Pneumatics Activations

There is some confusion on my team about how many FULL strength actuations can you get with one piston and cylinder?
someone answered 40ish but that number doesn’t match the math my teammate has done so can anyone else agree with this number

That makes sense… Between the Solenoid and the Piston, all the Air gets vented, the shorter the distance, the less Air removed from the Reservoir…

You can get 0 “full strength actuations” with one cylinder and one reservoir.

The instant the solenoid opens and air goes into the cylinder, the pressure is dropping, so when the piston is fully extended you no longer have the pressure in the system that you started with.
Pressure is inversely proportional to volume, so as volume increases, pressure decreases.

The change in volume of the inside of a cylinder is .242in^3 per stroke. There is space in the rear of the cylinder, space in the fittings, and space in the tubing which all cause losses, so let’s just say each time you fire a piston, the volume of the system increases by 0.25in^3.

The volume of a reservoir is 9.153in^3. Let’s just say it’s 9.15in^3 because no one cares about 3 thousandths of a cubic inch.

That means that after each firing and subsequent retracting, the pressure has decreased to 9.15/9.4 = 97.3% of its starting value.

Now I’m going to list the volumes and pressures after each actuation (meaning after it has been fired and then retracted):

The 40 that you were hearing probably comes from doing the calculations without doing the rounding that I did.

Thank you that is what my teammates math also got but we havent used vex pistons and wanted to double check because we thought that the 40 at “full” power didnt make sense.

One thing that some pneumatic systems use is a compressor to charge a reservoir, and then a pressure regulator that leads to a second reservoir. The idea is that the first tank can be fluctuating in pressure, but as long as it stays above the pressure set by the pressure regulator, the pressure in the second tank and therefore in the cylinders will remain constant.

To apply this to what we have in VEX (no compressors), just have one tank that you pressurize to say 120psi and then have a pressure regulator that provides your cylinders with 80psi (or however much you need). If you halve the pressure that the pressure regulator is set to from 80psi to 40psi, you will lose half the air per actuation and you will also have 2x the air available before you hit your minimum pressure, so you will get 4x more actuations before you run out of air. Which means you are getting 2x the energy out of your reservoirs for each time you pump them up.

The USFIRST, FRC Robots at 120 Lbs, MAX Weight and a 12 VDC Lead-Acid battery can have Compressors on them, but they also have 4-8 Reservoirs, and an Output Regulator, and Most Important, an Over Pressure Switch and a Relay that cuts the Power to the Compressor.

My team uses this kind of general setup, but I wasn’t sure how common it was among FRC robots. Thanks!

Very common in my area, Oregon, U.S.A…

To get something to Actuate Fast, or lift a lot of Weight, Pneumatics is the Only way to go…

FRC 2007, you got points for lifting a Alliance Robot off the Ground a Minimum distance at the End of the Match. In order to Maximize the Field Time until the Last 15 Seconds, your Lift had to be Fast, and Lift up to 120 Lbs.

To give an example of their use under load, my old team 2941A, which used them to support our gateway intakes (for fold down de-score) got about 3-4 cycles before they were getting a bit low, and after 8 the robot was almost unusable. So although using them for a high force application doesn’t increase the amount of air used each time, it does affect how long before they no longer can apply enough force.

Remember, that was 2 cylinders on 1 reservoir though. (1 cylinder wouldn’t have been enough to hold the intake up)

We used one reservoir on our Round-Up robot to fire 4 pistons in order to high-hang.

We only fired them once, but keep in mind that the force when it is fired and extended is 90% the force when it is fired but not yet extended.