DIY Switch Machines?

conrailandrew's picture
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Has anyone ever attempted to build their own motorized slow motion switch machine?

I am a low-budget N scale modeler who would like to build my own if I can.

I can't afford the amount of Tortoise switch machines I would need, but I would like a solution I can use with my DCC system.

Thanks,  Andrew




DKRickman's picture

I got as far as thinking about it

I haven't built one, but I have given the matter considerable thought.  I once purchased a switch machine kit which consisted of a motor which drove a length of threaded rod, an arm driven by a nut on the rod, and a set of contacts to form a DPDT switch actuated by the arm.  Power in one polarity drove the motor until the contact was opened at the end of travel, and reverse polarity did the opposite.

The design is so simple that it should be easy to duplicate.  Micro switches could be used in place of the custom made ones, or all sorts of creative solutions could be devised.

I have wondered how hard it would be to make a small unit out of a pager motor.  It should be small enough that it could be mounted on top of the sub-roadbed (or very slightly recessed into it, I suppose).  I have been collecting old electric toothbrushes, just to scrounge the motors.  When you can buy a toothbrush for a few dollars, and they're made to be disposable, I think of the motors as nearly free!

Ken Rickman

Danville & Western HO modeler and web historian

http://southern-railway.railfan.net/dw/

dfandrews's picture

Cheap jackscrew machine w/contacts

Here's a sketch of a machine I've built in the past, that is along the lines of what Rick mentioned.

It consists of a spare DC motor (3 volt -12 volt) connected via a piece of rubber tubing to a 6-32 treaded rod (long screw with the head cut off. 

The threaded rod is the jackscrew that turns in a 6-32 brass or cad-plated nut soldered to a piece of printed circuit (PC) board.  The PC board slides back and forth in a couple of plastruct channels out of the scrap box.

I make separate traces on the PC board by cutting away the copper-cladding.  I use phosphor-bronze strips (the same stuff I use for wheel wipers) as contacts that ride across the PC board traces.  I grind away portions of each trace where I don't want electrical contact.

To drive switches, crossing gates, etc., drill a hole in the PC board, and hook a piece of piano wire or stiff brass or steel wire in, and away you go.

It's a very cheap, but very useful and effective solution to a lot of mechanical-electrical problems.

edit:  For DCC control, just wire your motor to the cheapest minimum function decoder you can find.  Voila!  Experts in the area of fixed decoders need to chime in here.  It's all do-able, but I can see some wrinkles in the control and direction that fixed decoders should specifically be able to handle.  I don't know; never used 'em.  I rely on pushbuttons on the fascia, 'cause they're the cheaper way.

Hope this helps.

Don

Rincon Pacific Rwy, 1960.  HO scale std. gauge - interchange with SP.

DCC-NCE, CMRI, JMRI

DKRickman's picture

Another way of limiting travel

I've been thinking about this one this morning, and I have an idea...

You could solder a pair of nuts onto either side of a piece of copper-clad board (using the threaded rod to make sure they're lined up).  Each side of the board would be connected via a diode (opposite directions for each side) to a wire connected to one of the motor terminals.  Power would flow through the metal jack screw into both buts, and conduct via one of the diodes.  When the nut runs off the end of the screw, conduction stops, but reversing the polarity lets it start in the opposite direction.  To work properly, of course, the threaded rod needs to be free at both ends.  The simplest way would probably be to turn down a length on each end to run in some type of bearing, or even to turn away a section of the threads a little wider than the thickness of a nut.

Of course, there is no way to adjust the travel.  On the plus side, there is no way for the travel or limit switches to get out of adjustment.

Power routing would require some sort of wiper or contact if you want it in the switch machine.  Personally, I'd use a DPDT to control the machine and frog polarity at the same time.

Ken Rickman

Danville & Western HO modeler and web historian

http://southern-railway.railfan.net/dw/

Question

you have to ask yourself. How much will parts cost for each machine? I have a commercial one that pretty much looks like the one in the sketch.

