View Full Version : Filling Robot Pneumatic Systems
Tom Line
23-01-2014, 09:44
This year, we will be using a fair amount of pneumatics. With multiple storage tanks the fill time using the viaair compressor is problematic.
What unique and legal method of filling high-volume pneumatic storage have you come up with?
I'm currently considering some type of tank 'storage' farm made of cots components that can be filled during our down periods with the robot compressor. We can use the stored air to fill the robot during the quick turn around matches of the playoffs.
Jimmy Nichols
23-01-2014, 09:52
This year, we will be using a fair amount of pneumatics. With multiple storage tanks the fill time using the viaair compressor is problematic.
What unique and legal method of filling high-volume pneumatic storage have you come up with?
I'm currently considering some type of tank 'storage' farm made of cots components that can be filled during our down periods with the robot compressor. We can use the stored air to fill the robot during the quick turn around matches of the playoffs.
Last year we designed our storage system to fill at the duty cycle of the Viair compressor. We would pre-charge well before the match so that the compressor would not turn on as much during the match. We calculated the amount of air needed, approximating how many times we would actuate each of our cylinders.
An option if your storage exceeds the duty cycle would be to pre-charge up to the duty cycle, pause and then continue pre-charging. This assumes you have enough time in between matches.
Nate Laverdure
23-01-2014, 10:12
You can use the attached formulas to calculate the stored energy in your tank farm, and thus evaluate the risks involved with your design. These formulas assume that the stored pressurized gas expands isentropically and instantaneously to atmosphere.
For example, say you have a 1 cubic foot container of air pressurized to 120 psig. If a catastrophic failure occurred to the container, the rapid expansion of the pressurized air could release 31 kJ to the atmosphere. There could be physiological effects (eardrum rupture, low-velocity impact from shrapnel) within a 7.5 ft radius around the container.
Jon Stratis
23-01-2014, 10:27
For example, say you have a 1 cubic foot container of air pressurized to 120 psig. If a catastrophic failure occurred to the container, the rapid expansion of the pressurized air could release 31 kJ to the atmosphere. There could be physiological effects (eardrum rupture, low-velocity impact from shrapnel) within a 7.5 ft radius around the container.
To give you a practical example of how much energy that is... an ICD (Internal Cardiac Defibrillator) uses around 35J (1000 times less energy) to shock a heart, and patients complain that it "feels like being kicked in the chest by a horse". Of course, that shock probably saved their lives, so it's a pretty mild complaint :P
Look at the pneumatics section of the rule book. Between R78, R85 and R86 I personally don't see how having off-board storage to help charge your on-board tanks is legal. If you are seriously considering this route, please ask on the Q&A so your inspectors have some guidance from the GDC before you show up at the competition!
Also, please note that the rules (R79) specify that all compressed air comes from "one and only one" compressor, with the provided specs for the compressor. Do NOT bring a second robot compressor with the intent of using one to pre-charge and a different one for use during the match. Do NOT bring a normal shop compressor at all. The current those things pull is generally not supported in the pits, and you will most likely be asked to remove it from the venue.
Be careful with using off board storage. We did this in 2012 and used a 1 gallon storage tank filled painfully slow from the robots compressor. We then used the remote tank to top off our robot for eliminations or when we had a long wait in the que. We had a few teams complain and the LRI at the Michigan state championships told us it was against the rules and we had to abandon it.
This brings up another question. What is the duty cycle for the Viair compressor? Is it published somewhere? After running for several minutes it gets very hot. We have run ours during prototype testing at >50% duty cycle for up to ten minutes at a time with no issues.
ebmonon36
23-01-2014, 11:07
The duty cycle of the Viair compressor is printed on the label of the compressor: 9% at 100psi. AndyMark also has it listed on their website. http://www.andymark.com/product-p/am-2005.htm
The duty cycle of the Viair compressor is printed on the label of the compressor: 9% at 100psi. AndyMark also has it listed on their website. http://www.andymark.com/product-p/am-2005.htm
Thanks. I also found the manual online.
http://www.viaircorp.com/images/manuals/00090_92_95_Manual.pdf
What they are not specific about though is the max run time of the compressor before you have to shut it off to let it cool. They give some examples that show you can run it for over 5 minutes before shutting it off. There is also a thermal overload that is supposed to shut it off when it overheats. I don't believe we have ever got to that point.
