Is there a neutral with the solenoids given?

[Transformers]

We have tried both types of the solenoids provided in the kit, but neither of them have a neutral state or where the actuator will stop when the button is let go and continue when pressed again. Would we have to purchase seperate solenoids with such a state already part of them? Thanks.

[gburlison]

Originally Posted by Transformers

We have tried both types of the solenoids provided in the kit, but neither of them have a neutral state or where the actuator will stop when the button is let go and continue when pressed again. Would we have to purchase seperate solenoids with such a state already part of them? Thanks.

In general, that is not the way pneumatics work. If you can connect a solenoid valve up to the exhaust port on the existing valve ( with some solenoid valves this is not easily done ) then you can stop the cylinder by not letting the air exhaust. This can be very inexact and will change as the load changes because the air will compress. With proper programming this can work, but the positioning of something like an arm will not be very precise.

[Gary Dillard]

You will find a white paper on how to do this here

[kmcclary]

Originally Posted by Transformers

We have tried both types of the solenoids provided in the kit, but neither of them have a neutral state or where the actuator will stop when the button is let go and continue when pressed again. Would we have to purchase seperate solenoids with such a state already part of them? Thanks.

You are correct. No single supplied kit valve will give you a "center off".

Now you can use the "exhaust plugging" trick already mentioned, by tying the two exhaust ports together, and running them through another valve.

But, a simpler (and more reliable) solution is to purchase a replacement valve body from SMC that allows for "3 Postition - Closed Center" (center off) operation. Go to this page:

http://smcusa.com/sections/first/assembly.asp

Download the Sub-series Catalog for the SY3000 series valves. We get the SY3240-6HZ-X70 valves in the kit. This is their basic "two position" unit (with 12VDC coil, 600mm leads, and indicator - don't sweat the X70...).

As you can see on the left hand side of the first page, there are a number of OTHER standard SMC valve body options. The two of most interest to FIRST people are:
- SY3340-(etc) a "3 Position Closed Center" valve. This seals both ports making it "stiff" when both coils are off, and
- SY3440-(etc) a "3 Position, Exhaust Center" valve. This makes the cylinder "limp" when both coils are off.

Note: AVOID the SY3540-... valves! They sound like a good idea, but applying pressure to BOTH ports is normally only done with double ended cylinders (cylinders with shafts coming out BOTH ends) to stiffen them up with full power air.

We have double acting cylinders (air pushes on both ends instead of air-vs-spring), but they are only single ended (one shaft, out of one end). Using a SY3540 valve on one on OUR cylinders will make it creep to the extended end every time, because there is a difference in the piston's working surface area on the two sides.

We're darn close to ship day now (two days and counting!). So unless you have a stocking SMC distributor near you, buying another valve body won't get it to you in time for ship. You should probably try the "plugged exhaust" method instead.

Does this answer your question?

- Keith McClary
Chief Engineer, Team 1502 "Technical Difficulties" (AKA The "Ec-Pneumatical Counsel")