Re: Industrial switch
 

This web page covers the difference between NO and NC pretty well. It's based on the 2014 control system, but I don't think any of the concepts at this level of detail have changed.

Re: Industrial switch
 

Here is the 2015 version. The only "change" is the picture of the switch is slightly brighter.

One thing to point out (and I edited my post saying I assumed wrong), is that the digital input on the roboRIO will be 1 when the switch is open, and 0 when it is closed.

Example Java code is provided in the link, and the code will be the same for C++.

Re: Industrial switch
 

So, the problem that we've always have is having the limit-switches wired in a way that is failsafe. If the mechanism or action that the limit-switch is meant to stop is one that could be destructive or harmful, then if somehow the limit-switch itself fails or the wiring connecting it to the RoboRio fails (cut or is disconnected), the software won't read this limit condition and the destructive process will proceed... In this case, we like to use limit-switch that are wired as NC (and open when contact is made)... that way, if there's a failure in the limit-switch (or the wiring) it stops the mechanism from working altogether.

I don't think there's a way for a NO limit-switch to be fixed in software to detect a limit-switch failure scenario. It would look like everything is fine until when it's suppose to signal the contact.

Re: Industrial switch
 

As mentioned before Automation Direct literally has industrial grade switches. Many of them have wires for both N.O. and N.C. Operation at the same time so if you wanted to tell if the switch wasn't connected you would know for sure if both N.O. and N.C. were off at the same time. And Automation Direct gave everyone a voucher for $30 and one switch runs for $24 - $28 depending on what kind.

Re: Industrial switch
 

Automation Direct.
AAP2T51Z11

$14.50 each

Limit Switch style with adjustable arm.

We are using these for overtravels on our elevator.
Plastic body means they are light as compared to other industrial switches.

Re: Industrial switch
 

As Al mentioned, overtravel is very important when you're slinging big masses. I recommend industrial limit switches, rather than push buttons (which are meant for humans to press, not machines). Something like this: http://www.mcmaster.com/#7988k2/=vw63cb