Oh look, its the yearly thread about how silly the pneumatics rules are when it comes to pre-charging your tanks.
My stance is unchanged.
1) You are allowed to pre-fill your tanks, regardless of whether or not your robot has the compressor on board.
2) You are allowed to change your battery AFTER you pre-charge the tanks and BEFORE the start of a MATCH.
3) If you have the compressor off-board, for some inexplicable reason, you have to power and control it via the cRIO, rather than some other system that safely shuts off at 120psi and would otherwise meet pneumatics rules (particularly in terms of safety features).
#3 is the one I don't understand. Since #1 and #2 are true, it literally makes no difference to a match HOW the air got in the tanks. There are dozens of ways I can think of to safely control my compressor that don't involve me needing some way of attaching it to the cRIO (and ostensibly, through a Spike and DSC and PDB)
Relevant 2014 rules here: http://frc-manual.usfirst.org/Search_Results/off-board
Jon Stratis
23-01-2014, 11:51
3) If you have the compressor off-board, for some inexplicable reason, you have to power and control it via the cRIO, rather than some other system that safely shuts off at 120psi and would otherwise meet pneumatics rules (particularly in terms of safety features).
Yes, there are other safe ways to charge a pneumatic system (generally speaking). That said, there are reasons we don't allow some of them.
For example, most (maybe all?) pit power supplies are limited - if you bring in a shop compressor and power it on while your neighbors are charging batteries, laptops, and running their bandsaw you'll probably blow the breaker and cut power to multiple pits (individual setups vary, but probably 4+ pits). That's why most inspectors will ask teams to remove any shop compressors from the building - we want to ensure you don't ruin other team's days by cutting power to their pits.
Additionally, when it comes to something as potentially dangerous as pneumatics (an exploding tank can be very dangerous!), FIRST has to take the safe path. We can't assume that every inspector will recognize a safe pneumatics set up, or that every team will be able to create a safe set up from scratch. Thus the strict rules - if FIRST provides explicit instructions on how EVERYONE has to set up their system, then it's much more likely that everyone will be safe, both at the events and in their shops. It's the same reason FIRST has strict rules on how to connect your battery to the robot... there are many ways you could do that, but only 1 method that you're allowed to use.
Safety FIRST!
IMHO, the requirement to control the compressor via the cRio at all (on or off-board) is meaningless.
You can start the match with 120psi of air in the tanks. You can change the battery after you charge the tanks. You don't even have to have the compressor on your robot. And there isn't even a requirement for a specific pressure switch or compressor. There is no competitive advantage to running the compressor when the robot is not enabled, as long as the valves cannot be actuated (which is true now).
A simple pressure switch and relay would suffice, but instead we need to use a control system programmed by the teams (which IMHO is less safe than a simple relay), which has a significant boot time and requires a laptop just to fill up the robot in the queue line.
I also don't see how preventing a shop type compressor from being used to fill the robot is any less safe than a team using the same compressor for an air riveter in their pit. The compressor is running, the commercially made tank is full of air, and the pits are fine.
In the same way, we currently use a 50a rated battery connector which has proven itself unfit for the hundreds of amps a modern FRC robot is capable of drawing. It will (and has, in several cases) melted before the main breaker trips. The manufacturer even makes larger connectors which are perfect for us, but we can't legally use them.
Tom Line
23-01-2014, 12:40
Look at the pneumatics section of the rule book. Between R78, R85 and R86 I personally don't see how having off-board storage to help charge your on-board tanks is legal. If you are seriously considering this route, please ask on the Q&A so your inspectors have some guidance from the GDC before you show up at the competition!