Rich

dfandrews's picture

Costs

Rich,

Cost is a tough question to answer when the parts are 100% out of the scrap box.  Motors can come from old locos, toys, retail displays.  The PC board material is maybe a buck per unit if you buy a big piece new and cut it up.  Screw and nut = $0.10 + $0.15, or less if you buy by the box.  Plastruct is getting more expensive, but Evergreen Scale Models has styrene shapes in 14 inch lengths @ 4 for $2.99.

Rick,

I didn't go in to detail, but two of the wipers would be for motor control:  you would cut a gap across a trace near the end of the throw, and solder a diode (1N4001) across the cut, so that when the wiper passes the cut trace, current flow stops and the motor automaticaly stops.  With polarity reversed (your DPDT reversing switch), the diode would then conduct current in the other direction to back out of the cut trace area.  You have the same thing at the other end of the trace, with a diode soldered across the gap in the other direction, so your have auto-stop at each end.

Other traces could be used for lights, indicators, sensor feeds to other electronics, etc.

Whew!  This is a lot harder to explain that to throw together.  I hope I made some sense of this.

Don

Rincon Pacific Rwy, 1960.  HO scale std. gauge - interchange with SP.

DCC-NCE, CMRI, JMRI

Home built switch machine

I use Servo Motors to control my turnouts. I only have two right now but they work great. I use an S88 module to control the servo. The module was designed by a friend but he hasnt released it to the public. Others have used servo motors for turnouts and if you search google you may find a cheap controller circuit. Servo motors can be purchased very cheaply. This link will get you to a DIY system that works with Rocrail. Not sure if it will work with JMRI.

http://wiki.rocrail.net/doku.php?id=mgv84-en

Here is a link to Paco's site. I think this is one of the best DIY sites going. Everything you need is posted on this site and he asks for nothing! http://usuaris.tinet.cat/fmco/home_en.htm

Rob teed

Bullfrog switch machine

Right at the top of the page when I log in. $6.00 each. Use your imagination to keep the cost down.

http://www.handlaidtrack.com/BullFrog-Manual-Turnout-Control-Unassembled-p/bf-0002.htm

Yes, a well stocked junk box can work wonders.

Rich

dfandrews's picture

Time is money

Alan, Rich:

Yes, I must concede:  time is money.  I'm just stubborn enough when I'm reaching for my wallet that I just may spend twice what it's worth in time, just to say I built it out of the scrap box.  (But, but;  I am having fun, I'm having fun, I'm having fun...)

Regarding servos, I am reminded of the MRH sponsor in San Diego,  Tam Valley Depot.  He has some great products combining servos and DCC control.  Check him out through the "Advertisers" tab at the top of the page.

Don

Rincon Pacific Rwy, 1960.  HO scale std. gauge - interchange with SP.

DCC-NCE, CMRI, JMRI

5 dollar switch machine

i too have been thinking about this issue for a while and have come up with my own solution. using some styrene and a modified rc servo and a microswitch. the rc microservos can be bought off ebay for as little as 25 dollars for ten. $2.50 each plus a 2 dollar microswitch and some scrap 40 thou styrene. The speed is dependant on the input voltage you use and the microswitch provides frog polarity. takes 5 mins to build. in my opinion excellent value. i knocked up 10 in an hour the other day. as previously stated i do not know how you can "cheaply" control switch motors with dcc. when you factor in the decoders  the idea of budget is really streching its limits.

 

Dan

Why would anyone want to control switch machines w/dcc?

If you are building a layout to use a walk around throttle to follow your train around the layout, just put a turnout control switch on the fascia in close proximity to each turnout, and flip the switch as needed when you get to the turnout.

The only place where I can see the advantage to using dcc to control turnouts is when you have a large club style layout with a dispatcher who is doing ctc control of mainline turnouts in combination with signals.


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