Solenoid Control Valve Question

[ttldomination]

Hello Everyone,

First off, I'm an extreme noob when it comes to pneumatics, so I apologize for any stupid questions.

My question for today is that my team is having a little bit of trouble with the kicker.

We're using cylinder with a 9" stroke and I believe a 2" bore. We're trying to use the festo solenoid control valves that were provided in the kits. Actually, I think we're using the '09 valves.

We can't seem to get a decent kick out of the system. Now an obvious change was to use a cylinder with a smaller bore and a shorter stroke, but some of our mentors also suggested getting a valve with a large flow rate.

Now, I'm wondering those of you who are using pneumatic kickers, what kinds of valves are you having success with? Or if you are using pneumatics, which valve would you recommend?

[ebarker]

A couple of suggestions.

1) read robot rule <R72> part 'C' - make sure your mentors and students understand that. ( hint: there are rule limitations as to how big a valve you can use )

2) search around on Chief Delphi about other folks ideas on implementing pneumatic based kickers. there are some pretty decent ideas floating around on how to implement a system.

[scottydoh]

Per Section 8, The Robot

<R72>
C. Solenoid valves. All such valves must have a maximum ⅛” NPT port diameter, and a maximum Cv of 0.32 (if non-KOP valves are used, the team will be required to provide part documentation validating that the valves meet these constraints).

I interpret the highlighted part as not allowing the "large flow rate" you talked about. The maximun flow coefficient (Cv) for the valve is .32 as stated.

My suggestion is to use a smaller bore cylinder or possibly augmenting the cylinder with some sort of mechanical energy (spring, latex tube etc.).

[dude__hi]

We finalized our kicker today. we're using a 1.5 in bore 8in stroke pneumatic piston. We're using a gate latch to keep the rod from extending when pressurized then opening the latch gate to release all the force at once. We're adding a spring to further increase the amount of force output.

http://www.youtube.com/watch?v=QLH-XqNyQ-0

These are the early prototypes. The recent ones are more complete and don't need people to reset them or hold them in place. The video displaying the final design for the pneumatic shooter we settled on should be up today or sometime tomorrow.

[Mrpalmere]

It may be helpful to move the solenoid valve up close to the inlet port and have the air storage tank directly before the solenoid. Also, try using an open return port and use a rubberband to return the cylinder. Use a single solenoid or close off the ports on the double. Using a smaller diameter cylinder will increase the velocity of the actuation and using an open exhaust port allows for the freeflow of air on actuation. Hope this helps.

[IndySam]

Originally Posted by Mrpalmere

It may be helpful to move the solenoid valve up close to the inlet port and have the air storage tank directly before the solenoid. Also, try using an open return port and use a rubberband to return the cylinder. Use a single solenoid or close off the ports on the double. Using a smaller diameter cylinder will increase the velocity of the actuation and using an open exhaust port allows for the freeflow of air on actuation. Hope this helps.

This is great advice. I would even go as far as saying plum the valve directly on the cylinder.

[scottydoh]

Yea, accumulator > solenoid > cylinder is probably your best bet, with little to no tubing between.

[Ether]

Originally Posted by Mrpalmere

... try using an open return port and use a rubberband to return the cylinder ... using an open exhaust port allows for the freeflow of air on actuation.

"open exhaust port"... is this legal? has it been used in competition and permitted by the inspectors?

I was wondering if Rule <R72> Part C in Paragraph 8.3.9 applies in any way to this question:

"valves must have a maximum ⅛” NPT port diameter, and a maximum Cv of 0.32"

I was trying to figure out the purpose/intent of this Rule, and whether leaving the exhaust port open (or using more than one solenoid to feed the input) violates the intent of the rule?


~

[IndySam]

Originally Posted by Ether

"open exhaust port"... is this legal? has it been used in competition and permitted by the inspectors?

I was wondering if Rule <R72> Part C in Paragraph 8.3.9 applies in any way to this question:

"valves must have a maximum ⅛” NPT port diameter, and a maximum Cv of 0.32"

I was trying to figure out the purpose/intent of this Rule, and whether leaving the exhaust port open (or using more than one solenoid to feed the input) violates the intent of the rule?