Consider a system where you have 15 Cots storage tanks attached to a portion of your robot cart. These storage tanks have the mandatory emergency release ball valve and pressure gage on them. While in the pits, you run a piece of pneumatic tubing from the pressure release ball valve on your robot to the pressure release ball valve on your storage farm. Open both ball valves, and turn on the compressor.
The compressor fills both the storage farm and the robot.
Close both ball valves, pull the pneumatic tube, and keep the storage farm for the play-offs.
Would that violate a rule?
IMHO, the requirement to control the compressor via the cRio at all (on or off-board) is meaningless.
You can start the match with 120psi of air in the tanks. You can change the battery after you charge the tanks. You don't even have to have the compressor on your robot. And there isn't even a requirement for a specific pressure switch or compressor. There is no competitive advantage to running the compressor when the robot is not enabled, as long as the valves cannot be actuated (which is true now).
A simple pressure switch and relay would suffice, but instead we need to use a control system programmed by the teams (which IMHO is less safe than a simple relay), which has a significant boot time and requires a laptop just to fill up the robot in the queue line.
I also don't see how preventing a shop type compressor from being used to fill the robot is any less safe than a team using the same compressor for an air riveter in their pit. The compressor is running, the commercially made tank is full of air, and the pits are fine.
In the same way, we currently use a 50a rated battery connector which has proven itself unfit for the hundreds of amps a modern FRC robot is capable of drawing. It will (and has, in several cases) melted before the main breaker trips. The manufacturer even makes larger connectors which are perfect for us, but we can't legally use them.
This is, at it's core, a safety issue. The compressor must be controlled by the Crio so it can be disabled by the FMS, just like every other robot mechanism. A simple commercial solution may well work to put air in the tanks to the right pressure, but it would not be something that could be remotely disabled through the FMS or if the control system loses comms or whatever.
The programing related to safe operation of the compressor is verified by a specific set of tests conducted during inspection (pressure switch set point, vent plug setpoint and compressor shutdown on robot disable). If a robot fails any of these, the programming is fixed till it can pass.
Shop compressors in the pits have been unwelcomed for a long time. They're loud, trip breakers and encourage the use of tools that probably shouldn't be used in a pit. Yes, there are valid uses for one and I'm sure teams will continue to bring them and some venues will be inclined to allow them. That doesn't make it a great idea, though, and teams that want to use one should be prepared to be told to put it away. I'm really apprehensive about using them to pre-charge storage tanks on the robot. Again, it's a safety thing. The safe operation of the robots pneumatics is verified by the inspectors, whereas it would be impossible for inspectors to verify the safety of every robot/shop compressor combination, and the implications of failed pneumatics storage are incredibly serious.
I agree that the current Anderson connector is probably underrated for our needs. While the manufacturers rating and it's application specific rating aren't necessarily the same, and the majority of melted connectors are probably due to poor maintenance and other issues, a larger capacity connector would be reasonable. But rules is rules.
This is, at it's core, a safety issue. The compressor must be controlled by the Crio so it can be disabled by the FMS, just like every other robot mechanism. A simple commercial solution may well work to put air in the tanks to the right pressure, but it would not be something that could be remotely disabled through the FMS or if the control system loses comms or whatever.
The FMS doesn't control the cRIO when you're charging in queue.
The FMS doesn't control the cRIO when you're charging in queue.
Very true, but the crio can still disable the compressor if the tether falls out, the disable button is hit, a watchdog barks or whatever. Enabling the crio requires the users effort and consent and fails to a relatively safe mode; a relay/pressure switch just requires power.
Why do you care if you can disable the compressor via the cRio?
The danger is not the compressor, it's the air in the tanks. Control via the cRio does not change that.
All the inspectors are doing in their checks is testing that a) the 125psi relief valve is functioning properly, b) that the nason switch is shutting off the compressor (under control of the cRIO) at 115-120psi, c) that the working components are all downstream of a 60psi reg.
I'm not suggesting that any of these tests be abandoned. Just changed such that as long as I prove the reliefs are working and the compressor shuts off when it should (below 120), it doesn't matter what controls I used to achieve it.
