I am working on designing a compliant intake system and have 2 pistons used in the design, found the perfect item for the idea, a steel reservior that is small enough to fit all of our requirements. It is made by vex, inteded to be used for VEX robots it says it is legal for just that but I dont know if that translates into being legal for FRC
Link to part: Pneumatics - VEX Robotics
Do you have any pictures of your design? I’m not sure I follow why you need the small metal tank over one of the bigger plastic ones and route longer lengths of tubing.
Do not buy from Vex. That is an SMC product and you can purchase it straight from SMC at a lower price.
The intake is the only part of the robot where we would be using pneumatics and our plan is to use a pink arm with the intake at the end. If we were to use the larger black plastic ones we would have to put on the frame of the robot or at the very bottom of the pink arm due to the comparative fagility of it, additinally we would have to use a ton of tubing with slack to extend with the arm. Instead since the entire pneumatic system is just two pistons that serve a passive role so we dont exactly need much air. The tank just being 9 inches can fit with the intake itself, meaning no need for a ton of tubing. And the main reason we are looking at this over other gas springs is that its cheaper and also we are able to adjust the force at any time by adding or releasing air
Thats great, i only knew of the part through vex and tried to see if there was another retailer for it but couldnt find anything. Also it still doesnt say if its FRC legal here, would you by any chance know if it is?
Will mounting a small tank at the end of the arm, along with all the other necessary pneumatics components (pressure regulator, release valve, solenoid valve, etc), be easier than figuring out routing for the supply tubes for the cylinders?
Yes it is.
You still need the compressor onboard. And if you’re cycling the cylinders a lot then you can burn through air quickly.
For future reference, if you’re not sure if a pneumatic component is legal, check the robot rules for pneumatics. Generally speaking, off the shelf unmodified parts rated for 120 psi or more and with a certain fitting size are OK (within certain categories, including tanks).
Your problem here is not the tank (which is legal in itself), but that you need all the other components of the standard pneumatic system in order to be legal otherwise. You cannot, for instance, charge any kind of pneumatic system with air from off the robot. You must have a compressor on-board. Then you need the other required components (pressure regulator, pressure gauge, etc.). By the time you have all this, you really can’t just stick it on the end of your intake, so you may as well go ahead and use a plastic tank and keep everything on the body of the robot.
This was going to be my second question, even if serving the purpose of a passive gas spring, would it still require all of the comonents of a standard pneumatic system to be legal, and from what youve said here i do. Our team is very new to pneumatics so this is helpful
Yeah, it’s one of the quirks of the pneumatics rules. You can have gas springs that aren’t considered pneumatic systems because they’re completely sealed, essentially, and can’t be over-pressured, etc. But using a pneumatic actuator in that role, it isn’t technically sealed, so it’s a pneumatic component and has to be treated that way with all the rest of the requirements applying. You’re probably better off just springing for the extra expense of the gas springs you need, painful though that can be when you’re operating on a tight budget.
You may be better off calculating the stroke and force needed and purchasing a gas spring from an industrial supplier. It is less likely to attract scrutiny when your robot is being inspected.
You can’t legally build custom gas springs with a piston and tank. R806 states that all compressed air on a robot always has to come from an on-board compressor. The exception is COTS closed-loop air springs in R608, like the ones that hold up the trunk lid on your car. They’re a common automotive part and widely available in many varieties.
Though I suppose if you rigged it to pull a vacuum instead of compressing air, that might be legal? 
See: Team 4907 Presents: Darth Theta - FIRST / Robot Showcase - Chief Delphi
you could also use a torsion spring instead of a gas spring
Yeah, you don’t want to use pneumatic components, you want gas springs: McMaster-Carr
If you don’t know the force you need, you can calculate that from the pressure and cylinder bore in your current design or just buy several and test them.
From the game manual:
R806 Compressed air from ROBOT compressor only. Throughout an event, compressed air on the ROBOT must be provided by its 1 onboard compressor only. Compressor specifications must not exceed nominal 1.1 cfm (~519 cm3/s) flow rate @ 12VDC at any pressure.
According to rule R802 you can use a COTS compressor tank, if it’s rated at =>125 psi. Check out the tank on this 'bot: Barker Redbacks FRC Team 4613 - Robot Reveal 2018 - YouTube
R802 No custom pneumatics and meet minimum pressure ratings. All pneumatic items must be
COTS pneumatic devices and either:
A. rated by their manufacturers for pressure of at least 125psi (~862 kPa) or
B. installed downstream of the primary relieving regulator (see R809), and rated for pressure
of at least 70psi (~483 kPa)
Regarding using an air cylinder as a gas spring:
If cost is an issue, put a request on this forum, with an approximate load rating and length. I’ll bet a lot of teams have a few in their inventory that they’re not using. Teams will share.
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