(New)matics advice

[mman1506]

Originally Posted by euhlmann

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?

[jfitz0807]

Originally Posted by mman1506

Why would you need to use a double solenoid for shifting?

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.

[mman1506]

Originally Posted by jfitz0807

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.

[euhlmann]

Originally Posted by mman1506

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.

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.

[simpsonboy77]

Originally Posted by euhlmann

If you'll excuse bad diagrams finger-drawn at 1am, here's how a double solenoid does shifting
*snipped 2 images*

Here's a single solenoid connected to the same shifter
*snipped 1 image*
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..

[ShIfTiNgBoT]

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.

[Wren Hensgen]

Originally Posted by ShIfTiNgBoT

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.

[Wren Hensgen]

Originally Posted by euhlmann

If you'll excuse bad diagrams finger-drawn at 1am, here's how a double solenoid does shifting

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.

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.

[MBimrose16]

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!

[rich2202]

Mount the following where the Robot Inspector can easily see (read) them:
1) High Pressure Guage
2) Low Pressure Gauges
3) Switch (RI will need to short it out)

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.

[Wren Hensgen]

Originally Posted by rich2202

Mount the following where the Robot Inspector can easily see (read) them:

Be prepared to teach the robot inspector about pneumatic systems. At least three times in my FRC career I've had to coach an inspector through our air system, how it worked, and which rules it obeyed.

[Ari423]

Originally Posted by Wren Hensgen

Be prepared to teach the robot inspector about pneumatic systems. At least three times in my FRC career I've had to coach an inspector through our air system, how it worked, and which rules it obeyed.

Honestly, I'm not surprised at this. Since the pneumatics rules were opened up, they have been relatively lax. Instead of listing the allowed motors by part number and specifically detailing how they need to be wired, the rules allow you to use an unlimited variety of pneumatic components provided that they are rated to a high enough pressure and allows them to be connected in almost any configuration, save for a few specifications. That means every team will have different components connected in a different way threaded throughout their robot. Expecting inspectors to know the pressure ratings for every pneumatic part and being able to instantly identify how they are connected on your robot does not make sense. You know your robot a lot better than the inspectors. You need to prove to them that your robot is safe, not the other way around.

[Ben Martin]

Originally Posted by Ari423

Honestly, I'm not surprised at this. Since the pneumatics rules were opened up, they have been relatively lax. Instead of listing the allowed motors by part number and specifically detailing how they need to be wired, the rules allow you to use an unlimited variety of pneumatic components provided that they are rated to a high enough pressure and allows them to be connected in almost any configuration, save for a few specifications. That means every team will have different components connected in a different way threaded throughout their robot. Expecting inspectors to know the pressure ratings for every pneumatic part and being able to instantly identify how they are connected on your robot does not make sense. You know your robot a lot better than the inspectors. You need to prove to them that your robot is safe, not the other way around.

On this point, we now always bring datasheets for our non-standard (but compliant) pneumatic components to competitions.

[Wren Hensgen]

Originally Posted by jfitz0807

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.

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.