Calibrate Pressure Switch?

[ArtemusMaximus]

Originally Posted by 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.

I wish the rules and manual's language would be a lot clearer.
I am reading same paragraph and I do not see that it means prohibition of pressure switches other than Nason switch provided in KOP

[Alpha Beta]

Originally Posted by 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.

The pneumatics manual clearly says it cannot supersede the rules.

The 2014 FIRST Robotics Competition (FRC) pneumatic components are outlined in this document. It is being provided as a courtesy, and therefore does not supersede any information or rules provided in the 2014 FIRST Robotics Competition Manual. For official questions, please go to the FIRST Forums at http://forums.usfirst.org.

Al has hinted that there will be some rule changes for 2015. Hopefully this will get cleared up. I still can't find the leg that the inspectors are standing on when disallowing adjustable pressure switches this year. As always the LRI has the final say at the tournament, and we will continue to respect that. At the same time we hope their decisions can be fully backed up by a reasonable interpretation of the rules.

[Steve W]

Originally Posted by Alpha Beta

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.



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.

The inspector was actually Big Al and Frank was also in on the decision I believe.

[wilsonmw04]

Originally Posted by ArtemusMaximus

Can pressure switch be replaced with this pressure sensor and then calibrate within the code?
http://www.digikey.com/product-searc...ds=734-1003-ND

not within the current rules.

[Nirvash]

Originally Posted by Steve W

The inspector was actually Big Al and Frank was also in on the decision I believe.

What rule was cited in the decision?

[Al Skierkiewicz]

The pressure switch that is being discussed was resettable in seconds, without tools, to a max of 145 psi. For those reasons and others that I discussed with the team, it neither meets the rules, the Q&A nor the intent.

Frank, the calculation I was looking for is the pressure volume conversion. So with two Clippard 41 cu. in. tanks, the conversion to 60 psi results in 157 cu in. @115 psi and 164 cu. in. @ 120 psi. About 4% increase in volume at 60 psi.

Sorry I didn't answer sooner, I was at the Minnesota State HS Champs this weekend.

[ArtemusMaximus]

Originally Posted by Al Skierkiewicz

The pressure switch that is being discussed was resettable in seconds, without tools, to a max of 145 psi. For those reasons and others that I discussed with the team, it neither meets the rules, the Q&A nor the intent.

It seems to me that inspectors have to interpret rules rather than rules being clear enough so they don't need to be interpreted. It puts inspectors and teams in hard position: inspectors to interpret rules and teams to comply with interpretations of the rules rather than comply with clear rules themselves.

If we are going to include "ill-intent" in the considerations, then there are few more ways that things can be reset after passing inspection (i.e. Pressure release valve, or even code itself). What makes pressure switch to be under more scrutiny? After all, for it to work (for pressure above 120 PSI), pressure release valve has to be reset as well.

I suppose asking simple questions on Q&A and getting clear answers would help this situation.

[Al Skierkiewicz]

Art,
We are not saying that the team intended to increase pressure, nor are we saying that they would recalibrate the relief valve. Inspectors do need to make interpretations all the time. This is only one of a hundred + that I made this season. A few were... Are tywraps suitable fasteners for springs? Can a team use barbells for ballast? Is a 16 pound mallet legal for a ball shooter? Can I use a leg lamp from the Christmas Story as a kicker? Can I bring in my protobot and my alternate drive base in addition to my bagged robot? Can I use a ratchet wrench as a mechanism for my shooter release device? Can I use an electro magnet that we rewound for use at 12 volts? When I replace the nylon stockings on my leg lamp that are damaged during a match, is that a repair or modification? Can I put this "mini=sun" on my robot to help my vision system? Can I make a 300 volt power supply to power the neon lights our sponsor would like to see on the robot? Can I write my own protocol software, I don't like that which is provided? These are in addition to the questions asked on the Q&A.

[Jon Stratis]

Al, you missed a classic one at the State Champs over the weekend... Our bumper fell off in the last match, can I attach it to the robot with Duct Tape for the next match?

[ArtemusMaximus]

Originally Posted by Al Skierkiewicz

Art,
We are not saying that the team intended to increase pressure, nor are we saying that they would recalibrate the relief valve. Inspectors do need to make interpretations all the time. This is only one of a hundred + that I made this season. A few were... Are tywraps suitable fasteners for springs? Can a team use barbells for ballast? Is a 16 pound mallet legal for a ball shooter? Can I use a leg lamp from the Christmas Story as a kicker? Can I bring in my protobot and my alternate drive base in addition to my bagged robot? Can I use a ratchet wrench as a mechanism for my shooter release device? Can I use an electro magnet that we rewound for use at 12 volts? When I replace the nylon stockings on my leg lamp that are damaged during a match, is that a repair or modification? Can I put this "mini=sun" on my robot to help my vision system? Can I make a 300 volt power supply to power the neon lights our sponsor would like to see on the robot? Can I write my own protocol software, I don't like that which is provided? These are in addition to the questions asked on the Q&A.

