Micro Linear Servo as Switch Machine?

[VonRyan]

After I stopped using commercial stuff like early Trix and Atlas Snap Track, I've never used twin-coil machines on any layout. I've either used a Tortoise, a DIY slo-mo, or a manual throw. I just think twin-coils are way too hard on N scale track, especially handlaid.

Hmm, perhaps i shouldn't have bought 30 of them then...

-Cody F.

[DKS]

David:
What size limit switch and where do you get them. Was it ever decided whether the motors on
the on  like you have would burn out if used like a stall motor?
Thanks
Al

You can get ultra-small micro-switches on the Bay or through dealers like Digi-Key. I would be using them in places where a stall motor could not possibly fit. Plus, the fact that they already generate linear motion means not having to convert the rotary motion of a stall motor by some means.

Here are a bunch on eBay: http://www.ebay.com/sch/i.html?_trksid=p3984.m570.l1313&_nkw=Mini+Micro+Limit+Switch&_sacat=0

I like the ones with the levers because they're easier to adjust.

Hmm, perhaps i shouldn't have bought 30 of them then...

-Cody F.

Well, think of it this way: how long do you think a push-pull type faucet will last if you use a hammer to turn it on and off? The nearly instantaneous action of a solenoid creates tremendous impact forces. Rick Spano has a lot of twin-coils, and about every month or so we're down there replacing a shattered turnout. But he doesn't like slo-mos; he prefers the twin-coils because he can hear them and know the switch was thrown. Just one of those quirks that makes Rick unique...

[VonRyan]

I've debated whether or not a "z" like cushion spring made from some brass wire would help to take some of the rough impact off of the turnout, but with the small tolerances of handlaid code 55 Nn3 turnouts, I'm worried about solder joints breaking more so that the actual points.

-Cody F.

[Lemosteam]

Instead of limit switches couldn't one just add a sprung fulcrum as TiVoPrince suggests and limit the motor using a time circuit stopping the motor after a certain length of travel on the screw?  Sort of a push button with a timer just long enough to throw the points before the slide on the screw bottoms out?

[SkipGear]

Time is not a reliable way to do it. These are not stepper motors and load will change the time it takes to travel. All it would take is for the mechanism to be a little stiffer one way than the other to quickly get it out of time. Limit switches are the best way for the mechanism only to be used reliably.

The best solution would be to etch a board with the limit switches built in, using the existing wipers on the servo mech as the contacts to control it. That may get into transistorized control of the motor though because I don't think the wiper contacts would handle the current load to use them as the switch, maybe they would though, it could be worth a try.

[DKS]

The best solution would be to etch a board with the limit switches built in, using the existing wipers on the servo mech as the contacts to control it. That may get into transistorized control of the motor though because I don't think the wiper contacts would handle the current load to use them as the switch, maybe they would though, it could be worth a try.

In looking at the wipers on mine, I'd say they are more than adequate to do the job of limiting travel--those pager motors draw a trivial amount of current. 2 diodes, 1 etched PC board, done.