Track Repair and Turntable Polarity Test

In my excitement after securing the turntable motor last night, I turned the module over and knocked it against my knee (I tend to work on the floor). Normally that wouldn’t have been an issue, except my knee struck the excess rail that extends beyond the module surface, where the fascia will eventually lengthen the module a bit.

That made for a big mess. The rails popped right off the ties and bent upward, severing forty or fifty plastic “rail spikes.” There was nothing I could do except replace that length of track. Here’s the damage:

So tonight I pulled out the soldering iron and desoldered the feeders. Then I pulled the track up to the first turnout and laid a new length of Flex-Track in its place. After gluing it down, putting some weights on, and soldering the feeders on, it looks like new.

After that repair I needed to do something a little more exciting, so I temporarily wired the turntable up.

I was afraid the locomotives would get hung up on the gap between the approach track and the turntable deck rails, and I was also afraid that the polarity of the tracks wouldn’t switch when rotating the deck.

For those who are unfamiliar with Peco’s turntable, I may need to explain this “polarity” piece a bit. The reason I opted for Peco’s turntable instead of another plug-and-play turntable is because it has a genius system for switching the polarity of the rails whenever the deck makes a full rotation.

This system depends on two separate brass collars beneath the turntable deck. Two spring-loaded brass plungers move across the collars when the deck rotates. Each plunger conducts electricity up to one of the two rails, and after both rails pass over the gaps between the collars, the polarity reverses (i.e. the positive rail passes over the negative collar and vice-versa). If this didn’t occur the layout would short out every time the deck made a full rotation.

Another benefit of the polarity changing is that a locomotive moving forward onto the deck can be turned 360 degrees and continue to move forward off the deck. It doesn’t matter that it just came from that direction; with the reverse in polarity, the locomotive still registers as moving forward.

Good news all around: the locomotives can get on and off the deck with no extra effort, and the polarity changes as it ought to.

Here’s a video of the turntable in action. Pretty soon, my hands won’t be needed except to push a button on the DCC controller. Next up, I hope to begin working on the software and hardware that will allow me to do just that. On that note, my brother-in-law sent me some documents and instructions earlier today, so I have some reading to do.

Turntable IV

Well, it isn’t pretty, but after a whole lot of head-scratching and futzing, I now have the stepper motor attached to the turntable, and am able to rotate the turntable deck with minimal friction.

As you can see here, the biggest initial obstacle was the mass of wires and switch motors. To clear them, I had to extend the mounting beam a foot longer than expected. Once in place, I drilled the hole for the motor, then sanded it out a bit.

Yep, pretty much like that. At this stage I could tell there would be some friction issues to deal with between the deck and the well. Both components are plastic, and the slightest lean in the pivot mechanism sends one side of the deck screeching to a halt against the wall or floor of the well. I sanded some of the well, then I filed down the underside of the deck ends. That helped a little, but I could tell I’d need to place some shims under one end of the mounting beam.

Before I got into fine-tuning, I wanted to make sure everything was situated and solid. I attached the motor to the mounting beam with a couple of machine screws.

I then used CA glue to fix the iron axle inside the deck. Now the deck can be dropped in and pulled out at will by loosening or tightening two small inset hex bolts on the shaft coupler.

After putting a couple of shims between the baseboard and the mounting beam (to reduce a lean which caused one side of the deck to dip down while the other lifted), the deck could be moved slowly and without much friction.

Turntable III

 

Remember last year when I asked Peco about the DCC turntable motor that was slated for release in 2016, and they told me it would be released later in 2017? Well, it wasn’t released in 2017. When I asked them about it more recently they told me they were having some technical difficulties with the indexing, but assured me that it was slated for release in 2018. They thanked me for my patience.

I do have patience, but I’ve come to realize that I don’t have much faith in Peco’s ability to manufacture a motor that will work well. Judging by the prototype, there will be modifications necessary to mount the motor directly to the underside of the turntable. Also, the motor probably has a gearbox, which probably has plastic gears, and that means it will not be very accurate (especially an earlier model, while the kinks are being worked out).

So, I reached out to my brother-in-law and told him what I needed to do, and asked him to guide me through the hardware and software setup of an Arduino-based, DCC-interfaced turntable motor. He knows far more than I do about circuitry and programming–it’s what he does for a living.

After a few days he gave me a shopping list:

  • Arduino Uno
  • Adafruit Motor Shield
  • Iowa Scaled Engineering DCC Shield

To power the Arduino, I sourced a power cable from the electronic graveyard at my office. The motor shield stacks right on the Arduino and drives the motor via jumper wires. The DCC shield (which is slated to arrive next week) will translate commands from the DCC controller to the Arduino, which will then tell the motor shield what to do.

I got the Arduino and motor shield today:

As you can see, I also got a stepper motor, a 4mm to 5mm flexible motor shaft coupler, and a 4mm steel rod.

Figuring out a mounting system for these mechanical components will be my primary goal for the next few days while I wait for further guidance from my brother-in-law. The mechanism may look something like this:

unnamed

So, although it doesn’t seem like it, there’s quite a bit of activity happening underneath LSR, and if all goes as planned, I will have an indexed, programmable turntable soon.