AR-1 VS AR-2, Active VS "dumb" shuttle systems...
Dear ???, Jerry, Shuttle curious,
Technically either the AR-1
http://www.circuitron.com/index_files/ins/800-5400ins.pdf
or AR-2
http://www.circuitron.com/index_files/ins/800-5401ins.pdf
will do as Jerry requires.
However, it should be noted that the Circuitron (and most US-made units) require some form of active detector at each end-point of the shuttle-route to tell the unit when "something" has arrived and needs reversing/polarity-change/"throwing-back the other way".
In contrast, the typical UK-made units
(GaugeMaster SS-1, Anton's Trains, "Misc Electronics for Model Railroads" homebruise unit linked-to above)
do not need any active end-stop detection,
they only use a standalone diode at either end to "catch" the loco,
and hold it until the track polarity reverses to "send it back the other way".
(IE the diode is entirely electrically, physically, and wiring-independent of the Shuttle unit itself.
Indeed, One can add a diode as a "dead mans safety" systems to single-ended spurs even without a shuttle-unit in play. Works great for Point-to-point layouts where kids are frequent guest operators... ).
Both approaches have their Pros and Cons:
"Active detection" systems (as typically found in the US)
PROs
- Can handle any-length "shuttle route" (Will only "change direction" when the end-detector is tripped)
- Adds capability for "controlled slow-down/accell"
- Can easily adapt to "loco at either end of the train consist" situations
CONs
- Requires more wiring (not just the track feeds, but also the mandatory feeds to either end's "detector" units
- Cannot work _without_ the detectors connected
- Can in some cases be "spooked" by spurious/intermittent noise picked up by the "detection wiring"
- Needs extra detectors, and sometimes extra $$$ circuitry, to handle "multiple end points"
(IE anything more complex than literally a straight-track "A-to-B and back again" situation)
- Can be faked-out by something triggering the detector which is not actually the desired shuttle train
- No automatic "dead man's safety" auto-stop capability
(train _can_ be made to "run off the end-of-track" if incorrect detection occurs)
- Cannot handle spontaneous (0-5-0 switcher) replacement of the loco, or starting-of-the-shuttle with a loco in the End-stop sections (likely mis-trigger condition resulting in loco happily chuffing straight off the end-of-track...)
"Dumb Timer" systems (as typically found in the UK)
PROs
- Requires less wiring (Throttle> Shuttle unit> Track feed)
- Switching between "Shuttle" and "Manual drive" mode is a 1x toggle switch action
(drop power to the Shuttle unit, and the Manual throttle track-feed passes thru un-affected)
- Handles complex shuttle routes with multiple-end-points easily, at only AUD$0.05c additional per end-point
(just add a diode on the new/extra end-point)
- Absolutely reliable "dead mans safety" stopping any any, every, and all trains at either end of the shuttle route, irrespective of the shuttle-unit or manual throttle state.
(Loco literally cannot go past the diode point, unless the loco is wired up incorrectly!!!!)
- can handle "loco placed any orientation relative to the track" and "loco placed anywhere ion the shuttle route including within the end-stop sections" conditions without causing a "false detection" condition, or provoking a "loco over the edge" condition.
CONs
- Being a "Dumb" timer, it literally counts off X seconds, then changes direction.
Ergo, if the length of the shuttle route divided by the train speed> the timer setting,
the train will reverse before it "gets to the far end of the route".
NB that this is easily solved with the addition of a capacitor to the 555 timer circuit.
(I built a unit following the "Misc Electronics" article linked above, with a 10-minute maximum shuttle-time,
dead easy to adapt to requirements)
- Requires accurate/predictable placement of the diode-stopping gaps.
- Requires fore-thought re "which end of the train the loco will be on",
and "how much track beyond the diode is required to hold the typical shuttle train"
(the shuttle does not care which end of the train the loco is on, it will still count off X seconds and then change-polarity/direction. However, if the train is too long, the loco will attempt to shove the excess-length train consist off the edge-of-track)
- Does not give a controlled "decel/accel" behaviour at end-of-track.
(Realistically, if running at scale-speeds, this is far less visually jarring than it sounds on paper.
Furthur, with the addition of a simple capacitor at each end in parallel with the stopping diode,
predictable consistent Decell can be added/tweaked/modified/played-with easily!)
Personally, I have used and taught "scared of wires" modellers how to install "dumb timer" shuttle systems in scales N thru O2R (and most of the NG variants in between). Said units have then gone on to reliably keep show layouts running for literally years. The flexibility of the "diode stop" system has allowed sectional layouts to be freely remixed ands re-assembled without any change in Shuttle settings or track buss wiring, and no need for excess "detection wiring"...
Happy Modelling,
Aim to Improve,
Prof Klyzlr
