Minibot switches...

[Mike Betts]

Originally Posted by Alpha Beta

So is something sold as a "safety limit switch" still a limit switch?

http://www.automationdirect.com/adc/...Limit_Switches

These advertise pull-reset instead of momentary functionality.

Way out of my area of expertise here, but I wanted to make sure that "momentary" was not part of the definition of limit switch.

I also think teams could design their own latching mechanism for a momentary limit switch with a little aluminum and surgical tubing.

Aaron,

Perhaps we can persuade Al to comment on this. Although I am sure that a "pull to reset" type of switch was not what they had in mind at game design time, it is marketed as a limit switch and, IMHO, legal.

Regards,

Mike

[Alpha Beta]

As best I can tell what does and does not qualify as a limit switch is up to the marketing department of the electronic supply companies and the inspectors at each tournament.

Those who has been to multiple tournaments know that what passes inspection at one tournament may not pass at the next, or at the FIRST Championship Event. I could see a very engineering oriented inspector use a functional definition of a limit switch.

Globalspec.com has the following definition.

limit switch
(Electricity) A switch designed to cut off power automatically at or near the limit of travel of a moving object controlled by electrical means.

An inspector with this working definition wouldn't need to ask for documentation if a Cherry E79-20A showed up on a mini-bot as long as it was being used as a limit switch. Both Mouser and Digi-Key lump their switches into catagories. Snap-Action, Lever and Limit switches are lumped into the same family of switches in their marketing. On the Cherry E79-20A Digi-key lists it in the CATEGORY of switches and the FAMILY of Snap Action, Limit, Lever. The actual DESCRIPTION says SWITCH SNAP DPDT 10A QC TERM. The word LIMIT is not used. So, is it a limit switch? Is it being marketed under the Family of limit switches? Would every inspector come to the same conclusion on this? The GDC appears to place this decision squarly on the shoulders of the inspector to judge the quality of documentation.

Mouser has a similar switch from Omron Electronics. Their DESCRIPTION reiterates the general catagory "Basic / Snap Action / Limit Switches DOOR INTERLOCK SWITCH" However, the DATA SHEET doesn't use the word limit at all. It is a door interlock switch. Would all inspectors agree that this is marketed as a limit switch?

Lastly, the limit switches that have come in the kit of parts are huge and heavy compared to some of the other switches which are used as limit switches. A couple of smaller momentary switches that everybody can agree are marketed as limit switches include a small lever switch from E-stop and one from VEX.

I'd love to hear comments from inspectors on this issue. Thanks.

EDIT: I imagine that e-STOP only used the word LIMIT SWITCH in their online listing because they are aware of FIRST, and the restrictions we are under for this years game. Plenty of other vendors sell this switch without specifically calling it a limit switch. So, is it a limit switch because their marketing department called it one, or is it a limit switch because it meets the functional definition?

[kmusa]

Aaron - well said! I have been very frustrated trying to work this out with the GDC.

Just a clarification on the switches you mentioned. There is a similar part to the E79-20A. It's the Honeywell 2DM301.

The Omron part you mentioned is usually referred to as a "cheat" switch - on with door closed, off with door open, with optional override by pulling out the plunger during maintenance. Which could be still used for a steady ON or steady OFF, but one needs to be more careful about not reaching the momentary "plunger fully in" state.

--Karlis