Peter Matteson
23-01-2014, 13:24
This is, at it's core, a safety issue. The compressor must be controlled by the Crio so it can be disabled by the FMS, just like every other robot mechanism. A simple commercial solution may well work to put air in the tanks to the right pressure, but it would not be something that could be remotely disabled through the FMS or if the control system loses comms or whatever.
Right idea but a little off in the reasoning.
This is as simple as the inspectors and safety personnel needing to be ensured of safety by the teams.
I as an educated engineer can make several simple systems that will work for off board pnuematics charging, however it becomes incumbent on me to prove this is safe to the event staff. If everyone has a different system how do I as an inspector or safety personnel at the event know that your system is properly designed and tested? How do I know if you're not using my pressure transducer that you aren't overpressuring your system?
It is easier for FIRST to legislate the design of the system so that they know it is safe because the design is tested and proven.
Also when you consider off board compressors please think about this, Do you want to be sweatting a slow leak in the system when you're queued on the field through opening ceremonies or a long Dean speach? You may regret this decision...
Al Skierkiewicz
23-01-2014, 13:37
Everyone,
The basis of all this discussion comes down to one very simple rule...
R34
Non-electrical sources of energy used by the ROBOT, (i.e., stored at the start of a MATCH), shall come only from the following sources:
A. compressed air stored in the pneumatic system that is legal per R79 and R80,
B. a change in the altitude of the ROBOT center of gravity, and
C. storage achieved by deformation of ROBOT parts.
Referenced in the preamble...
"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."
Every team believes and expects that the inspectors are insuring that this rule is met. To assist us with that task the remaining pneumatic rules are in place.
If you think that teams would never bypass the rules or do something unsafe (intentional or unintentional), I suggest you spend a weekend as an inspector. Every bad scenario that you can think of, we have seen. Including the team who had a student holding the power cord for the shop compressor and would pull the power when he thought the system was sufficiently charged.
Jon Stratis
23-01-2014, 13:48
Consider a system where you have 15 Cots storage tanks attached to a portion of your robot cart. These storage tanks have the mandatory emergency release ball valve and pressure gage on them. While in the pits, you run a piece of pneumatic tubing from the pressure release ball valve on your robot to the pressure release ball valve on your storage farm. Open both ball valves, and turn on the compressor.
The compressor fills both the storage farm and the robot.
Close both ball valves, pull the pneumatic tube, and keep the storage farm for the play-offs.
Would that violate a rule?
When you're hooked up this way, is there any easy way to release stored air? It sounds like your manual vent plug isn't accessibly as it's connected to your off-board storage. I also read the rules as implying that off-board storage isn't allowed - the diagrams for off-board compressors explicitly show what is allowed off-board in those situations, and storage is not included off-board. Why would storage be allowed off-board for an on-board compressor, but not be allowed off-board for an off-board compressor?
Al,
Is there any official way to suggest a rule change for the future? The rule is not ambiguous at all now, so it dosn't seem like the Q and A is the right place, but neither is CD.
Everyone,
The basis of all this discussion comes down to one very simple rule...
R34
Non-electrical sources of energy used by the ROBOT, (i.e., stored at the start of a MATCH), shall come only from the following sources:
A. compressed air stored in the pneumatic system that is legal per R79 and R80,
B. a change in the altitude of the ROBOT center of gravity, and
C. storage achieved by deformation of ROBOT parts.
Referenced in the preamble...
"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."
Every team believes and expects that the inspectors are insuring that this rule is met. To assist us with that task the remaining pneumatic rules are in place.
If you think that teams would never bypass the rules or do something unsafe (intentional or unintentional), I suggest you spend a weekend as an inspector. Every bad scenario that you can think of, we have seen. Including the team who had a student holding the power cord for the shop compressor and would pull the power when he thought the system was sufficiently charged.
Al,
I know you and I have hashed this out in the past.
