Calibrate Pressure Switch?

[Al Skierkiewicz]

Sorry but no.

[ArtemusMaximus]

Originally Posted by Al Skierkiewicz

Sorry but no.

Now that you mentioned it I looked at the rules. I should've looked at it first.
R78

So, it seems simplest method to workaround for inconsistent pressure switch is to add more air tanks on High-Pressure side, thus even at 100 PSI it will have more volume to be able to fill "Working" pressure side at 60 PSI.

[Tungrus]

In our setup we normally have two tanks on high pressure side and one or two on the low pressure side (after the regulator). For our practical purpose it works great. On related topic, last year one of the inspector wanted to test pressure relief valve by shorting the pressure switch. Unfortunately the pressure switch was not easily accessible, he was not very pleased. We believed pressure relief valve was factory set and this year we made sure that pressure relief valve was explicitly tested before mounting on the robot. Had the pressure switch next to the gauges and behold, we had the same inspector but this time he did not want to test it. Anyways SAFETY should be top priority, a lesson learned (no, we did not blow any tanks, just the discussion with inspector) and enforced by our team.

[FrankJ]

Hard to say what will be legal in 2015, but by the 2014 Q& A, this would be legal. Or you could send the first choice pressure switch back to Nason & asked that it be re calibrated so that it actually switches at 115 psi rising. Or order one from Nason with a 118 psi rising SP. That would keep you keep you below the about 120 PSI stated in the rules.

The instructions from Nason for recalibrating the SM series pressure switch calls for rotating the barrel 1/2-3/4 turn. Not dissembling the switch. I have done this on our tee shirt cannon & it has been working fine with a consistent set point (120psi) for the last year or so. Per the 2014 Q&A you cannot do this on your comp bot whether or not it works is a mute point for FRC. As in all things, you should always thoroughly test your adjustment to be sure they have the result you intended.

[Mr V]

Adjusting or attempting to adjust the switch to a higher pressure is a huge wast of time. If anything you want a switch that shuts of and turns back on at a lower pressure. The compressor will thank you with building up less heat over time and getting it back up to pressure quicker. Take a look at the rated outputs of compressors the lower the pressure it is working against the higher the cfm. Or take a look at your gauge when you fill the system from empty you'll find the rate of increase in stored pressure decreases dramatically as the stored pressure rises.

[FrankJ]

Originally Posted by Mr V

Adjusting or attempting to adjust the switch to a higher pressure is a huge wast of time. If anything you want a switch that shuts of and turns back on at a lower pressure. The compressor will thank you with building up less heat over time and getting it back up to pressure quicker. Take a look at the rated outputs of compressors the lower the pressure it is working against the higher the cfm. Or take a look at your gauge when you fill the system from empty you'll find the rate of increase in stored pressure decreases dramatically as the stored pressure rises.

This discussion got started because the OPs switch was turning off at 105 psi. I am not sure where the point of diminishing returns on your system is, but I would say generally speaking I expect it is more than 105 psi. Our comp bot was good at 110 psi. I think our compressor was on for most of the match so the HP cutoff wasn't that important. If you are running a off robot compressor, there is a big difference between 105 & 120 psi in terms of storage. Compressor efficiency is less of an issue if you are running an off board compressor.

[Mr V]

Originally Posted by FrankJ

This discussion got started because the OPs switch was turning off at 105 psi. I am not sure where the point of diminishing returns on your system is, but I would say generally speaking I expect it is more than 105 psi. Our comp bot was good at 110 psi. I think our compressor was on for most of the match so the HP cutoff wasn't that important. If you are running a off robot compressor, there is a big difference between 105 & 120 psi in terms of storage. Compressor efficiency is less of an issue if you are running an off board compressor.

Yes if you are running an off board compressor that is a different story but with an on-board compressor having it shut off at 105 is perfectly fine and I would say desirable.

[Al Skierkiewicz]

Has anyone actually done the math? How much more storage volume conversion at 60 psi do you get with 110 psi stored in two tanks as opposed to 120 psi? Assume that the regulator is the same efficiency at both pressures, and that the compressor efficiency doesn't matter.

[FrankJ]

Originally Posted by Al Skierkiewicz

Has anyone actually done the math? How much more storage volume conversion at 60 psi do you get with 110 psi stored in two tanks as opposed to 120 psi? Assume that the regulator is the same efficiency at both pressures, and that the compressor efficiency doesn't matter.

In terms of air storage, it is a linear calculation. Essentially ideal gas law, PV=nRT. So saying 60 psi is the minimum useful pressure. 110 PSI gives a delta P of 50. 120 PSI gives a delta P of 60. A 20% difference. That is in the physics lab with no friction, a perfect vacuum & ignoring entropy. All of this will effect how useful the extra air will be.

Life is always more complicated than that. In our case, the minimum useful pressure was 100 psi because that is what it took to consistently shoot the ball. What was important for us was that the compressor turned on before then. 120 psi would have been useful for precharging before the match, but 110 was good for during the match. We also went with minimal on board air storage to keep the recharge time low. So I largely agree with Mr V about what is a good set pressure.

