*R79 Compressed air on the ROBOT must be provided by one and only one compressor. Compressor specifications must not exceed nominal 1.10 cfm flow rate @ 12VDC. *
A small change from 1.05 but this brings some better more reliable compressors from the Viair line into play. Thanks FIRST
Hi,
Have you looked at the VIAIR website? They have a few compressors that have been dubbed “approved for FRC”. But none of them go beyond the .73CFM that the KOP compressor has. A couple of years ago we had a very porous system and actually burned up one of these little compressors at competition (it was our first attempt at pneumatics. Were thinking about using pneumatics to loft the robot in the end game for this years competition and based on calculations, we’re going to need 2 - 1.5" cylinders to get the bot up the required 2 ft in time. so we’re thinking about getting a beefier compressor. Do you have any suggestions? Thanks!
Such as this one? Yes, very nice!
If you plan on pushing out the bottom of the robot, then you might want to be careful about keeping the Bumpers in the Bumper Zone at all times.
Doesn’t the 100C beat the 98C hands down on rates? It’s only 10% faster for 0 to 120 psi fill, but it’s like 25% faster for 90 to 120 psi, which is what would count during a match. I’ll grant you that the amp requirements are a little hair raising, but still. It seems like it should be FRC legal, and it seems like it was FRC legal even last year.
It’s also a full pound heavier than the 97C and 98C. The 98C weighs only a few ounces more than the 90C many teams have been using for years. We will be using the 98C most likely on our robot.
IG series is better, given that they are 100% duty cycle. That is if you can afford weight penalty
250C-IG http://www.viaircorp.com/250C-IG.html
330C-IG http://www.viaircorp.com/330C-IG.html
I think 5 pounds of air tanks would do a lot to offset the duty cycle and flow rate advantages of the IG series…
If you could find a place to put all the air tanks. Filling them would also eat up most, if not all, of your 6 minutes per 60 minutes duty cycle.
As I mentioned “… if you can afford weight penalty …”.
Considering that most teams (AFAIK) push their compressors beyond 10% duty cycle, I am surprised they don’t fail more often.
First off, if you’re using the 100C like I think you should be, it has a 9 minutes per 60 duty cycle.
If you need LOTS of air, I think an onboard 330C-IG makes sense. It weighs as much as 2 gallons of storage using the standard plastic tanks. 2 gallons of storage at 120 psi gets you 2 gallons of air to use at 60psi. If you’re putting air back in at 100 psi, you’re putting in .6 SCFM, which in 2 minutes gives you 9 gallons of air at 14.7 psi, or 2.2 gallons at 60 psi. So if you’re constantly using air such that you need more than 2 gallons of it per match, you can increase the density of your storage by putting a 330C-IG onboard. If you’re using less than 2 gallons per match, you’d be better leaving the 350C-IG offboard unless you can’t find room for storage. Which I think means that the 330C-IG offboard is the correct solution for almost all robots unless you can’t find room for enough storage.
EDIT: The 330C-IG has a 0.08 SCFM at 100psi advantage over the 100C. That’s 0.3 gallons of air at 60psi in a 2 minute match. For a 5 pound penalty. You can make that up with 2 tanks for a 1.2 pound penalty. So, really, the only reason to use the 330C-IG onboard is if you don’t have room for 2 more 36 cu.in. tanks. The 100C can fill 4.5 gallons from 0 to 120 psi in its 9 min per 60. So call that 2.25 gallons every match, since 30 min per match is worst case-ish. And that’s assuming you’re draining the tanks every match. So yeah, I think the 100C is the weight/performance tradeoff winner unless you’re using absolutely massive amounts of air per match and really need that 100% duty cycle or you really don’t care about wasting weight and power, since the 330C-IG has a slightly higher current draw.
You kind of lost me with the calculations. How does 0.08 CFM difference at 100PSI over 2 minutes equates to to 0.3 gallons of air at 60PSI?
