Great Article!

Michael,

I very much enjoyed your article on stall motor turnout control.  What most intrigues me is the ability to have multiple locations control the same turnout.  I can think of several places where this would be most convenient on my own layout.  I also really enjoy "mechanical" or "old school" solutions like this, as apposed to those involving complicated integrated circuits, arduinos, programming and computers.  (probably because I work in IT and get enough of that on the job !)

One refinement I thought of is to add LEDs in the layout panel, controlled by the Tortoise switch contacts.  The LED glows only dimly while the Tortoise contacts are moving, and then more brightly when the movement is complete.  The machine itself provides the resistance for the LED.  In this way, a bright LED would indicate the chosen route, an off LED would be not chosen, and a dim, flickering one would mean "keep holding that button!"

If I'd had your article 5 years ago, I would have wired ALL my tortoise machines this way!  Thanks for the idea!!

latching relay approach

an alternate approach is to use a DPDT latching relay as a reversing switch that provides either +12 or -12V to the Tortoise machine.   Only a single 12V supply is required.   Of course, a relay will maintain power to the stall motor to hold it in position.

DP momentary switches wired to both sides of the switch machine could also be used without relays to avoid needing two 12V supplies (the switch machine requires no more current than an LED).

momentary switches can also be used to pulse one or the other coil from multiple locations on the layout.   In addition, the switch machines can also be controlled thru a computer interface that can pulse the relay coils.

Holding power, tradeoffs

A big point of a stall motor switch machine is that it’s got holding power while it’s stalled, take the power away and depending on the mechanics of the situation the points may spring back a little immediately, slowly over time, or not at all.  For a fast tracks non-hinged style point you need the holding power.

A bunch of paralleled push buttons certainly is a simple and cheap solution to have multiple panels control the same switch, if you can accept the lack of holding power, the need to hold the button in for a while, and the occasional oopsie short when both buttons get pressed at the same time.

Latching relays seems like a more robust solution also allowing push button control, but it’s certainly nowhere near as simple as a bunch of push buttons in parallel.  And not as cheap.

DCC (and/or LCC) could also be set up to allow push button control of the same turnout from a number of panels, with less wiring, but more electronics and expense and setup time.  No need to find and call up switch numbers - the panels would look and work exactly the same.  (For example you could do this with NCE switch-IT’s and mini-panels, and I’m sure other brands have stuff that would do it too.)

Holding power

How much of the holding power from a tortoise actually comes from the stall motor and how much comes from the piano wire? Don't servos connected to the throwbar via a stiff wire do a good enough job holding even fast-tracks style points in place?

Holding power

The piano wire provides spring action which allows for a mechanical setup that doesn’t have to be precisely aligned, not holding power.  It’s the power to the motor that provides the holding power.  When I had tortises on my O scale hingeless point turnouts, you could hear them all get wound back by the combined spring action of the piano wire and the points. Sometimes the points would still appear to be in place, but often they had moved just a bit away from the stock rail.

Servos are a little different - they actively try to hold the same position using a position sensor of some sort, and actively drive the motor to get back to that position if they get forced off it.

@Eastwind

Hi Eastwind,

I've found the position of the wire and the Tortoise is plenty to hold the points of my HO Scale, Code 83 Fast Tracks switches in place, with no stall power necessary.  Your mileage may vary.  Some factors might include the size of the wire and the thickness of the roadbed, which effects the throw angle and distance.  In my case, I have 1" thick subroadbed and standard cork roadbed.  I set the Tortoise wire adjustment somewhere in the middle of the range so I get a firm connection of the point rails against the stock rails, but not so firm as to break the solder connections.

You can't move a tortoise actuator very far without power.  In fact, the instructions say you risk damage if you do.  So if the wire has some tension on it, it will hold the points even if the actuator moves a little bit.  When I turn off the power to my layout, all my points stay in place.  I can flick them with my finger, and they snap right back into position.

I really enjoyed this article.

Well written and very practical.  I don't want to operate switches with dcc.  I was planning to put up with out of scale ground throws to avoid switch motor burnout.  I have a few tortoise machines, but never thought of this sort of control for them.  I'm also thinking that double throw toggle switches with a spring load to center off would do the same thing without allowing both directions to be thrown at the same time.  Of course my layout is planned to be a switching layout with walk around control and no central panel, so there would be only one electrical switch for each turnout.

Tortises are designed to stall

You don't need to worry about burning out a tortise by leaving power on it when it's stalled - they're designed to handle that.  If you only want one switch per turnout, a plain old toggle that's not spring loaded will work great.

Plain old toggle

That’s true, that’s what I did in staging on SL1. The advantage is the toggle shows the last direction thrown. However, you can’t do the auxiliary panels with a regular toggle, but you can if the toggle is a spring loaded momentary contact center off toggle.

Terrible Design

If both the thru and diverging buttons for a turnout are pushed at the same time, there is a direct short across both power supplies which will blow one or both of the fuses.

Paul O

True, and that was pointed out

True, and that was pointed out in the article.

No system is perfect, and this one has the advantage of being very simple, but it does take some consideration to get perfect operation. Consideration 1 is holding down the push button 3 seconds. Consideration 2 is don't push both the red and black buttons at the same time. Consideration 3 is two different people at different panels pushing the opposite button for the same turnout will also cause a short.

Those were pointed out in the article, so it's up to the modeler to decide if they are okay with these shortcomings. Some will be, others will not.

That's fine, more complex (and more costly) but also more dummy-proof is certainly an option as well. There's room for both approaches.

Simple Solution to Shorts

Hi,

By simply replacing the fuses with resistors you can eliminate the issue with this design. Something between 47 ohm at 3W and 100 ohm at 2W would work fine. Another option would be to use an automotive tail light filament as a resistor. (not the stop light) In either case if two conflicting buttons are pressed the series resistance protects the power supplies. Using a fuse is really not a good solution unless you are OK with profanity among your crew.

Dick

momentary DPDT center off

a momentary toggle switch ($2), as Joe suggested, would prevent a short 

Servos are a little different

Only if the servo circuit is badly designed. You don't want the servo to be active all the time, you want it to move to a position, then stop and remove power (or at least the position signal) from it. Servos have a rather significant amount of holding power on their own, due to the high gear ratio. Try holding one and seeing if you can stop it or keep it from moving. They'll hold position just fine without power applied, even with fairly significant back pressure. (There's a potentiometer inside on the shaft that reads the position, and feeds back to whether it's where it's supposed to be...)

As for as multiple control positions...  If you use an Arduino, (a Nano is about $3.50 each in bulk) with home-made touch sensors (literally, a penny, plus wire) , to operate your micro-servos (about $1.50 each) you can place the sensors in multple positions wired to the same pin, and create multiple panels...  with only a single wire to each sensor / switch, to operate several turnouts for much less than the cost of a single Tortoise. I'm working on such a project now. See my blog entry for the ongoing saga

.

Helpful suggestions, thanks

I'm glad you generally enjoyed my article. 

1.  If I had to do it over the momentary contact SPDT would be my choice, and the resistors instead of fuses, and I will change to the "slow-blow" fuses are suggested.

2.  I have routinely "flicked" my points open to clean behind them, the Tortoise always snaps them back with their recommended spring wire throw bar. 

3.  I only rarely have more than one operator so the two control buttons at once simply doesn't occur.  For a layout with regular operating groups a more elegant solution would be worthwhile. 

This was a combination of cheap, lazy, and simple for me.  Your priorities will lead you to other choices.  I try to remember "The perfect is the enemy of the good" in getting things accomplished.

Regards, Mike