Hi everyone!
This me and my team’s fourth year, but the first year we decided to use pneumatics. More specifically we are using the Vex 3 CIM Ball shifters. Is there any advice anyone has to someone who has never tried pneumatics at all?
Your help is appreciated!
I took a class on Pneumatics/Hydraulics this past summer, and my advice would be this: don’t over-complicate things, but make sure you learn symbols. Draw your circuits out before trying them. Pneumatic understanding is something that can potentially be picked up very quickly. Don’t be afraid to play around with your resources, but understand why certain events happen. Also, use youtube. There are tons of videos and tutorials out there.
Use these manifolds (http://www.vexrobotics.com/vexpro/pneumatics/solenoids-and-manifolds.html) they are a godsend. Don’t use double solenoids unless you have to.
But if you use single solenoids, make sure that you pick the correct position for the cylinder as your default!
We use mostly double solenoids. Last year, everything fit the model. Intake arm up and down, cheval/portcullis wedges up and down, shifting up and down (yes, vex 3-cim ball shift gearboxes).
So if you have something like shifting, it doesn’t make sense to use two single solenoids when you can simply use a double solenoid.
Why would you need to use a double solenoid for shifting?
I don’t think you understand what “single solenoid” and “double soleniod” means. It doesn’t mean that a single solenoid only has one output. It means that when you apply power to the solenoid, one of the outputs gets air and the other doesn’t. When you don’t apply power, a spring returns the solenoid shaft and the output switches ports. This compared to a double solenoid, where a second solenoid forces the return of the inner shaft, not a spring. For a standard double solenoid, one solenoid is on and the other is off at any given time. Otherwise either the solenoids will be fighting each other or the shaft will be free to slide around and change outputs at will. You can see whether you’re using a single or double solenoid easily because a single solenoid has one pair of input wires where a double solenoid will have two pairs. In FRC (as far as I’ve seen), there is generally no reason to use more complicated double solenoids over single solenoids unless you are working with 3-position solenoids, in which case you can’t use the manifolds posted above either.*
That isn’t to say that you can’t*, just that it usually isn’t necessary.
**I have a number of times because we had them in storage. They work fine and are basically the same to program. They are just a bit more complicated electrically, more places for things to fail, and more expensive.
I don’t think you understand what “single solenoid” and “double soleniod” means. It doesn’t mean that a single solenoid only has one output. It means that when you apply power to the solenoid, one of the outputs gets air and the other doesn’t. When you don’t apply power, a spring returns the solenoid shaft and the output switches ports. This compared to a double solenoid, where a second solenoid forces the return of the inner shaft, not a spring. For a standard double solenoid, one solenoid is on and the other is off at any given time. Otherwise either the solenoids will be fighting each other or the shaft will be free to slide around and change outputs at will. You can see whether you’re using a single or double solenoid easily because a single solenoid has one pair of input wires where a double solenoid will have two pairs. In FRC (as far as I’ve seen), there is generally no reason to use more complicated double solenoids over single solenoids unless you are working with 3-position solenoids, in which case you can’t use the manifolds posted above either.*
That isn’t to say that you can’t*, just that it usually isn’t necessary.
**I have a number of times because we had them in storage. They work fine and are basically the same to program. They are just a bit more complicated electrically, more places for things to fail, and more expensive.
In 2015, we used double solenoids for things like the ingestor arms so that they couldn’t close into a stack when the match ends but start closed if we wanted. We also used one on the arm tilting mechanism since we had to start with the arm tilted back but don’t want it to change position when the match ends.
Good morning! I’m a former member of FRC 225, and still an active FTC mentor.
Through FIRST, I landed a job with a hydraulics, pneumatic, and automation company. If you have any questions on parts, terms, setups, connectors, anything, I’d be happy to work with you to get your questions answered. Please feel free to send me a PM or just talk here.
Some suggestions:
Buy a tubing cutter. For the fittings used in FRC (Push-to-connect), the ends of cuts have to be perfectly square to seal.
Buy quality tubing, and parts. Freelin-Wade, the default supplier for FIRST tubing is a really solid company. I’d also recommend Norgren for fittings.
Understand your terms. You have air cylinders, who’s force is decided by their bore (Diameter) and the distance they work over, called the stroke. You can have a double acting cylinder that needs air to move it both ways, or a Single Acting that will retract if the air pressure is removed. You can even have a Reverse Single Acting, which will extend with air pressure removed.
Understand when and where to use pneumatics. It’s not always the right choice. Air actuators are smaller, lighter, and faster than electric in most cases, but you only get 2 (Sometimes 3) positions. You get better granularity with electric.
Understand your solenoids. Use Single-Acting solenoids when you want an item to revert to a default state on power-off. Use a double acting if it’s important to stay in the last state on power off.