By my calculations it’s almost 1 gallon (0.97)
But in any case, I think mentally I was still comparing it to old 90C compressor. Looking at stats again, 100C does look a lot more impressive.
The 10% duty cycle is 6 mins On and 54 mins Off. Most teams except in eliminations aren’t running 2-3 matches per hour. Yes teams push the compressors limits but rarely far beyond what is designed for.
I should do up a tutorial/whitepaper on this to save people time and annoyance, probably. It mostly comes down to Boyle’s Law: P1 * V1 = P2 * V2. Short-ish version:
First off, you don’t use all the air in your tanks. Not unless you have actuations that require no force. Tanks at 1 psi do almost nothing, right? So let’s assume you always keep your tanks at or above working pressure. 60 psi is the usual, though as we’ll see, lower pressures can be better.
So you have a 1 gal tank at 120psi. Boyle’s law says 1 gal at 120psi = 2 gal at 60psi. But you can’t use all 2 gal. You have to leave 1 gal in the tanks at all times because you don’t have a magic gnome making your tanks smaller to squeeze the air out. So storing 1 gal at 120psi mean you can use 1 gal at 60 psi. That’s where lower working pressure helps, you leave less air in the tanks. I’ll let you work out those details.
So on to compressors. The flow rate stats you see listed on the compressor page say CFM. You might think that’s a cubic foot of air at whatever pressure is listed there, but no. I confused myself that way once before I sanity checked and realized that meant things got more efficient at higher pressures. No, what they mean is SCFM. Standard Cubic Feet per Minute. That’s a cubic foot of air at 1 atmosphere gauge, or 14.7 psig.
And we’re back to Boyle’s law. I was assuming we were pumping at 100psi, since that seemed a reasonable average pressure an air hungry robot would be at most of the time. At 100psi, the 100C pushes 0.52 SCFM, the 330C-IG pushes 0.60 SCFM. So 0.08 SCFM difference, for 0.16 SCF a match = 1.2 gal at 14.7 psi = 0.29 gal at 60psi. And that’s where the number comes from.
Lots of my other estimates like the 2.2 gal per match total for the 330C-IG work similarly converting air at 14.7 psi to air at the 60 psi you likely would use it at. I’ll grant that everything gets changed drastically if you’re working at 45psi, or 30 psi. I’m seriously doubting an air hungry robot is working at those pressures however, since using a 2x multiplier cylinder at 30 psi is heavier than a 1x multiplier at 60 psi. Plus you can pull more air out of a tank at a lower working pressure, so your storage is more efficient and you’re less likely to need a pump in the first place.
I had noticed that the VIAIR 100c came into spec upon reading the rules the first time through, because in December I was researching parts and noticed that it was just over the line. Last year, a 100% duty cycle compressor was a must if you were using pneumatics to stack totes, because a good stacker would run the tote lift alone a dozen cycles or more per match, and the lift of five totes and an RC over the last tote last cycle in each stack would require about than 50 ft-lb of energy. Even if you manage the air use, you’d need a lot of it.
This year, like 2013 Ultimate Ascent, does not seem to call for such air-hungry robots. Even a great team is probably only going to cycle their boulder pickup and launch a dozen times per match, and each time it’s moving one 10oz item (plus robot parts), not up to a half dozen 8 pound game pieces. If you do a pneumatic climb, that’s going to have to be largely from the tank, due to the short duration which the robots are allowed to be tall. Unless you’re doing a pneumatic powered intake or drive system, you shouldn’t need to run the compressor continuously.
In 2013 we had a pneumatic triggered launcher (motors did the real work) and a mostly pneumatic climber. The only time we got the compressor so hot that we had a problem was when we were zeroing in the aim (running a dozen cycles a minute at times) and practicing the climb repeatedly. Even in the match where the pit crew forgot to close the quarter-turn exhaust valve, the compressor never really got hot as there was no back pressure.