Peter's Model Railroading - Modeling Articles

Modifying Tortoises

Circuitron makes switch machines called "Tortoises". They derive their name from the fact that they are slow-motion switch machines. As opposed to the snap switch machines, these machines move the turnout's points very slowly. This is more inline with the prototype.

Modifications

The problems I experienced with the Tortoises on our second layout were primarily due to the shorts that would happen when the points were being thrown. I used Micro Engineering turnouts on that layout, which were partially to blame. However, a large part of the problem with shorts was also due to the Tortoise themselves. I use DCC, and what happened was that the internal mechanism of the Tortoise would effectively move faster than the points. So, the internal contacts would switch the power supplied to the live frog before the points had mechanically moved to the opposite track. This would lead to a short. Below is a description of how I modify our Tortoises to eliminate these shorts.

	The first thing to do is to remove the label. According to the manufacturer (Circuitron) THIS ACT VOIDS THE WARRANTY! Under the label are 5 screws that hold the two halves of the Tortoise body together.

	Once the body halves are separated you'll see the internal workings of a Tortoise. It consists of a motor soldered to the PC board. There are series of gears to help reduce the speed of the throw arm. The throw arm (to which the linkage rod is attached) has a set of copper contacts that slide across the PC board.

	Here I have removed the parts and marked the approximate location of the cutting line. Our objective is to increase the area of dead contact as the wipers make their way across the PC board from left to right (and vice versa). If you cut off too much, then the Tortoise will no longer be useful as a power router for the turnout's live frog. Above the PC board you can see the copper wipers on the throw arm.

	Rather than removing all the material (which is not easy), I decided to just cut the contact areas so that the center parts will be dead areas. Use a volt meter to verify that you have made the separation. I use an Exacto knife to make the separations. This completes the modifications. I reattached the 5 screws and I'm in business. They work great, with no shorts. The only down-side I have experienced with this modification is that if the actuator rod is not fully moved to the left or right when the turnout is thrown, the copper contacts can stop in this "dead zone" and thereby not provide any power to the frog. I have found that by using a slighly thinner actuator rod, I was able to solve this issue for all the turnouts that gave me this problem.

Installation

In some difficult-to-reach places I have installed Tortoises onto a ź" piece of plywood and then attached the plywood to the subroadbed. In other places I installed the Tortoises directly to the subroadbed. Here you see the Tortoise, the plywood piece, and the drill template.

Here is the assembled collection of parts. The arm in the Tortoise moves left and right, which causes the linkage rod to move right and left above the layout surface. You may notice that I use a thicker linkage rod than that which comes with the Tortoise. The friction at the points is too high to overcome with the default linkage rod. However, to still have this rod fit the throwbar of the turnout, I have to grind down the tip of the linkage rod a bit. Music or piano wire might also do the trick.

And then, finally, the completed product. I cut off the tips of the screws that attach the Tortoise to the plywood piece. After attaching the Tortoise to the subroadbed using clamps I was able to fine-tune the location of the Tortoise relative to the turnout. I also had to bend the linkage rod on this one to get it to throw the points in both directions. It is operating perfectly now. For this layout I also switched from powering the Tortoises with a Radio Shack 9V power supply to an All Electronics 3V power supply. The turnout now moves just about as slow as you can get, and they make almost no sound to boot.

This simplified wiring diagram shows how the Tortoise is connected to the turnout electrically.

There is some sort of switch between the left-most and right-most connector of the Tortoise (solid black lines connected to the 3V power source). I used a cross-wired DPDT toggle switch on a couple of turnouts. Most used the Digitrax DS44 stationary decoder. To keep the diagram simple, I left off the switch.

The remaining three contacts (not connected in this diagram) on the Tortoise are for controlling the turnout's signal on either the layout's control panel or a signal placed next to the turnout on the layout.