Re: A LEGO double-throw switch?

"Steve Hassenplug" <[email protected]> wrote in message 
news:[email protected]...
> On Mon, August 22, 2005 2:05 pm, Brian Davis wrote:
>>    So I've got an application where a forklift loads a crate onto a 
>> conveyor
>> belt. I could then start the conveyor belt up by having the forklift 
>> throw a
>> polarity switch. What I would *like* is that when the crate gets to the 
>> other
>> end, it somehow stops the conveyor motor again, (here's the tricky part),
>> leaving the system in a state where the next forklift delivery can 
>> re-trigger
>> the whole system from the "front end", as it were.
>>    Oh, did I mention I wanted to do this with just polarity switches, no 
>> RCX or
>> other "intelligent" systems in the loop?
> When the switches are in the same position, the belt will not move.  When 
> in
> opposite positions, it will run (some direction)
>
> Two problems:
> 1) Half the time, the motor will run backwards (can be fixed using diodes)

I required something that will elimiate the need to worry about which way 
the motor is running, a one way foolproof motor drive mechanism might help, 
such as this one I was shown by someone in this thread:

http://news.lugnet.com/technic/?n=13659&t=i&v=a

Unfortunately the original picture depicting the drive I actually built is 
no longer online, although one can see the general idea used in my own 
creation that I built on from that idea, I didn't get a photo of the actual 
mechanism itself, although I'll have to see if I can rectify that problem in 
the next couple of days.

http://www.brickshelf.com/cgi-bin/gallery.cgi?f=117590

My GBC feed-hopper, which fed basketballs and was a bit primitive at that 
time.  I'm still accumulating parts for the next revision of the design.

The feed-hopper's one-way drive was made with much help from those who 
responded in the thread, and as such this is not my idea, however, if Brian 
want motor direction to do more than control a conveyor which will only go 
in one direction, as is the case in most assembly-line production models, 
this solution might not be the best one for Brian.

The above mechanism provides a simple, yet foolproof way to let a polarity 
switch control an on/off function, regardless of which way the motor is 
getting driven, as has been detailed by other posters in the 
above-referenced thread.  It's 100% foolproof, doesn't require messing about 
with polarity issues or complex gearing arrangements, and requires a minimum 
of space to implement.

> 2) The "dead" zone where a crate can turn "off" switch 2, but not move it 
> all the
> way to the "reverse" direction.
>
> I'd suggest mechanically linking the switches (making it so the same 
> switch is
> triggered on both ends)
>
> Get it?
>
> Steve
>