Re: Solution: Variable position of cylinder in compliance with <R74>
 

question to GCD 03/04/2011

2011FRC2221
Pneumatic Solenoid
R73> The pressure vent plug valve must be connected to the pneumatic circuit such that, when manually operated, it will vent to the atmosphere to relieve all stored pressure. The valve must be placed on the ROBOT so that it is visible and easily accessible. If the compressor is not used on the ROBOT, then an additional vent valve must be obtained and connected to the high-pressure portion of the pneumatic circuit off board the ROBOT with the compressor (see Rule <R69>).
First forums GDC reply 01-31-2011, 02:05 PM “Trapping the air under pressure as described would be a violation of R68/R73. The rule clearly states that when the required relief valve is opened, it will vent to the atmosphere to relieve all stored pressure.”
<R66> In addition to the items included in the KOP, pneumatic system items specifically permitted on 2011 FRC ROBOTS include the following items.
Pneumatic pressure vent plug valves functionally equivalent to those provided in the KOP,
<R66> allows multiple pressure plug valves.
Question: Can you plumb pressure plug valves in the pneumatic lines to the cylinder using a 5 port 3 position center port closed solenoid valve and position these valves adjacent to the original pressure vent plug valve and still be in compliance with <R73> .
Thank you
Team 2221
2011FRC2221

Reply from GCD
03-15-2011, 01:35 PM
The purpose of this forum is to answer specific rule questions, not to perform design reviews for legality. That decision will be left up to the inspectors at each event.
GDC

Look like you can proceed at your own risk at each regional

Re: Solution: Variable position of cylinder in compliance with <R74>
 

I think this would be illegal. From what I have read/heard/understood is this: your system must be void of all stored and working pressure when any one relief valve is opened. If there is pressure anywhere in the system after the valve is opened, the system is illegal.

Re: Solution: Variable position of cylinder in compliance with <R74>
 

Why not just use multiple cylinders, mounted end to end?

Re: Solution: Variable position of cylinder in compliance with <R74>
 

When you open the purge valves on the inlet and outlet of the cylinder you will release all stored energy. Let me draw up a sketch and I will post it shortly.

Re: Solution: Variable position of cylinder in compliance with <R74>
 

multiple purge valves (which are legal) sketch. You do not need check valves (which are illegal)

Re: Solution: Variable position of cylinder in compliance with <R74>
 

The fact remains that if you open up one of the valves (only one) ALL of the pressurized air must be released. Also, some other components, such as some flow control valves (which are legal), can act as check valves so the check valves in the schematic don't have to be actual check valves. If it was as simple as adding more plug valves, we would never have designed the other two, more complex, systems featured in this thread.

Re: Solution: Variable position of cylinder in compliance with <R74>
 

We had to change our design also. The rules do not limit the number of purge valves. The GCD failed to set a quantity and they do not state opening only one purge valve. They have shifted the responsibility to the inspectors. It is kind of a mute point for us this year because our competition is over. The GDC did not answer our question till two days before we had to compete.

Re: Solution: Variable position of cylinder in compliance with <R74>
 

ouch! I did notice a large gap in Q&A responses, what was up with that? IDK how much luck you had this year, but I hope you have better luck next year:D

Re: Solution: Variable position of cylinder in compliance with <R74>
 

We ended up keeping the system as a "Plan C," since the BaneBots motor on the shoulder of our arm burnt up the night before shipping, and we weren't sure if we could get the new gearbox to work at the San Diego regional. However, in testing, we did find that we needed "purge valves" on each line to the cylinder, since we would be trapping atmospheric pressure in the cylinder, preventing movement. Since it wasn't technically pressurized, it was still a legal setup. We haven't actually implemented the system in a competition. Our motor/gearbox setup has worked through two competitions, so far (San Diego and LA), so we haven't seen a need to change it out, despite the fact that the pneumatic system would be lighter and easier to control. However, this was an interesting learning experience, and I hope to implement something to this effect in next year's competition.

EDIT: I created a PDF documenting the process of designing our system. I thought you guys might find it interesting.

Re: Solution: Variable position of cylinder in compliance with <R74>
 

If it is trapped, any change in volume can lead to pressurization (that's why we aren't allowed to block the ports on cylinders to make gas shocks). I don't know if this affects you, but if it does, it could be important to know.

Re: Solution: Variable position of cylinder in compliance with <R74>
 

Thanks for the heads-up, but it doesn't really affect us. The push-button valves are just in case we need to move the arm, since it would generate a vacuum in one side of the cylinder. The check valves will allow any built up pressure to equalize with the atmosphere, but they will not allow air in. I tested the arm with a pressure gauge in each cylinder supply line, and the vent valve dumped all pressure when opened. Under load, the vacuum usually isn't enough to hold the arm up on its own, but it does make manual repositioning slightly more difficult.

Re: Solution: Variable position of cylinder in compliance with <R74>
 

I am just wondering how you read...

R68
D. An easily visible and accessible pressure vent plug valve to manually relieve the stored pressure (see Rule <R73>).

to mean more than one vent valve is legal? Everything in that sentence looks to be singular in my mind.

Re: Solution: Variable position of cylinder in compliance with <R74>
 

As per my understanding, you can have more than one vent valve, as long as there is a singular valve that will relieve the entire system. The two extra valves are only there to allow us to move the arm after we depressurize the system.

Re: Solution: Variable position of cylinder in compliance with <R74>
 

That sentence would make the system illegal. Any one valve would have to remove ALL pressure from the system. We had two on our robot last year (because we forgot to take one off while testing part of it) and the inspector made sure that we didn't have any pressure behind it when the main valve was released.

Again, any air trapped when any one valve is opened will cause your robot to fail inspection. Ignore our multiple warnings at your own risk.

Re: Solution: Variable position of cylinder in compliance with <R74>
 

Trapped air that is not pressurized beyond atmospheric pressure is legal, to my knowledge. The only thing that is making the arm difficult to move is the vacuum generated inside the cylinder, since the check valves prevent air from entering the system. The extra push buttons let air into the cylinder. Vacuums are not subject to the rules governing pneumatic systems, according to <R66>, part G. Once the vent plug valve is open, any positive pressure created by the movement of the arm is exhausted as it is created, through the check valves, and the only pressure that exists is negative (vacuum).