R79 states I must use one and only one compressor, with flow rate not exceeding 1.05cfm. While I would argue that since I can change my battery after precharging and before a MATCH, the compressor used to pre-charge my tanks is irrelevant in terms of competitive advantage, I could see an argument that using some high-flow compressor gives me an unfair advantage because I don't need to wait around while my compressor charges, even in the pits. I don't really take issue with R79. So I have to use a Viair C90 or old KOP Thomas compressor, or something very similar, no big deal.
R80 is the one that I am taking issue with. I disagree that its restriction that I must use my ROBOT's control system to control my compressor has any competitive or safety based reason for existence -- provided that I'm still proving that the reliefs and system-full shutoff are working properly. If the safeties are the same, this restriction is completely arbitrary and unnecessarily stifles creativity. Competitively, its the 120psi air that gives me a competitive advantage. Its source, and how its source is controlled are irrelevant. Safety wise, I'm recommending the checks be kept, so its still safe.
Al Skierkiewicz
23-01-2014, 14:59
Andrew,
While people may not post, that does not mean they are not reading and lurking here on a regular basis. I would bet that the GDC and HQ have read your posts and understand your feelings. Posting the question on the Q&A will give you a definitive answer from GDC.
kramarczyk
23-01-2014, 22:27
I'm currently considering some type of tank 'storage' farm made of cots components that can be filled during our down periods with the robot compressor. We can use the stored air to fill the robot during the quick turn around matches of the playoffs.
Tom,
Since it looks like you are going the Centerline for week 1 where I will be the LRI I would like to tell you that I see no provisions in the rules for off board storage of air, just provisions for an off board compressor. Additionally, the illustrations with R85 & R86 explicitly show the air storage on board the robot. Unless there is a rule update, relevant Q&A or specific instructions from the Chief FRC Inspector, I do not see off board air storage as legal. It can absolutely be done safely, but I don't think it is legal at this time. Feel free to make a counter argument.
MK
Tom,
Since it looks like you are going the Centerline for week 1 where I will be the LRI I would like to tell you that I see no provisions in the rules for off board storage of air, just provisions for an off board compressor. Additionally, the illustrations with R85 & R86 explicitly show the air storage on board the robot. Unless there is a rule update, relevant Q&A or specific instructions from the Chief FRC Inspector, I do not see off board air storage as legal. It can absolutely be done safely, but I don't think it is legal at this time. Feel free to make a counter argument.
MK
I also don't see any rules or Q&A that explicitly disallow this setup either. It's a grey area and definitely warrants a Q&A.
kramarczyk
24-01-2014, 06:56
I also don't see any rules or Q&A that explicitly disallow this setup either. It's a grey area and definitely warrants a Q&A.
I understand that as written, this is a grey area within the rule. The grey area was removed at LRI training this year (and is consistent with prior years). Conveniently, the same guidance that was provided at training was captured in the recent FRC Ask an Expert webcast on Robot Inspection located at
https://www.youtube.com/watch?v=jW_Xf3H2i2Y&feature=youtube_gdata_player
It is a lengthy video. The portion relevant to this conversation is at 35:10. I realize that this is not an actual rule, but I think it is only fair for the teams to know what guidance was given to all the LRI's. For this that are not aware, this training takes place at FIRST HQ with members of the GDC in the room. Consequentially, there isn't much room for me to have an opinion on this issue.
Fortunately it is only halfway through the build season and there is plenty of time to get a Q&A submitted.
MK
Al Skierkiewicz
24-01-2014, 08:07
Spoiler Alert! History lesson coming....
When FRC first allowed compressed air to be used on robots, (no it was not always the case) the rules were written for very specific implementations. On board compressor and a maximum number of metal storage tanks only. Then one day Bill Beatty of the World Famous Hammond Team asked if they could take the compressor off the robot to add weight for another device. The GDC at the time decided to agree with Mr. Bill. These were the provisions, moving the compressor off board could buy the team nothing but the weight savings in return for the risky choice to have no additional air for the match. That is the quid pro quo, weight for risk. We have added a few items to that original list, as listed in R86. So regardless of how you look at this, consider that the the compressor is on board and all rules apply. If you move the compressor off board, all the rules still apply but you are taking the risk that you run out of air.
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