General Question About Pneumatics

[itsme]

My team wants to build a pneumatics system.
I need to know what connects to what and how it works.
From what I understand the compressor is connected to the spike that is connected by PWM to the relay port on the RC.
Another PWM is connected from the digital input port on the RC to the pressure switch. It gives 0 if pressure is 115 psi and 1 if its under that (correct me if I'm wrong).
There is a function in EasyC pro that's called Pressure Switch.
My question is: how do I do all the connections of the pneumatics and then use it with the function in EasyC Pro.
Sorry for the messed up question.

Thanks in advance,
Team 2217

[TheOtherGuy]

Sounds to me like you got it right! You can initialize the pressure switch in EasyC Pro so that everything is handled and out of the way. All you have to do is, like you said, connect the pressure switch to a digital input and the compressor to a spike (and that spike to a relay output), and then open the pressure switch block, insert the correct ports, and you're done!

[itsme]

OK.
Some more questions that popped out: Do I connect the pressure switch to a spike too?
And if not, then how do I connect it directly to the digital I/O port?
I could also use some sketches according how to connect everything (where does the pressure switch go, where and how do I put the air tanks (the accumulators), how do I use the solenoid valve? Where do I connect the solenoid valve (to a spike?)).
As you can see I have no idea in pneumatics, so I'll need some basic information about everything.

[MrForbes]

The pressure switch is a sensor, so it cannot be used to directly control a relay. You have to connect the pressure switch to a controller input (using a PWM cable with ring terminals soldered/crimped to the ends of it), and connect the spike to the controller output.

You need to download the pneumatics manual and read it a few times to help you understand all that other stuff.

http://www.usfirst.org/community/frc...nt.aspx?id=452

[itsme]

Originally Posted by squirrel

The pressure switch is a sensor, so it cannot be used to directly control a relay. You have to connect the pressure switch to a controller input (using a PWM cable with ring terminals soldered/crimped to the ends of it), and connect the spike to the controller output.

Not sure I understood. Do I connect the pressure switch directly with a PWM to the RC?
And I read the pneumatics manual now, helped a bunch

EDIT:
OK, I searched a bit and found out that I'm supposed to connect the pressure switch to a PWM cable, and connect only the white (signal) and black (ground) connections. Is that right?
Should I cut the red connection and insulate it?

[mta]

Actually, you can just put the sensor inline with the power cables for the compressor. lilke This:

-------------------
= -sensor
|
x -compressor
+++++++++++++++


because if the sensor reaches over 115 psi it will return a zero, efectivly stopping the power to the compressor. This is what our team did on a practice build. it worked great.

There is actually no need to connect the sensor to the controler board at all. It works just a like a switch.

[dlavery]

Originally Posted by mta

Actually, you can just put the sensor inline with the power cables for the compressor. lilke This:

-------------------
= -sensor
|
x -compressor
+++++++++++++++


because if the sensor reaches over 115 psi it will return a zero, efectivly stopping the power to the compressor. This is what our team did on a practice build. it worked great.

There is actually no need to connect the sensor to the controler board at all. It works just a like a switch.

You should absolutely NOT do this!!! The compressor can have a start-up surge of 25 amps or more. The pressure sensor is not rated for this current, and it is almost certain that you will burn it up sooner rather than later.

To back this up, and basically to save you from yourself, Rule <R91> makes it clear that the Pressure Switch must be connected to the Robot Controller. Furthermore, Rule <R96> again makes it clear that the pressure switch muse be connected to the Robot Controller, and not anywhere else. The RC must then activate a relay to power the compressor. Connecting the pressure switch anywhere else is a violation, and will get you nailed during inspection.

-dave



.

[itsme]

OK, I know I should not do that.
I didn't clearly understand: how do I connect the PWM from the pressure switch to the RC?

[MrForbes]

You cut off one end of the PWM cable, and get some small "red" crimp on ring terminals which fit a #8 screw, and crimp them on the white and black wires, and you insulate the cut off end of the red wire.

Then screw the ring terminals of the black and white wires onto the pressure switch.

Then you plug the other end of the PWM cable into an input on the robot controller.

And you ONLY connect the compressor power wires to the output of a Spike relay. The spike relay requires a PWM cable connected to a Relay output on the Robot Controller.

Then you have to get the programming team to make it so that the Spike turns on the compressor only when the pressure switch senses that the pressure in the system is less than 115 psi, and shuts it off when pressure reaches 115. And be sure to have the 120 psi pressure relief valve installed on the compressor when you test this!

[itsme]

OK I connected it the way you said.
Everything is working fine exept the pressure switch.
It allways shows 0 on the online terminal. Never showed 1, even when pressure was 115 psi.
The backup battery is charged and the black and white wires are connected to the pressure switch.

Oh and another small question:
Where do I connect the relief switch?
I connected it after the pressure switch.

[MrForbes]

The relieve should be near the compressor, it can be connected to a T fitting along with the pressure switch, or screwed into the other side of the compressor (it has two output ports)

[EricH]

Originally Posted by squirrel

The relieve should be near the compressor, it can be connected to a T fitting along with the pressure switch, or screwed into the other side of the compressor (it has two output ports)

Squirrel, the 125 psi relief (the one with a cork protecting one end) goes in one of those. That leaves you only one port open.

<R95> Teams are not allowed to adjust the 125-psi relief valve. The valve has been calibrated prior to shipping. The relief valve must be attached to the compressor. If the compressor is not used on the ROBOT, then an additional relief valve must be obtained and included in the primary pneumatic circuit on the ROBOT (see Rule <R91>).

[itsme]

Umm.. A bit confused
Can I connect the relief valve right after the pressure switch in the circuit (as described in the pneumatics manual). And where do you mean the 2 output ports, on the compressor?
And what do you mean about the calibration? My team spin it a bit because we had air coming out from there (on low pressure, something like 20 PSI).
In the manual the relief valve isn't mentioned in the pneumatics sketches.
So is it or isn't it an obligation to put it in the circuit? (ErichH just mentioned that one output port of the compressor already has a relief valve, and I'm pretty sure my team didn't touch that relief valve).

By the way, the pressure switch is now working perfectly. On 115 PSI the compressor stops its action and starts again when pressure is under 95 PSI.

[EricH]

Originally Posted by itsme

Umm.. A bit confused
Can I connect the relieve valve right after the pressure switch in the circuit (as described in the pneumatics manual). And where do you mean the 2 output ports, on the compressor?
And what do you mean about the calibration? My team spin it a bit because we had air coming out from there (on low pressure, something like 20 PSI).

On the top of the compressor, there are two ports. The 125 psi relief goes into one of them. The manual relief could go almost anywhere in the system, as long as it completely drains it.

On the calibration, the 125 psi valve cannot be tampered with and remain legal. If air was leaking at low pressure, you should try teflon tape on the threads first, as that will help seal the threads.

[itsme]

We put teflon and now it's fine (just a tiny bit air running out, but not really significant). But if we screwed a bit the valve (the inner screw-nut) did it change the calibration?
If you say there is already a default relief valve on the compressor, is it a must to put another relief valve in the circuit?