well we decided to stick to this idea ( the two PISTONS )… we are going to do our best to make it work as we want it to work…
any comments ???
Wow! Are those TWO 2" bore, 24" pistons? That’s a lot of air…
Yes. That is what they seem to be. Downsizing the bore size might be a good thing…I know a team that had two of those monsters, and it took them most of the match to charge for a second shot.
Some ideas for more air storage. Put the solenoids close to the front of the robot and use coilhouse pneumatic lines. It helps. From the compressor three way to the regulator, tanks, and release valve. Set the pressure of the tanks at 120. But allow the regulator at the pressure of 60 for the competition.
Hope that helps, rc
**Get Coilhouse from freelin-wade.com
That use of tubing is going to come under scrutiny. <R01> bans using extraneous lengths of tubing as a tank. I can kind of see how the three-way connection would work, but it might be easier to do it in line. Just make sure that every single line before the regulator (other than the vent line) goes through the regulator and you should be OK.
Although this robot has large cylinders, there are several steps that you can take to reduce air consumption.
First of all, a 2" diameter cylinder at 33psi consumes the same amount of air and produces the same amount of force as a 1.5" cylinder at 33psi… about 100lbs of force. If it turns out that you don’t need that much force you can drop the pressure down to about 20-25 psi, so long as you use the correct valves. (I believe the SMC valves operate at a minimum pressure of 20psi, while the Festos require 30psi, but don’t have the specs in front of me to confirm that.)
Secondly you can likely set at least the vertical piston up to be single-acting*, as the weight of your arm is likely more than enough to return it to the retracted position. In other words, rather than running a tube from the valve to the top side of the vertical cylinder, just plug the valve where the tubing comes out, and leave the top side of the cylinder open to atmosphere… or just put one of the needle-valve flow restrictors on it and leave that open to atmosphere if you want to control how quickly it extends and retracts. This way you only use air to lift, and let gravity do the work when the cylinder retracts… a 50% savings in air consumption.
If you use bungee cords/surgical tubing on the arm cylinder, you can achieve a similar effect… use the tubing to retract the cylinder and you only need to use air to push it open.
So if you do find you are using too much air, just these simple steps could cut air consumption to about 1/6 of that when running the cylinders as double acting at 60psi.
Good luck,
Jason
- note that this is different from using a single-acting cylinder, which has a spring inside to power the return stroke. Single-acting cylinders are not an allowed component. Legal double-acting cylinders, however (such as you have) may be left open to atmosphere at one (or both, although that would be silly…) ends.
**EDIT: Just looked at the photos again and noticed that the weight of the arm will cause the vertical cylinder to extend… not retract. The concept works the same, but I had it upside down… connect pressure to the top of the cylinder, and leave the bottom port open to atmosphere. The weight of the arm will pull the cylinder open, then pressurize the top half of the cylinder to raise the arm.
P.S. Love the “jack stands” that the robot is sitting on, but hopefully all team members will remember to wear shoes that cover their toes to the competition.
Hey Edgar its Carlos once you get done today post a picture so i can see it please
fundamentals, fundamentals, fundamentals,
When using a Festo valve on a cylinder you can do a double acting cylinder super easy. solenoid on or solenoid off.
Question:
when using the SMC valves how do I do a single acting and a double acting cylinder arrangement ?
the documentation says you can ‘pulse’ the solenoid to make it actuate. Okay, so how do you de-actuate it ?
on a double deal, if you pulse both coils then both ends of the cylinder are connected to the hp air and the piston finds its ‘home’. how do you de-actuate this ?
It is the pulsing that I don’t understand. If it is pulse to open, what to close ?
All I got to say is that your gonna have a problem with air. During the year with the tetris. Team 1323 used 2 rams like yours and we got of 3 fires a match max.
I can see how the word “pulsing” might cause confusion. First of all note that there is a slight difference between a double-acting valve and a double-acting cylinder. In the valves the SMC with “one end and two wires” and the Festo are single acting. That means you can hook the ground to the M- side of the spike and the red wire to the M+ side. When you make the spike go “forward” the valve activates. When you stop (or when you disable the robot or power down…) the single acting cylinder activates in the other direction. It requires power to stay in position and must always stay “on” in order to keep the cylinder locked in place. With the double acting solenoid valves (the SMC’s with two ends and four wires) you have to actively signal the valve to change position. You can hook the two black wires to ground (not the spike, but direct to ground) then hook one red wire up to M+ and the other to M-. Now when you tell the spike to go “forward” the valve will activate in one direction. When you turn the spike off, or deactivate or power down, nothing will happen. You will have to tell the spike to go “reverse” in order to force the double-acting solenoid activate the cylinder in the opposite direction. This can be handy if you want an arm to stay in the position it is in at the end of the match, while the automatic “off” of the single acting valves allows us a margin of safety by automatically venting our pneumatic launchers for us at the end of a match.
I suspect the word “pulse” was used for the double acting valves because in comparison to the single-acting valves you only need to apply power briefly in one direction to get them to hold the cylinder in that position, while with the single-acting valves you require a continuous voltage.
A single acting cylinder is one that returns by itself to it’s start position when pressure is relased. In commercial single acting cylinders this is achieved by placing a spring inside the cylinder. Apply air to one end, the cylinder extends. Vent that end and it retracts. Although we are restricted to double-acting cylinders in FIRST, by leaving one end of the cylinder open to atmosphere and providing an external force to return the cylinder to a start position you can achieve a similar effect. In this robot, for instance, retracting the cylinder rod will cause the arm to lift. It is not necessary to use air to extend the cylinder… gravity will do that nicely. So in this case just plug one of the outlets from your valve (you can either choose the one that is pressurized at power-down or when power is applied, if using a single-acting valve) and leave one end of the cylinder open to atmosphere.
If gravity won’t do the trick of returning your cylinder for you… perhaps a nice bungee cord or surgical tubing will.
Jason
P.S. I just noted a typo in my previous post… when I said “33psi consumes the same amount of air and produces the same amount of force as a 1.5” cylinder at 33psi" I meant a 1.5" cylinder at 60 psi.
Thanks, That clears up a lot. SMC single coil must be ‘held’. SMC double coil is ‘latching’.
The approach we have taken the past two years is to build a little beyond where ‘we can see’ in terms of total design approach. Both years we built a full pneumatics deck, everything from compressor to the valve outlets.
It turns out that this year we have nothing to do with the pneumatics but it was a good training exercise plus it keeps part of the team busy and engaged. We have a big team now.
In prior years we used the FESTO but are changing to the SMC.
We may take a pneumatic solenoid and have it “dance a decoration” around for grins and giggles.
I just thought something that is confusing me again. The documentation says if you hold both coils on the double SMC the both ends of the cylinder are charged. That makes me think that the internal valve mechanisms are not linked together or at least can float around until both are moving air to the cylinder.
I need to do some bench testing.
Thanks