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The Randall Museum in San Francisco hosts a large HO-scale model model railroad. Created by the Golden Gate Model Railroad Club starting in 1961, the layout was donated to the Museum in 2015. Since then I have started automatizing trains running on the layout. I am also the model railroad maintainer. This blog describes various updates on the Randall project and I maintain a separate blog for all my electronics not directly related to Randall.

2016-11-18 - Non-Tortoise Slow Motion Turnout/Switch Motors

Category Randall

After repeated failures at trying to control the T330 turnout using an NCE Switch-8, I finally crawled under the layout and I find this:

That is definitely not a Tortoise turnout motor, which is what I had been planning for all along.



Turns out the layout uses:

  • Old-style twin-coil snap turnouts. Mostly in the yards. It seems these were everywhere and changed overtime.
  • New-style Tortoises, mounted on a L-shaped board, each with a terminal block. These with new wiring such as those used on SIA work as expected with the NCE Switch-8.
  • Slow Motion Turnout/Switch Motors with gear drive. These work like the Tortoise. However I'd like to know the type and how much the power supply can deliver.

Regarding these last one, googling these I found 2 possible references:

  • According to DCCWiki, these are called "Limit-Switch DC Motors"; they don't stall, instead they have internal switches to stop them.
  • Fulgurex brand.
  • Lemaco brand.
    • Image here. Motor on one side with the 2 contacts on the other side.

⇒ Checked on layout, these are Fulgurex motors.

Switch-8 delivers 40 mA per output. Not enough for the 200 mA motors from Fulgurex.

One issue is control panel support. The NCE Switch-8 + Button Board is perfect in that regard:

  • The Switch-8 remembers the last state and re-applies it when powering up.
  • The Button Board is active on edge, it only transmits "changes". DCC accy cmd override the button, or the button change triggers a change -- e.g. the "last one" wins. But when powering up, the button board sends a signal and thus resets to match the button.

Alternatives to control them?

  • Team Digital SMD84 - PDF here 
    • ⇒ clearly states will not drive Fulgurex.
    • Does seem to only support momentary switches.
    • Doc is overly complicated.
  • NCE Switch-Kat. 1x output control.
    • Does not clearly states whether it could work or not.
    • However clearly indicates the button supported are momentary, not rotary toggles.
  • Digitrax DS64 - PDF here. Maybe? 4x outputs.
    • Has button inputs but not clear whether they work with "permanent" rotary toggles.

See discussion on why I can't use the Switch-8 directly and suggestions on how to work around it.

Using relays:

Using a "H-Bridge", e.g. 2x2 push-pull transistors to drive each side of the motor:

See for L293D (H Bridge)

L293D is a "half-H" and has 4 drivers. 2 are needed (one per side of the motor). Thus needs 4x L293D for one Switch-8. Vcc1 for control us 4.5V - 36V, and Vcc2 for driver is up to 36 V. Connect both to the 12 V DC for the Switch-8 power.


Somewhat unrelated, proper way to get 5 V out of 12 V:

Creating a board using L293D:

  • Switch-8 has 8 outputs, 2 pins per output.
  • 4x L293D … DIP 16 each (2x8 pins)
  • (8+8)x 2-pin PCB Mount Screw Terminal Block 
  • 1x 2-pin Terminal blocks for Vcc power
  • Solder board max pin out is 4x(8+3) = 33 for the DIP, 8x2 = 16 for the terminal blocks. In the other direction we're roughly looking at 5-6 rows for the DIP and 2x 3-4 rows for the terminal blocks so conservatively a board using 30-40 x 20 holes would work.

In reality, I will not have all-Tortoise or all-Fulgurex. First thing to do is list each type of turnout -- Tortoise or Fulgurex and check on the map. In some places I was going to have 2 Switch-8 per panel so might do one Tortoise vs one Fulgurex or a mix.

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