~

There is no rule that says you have to to have a valve on a cylinder just a rule of what the valve size must be. Teams have been leaving them off of cylinders for years.

[Ether]

Originally Posted by IndySam

There is no rule that says you have to to have a valve on a cylinder just a rule of what the valve size must be. Teams have been leaving them off of cylinders for years.

Do you have any insight you could share about the purpose of the 1/8" and .32 Cv rule R72 partC? If you're allowed to leave the valves off the exhaust port and you're allowed to use multiple valves to feed the input port, I don't understand what purpose the rule serves. This leads me to believe I'm probably misunderstanding an important aspect of this issue.


~

[IndySam]

Originally Posted by Ether

Do you have any insight you could share about the purpose of the 1/8" and .32 Cv rule R72 partC? If you're allowed to leave the valves off the exhaust port and you're allowed to use multiple valves to feed the input port, I don't understand what purpose the rule serves. This leads me to believe I'm probably misunderstanding an important aspect of this issue.


~

<R72>
C. Solenoid valves. All such valves must have a maximum ⅛” NPT port diameter, and a maximum Cv of 0.32 (if non-KOP valves are used, the team will be required to provide part documentation validating that the valves meet these constraints).

Valve refers to the solenoid assembly not the connectors. The 1'8 NPT refers to the size of the port fitting on the solenoid valve. This and the quoted flow rate along with the mandated hose size and working pressure are limiting factors of the system. They limit the amount of energy that can be used at any time and the rate of that energies delivery.

Doubling the valves may double up on the flow rate (in theory) but it will not increase the amount of working energy delivered. Also leaving off the connector on the exhaust end of your cylinder will not increase the amount of working force but it will increase the speed of the mechanism.

The entire system is limited by that little hose coming of the low pressure regulator. This is the big limiting factor.

The GDC has to set some limits to the amount of energy available to the teams. They also want to make the inspectors jobs easier. Giving limiting specs significantly reduces the things the inspectors have to deal with. A lot of the inspectors I have dealt with over the years only knowledge of pneumatics is what the have learned through FIRST. Imagine what it would be like for them if they would allow me to use things like ultra high resolution pressure control valves.

[vamfun]

Team 39 used a much simpler system where three valves fed into one pneumatic cylinder."

At the Sat scrimmage I saw what Matt spoke of... don't remember the team.

One team had ordered a large bore cylinder from BIMBA that had multiple ports feeding each end of the cylinder which allowed more than one valve to feed the big mother hence increasing the effective flow rate.

This is probably legal based upon the rule:
D:...Cylinders may be of any configuration, and may be of any size up to a maximum of 24-inch stroke and 2-inch diameter.

but I'm concerned that it violates the intent of the valve port/Cv size limits.

Any thoughts?

[abross]

Originally Posted by dude__hi

We finalized our kicker today. we're using a 1.5 in bore 8in stroke pneumatic piston. We're using a gate latch to keep the rod from extending when pressurized then opening the latch gate to release all the force at once.

What exactly do you mean by 'gate latch.' I understand the theory, but what exactly does it look like? Thanks.

[Hastypickle]

You could try using a lever to help get the speed that you need out of the kicker. We tried a 1.5 inch bore cylinder directly, but the ball only went a few feet. We then added a lever and the ball would go 15+ feet.

If you play around with it you can get a really good kick out of a large cylinder.

[Matt H.]

In 2008 several teams (including 1726) used Pneumatic Launchers. Because the valves restrict flow rate every successful pneumatic launcher (that I can remember) used some kind of trick.

1726 used a system where the cylinders where never completely collapsed. Levers were arrange to make the launch mechanism provide very little force for the first few second allowing enough air to fill the cylinder such that when the ball passed a certain point it launched very quickly.

Team 39 used a much simpler system where three valves fed into one pneumatic cylinder. They also used levers for speed. I find this method most appealing.

Remember that with all pneumatic mechanisms safety should be paramount.