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-   -   Pre-filling stored air (http://www.chiefdelphi.com/forums/showthread.php?t=154618)

mwmac 03-02-2017 11:28

Re: Pre-filling stored air
 
Quote:

Originally Posted by SM987 (Post 1639860)
We're usually more concerned about the performance hit everything else on the robot takes when the compressor kicks on. I can't remember the last year we had an on board compressor.

Agreed. Would rather trade the weight and volume associated with an onboard compressor toward mechanisms.

Chris is me 03-02-2017 11:30

Re: Pre-filling stored air
 
It has always been legal to charge your air tanks with one battery, switch to a fresh battery, and then go out for a match. I don't see any ambiguity in that rule this year. Pro tip: just use the battery you used in your previous match to charge up your air.

There are numerous reasons to go off-board if you can create the air capacity needed to pull this off. The biggest one is current draw - with all these high power motors, adding another 20A load to your system is that much more current to deal with and that much more voltage to drop. There's also the secondary concerns of weight and space.

Ultimately the only reason to use an onboard compressor is if you don't have space, budget, or weight to use sufficient air tanks for an entire match of air - or if you don't have time to charge your air tank within 5 minutes after a match ends (back to back finals matches).

I'm also in support of field-side air. I am aware it relieves one design constraint to do this and thus isn't zero change to the rules, but that's not a good enough reason to not at least consider it for 2018. That restriction isn't the end of the world to see gone.

AdamHeard 03-02-2017 11:37

Re: Pre-filling stored air
 
Quote:

Originally Posted by Kevin Sevcik (Post 1639789)
It's not unlimited free energy. There's a definite difference between the amount of air you can compress between finals matches with a 1.1 cfm 12v pump and the amount of air a $300 120v compressor can generate. I'll grant you that's something like 10 standard tanks, but still. Wishing for free compressed air is about like wishing for a bigger battery. It could happen some day, but only when the GDC wants to increase our power budget.

The amount of energy in just 5 AH of the Battery is far greater than what can plausibly be stored with air on the robot.

FrankJ 03-02-2017 12:30

Re: Pre-filling stored air
 
Quote:

Originally Posted by AdamHeard (Post 1639865)
The amount of energy in just 5 AH of the Battery is far greater than what can plausibly be stored with air on the robot.

But the explosive decompression of a large air tanks (or a chain of small air tanks.) risks are a lot bigger than a crowbar short of a 5 AH battery. I don't want to be alarmist or go down the rabbit hole of risk analysis, but that is a consideration. Granted you could go back to limiting the volume air air stored.

Kevin Sevcik 03-02-2017 13:50

Re: Pre-filling stored air
 
Quote:

Originally Posted by AdamHeard (Post 1639865)
The amount of energy in just 5 AH of the Battery is far greater than what can plausibly be stored with air on the robot.

The Andymark 1.1 Pump pulls 12A on average from 0-120 psi. So running it for 5 minutes between finals gets you an extra 1 AH stored on your robot that doesn't cost you any current draw during a match. Right now to get that you have to jump through all the compressor hoops and leave your robot running on its old battery for the whole timeout, instead of whatever else you'd do with it. I'm assuming the GDC is aware of all the costs associated with that, and figures that's what you have to pay to get that advantage, because it is an advantage. If you want that for free, someone's going to have to convince the GDC to ease up on that constraint.

As a separate matter, allowing 120V compressors for airing up the robot is just going to add another inspection item, because we'll need to make sure the 120V compressor is regulated down to 120psi so teams don't dump high pressure air into their tanks fast enough to exceed 120psi.

FrankJ 03-02-2017 14:02

Re: Pre-filling stored air
 
Quote:

Originally Posted by Kevin Sevcik (Post 1639939)
As a separate matter, allowing 120V compressors for airing up the robot is just going to add another inspection item, because we'll need to make sure the 120V compressor is regulated down to 120psi so teams don't dump high pressure air into their tanks fast enough to exceed 120psi.

The advantage of a field provided compressor is the max PSI can be controlled. and the electrical load required to run the compressor can be planned for. (One issue with team compressors is that most pits are extremely power limited.)

AdamHeard 03-02-2017 14:09

Re: Pre-filling stored air
 
Quote:

Originally Posted by Kevin Sevcik (Post 1639939)
The Andymark 1.1 Pump pulls 12A on average from 0-120 psi. So running it for 5 minutes between finals gets you an extra 1 AH stored on your robot that doesn't cost you any current draw during a match. Right now to get that you have to jump through all the compressor hoops and leave your robot running on its old battery for the whole timeout, instead of whatever else you'd do with it. I'm assuming the GDC is aware of all the costs associated with that, and figures that's what you have to pay to get that advantage, because it is an advantage. If you want that for free, someone's going to have to convince the GDC to ease up on that constraint.

As a separate matter, allowing 120V compressors for airing up the robot is just going to add another inspection item, because we'll need to make sure the 120V compressor is regulated down to 120psi so teams don't dump high pressure air into their tanks fast enough to exceed 120psi.

Since you do that on a separate battery, it's really no different.

Also the 1Ah works out to be far less than 1 AH (converted to J) of energy to be used for motion since the conversion is so inefficient.

Skyehawk 03-02-2017 19:31

Re: Pre-filling stored air
 
Quote:

Originally Posted by scaryone (Post 1639773)
R44
The one (1) ROBOT battery, a single pair of Anderson Power Products (or APP) 2-pole SB type.....

If you precharge your air system with a battery, then change out said battery for a fresh one, you are using two batteries (starting the match with more energy than one battery normally holds). This seems like a good Q & A.

I also recall this being a rule at some point in time. However if this thread has proven anything (other than a general consensus for field-side air) is rules are always open to interpretation. Part of my recolection may be due to how things were run at the Lake Superior regional for the first two years of its existence, or my being a new team member at the time, or how we as a team operate.

If you are smart about how much air you use, having fully charged batteries, and having a design that doesnt run 6 Cims, a minicim and a compressor at the same time you will be just fine. Simplicity trumps complexity when they are performing the exact same task.

Kevin Sevcik 03-02-2017 19:50

Re: Pre-filling stored air
 
Quote:

Originally Posted by AdamHeard (Post 1639952)
Also the 1Ah works out to be far less than 1 AH (converted to J) of energy to be used for motion since the conversion is so inefficient.

On this I totally agree and I try to explain this to everyone that asks me about using pneumatics. But if you're powering it with a robot battery, it's effectively 1Ah of battery life, so that's the appropriate comparison.


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