Re: Pistons not extending fast enough?
 

Agreed, I would not want to spend precious time between competitions tuning a system only to arrive at an event and find its illegal.

Re: Pistons not extending fast enough?
 

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?

Re: Pistons not extending fast enough?
 

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

Re: Pistons not extending fast enough?
 

What do you mean by directly attaching them to the shooter?

I will be working on modifying the catapult so that it starts in a lower position and the pistons are closer to the hinge point. I'm also going look into 842's design a bit more, thank you for pointing that out. It seems they're using the same size pistons as us; if they are having no issues shooting, maybe we'll be able to do the same.

Re: Pistons not extending fast enough?
 

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?

Re: Pistons not extending fast enough?
 

Thanks for the clarification. I will go ahead and calibrate the system tomorrow so that we are working at the regulated 60 PSI.

By a hard stop, do you mean something to stop the ramp before the pistons make it all the way to the end of the cylinder?

Re: Pistons not extending fast enough?
 

We are using this trick as well, to eliminate unneeded tubing and fittings between the solenoid and the piston to increase flow rate. See this image of our setup; it shows the solenoid valves directly attached to the pistons and how our plumbing is laid out.

Re: Pistons not extending fast enough?
 

Yes. A strong strap (like a tie-down strap) would be a good option. You just want to prevent the piston from striking the end-cap with high speed/force.

Re: Pistons not extending fast enough?
 

This is a recommendation I've seen before, and it seems reasonable to me.... however, we have something on the order of 1000 cycles on our practice robot catapult with no noticeable wear or potential failure of the cylinders, and we are using the cylinders with no hard stop. Mind that we avoid dry-firing like the plague, and under normal launching conditions the cylinders aren't hitting their end of travel with such an absurd velocity.

Re: Pistons not extending fast enough?
 

This is immensely helpful. Thank you.

Apart from having the solenoids connected directly to the cylinders, adding tanks before the pistons, and having them vented to the atmosphere is there anything else you've done to increase you efficiency? While I certainly believe that will help I find it hard to believe that this will bring our dysfunctional setup to working capacity, though I'm certainly going to try.

EDIT: Also, how do the pistons fall back in the cylinder? Does gravity do the work?

Re: Pistons not extending fast enough?
 

The only other big trick is to use a high-flow solenoid valve; we are using McMaster part number 6124K511 to feed each of our pistons. The valves you get from AndyMark or Vexpro flow about 3x less air (these were the maximum flow rate that we could use in the past... this year's rule set has allowed us to use a much larger variety of solenoids).

The geometry of the arm also plays a big role. Based on the videos you posted, I would extend the length of the platform that is shooting the ball, and move the piston locations on the base mounting board back about 0.5"-1" from the pivot location to allow it to sit "flatter" before firing. These pivot locations will all probably need a bit of adjustment as you continue testing.

Oh, and if you can get rid of the miles and miles of tubing between your pneumatics testing board and the catapult, you will probably see an immediate improvement. :)


EDIT: as far as gravity returning the catapult arm to the starting position, we have never had any trouble with this. It falls right back into place with ease.

Re: Pistons not extending fast enough?
 

Yep.

Re: Pistons not extending fast enough?
 

All the mentioned changes will help for sure.
Set the cylinders at a better angle.
Since your cylinders are a larger boar and stroke it will need lots of air quickly.
A separate solenoid per cylinder is a must with, if possible, higher Cv flow.
We got these really quickly using one of the vouchers from FIRST.
http://www.automationdirect.com/adc/...)/AVS-3211-24D
They are 24v and the price was reasonable.. About 20 dollars. Not sure if you are using the older 12v solenoid from previous kits. Some FIRST KOP came with 12v others 24v. You will have to make some adjustments if you are running 12v.
You will have to have the solenoid breakout on the cRio run it.
Ideally, like mentioned, mounted on the cylinder. If not as close as possible!
Air lines after the solenoid have to be filled before any air reaches the cylinder.
Storage of high pressure as well as having working pressure tanks for each cylinder. Try having the low pressure tank as close as you can to the solenoid.

As for venting. Take off the unused hose fittings!!! You are reducing the flow of escaping air and slowing it down.

We are running a system similar to 842, ( well done by the way 842!)
(2) 10" 1-1/2"bore cylinders and it will consistently hit the high goal at 20 feet away with a release point of 3.5 feet off the floor..
You can look at our Youtube stuff and freeze frame for ideas..
http://www.youtube.com/watch?v=LfKh6...po3XAn15-6TXDg

Send me a message if you have additional questions. I will try to get some photos from the students.

Good luck this season,

Aloha!

Re: Pistons not extending fast enough?
 

All glory to the gate latch!!!

Every since I built a 16ft trebuchet for my 9th grade woodshop project I have LOVED using gate latches as a quick, easy, reliable, and cheap release mechanism. Picture Here Additional Info Here

Re: Pistons not extending fast enough?
 

We have found similar results with McMaster 6425k11

There are a large number of teams successfully launching with various length 1.5" Bores, with a single solenoid on each of the cylinders "extend" side and no valve on the "retract" side.

You may want to take a look at the geometry of 842, 624, or 2587.