Our team is concerned about the number of pneumatic pistons being used on the robot and whether the compressor will run down the battery trying to keep up the air pressure.
Is there a way to calculate how long a battery will last based on the number, size, and how often the pneumatic cylinders are used?
TIA
I don’t know about any calculations, but in 2005, team 1279 used a 24" long ~1.5" cylinder, plus 2 18"x1.5" cylinders, plus 2 12"x 1.2" cylinders to lift and drop tetras, and we didn’t kill the battery in one round, and I am pretty sure we went 2 rounds on one battery a couple times.
The issue is more about the refill time of the cylinders, not battery power. Our compressor was constantly running and wasn’t able to keep up with our air usage.
second that…we had the compressor running throughout the match in 2008 and didn’t have trouble with battery life because of it. We had trouble with battery life because of our drivetrain 
OK…
The compressor pulls 10.5 amps nominal at “full load” as per: http://www.drillspot.com/products/35745/Thomas_Industries_405ADC38_12_Piston_Compressor_Vacuum_Pump
The Battery will reach 1.6 volts per cell (full discharge) at a 1C (10.3 amps nominal) discharge rate in one hour as per http://www.batterystore.com/Yuasa/NP18-12.html
In gross terms, you can run the compressor continuously for a little less than one hour.
Disclaimer and warning: The compressor is going to get really hot if you run it continuously. I’m guessing that you will cook off the internal lubricants and seize the pump way before you discharge a full battery…
JMHO,
Mike
I don’t have an exact inventory of what we are planning to use, but generally we are planning on one large piston for the lift, two medium size and one small for the kicker. So the kicker pistons would be firing often throughout the match and the large piston(s) will operate once.
Thanks for all the input, sounds like we should be safe with what we are planning to use.
Be sure to figure out how much air the kicker uses, ensure that there will be enough in the tanks at the end of the match to use the big ones!
Make sure you do an analysis on whether you have enough air. In my experience, you run out of air much faster then you run out of battery.
You can use the volume of the pistons, volume of the storage tanks, your number of uses (and a worst case timeline of when they are activated) and use the ideal gas law to figure out if you’ll have enough air throughout the entire match.
Note that you can also charge your storage tanks before the match. You could do that using some spare battery and then swap in the match battery at the last minute. This way, the match battery would only be responsible for running the compressor to refill air expended during the match.
If you will be using a lot of air, get as much storage as you can.
Here’s another thought. What if you were to have air storage for your lift (120psi) behind a checkvalve separate from the rest of the system. Are you allowed to have multiple paths from the 120psi area of the system to the 60psi area, so long as they’re all dropped to 60psi? I seem to recall that you are.
That way, your kicker can’t use the lift’s air.
Sorry. Check valves are, unfortunately, not being allowed this year: http://forums.usfirst.org/showthread.php?t=14516
Regards,
Mike