What kind of switch are y’all’s teams using to cut the minibot off at the top of the pole?
i would suggest using a limit switch that would kill the motor once it hit against the top of the pole.
By their nature, limit switches are usually momentary devices. A better choice would be a light switch…
JMHO,
Mike
good point. placed correctly, a light switch would probably work better
I would use a DPDT home light switch or a DPDT Mechanical switch. That way you can make the Mini-bot come back dow after it hits the top.
So is something sold as a “safety limit switch” still a limit switch?
http://www.automationdirect.com/adc/Shopping/Catalog/Safety/Safety_Switches/Safety_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.
Any chance for a picture? I just can’t see how to mount that…
a combitnation of a house hold switch on the top to turn it off worked. and once the bot hit the pole the minibot helped sending it up.
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
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?
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.
--KarlisWe are using both a limit switch and a light switch on our bot. The light switch is for the kill switch as it hits the top.
Guys,
The Gdc answered this question a week or so ago. Their response is
“Only items sold as “limit switches” are allowed on the MINIBOT. Documentation and/or packaging material should be used to document items that may not be clearly identified as such. "
It seems that is pretty clear that any switch labeled as a limit switch meets the criteria.
As to the automationdirect link, those switches meet the criteria but the fact that they mount and wire using 1/2” conduit fittings likely make them too heavy for minibot use.
As to the other links that show “limit switch” in the title, likewise those fit the GDC description above. Inspectors are guided first by written rules (including all Team Updates) and second by GDC Q&A response. If the rules do not cover a situation and their is no response from the GDC on the issue, an inspector then turns to his LRI for the answer. If the LRI is not able to come to a conclusion, they will turn to the FTA, Head Ref, and other key volunteers for advice. If the issue still is undecided, LRIs will have my phone number and I will be able to get to someone at First or Bill Miller if needed.
Thank you Al for the response. The word “Title” is a bit difficult to interpret. I have part numbers, descriptions, and family/catagories to look at in the Digi-Key and Mouser online catalogs.
Below is a breadcrumb trail for getting to a particular switch on Mouser:
All Products » Electromechanical » Switches » Basic / Snap Action / Limit Switches » D2D-1001
Even though the final identifier is D2D-1001, I wouldn’t consider that a title. The description is
Basic / Snap Action / Limit Switches DOOR INTERLOCK SWITCH
So the level of identification immediately before part number contains the word limit switch. I guess that would have to be legal then? :ahh:
Somebody stop me if I’m going down the wrong path. ::rtm::
That D2D-1001 looks like a winner to me. Just print the catalog page and bring it to inspection. 
What a hefty current rating too!
So, just wondering if any teams have gone out on a limb and used a “switch” made from the allowed minibot materials with the purpose of mimicking a two-way switch but saving weight over a purchased item? If you’ve done this and been inspected at a competition were you allowed to compete in this manner? Feedback either way would be appreciated.
tuy,
You can only use limit switches, a max of two lighting switches, and Tetrix switches on the minibot.
That doesn’t sound right to me, Al. What’s the problem with fabricating your own switch using the allowable MINIBOT materials such as aluminum and rubber bands? Can you cite a rule or Q&A ?
John Vriezen
FIRST FRC team 2530 “Inconceivable”
Mentor, Drive Coach, Inspector
John,
<R92> The following items are the only permitted materials for use on the MINIBOTS:
M. limit switches,
N. no more than two common household light switches,
The Q&A answered that only the Tetrix Rocker Power switch could also be used as it is a Tetrix part.
I am not aware that any other parts were approved as electrical and would expect that the Q&A would agree. In the case of the minibot, electrical using the list above, is the simplest problem to overcome. As always, the Q&A is the only definitive answer.
If you can afford it, you can go the route my team went and replace the fuse on the battery lines with a lower-rated one (we use 7.5A) and blow it once you get to the top and briefly stall the motors. We replace that fuse every match.
It may not be the most cost-effective solution, but it’s extremely simple.
-Nick