So after looking at all these electrical solutions I have to wonder why you
can't just do it mechanically. Put a pair of washers on the shaft and a jam
jut. Tighten the jam nut just enough to hold the gate at any position.
Power to motor only to move the gate and de-power it otherwise. 'Course
this assumes that the motor torque capability is way more than you need for
a simple model railroad gate. Very cheap. OK reliability. May have to play
with it to keep it from loosening up.
Have fun in any event.
Thought about a reflective opto sensor? Easy enough to put 3M
reflector tape or gloss/metallic paint on the bottom of the rolling
http://news.thomasnet.com/fullstory/458963 would be a nice starting
point, just stick them between the tracks.
Wouldn't it be easier to rig limit switches on the arm motor that
turn off the motor power at end of travel, rather than figure out a
way to cut current and have it sit stalled on a physical stop?
I'd have to sit down with a pencil and figure it out, but there
should be a simple and elegant way to open the motor power in 'Up'
when it hits the 'Up Limit' and take that switch out of the picture
when the 'Down' relay kicks in, all using relay logic. You won't need
any sort of braking or hold action if the crossing arm is properly
balanced neutral. Probably take a 3PDT or 4PDT relay to reverse motor
polarity and select the right limit switch. And you rig the crossing
lights so they run unless the arm is in 'Up limit' mode
And if you want to go into r.c.m overkill mode... ;-)
You can use slot opto sensors for the limits, a few TTL gate chips
to start and stop the motors, and a 555 or two for timing.
You'd want to add a time delay circuit of some sort so the gate
delays down a second or two for the warning lights, then holds down
while the crossing is fouled but comes back up automatically after the
crossing is clear - if this was a real railroad you could count on
track loop detection to see if the crossing was fouled, but not on
H.O. And even if you could, it would only see the engine, not the
rolling stock - no shorted tracks caused by steel axles and wheels.
And if you space the crossing trigger sensors out for realistic
advance time but where they can't see the train the whole time, you
might need four train sense switches or more - put two right at the
edges of the grade crossing so they'll see the rolling stock if it's
running slowly or stops.
--<< Bruce >>--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
Thanks. The switch is already working fine. Just a stupid contraption
from various junk that I had, but it works every time.
I think that sticking a resistor in series is the easiest solution
(and the one that I have done after receiving advice and it works).
I want to eventually have some timing, but not now.
Now that my gate works, I need to figure out a way how to make it all
apparent to my son, while somewhat proofing it from his destruction
(like if he steps on it). He is sometimes not paying attention.
I hope that rolling stock will keep the switch depressed, I have not
tried it yet. The engine does it.
I want to screw around with that stuff for several reasons. One is to
keep my son interested. Another is to learn about automation in a non
threatening setting (ie not a welding CNC setup as a first time
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