Al,
I hear what you saying and NEVER implied that inspectors purpose was to make teams life harder. I also recognize that it is not an easy job to do the inspections considering so many variables on each robot and decisions have to made quick. But now that we are discussing it without added pressure of the competition event, reasoning you provided did not seem fully align with the rules and that's why I was questioning it.
I wasn't hoping for FRC to include all the variety of weird questions in the rule book. What I was hoping is the rules that already exist to be more clear. In the instance of Pressure Switch something like these would be a lot more definitive:

• Only pressure switch that can be used is Nason fc14-006 (part #SM-2B-115R/443)
  or
• Any COTS pressure switch can be used that switches at 120PSI or less
  or
• Any COTS pressure switch can be used that switches at 120PSI or less. However, no adjustable switches allowed.

This is probably an idealist speaks in me, but I cannot see a reason why rules cannot be clearer.

[Al Skierkiewicz]

Might be more like:

R78
If pneumatic COMPONENTS are used, the following items are required as part of the pneumatic circuit and must be
used in accordance with this section, as illustrated in Figure 4-15.
A. Compressor
B. Pressure Relief Valve, calibrated for release at 125 psi.
C. Pressure Switch, Nason #SM-2B-115R/443 or identical specification (115-120 psi), non-adjustable, equivalent.
D. Pressure Vent Plug
E. “Stored” Pressure Gauge (upstream from Primary Regulator)
F. “Working” Pressure Gauge (downstream from Primary Regulator)
G. “Working” Pressure Regulator

For everyone, the part number shown above is the device sold by AndyMark and the part number refers to a set point of 115 psi. The data sheet specifies the set point at +/- 1 psi with a differential (hysteresis) of 8-16%. That translates to turn compressor back on when the pressure falls below 97-107 psi.
While it is hard to see due to the formatting of the pdf, remember...
R81
“Stored” air pressure on the ROBOT must be no greater than 120 psi.

[ArtemusMaximus]

Originally Posted by Al Skierkiewicz

Might be more like:

R78
If pneumatic COMPONENTS are used, the following items are required as part of the pneumatic circuit and must be
used in accordance with this section, as illustrated in Figure 4-15.
A. Compressor
B. Pressure Relief Valve, calibrated for release at 125 psi.
C. Pressure Switch, Nason #SM-2B-115R/443 or identical specification (115-120 psi), non-adjustable, equivalent.
D. Pressure Vent Plug
E. “Stored” Pressure Gauge (upstream from Primary Regulator)
F. “Working” Pressure Gauge (downstream from Primary Regulator)
G. “Working” Pressure Regulator

For everyone, the part number shown above is the device sold by AndyMark and the part number refers to a set point of 115 psi. The data sheet specifies the set point at +/- 1 psi with a differential (hysteresis) of 8-16%. That translates to turn compressor back on when the pressure falls below 97-107 psi.
While it is hard to see due to the formatting of the pdf, remember...
R81
“Stored” air pressure on the ROBOT must be no greater than 120 psi.

Yeah, something like that. Clearly specifying "non-adjustable" or "adjustable" definitely helps to determine if ability to adjust is allowed or not.

[Tristan Lall]

Do we have confirmation on how the pneumatics control module (PCM) works on the 2015 control system? It has two dedicated Weidmüller terminals for a pressure switch. If there's a microprocessor on the PCM (almost certainly, since there's CAN to decode), can it handle enabling and disabling the pneumatics without influence from the user code and firmware of the RoboRIO (other than a state flag over CAN)?

If it's the case that the user code has no effect on pneumatic cutoff, then that's a big improvement. Perhaps even a big enough improvement to justify leaving out the ability to read an analogue transducer in place of a traditional pressure switch.¹ Right now, the prohibition on using a transducer instead of a pressure switch for sensing the 120 lb/in² limit is pointless, because the team has ultimate control over the compressor relay.

¹ If it's software-controlled in the user code, there's not much added overhead to run a transducer instead. If it's firmware-controlled on the PCM, it might be simplest to avoid providing a method to calibrate an analogue transducer, even though electrically it's equivalently simple.

[adciv]

The PCM works based on the Pressure Switch and the enable flag from the robot. The RIO is not directly in the loop for this.