First time I’ve really done pneumatics on a comp bot this year (how have I gone 10 years without doing pneumatics?? We used one on a 2014 bot, but I wasn’t very involved with it other than reviewing it to make sure we were legal for inspection).
We are using the versadrop modules. We plumbed the pneumatic system with double solenoids valves on the vex manifold, because we understood it and could get it to work. I’m fairly certain that we could get by with single solenoids instead and use less air, but we couldn’t figure out how to plumb it. Anyway that we did it we were leaking air - and I think we assumed it had something to do with needing to close an exhaust port somewhere (either on the manifold or on the cylinder) but we couldn’t figure it out.
Anyone have any diagrams of how you’d use single solenoids and a cylinder (that can be double acting) with the vex manifold? I’d appreciate it.
It should be the same as the double solenoid in that set up. The single solenoid is just automatically (spring loaded) returning to its non-powered state. So when you power the solenoid via the PCM the cylinder should extend (or retract) and when you unpower/disable the cylinder will retract (or extend).
Can you provide where you are getting leaks?
We used these for the versadrops this year and they worked well. They don’t save air, actually they use more because every time you disable the solenoids return to their natural state. Singles are nice in that they only require 1 PCM slot.
You have to be very careful with the SMC Double solenoids with that manifold. It is absolutely critical that the little gasket between the manifold and the solenoid is clean and well seated, otherwise there is the possibility of a leak, or air exhausting out of the manifold even when it is plumbed properly. It also has to be tightened down evenly since the only thing holding that seal is that little gasket.
We had a few issues where the gasket would get unseated and our manifold would start leaking air, but once we cleaned off both surfaces and re-seated it there wasn’t a problem.
I may have used some wrong terminology, or my lack of experience with pneumatics may be making me think that something is doable that isnt.
What I think we should be able to do is use the Pancake Pneumatic Cylinder, that comes with the versadrop that is designed to take air in both directions (for extend and retract) but only plumb it to extend. When we are no longer extending it via the solenoid valve - I think the weight of the robot should drop it down to the traction wheels - no spring return required. I think we tried both plugging the retract on the cylinder and/or manifold
I can’t recall because it was 2 months ago, but I don’t think we were ever fully convinced where we were leaking from.
I made this rough sketch pretty quickly but this is how we plumbed our single solenoids in 2015 to power only one direction. The tricky part with single solenoids is that they actually function exactly the same as double solenoids on the smc block from vex except double solenoids keep their state after the robot is disabled. In order to make a single solenoid only power one side of the cylinder you have to plug the other port on the block that the solenoid is mounted to or else when you flip the state of the solenoid you dump all of the air out of the system. Usually what we would do is cut a ~6" piece of pneumatic tube fold it in half and double zip tie it to create a plug (there are plugs made for the ports I just haven’t looked hard enough to find them, I’ve seen Texas Torque use them quite a bit they might be better to source those than me) Anyway, if this picture doesn’t make sense, or you have anymore questions feel free to message me.
Unless the cylinders you’re using are spring-retract cylinders, this diagram will only extend the cylinder, not retract it. If you want it to also retract the cylinder under pneumatic power, you will nead to attach the B solenoid port to the front cylinder port. That being said, the setup you have should only vent air when you switch directions (i.e. what you want), so you must have a leak somewhere else in your system. I’ve heard that method of plugging the port can sometimes leak. Maybe take a T connector and make a closed P shape (plugged tube in one hole, another tube connected to the other two holes) for a more durable plug?
Understood, but he said he would use the weight of the robot or gravity force to “Retract”. The plugs linked above from McMaster are a much better option.
I must have missed that. That should work, though you may still get some scrub if the traction wheels are just resting on the ground while you’re trying to strafe (I don’t have experience with this, just speculating).
i agree about the plugs from McMaster, but in the meanwhile what I suggested will work better than just folding over the tube.
Thanks y’all. I hope to do some testing tonight. I think we tried plugging the port B on the manifold before, but by looping them all together. It may be possible that we ended up not effectively plugging them - I didn’t oversee it too closely and even though we have some of the plugs linked above, we didn’t use them.
Our traction wheels are what we’ll be on with no pressure - so I think any extra scrub from free wheeling rollers on the mecanum (that can also raise up additionally off the ground) will be trivial.
Looping the B ports together is what caused us lots of hard to diagnose headache during build season. See this thread for our resolution. We also used the McMaster plugs mentioned.
Yes, don’t connect any of the outputs from the manifold to each other! If you are not using one of the ports, then plug it.
For this setup, you only need the one valve installed on the manifold and a hose running from either the A port or the B port out to the cylinders. The other port should be plugged.
On the pneumatic cylinders, they should each have a hose going to the fitting that will force the wheel into the ground, and the other fitting should be vented to the atmosphere (just don’t screw a hose fitting into it).
The big difference between single and double solenoid valves is that a single solenoid valve will have a ‘default’ state when you turn the robot off. You can pick whether you want the wheels to be up or down when the robot is disabled by changing the cylinder hose from A to B on the manifold, or vice versa.
Double solenoid valves will stay in whatever state you left them in when you disable/turn off the robot. They’re nice for mechanisms that try to smack you when you turn off the robot and they return to their default state.