[Steve W]

Originally Posted by FrankJ

Hard to say what will be legal in 2015, but by the 2014 Q& A, this would be legal. Or you could send the first choice pressure switch back to Nason & asked that it be re calibrated so that it actually switches at 115 psi rising. Or order one from Nason with a 118 psi rising SP. That would keep you keep you below the about 120 PSI stated in the rules.

The instructions from Nason for recalibrating the SM series pressure switch calls for rotating the barrel 1/2-3/4 turn. Not dissembling the switch. I have done this on our tee shirt cannon & it has been working fine with a consistent set point (120psi) for the last year or so. Per the 2014 Q&A you cannot do this on your comp bot whether or not it works is a mute point for FRC. As in all things, you should always thoroughly test your adjustment to be sure they have the result you intended.

Frank, I would suggest that the Q&A does not allow that part. The Q&A states that the part being substituted must be the same or equivilant to the Nason pressure switch. The fact that it is ajustable means that it is not the same or equivilant.

[Alpha Beta]

Originally Posted by Steve W

Frank, I would suggest that the Q&A does not allow that part. The Q&A states that the part being substituted must be the same or equivilant to the Nason pressure switch. The fact that it is ajustable means that it is not the same or equivilant.

Q258 Allows any pressure switch that meets the pneumatic rules.

Q459 Allows switches to be callibrated per manufacturer-provided instructions. It does not allow the end user to adjust a switch that the manufacturer did not intend to be adjustable.

R88 calls out the requirements for the pressure switch. The adjust-ability of the switch is not specified.

R88
The pressure switch requirements are:

• It must be connected to the high-pressure side of the pneumatic circuit (i.e. prior to the pressure regulator) to sense the “stored” pressure of the circuit.
• The two wires from the pressure switch must be connected directly to a digital input and ground pin on the Digital Sidecar.
• The cRIO must be programmed to sense the state of the switch and operate the relay module that powers the compressor to prevent over-pressuring the system.

Doing a quick control-F search on the game manual, the only time the word Nason showed up was in the word Panasonic when referencing allowable batteries. When searching Q&A only 258 and 459 mention the word Nason. Where does the phrase "must be the same or equivilant to the Nason pressure switch." come from. I can't seem to find it.

I heard there was an inspector who successfully got adjustable pressure switches removed from a robot at Champs. Clearly it was not a universal interpretation amongst inspectors, as we ran with this.

[ArtemusMaximus]

Originally Posted by Steve W

Frank, I would suggest that the Q&A does not allow that part. The Q&A states that the part being substituted must be the same or equivilant to the Nason pressure switch. The fact that it is ajustable means that it is not the same or equivilant.

Can I respectfully request that references are posted to specific Q&A?

Doing Q&A search I find these related answers:

Q258

Q. Are teams required to use the Nason Pressure Switch (am-2006) or can we use another switch that stops below 120 psi?
2014-01-30 by FRC3669
A. Any pressure switch may be used, provided it meets all applicable ROBOT rules.

Q459

Q. Can the pressure switch be calibrated per the manufacture's directions? (Specifically the Nason SM-2b-115R supplied in the kit of parts)
2014-03-18 by FRC2974
A. Calibration of pneumatic components per manufacturer-provided instructions would bot be considered alteration. The specific part in question is not marketed to be field/user adjustable so any calibration would be considered an alteration and therefore illegal per R76.

From which I draw conclusion that any pressure switch can be used that meet rules requirement.
In fact I cannot even find the rule the prohibits replacement Pressure Switch with Pressure Transducer.

[ArtemusMaximus]

Alpha Beta beat me to it LOL

[Al Skierkiewicz]

OK, to be a stickler here, the Pneumatic Rules also include the 2014 FRC Pneumatics Manual which lists the specifications for the switch as "This switch is normally closed. The switches will open at approximately 115 psi and will not close again until the pressure drops to approximately 95 psi." In addition paragraph 4 of Section 4, "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."
For those reasons, adjustable pressure switches are deemed illegal, in particular any switch that can be set to a pressure higher than 115 psi. Throughout section 4.10 the Nason Pressure switch is shown as the pressure switch. BTW, I am betting that the OP is using a standard robot pressure gauge that may or may not be accurate. Tapping on several (hundred) over the years have caused them to change pressure displayed.

[FrankJ]

Where in the rules is the pneumatic manual referenced? It seems to be more guidance than a rule. If it going to be taken as rule then it needs to be incorporated into the rules at least by reference so team know they are a rule.

R81 only says stored pressure needs the be below 120 PSI.
The Robot inspection checklist under power on checks specifies the compressor turns at about 120 PSI.
The Q&A Q459 specifically allows pressure switches to be calibrated if intended to be so by the manufacture.
All of this seems to be in conflict with pneumatic manual.

Using cheap non calibrated gauges to verify pressure settings, particularly safeties is a separate thread.