Pre-charging pneumatic air tank

[Steve W]

Originally Posted by 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.

Do yo really believe that this is legal? ONE and only ONE compressor is allowed to be used on the robot. If you charge with one then connect another you MUST discharge all of the air in the tanks or you would have used 2, count them, 2 compressors.

It must be that many people are using compressors for the first time and just skimmed over the rules. Some however just want to cause controversy so they are shaking the cage to see what happens.

[Al Skierkiewicz]

Guys,
While this often gets into a safety discussion, that is only part of the issue. In the preamble of the robot rules you will find this reference...
"In addition, another intent of these rules is to have all energy sources and active actuation systems on the
ROBOT (e.g. batteries, compressors, motors, servos, cylinders, and their controllers) drawn from a
well-defined set of options. This is to ensure that all Teams have access to the same actuation resources,
and to ensure that the Inspectors are able to accurately assess the legality of a given part."

[pfreivald]

As Al says, safety is only one of the reasons behind it--but to be honest, it would be unreasonable of the FRC community to expect the GDC to explain the reasoning behind every rule they make. (Especially but not limited to the fact that people will then use that reasoning as a starting point for an argument.)

What matters here is that there is an unambiguous and clear rule that teams need to follow, and that attempts to end-around that (or any other) rule is unacceptable.

[wilsonmw04]

Originally Posted by 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.

The rule has to be there for the safety of all. It is the most accessible way for all teams to store this form of energy safely. whether you/I agree with the rule is irrelevant.

[cgmv123]

Just a note that is legal to replace the battery used to charge with a fully charged one after precharging per Q88.

[mikets]

Okay, I am convinced it's not worth doing at the competition. However, in the spirit of learning the intention behind the rules, I would still like to understand why. I understand it's about safety. But would somebody tell me why is my proposed setup not equivalent to the onboard setup? It has the same model pressure switch that will cut off compressor power. It's using the same compressor model and spike as the onboard system. The only difference is the missing cRIO. Regarding the Emergency stop feature, there is a master power switch. We can using a giant red button for it. Again, I will not do this for the competition but at the shop when we are building the robot, there is always a need for the build team to test the pneumatic system while the electronics is being worked on in parallel. We have a modular design so each subsystem can be built and tested separately. This setup will benefit that scenario. The students have been just powering an external compressor with a battery and I always don't like it. If I understand the safety concern, we will be able to build a safe testing setup.
We have many test setup in our shop to make life easier for the build team. For example, we have a PWM generator feeding a Talon so we can test motors without the cRIO. So the pneumatic test setup is equivalent to that.

[Mr V]

Using a system with a pressure switch that will control a relay whether it is a spike or simple 12v relay with a properly calibrated blow off valve would be safe in general, despite not being legal for use at an event.

The safety concern I would have is that if people are working on the rest of the robot while the pneumatics are pressurized there are potential safety issues. Power may inadvertently be applied to a solenoid causing an actuation that could harm someone who's hand or head was in or near a robot. A tool that slips or is dropped could potentially cause one of the plastic tanks to explode ect. It is for that reason that it is highly recommended that work only occurs on the robot when the power is off and the pressure has been relived from the pneumatics.

[Alan Anderson]

Originally Posted by mikets

But would somebody tell me why is my proposed setup not equivalent to the onboard setup? It has the same model pressure switch that will cut off compressor power. It's using the same compressor model and spike as the onboard system. The only difference is the missing cRIO.

There is one more very large difference. Your onboard pneumatics system (with its compressor and pressure switch and everything else) gets checked by the inspectors for proper operation. Your proposed setup does not. Its design might well be equivalent, but the execution does not get evaluated by people responsible for ensuring that every team plays by the rules.

(The more fundamental difference is that your proposed setup won't work. The Spike control input is a 5 volt signal.)

[NotInControl]

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.

Originally Posted by Alan Anderson

There is one more very large difference. Your onboard pneumatics system (with its compressor and pressure switch and everything else) gets checked by the inspectors for proper operation. Your proposed setup does not. Its design might well be equivalent, but the execution does not get evaluated by people responsible for ensuring that every team plays by the rules.

(The more fundamental difference is that your proposed setup won't work. The Spike control input is a 5 volt signal.)

