First, we’re a rookie team, so bear with me.
We plan on using 2 2" bore x 24" stroke pistons on our robot. If they are only used once at the beginning of the match to extend, and once at the end to retract, how many reservoir canisters are we going to need? We have four, but if we can use less, it’d help.
Depends on several factors. Of course, you’ll need the compressor on board, the maximum of four Clippard tanks will not supply enough air to even lift them once.
Let’s discuss what the tanks are for: Your compressor can only push out so much compressed air in a given time. But, you might need more volume than that, so you can store some of the air volume in the tanks.
So, your 24 x 2" cylinders need something like 150 Cubic Inches of air to extend. If your compressor can supply 10 cubic inches per second, you see that it will take 15 seconds to extend the cylinders. If, however, you have 100 cubic inches of air stored in 4 clippard tanks, then you need a lot less time to extend those cylinders, and your compressor isn’t working as hard (for that instant).
NOTE: The numbers given above are NOT ACCURATE, I have no idea what the output of the compressor is, nor have I accounted fr the fact that your cylinder uses 60 PSI air while the stored air is at 120 PSI.
So, what you need to do is figure out what your air requirements are, what your sources of supply are, and that will tell you how many tanks you need for a given performance.
Connect those tanks in parallel for better air volume, you need that for those huge cylinders.
Retracting the cylinders might be possible with just gravity, once you remove the pressure holding the pistons up.
Don
This can make a huge difference in air consumption with large cylinders!
How many air storage tanks are you using? We are using 4
ok well my team this year is also using a 24 inch pnematic and was wondering if you can use the large 24 inch pnematic and also have pnematic shifter and use all of them in the beggining of the match like hybred mode?
There is no rules limit as to when you can use pneumatics. There is, however, a practical limit. You could try to fire all three cylinders simultaneously at the beginning of the match…But you probably won’t have the air to do it. Pre-shift your shifter so you don’t have to fire it at the same time as the big cylinder.
we too ordered some 2"bore 24"stroke cylinders, and derived empirically that we are able to fire them every fifteen seconds (just one) without hurting the air level. two is a different story, i doubt that you would be able to fire them with much power.
also, you mentioned retracting at the end of the match. remember that you don’t have to return to starting configuration at the end of the match. i don’t know what you have in mind, but if you’re expanding your robot by 2’ on each side at the beginning, you don’t have to go back at the end.
good luck!
The clippard (model AVT-32-16)](http://www.clippard.com/downloads/general/pdf_documents/2006%20Catalog/Catalog%20by%20Section/Stainless%20Steel%20Cylinders.pdf) tanks hold 16 cu in (cubic inches) and each piston you want to use has an extended volume of 75 cu in. The clippards can be pressurized to 120psi (pounds per square inch).
Example: If you took 16 cu in (@1psi) and compressed it to 8 cu in, you would have 2 psi
So working backwards, if you contained 120 psi in (4) 16 cu in volumes, you would have 7680 cu in of air stored in the (4) clippards.
Now if you release that volume of air (7680 cu in) into (2) 24" pistons, and combine the (6) volumes (4 clippards and 2 pistons ) 164 + 752 = 214 cu in, or 7680/214 = 35psi
So (2) pistons connected to (4) clippards will fully extend with 109lbs of force and balance to 35psi.
That is only on the upstroke.
On the return, your tanks would then be at 35psi, or 2240 cu in
So 2240/214 = 10psi and 32lbs of force.
As far as dropping after the match, you can just let gravity do that and leave the top of your cylinders open.
I have attached a graph that shows what happens to the pressure in your system when you activate two 2x24 cylinders at the beginning of Hybrid. Assuming you have no leakage,start with the system at 120 PSI and with 4 tanks, but have no compressor - the cylinders will fire but will reduce the pressure to 40 PSI as the stroke ends. This means that the force at the end of the stroke will be reduced; so you have to take that into account.
I have also attached the compressor data for Don’s sake.
In case you are curious how I plotted this, attend my conference in Atlanta on Pneumatics and I will show you and will give out copies of the Pneumatic air management simulator that I developed. It is not ready yet for distribution.
Pressure over time.xls (42.5 KB)
Pressure over time.xls (42.5 KB)
Just as a point of reference…
It takes the compressor about 15 seconds to fill one accumulator (16 in3) to the max 120psi from 0psi.
Two accumulators take twice as long (30 sec.) to fill.
Four accumulators take four times as long to fill completely (1 minute).
The solenoids stop working when the system pressure falls below 20 psi (SMC) to 30 psi (Festo).
So when doing an initial rough estimate of the air available to you you can assume at MOST you will have:
– (4) accumulator’s worth of air from pre-charging your leak-free pneumatic system prior to a match
– (8) accumulator’s worth running the compressor for the 2 min. teleop period
– (1) accumulator worth during the 15 sec of the hybrid period
Thanks for the replies everyone. And for answering the question I didn’t ask concerning charging the system prior to the match.
we are using 1 of those pistons on our robot this year. We found that it will extend at 20psi based on our design so you could try lower the pressure so that the compressor doesn’t need to work as long
Anyone notice the OP’s handle? 
Careful; see my post here describing how to do the calculations. pressure*volume calculations use absolute pressure, while force uses gage pressure. You don’t get the same answer. taking 16 cu.in. of 1psig air (15.7 psia) gives you 8 cu.in of 31.4psia air, or 16.7 psig, not 2 psig.
My what? :]
Clippard is a pneumatic company.
Clippard/Clifford get it?
Ok so maybe it was just funny to me.