I was wondering whether anyone has experiences or suggestions regarding using a non-KOP compressor. The KOP compressor has run fairly hot in the past (we’ve used it the past two years), and the robot the team I mentor has planned has some large cylinders on it. The students have done the calculations and the KOP compressor will take somewhere between 5 and 10 minutes to completely pressurize the system. While this may not be that bad for competition, it’s not ideal, and the KOP compressor is only rated for a duty cycle for 9%, and I fear we will push it too hard if we use it this year.
Specifically, I was considering suggesting this compressor, also from Viair, which as far as I can tell is allowed by the rules. It has 16A specified current draw, so would we’d have to run it off of one of the Automation Direct relays (I couldn’t find specs for the PCM but I assumed this since it’s on a 20A fuse)?
Are there any other compressors to consider, or other things to think about regarding this? Also any suggestions on cooling the compressor are also welcome (though we saw the other thread on the subject)
The compressor at 12VDC meets R86 and R34. I would be weary though in inspection to prove that you have it regulated to 120 PSI maximum working pressure as this model is rated higher. Also make sure you follow all electrical rules and wiring regulations, such as using a relay or PCM [R37], a 20 Amp breaker [R59], 18 AWG wire [R60], and if using it off a Spike Relay to use a 20 Amp fuse or Snap-Action circuit breaker [R73.d].
Why is that a concern? As long as compressor shut-off is controlled by the mandated pressure switch, it’s perfectly fine for a compressor to have an allowable working pressure spec higher than that (and in fact it’s important it does).
Because I have seen many teams forget to check the actual pressure their switch opens/closes at. The standard KOP pressure switch is adjustable and with a compressor that has a maximum working pressure of 150 PSI, it is important for them to make sure their switch is triggering by 120 PSI. I have seen some pressure switches in the KOP trigger above 130 PSI straight out of the packaging.
Yes, there are no rules prohibiting the use of the compressor during a match. It all depends on programming though if it turns on once a “minimum” pressure in the system is reached, or if you additionally put it on a toggle switch to have manual control over when it runs.
Given that the robot rules prohibit the use of off-board compressors this year, you could actually say you’re ONLY allowed to run the compressor during the match (though I suppose you could pre-charge it with a tether).
No, it isn’t. Messing with the set screw on the side of the switch doesn’t actually adjust the pressure it triggers at, despite popular rumor. In fact, messing with it counts as a modification and makes the switch illegal to use on a robot.
The pressure switches are factory set and should not be tampered with.
Every team should be ready to prove this, regardless of the specs on the compressor. It’s written that way in the rules, on the inspection checklist, and is something every inspector will check with every pneumatic system.
If you want even better, check out the Viair 330C-IG. rated for 100% duty cycle @100PSI, has .53 CFM at 120 PSI - more CFM at twice the pressure! You pay for that with the weight, though - 8.25lbs. ouch!
The OP’s linked compressor looks legal to me. Actually looks like a good choice. It looks a lot like the AndyMark compressor. The relief valve limits the pressure to a nominal 125 psi. If the pressure doesn’t cut the compressor off at less than 120 PSI then it is broken and should not pass inspection.
Placing a cooling fan directed at the pump head really helps to keep it cool which increases the pumping volume
Speaking from personal experience with that compressor, the only real downside is the weight. We used one as an off-board compressor for a few years but could never justify the weight to put it on-board. Unless you’re using a crazy amount of air, running a fan over the KOP compressor works just fine for most applications.
I actually did some testing a few years back to see the difference putting a fan on it makes and it’s actually pretty substantial.
QFT. Compressed air is great for low-to-mid-duty two position stuff. At higher levels (like climbs), you can usually do better with motors, unless you have a really large pre-charged air tank and a compressor which is capable of close to a 100% duty cycle to pre-fill it, which is going to be relatively heavy and must (as of 2019 rules) be carried on the robot.