I believe the bigger difference is that the off-board compressor even with the same model compressor, and pressure limit switch directly wired to the realy (eve if that would work) and it's own E-stop button is: it is not controlled by the driverstation. So hitting the e-stop, or disable on the driverstation, would allow the compressor to still run. Which is considered an un-safe condiditon and must be avoided. Thus the reason for having air be controlled by the cRIO.

In any system where an E-stop is required you want one which kills all functionality which could cause harm/damage. Having mulitple mutually exclusive E-stop buttons as would be the case in your setup defeats the purpose of the E-stop.


Regards,
Kevin

[Tristan Lall]

Originally Posted by Steve W

Do yo really believe that this is legal? ONE and only ONE compressor is allowed to be used on the robot. If you charge with one then connect another you MUST discharge all of the air in the tanks or you would have used 2, count them, 2 compressors.

How about posing that to the Q&A? After all, Q88 says you can replace the battery (of which one is permitted); why not the compressor?

I'd rule it legal on that basis, absent a Q&A to the contrary.

[DampRobot]

Originally Posted by 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.

Here here.

[Steve W]

Originally Posted by Tristan Lall

How about posing that to the Q&A? After all, Q88 says you can replace the battery (of which one is permitted); why not the compressor?

I'd rule it legal on that basis, absent a Q&A to the contrary.

Tristan you better read the rules. It says 1 compressor. There are rules about filling tanks. If you have an issue you ask the Q&A. Plain and simple, as an acting LRI and reading the rules and going for training, I deem it illegal.

[Daniel_LaFleur]

Originally Posted by mikets

Okay, I am convinced it's not worth doing at the competition. However, in the spirit of learning the intention behind the rules, I would still like to understand why. I understand it's about safety. But would somebody tell me why is my proposed setup not equivalent to the onboard setup? It has the same model pressure switch that will cut off compressor power. It's using the same compressor model and spike as the onboard system. The only difference is the missing cRIO. Regarding the Emergency stop feature, there is a master power switch. We can using a giant red button for it. Again, I will not do this for the competition but at the shop when we are building the robot, there is always a need for the build team to test the pneumatic system while the electronics is being worked on in parallel. We have a modular design so each subsystem can be built and tested separately. This setup will benefit that scenario. The students have been just powering an external compressor with a battery and I always don't like it. If I understand the safety concern, we will be able to build a safe testing setup.
We have many test setup in our shop to make life easier for the build team. For example, we have a PWM generator feeding a Talon so we can test motors without the cRIO. So the pneumatic test setup is equivalent to that.

OK. I'll take this one:
1> Are the 2 setups equivalent? No they are not ... then next few answers will demonstrate why.
2> Same model pressure switch --- the pressure switches are set to 120PSI. There is no telling (IE Proof) that the offboard pressure switch is set to the same setpoint as the onboard one. Should it not be set, the pressure could reach almost 150PSI
3> The wiring on the pressure switch is rated for less than 3 amps. The compressor runs at ~ 8 amps with a startup over 20 amps. This alone should suggest you should not do this.

When it comes to pneumatics, I'll err on the side of caution every time (and I've worked with it for ~15 years).

[Seth Mallory]

I have worked with pneumatics for 26 years and I want to make 2 points.

1) The compressors on the robots will go far higher then 120 psi. That is why FIRST wants the compressor controlled by the cRIO.

2) It would be time consuming to make the inspectors have evaluate each unique none standard control system.

I still have dent in a leg from a broken air line 24 years ago and that was at 110 psi.

[magnets]

I think that some of the rules for the pneumatics are a little weird. All the "incidents" mentioned have not been due to over pressurization. The relief valve takes care of that.

I don't get why they think that the cRIO control is going to be a super safe solution. They're relying on programming and wiring done by inexperienced high school kids.

This question is for inspectors. Which of the following would be illegal?

-Connecting the compressor to a drill battery
-Connecting the compressor to a robot battery with breaker
-Programming the robot to run the compressor an additional 10 seconds after the pressure switch says its full to fill all the way to 125 psi because the pressure switch stops at 115 psi.
-Programming the robot in auto to run the compressor non stop and let excess pressure vent through the relief valve
-Having a button on the computer that runs the compressor when held, used to charge a system at 95 psi to 115 psi before a match starts
-Having a button on the computer that runs the compressor when held, used to charge the system until the relief valve starts releasing air

-shorting out the pressure switch to run compressor