to prevent the pistons from smacking into the end of the cylinders whey they extend.




https://www.youtube.com/watch?v=rbYT...m-upload_owner

[TheHolyHades1]

Originally Posted by Matt C

This might give you some ideas, and it's the clearest picture I have of our shooter which appears to be similar in geometry to what you are attempting to accomplish. The pistons are 7" stroke, both have a small air tank on the working pressure side attached to each piston. The pistons push just short of over center (they almost line up with the hinge point on the front of the "catapult"). This puts only a slight force on the modified gate latch(not seen on the left side of the picture inside the robot, actuated by a .5" stroke piston which lets go to release the pre-pressurized shooter. The pivot is a pair of door hinges and there is a strap to prevent the pistons from smacking into the end of the cylinders whey they extend.

The gate latch - when your pistons retract, I'm assuming that it locks back into place until the next time you're shooting? Also, do you have the pistons retracting with gravity or some other mechanism, or are you having them retract by sending air in the other side?

[Matt C]

Originally Posted by TheHolyHades1

The gate latch - when your pistons retract, I'm assuming that it locks back into place until the next time you're shooting? Also, do you have the pistons retracting with gravity or some other mechanism, or are you having them retract by sending air in the other side?

Gravity retract, the gate latch remains open until the 3/8" bolt that goes into the latch hits the microswitch to signal that the catapult is back in the down position. The solenoid for the small 1/2" stroke piston is then actuated and the latch closes.

We actually only have one solenoid going to both pistons. It's a slightly longer pressurization (about 2 seconds) for a full shot, but allows us a better lob/pass "shot" with no piston gate latch retention with slower motion and less air consumption (the solenoid is switched only for "x" time before it's switched back, allowing the ball to be shoved out, but not allowing the tanks and pistons to reach the full 60 psi, thus saving a bit on air.)

[TheHolyHades1]

Originally Posted by ttldomination

[Lovely explanation]

Thanks so much for the great explanation, it really helps understand the whole concept of airflow. Apart from changing from one solenoid to one per cylinder and adding a higher airflow solenoid (if possible), would there be anything else I could do to increase my airflow?

[Chris_Ely]

Originally Posted by TheHolyHades1

Thanks so much for the great explanation, it really helps understand the whole concept of airflow. Apart from changing from one solenoid to one per cylinder and adding a higher airflow solenoid (if possible), would there be anything else I could do to increase my airflow?

The pressure regulator also restricts flow rate somewhat. To compensate, you could add additional accumulator tanks on the low pressure side of the regulator.