Above all, stay safe. Air pressure can be extremely violent and dangerous if you’re not expecting it, and sometimes even when you are. Loose air hoses can whip through the air, air tanks can explode if damaged, cylinders can move faster than you can see with enough force to break bones.
If you have ANY questions, please ask! There are no stupid questions.
We used a double solenoid for shifting because we wanted to use pneumatic pressure for both shifting directions rather than relying on a spring inside the cylinder. Specifically we used very small pancake shifters. To use a dual port cylinder like this, the double solenoid is the way to go.
I don’t think that’s correct. As Ari423 explained above both single solenoids and double solenoids can charge both sides of the pneumatic cylinder and neither setup requires a return spring in the cylinder. The only practical advantage of a double solenoid in FRC is that they won’t return to a default state when the robot is powered off which can be useful in certain situations but certainly not shifting.
You’re confusing the acting of a valve (Sprung or unsprung) with the porting of a valve. A 5/2 valve will supply pressure in both actuation directions, while a 3/2 will only supply it in one.
The 5 or 3 refers to the number of input or exhaust ports a valve has, while the digit after the / refers to the number of positions it has.
If you’ll excuse bad diagrams finger-drawn at 1am, here’s how a double solenoid does shifting
and
Here’s a single solenoid connected to the same shifter
A spring is needed since there can only be pneumatic actuation on one side. We wanted pneumatic actuation on both sides, so we used a double solenoid.
This is a spring return single acting cylinder.
A single action solenoid can power a cylinder. A single solenoid internally has a valve, a spring, and a solenoid. When the solenoid is not powered, one pneumatic output is connected to pressure, while the other is connected to atmosphere. Think of this as the default state, the spring keeps it there.
When the solenoid is powered, the solenoid pulls the valve to the other position, against the spring. the pneumatic connections are reversed. The bonus is when power is cut (including at the end of a match*), the valve returns to it’s original state since there is nothing holding the spring back.
*= Not certain, depends on how WPILIB and the PCM are implemented. It should say in the source somewhere…
Otherwise either the solenoids will be fighting each other or the shaft will be free to slide around and change outputs at will.
I’ve never seen a double solenoid act like that. When unpowered entirely, it will use the air pressure from the inlet to prevent the valves from switching.
Good answer. You don’t need to keep one output powered to keep it in place. When you actuate it in one direction, the airflow is rerouted a little, and it actually serves to hold the spool (center shifty thingy) in place against vibration, shaking, or drops.
This means you can fire it with a pulse of power, and it will retain positions through power on and off, and even air supply on and off (There’s grease on the spool which is sticky, and little indents that help hold the shifted spool in place).
The one thing I’d advise against doing is leaving both inputs fired. This may cause them to slide or move.
There’s some confusion here over the cylinder and the solenoid valve.
The valve has a couple of traits. It can be single or double acting (or more), it can have one output or two (Or more), and the internal spool (Slidy bit that does the air shifting) can have two positions or more. You can have any combination of these traits.
The cylinder itself has a different set of traits. It can be double acting (You need air to move it out, and back) or single acting (You need air to move it out, but it springs back), or even reverse single acting (It extends via spring, but retracts with air pressure). You may have one, and only one of these traits. (Well, there are 3 position cylinders, but we’re not talking about them)
When a valve is single acting, it has one little coil that’s energized by an outside voltage. That shifts the spool inside, and sends air to a different output. When the voltage goes away, the spring returns the spool to the default position, and redirects the air.
When it’s double acting, it has two little coils. Applying a burst of power to one shifts the spool in one direction and it will stay there until a burst is applied to the other side, which will shift it the other way.
A single-acting valve is used where you want a item to have a default position, like an arm that must be retracted at the start and end of a match when your robot has no power. The spring will move the spool in the valve to the default position, and route air to the retract of the cylinder, so when you lose power, it will retract the arm.
A double acting valve is used when you want to keep the position of an item after a power loss. Once the burst of power has been applied, the spool stays in place until a burst moves it the other way.
EITHER ONE OF THESE VALVES CAN BE USED WITH ANY TYPE OF CYLINDER
If you have any questions, I’d be happy to answer them for you. If you’d rather keep them private, feel free to send me a PM.
As someone that has experience working with multiple pneumatic systems on past robots, I cannot emphasize enough the importance in taking the time to build a good system. Simplify it as much as possible, more connections increase the possible points of failure. Soapy water is good for finding leaks, but sometimes it’s faster to just redo suspect connections. Good luck and don’t take shortcuts!
Mount the following where the Robot Inspector can easily see (read) them:
Mount the dump valve where it can be easily and safely reached, and protect it from accidental bumping.
Follow the diagram in the manual so you have all the pieces in the right places.
Adjust your high pressure relief valve to the proper specs.
ONE AND ONLY ONE Compressor. Backup Compressor allowed in the Pit, but not connected to anything.