Pre-charging pneumatic air tank

[mikets]

At our last district competition, we routinely pre-charged the air tank while queuing for the match. We were plugging the compressor power directly to a battery with a switch. Once the pressure reaches a certain PSI, we turn off the switch and plug the compressor back to the system.The field staff told us not to do that. If we need to pre-charge the air tank, we must do so via the cRIO. I can see the reason behind it. I can see if the person doing that got distracted and not paying attention to the pressure gauge, that could be dangerous. However, I am thinking we could build a pneumatic charging station by putting together a battery, a master ON/OFF switch, a pressure limiting switch, a spike relay and a compressor such as in this diagram (sorry about the crude diagram, I am at a computer with only mspaint).

Is this allowed?

[Thad House]

No that is not allowed. All air provided to the system must be provided by the compressor controlled by the CRio.

[BigJ]

For more info see R80 and R85 (and the rest of the pneumatics rules)

[Chief Hedgehog]

You should not bypass the control system. See the following snippet from another post regarding charging pneumatic systems.

*Event though it is in regards to shop compressors, the intent is the same.

Originally Posted by Jon Stratis

There are multiple issues with having shop compressors in the pits.

First, as inspectors we don't know what you're using it for. You could use it to charge your robot at any point - while this is clearly not legal for competition use, doing so for use on the practice field and in the pits also bypasses half the safety mechanisms on the robot - stored air is not under the control of the robot, it doesn't turn off when the robot is disabled or e-stopped, and it doesn't automatically stop at 120 PSI (many shop compressors can be adjusted to charge to greater than 120 PSI). So using it to charge the robot for non-competition uses at a match violates R8 by creating a potentially unsafe condition in the pits or practice field.

.

[vgdude999]

What I'm going to be doing is keeping the battery used in the previous match in the robot until queue and use it to precharge the tanks before the match is over. Then I'm going to throw a fresh battery in and have someone take the used one back to the pit to charge. Slightly annoying, but we've got to do what we've got to do. Hope this helps

[mikets]

Originally Posted by Chief Hedgehog

You should not bypass the control system. See the following snippet from another post regarding charging pneumatic systems.

*Event though it is in regards to shop compressors, the intent is the same.

I still don't understand the intention of the rule. We are thinking of using the same model compressor as the one used in competition. So it is not a more powerful shop compressor. Also, we will be wiring in the same pressure limiting switch and the same Spike as used in the system. The only difference is there is no cRIO. The limit switch directly controls the FWD input of the spike so when the pressure is reaching the limit PSI, it opens the circuit and the Spike will shut down the current to the compressor.

[Chief Hedgehog]

IF you are using the compressor that is controlled by the robot using your robot's power supply and running it through the robot, I am not sure why they would ask you to not use it.

The reason for this rule is to keep all components regulated and all people in the area safe. If you were doing this correctly, I am not certain why they would ask you to stop. Maybe to stem the tide of other teams charging in a questionable manner?

[Tem1514 Mentor]

Originally Posted by mikets

I still don't understand the intention of the rule. We are thinking of using the same model compressor as the one used in competition. So it is not a more powerful shop compressor. Also, we will be wiring in the same pressure limiting switch and the same Spike as used in the system. The only difference is there is no cRIO. The limit switch directly controls the FWD input of the spike so when the pressure is reaching the limit PSI, it opens the circuit and the Spike will shut down the current to the compressor.

The INTENT of the rule is SAFETY.
I guess you missed the Ka-BOOM at GTRW when an air tank was turned into little flying pieces of sharp plastic. Even the crickets went silent.

Do what other teams do and have two compressors, one on the bot and then a standalone. BUT only use ONE compressor at a time that is controlled by the cRIO.

[Jon Stratis]

Originally Posted by Tem1514 Mentor

The INTENT of the rule is SAFETY.
I guess you missed the Ka-BOOM at GTRW when an air tank was turned into little flying pieces of sharp plastic. Even the crickets went silent.

Do what other teams do and have two compressors, one on the bot and then a standalone. BUT only use ONE compressor at a time that is controlled by the cRIO.

I'll remind you of R79 - "Compressed air on the ROBOT must be provided by one and only one compressor." That does not say "use only one compressor at a time". It says all air must come from only one compressor - if you precharge with an off board compressor then use an on board one during the match, you are violating this rule.

Originally Posted by mikets

I still don't understand the intention of the rule. We are thinking of using the same model compressor as the one used in competition. So it is not a more powerful shop compressor. Also, we will be wiring in the same pressure limiting switch and the same Spike as used in the system. The only difference is there is no cRIO. The limit switch directly controls the FWD input of the spike so when the pressure is reaching the limit PSI, it opens the circuit and the Spike will shut down the current to the compressor.

Mikets - The intent of the rule is safety. Any time you use a compressor at competition, it needs to happen under the control of the robot. In your proposed setup here, you're missing the ability to stop the compressor via the e-stop (something that is pretty important and found in all sorts of industrial applications) or to control it via enable/disable. R78 lays out the required pneumatic components for a minimal system, R80 clearly states that the compressor must be powered and controlled by the robot, and R88 clearly states that the cRio must respond to the pressure switch appropriately. There is no wiggle room here.

[FrankJ]

The reason for the rule is really unimportant. It is a rule. There are a lot of ways to charge the air system safely. All but one them are against the rules so you can't do it that way.

[Steve W]

The posters are correct. You can only use one compressor. On board or off board is up to you. There are rules that govern what must be used with an on board compressor and other rules for the off board compressor. Working with compressed air can be very dangerous. FIRST has allowed the use on the robots with many safety requirements that must be met. I agree that some may not seem necessary but it is better to err on the way of safety.

The rules for what is allowed and not allowed are quite clear. Please read and follow them to the word. For teams that have been competing for a while, read the rules as they have changed a bit this year.

[Racer26]

Welcome to the legions of FRC participants that believe this rule unnecessarily excludes a number of perfectly safe ways to charge tanks that give no competitive advantage.

[Racer26]

As long as you were only using one otherwise legal compressor at a time, I don't really see that you'd be breaking the rules to disconnect the on-board one and use an off-board one instead -- though I'm not sure what you'd hope to gain except a bunch of extra work (and perhaps save a couple minutes of run time on the on-board one). We're allowed to replace a compressor with a different one (the one and only one compressor rule doesn't intend to forbid us from replacing a failed compressor, but merely to limit us to exactly one compressor pressurizing the system), so I don't see that this sequence really violates the intent of that rule:

1. Build ROBOT with on-board compressor
2. Disconnect on-board compressor (as though to remove it and replace with a spare)
3. Connect spare compressor
4. Power-on test, let charge tanks.
5. Disconnect spare compressor
6. Reconnect on-board compressor.

As I said though, I'm really not sure why you would want to do this. Seems like a whole lot of extra work for no benefit.

[Tem1514 Mentor]

[quote=Jon Stratis;1356359]I'll remind you of R79 - "Compressed air on the ROBOT must be provided by one and only one compressor." That does not say "use only one compressor at a time". It says all air must come from only one compressor - if you precharge with an off board compressor then use an on board one during the match, you are violating this rule.


Mikets, at least he both agree on safety but I stand by my original comment as it was done at GTRW under the watchful eyes of Steve W.

Since I don't have posting rights to the Q&A for an official answer, may be someone could ask FIRST the question as we all know answers here are not official.

[tim-tim]

There was a thread that discussed this topic.

Although, I'm not sure a Q&A was ever submitted; at least I never saw one in my reading and searching the Q&A system.