Pre-charging pneumatic air tank

[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

[mikets]

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.)

Thanks for pointing out the 5V signal. I was about to check it out. So we would have to either use a resistor/Zener diode to step down to 5V or use a 12V relay instead. Just to reiterate, we are not using this at the competition. We are thinking of using it in the shop for testing and prototyping. The rake will have all the safety and relief valves in place. In my opinion, it is safer than the students trying to pressurize it with a battery and a switch box. I will get together with our pneumatic expert to make sure all the safeties are in place (i.e. safety relief valves, pressure gauges, emergency stop button etc). This is mainly used for testing a prototype that is not a complete robot, so there is no other electronics and certainly no cRIO.

[MrBasse]

Originally Posted by mikets

Thanks for pointing out the 5V signal. I was about to check it out. So we would have to either use a resistor/Zener diode to step down to 5V or use a 12V relay instead. Just to reiterate, we are not using this at the competition. We are thinking of using it in the shop for testing and prototyping. The rake will have all the safety and relief valves in place. In my opinion, it is safer than the students trying to pressurize it with a battery and a switch box. I will get together with our pneumatic expert to make sure all the safeties are in place (i.e. safety relief valves, pressure gauges, emergency stop button etc). This is mainly used for testing a prototype that is not a complete robot, so there is no other electronics and certainly no cRIO.

Why are you using FIRST components if you are just prototyping? What is the point of going through all this hassle when you can just use a shop compressor with a regulator? If you want to make this be as safe as possible and use FIRST legal components, then get another cRIO and complete the test robot.

When we test we use a small pancake compressor that shuts off at 110 PSI and we use the regulator to limit working pressure to 60 PSI. If we want a real cordless option we run an old 8 slot cRIO on our testing chassis. I just don't get why you would want to over work a small 12V compressor for shop testing.

For competition use see nearly every post above, especially DonRotolo's. It is hard to agree more with someone...

[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

[Jon Stratis]

Originally Posted by 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.

Do you have any idea how many relief valves I've had to help teams set at competition? The above setups would not have had that protection in their shops at home, as most often these relief valves come from the factory set well above 150 psi.

-Connecting the compressor to a drill battery No
-Connecting the compressor to a robot battery with breaker No
-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.No
-Programming the robot in auto to run the compressor non stop and let excess pressure vent through the relief valveNo
-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 startsNo
-Having a button on the computer that runs the compressor when held, used to charge the system until the relief valve starts releasing airNo

-shorting out the pressure switch to run compressorNo

The rules are pretty clear...

[Tristan Lall]

Originally Posted by magnets

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

I think it's important to specify the situation. Teams cannot be expected to maintain their robot in a perpetual state of rules compliance (for example, during maintenance, robots often are in no state to pass inspection or play). Instead, they must demonstrate compliance at inspection and during gameplay. There is a different set of rules (and guidelines) that are in effect throughout an event, largely due to safety considerations.

[DonRotolo]

I'm sorry folks, but which part of "One and only one" is not perfectly clear to you?

Aside from the other reasons mentioned, having two compressors gives a team an unfair advantage, since the on-board compressor is not being run as much. This keeps it cooler, allowing it to be more efficient and effective.

Seriously: Follow the rules or don't, but if you don't, stop trying to rationalize your cheating.

[orangemoore]

Originally Posted by DonRotolo

I'm sorry folks, but which part of "One and only one" is not perfectly clear to you?

Aside from the other reasons mentioned, having two compressors gives a team an unfair advantage, since the on-board compressor is not being run as much. This keeps it cooler, allowing it to be more efficient and effective.

Seriously: Follow the rules or don't, but if you don't, stop trying to rationalize your cheating.

This.
Seriously this conversation should be over. What else is there to talk about?

[pfreivald]

Originally Posted by orangemoore

This.
Seriously this conversation should be over. What else is there to talk about?

Yes, it should.

But we should talk more about this:

Originally Posted by 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.

First, the relief valve must be properly installed in order to do its job.

Second, relief valves bleed, they don't gush--it's entirely possible to overpressurize a system by adding air faster than the relief valve can relieve it.

Third, I'm 100% positive that you don't have personal knowledge of all the "incidents" mentioned, and so cannot speak authoritatively on what did or did not cause them.

Fourth, rationalizing unsafe or disallowed practices with shoddy handwavium arguments and invented "facts" is not useful. So please stop.

[EricH]

Originally Posted by pfreivald

First, the relief valve must be properly installed in order to do its job.

Which includes calibration. The one and only time I'd actually recommend shorting the pressure sensor is to calibrate the relief valve--and I can think of a way to test that without even involving the sensor. The idea, of course, is to run the relief valve up to about 130 psi and see if it vents before then (if not, immediately vent the system using a dump valve and readajust).