My team may be looking to use pneumatics for a catapult this year. We are not very experienced with pneumatics and we’re wondering what solenoid would be best for activating pistons quickly to get the catapult launch we need. We will probably be using 2 double acting pistons with 8 inch stroke for launching.
So our 2014 bot lessons learned… Automation Direct high flow solenoids. Also, you probably want to use Single Solenoids and the pistons should only have the shooting direction hooked up to a solenoid. The returning direction should not be pressurized. To return the catapult to the starting position, gravity is used. This reduces the amount of backpressure/resistance when shooting.
In 2014, we used a single acting solenoid with P/N 6124K511 from McMaster-Carr, and we were very satisfied with them. However, I would recommend having two of them and directly hooking the output to the input on the cylinder to get the least amount of distance the air has to travel to fill the cylinder. Also, have the return port of the cylinder simply be open, because gravity will just pull it down and force the air out of the bottom once the solenoid switches back to vent.
An air tank on the 60 psi side of the regulator with a short hose or direct connection to the solenoid input wouldn’t hurt, either.
Double check the rules. In past years they limited us to one solenoid valve per cylinder. If that’s the case this year, you can use two smaller cylinders with one valve each, to get the maximum speed.
The pneumatic rules this year allow for check valves as long as the they don’t prevent all pressurized air from being released when the main vent valve is opened.
R77 G. Check valves, provided that the requirements of R89 are still met
Something like this would allow you to still return the cylinder using air pressure from the other side of the solenoid but have the advantages of release the air to atmosphere instead of returning it to the solenoid exhaust port. This may not be quiet as fast as just venting to atmosphere but it should be close.
From the product spec sheet.
NITRA pneumatic push-to-connect in-line quick exhaust valves
have a technopolymer body and nickel-plated brass valve insert,
with a range of 7 to 150 psi. Normal flow is from inlet to outlet
ports. Reversing flow from outlet is directed to exhaust port. These
valve are ideal for use with pneumatic actuators that require a
very fast stroke speed.
Would two of these do well?
This is the same solenoid and setup we used in 2014, worked great! The other useful tricks, as mentioned above, are
- Hook the solenoid right to the pneumatic cylinder (see pic below)
- Leave the other end of the cylinder completely open (no hose or fitting is needed, gravity will bring the catapult arm back down)
- Put a small tank right in front of the supply side of solenoid so that the air doesn’t have to go through the regulator. This tank is at the 60psi working pressure.
http://i.imgur.com/VnhNhsv.jpg
We may or may not be using two of these solenoids on our robot this year.
We’ve built air catapults successfully before using a round electromagnet from mcmaster.com, http://www.mcmaster.com/#5698k116/=10s4olc
fast valves aren’t that important in my experience. What is important is that you must not retract the piston all of the way. Leave a ‘chamber’ of air about 2 -4 inches in the bottom of the air cylinder when your mechanism is retracted and position your mechanism so that it doesn’t have much leverage against the catapult when it starts.
Fill the cylinder(s) while holding the magnet. when the cylinder is up to 60psi, release the magnet. The ‘chamber’ of air will ‘explode’ the catapult forward.
When I said two, I meant order two and have one per cylinder. I can see how what I said would be interpreted that way though.
I have looked through all the recommendations and I think this solenoid would work best. It’s a 3-way 2 position and it seems good to me. I would just like confirmation from someone more experience with pneumatics to confirm it is good and also legal.
The same ones we use when only plumbing to one side of the cylinder. It is not the correct one for extend/retract. For that you need what Automation Direct calls a “5 port” Like this
The only real issue is the valve is rated for 115 PSI working pressure so you need a downstream relief valve per R77-D
We’re planning to go with a setup like s_forbes. We have a 1.5" bore, 4" throw cylinder and we’re shooting reasonably well using just the standard Vex solenoid/manifold through about a foot of tubing to the cylinder. We’re optimistic about using the higher flow solenoid directly connected to the cylinder.
We’re trying to figure out how to wire the solenoid. The picture only shows “12V” with arrows pointing to the two parallel leads. I’m not sure what that means. The PCM only has a black and a red wire. Do we connect red to one and black to the other? Does it matter which is which? What do we do with the third lead?
And oh, by the way, we’ll be using 24V so we’ll get a 24V solenoid.
Any guidance is appreciated.