Got my Z Scale SD75's today...

Yes, the AZL CN SD75's showed up. First let me say they look simply stunning! I am very happy AZL produced these models. But, they are not perfect, as Ajin needs to take a bit more care when assembling this precision mechanism.

These two were both way too slow of runners, as were 2 out of the 3 NS units I got last month.

They were very quiet, but just way too slow, doing what looks like 20MPH at 8 volts. I hung an ammeter on and measured 90 milliamps out of one, and 85milliamps out of the second.

I ran them for 15 minutes each dirrection, and the current draw on the slow one was 85ma and the faster one was 75-80ma, depending on weather it is on the straight away or a turn.

From my previous experiments I had found that anything less than 70 milliamps is ok, but any more and you have too much friction in the mechanism.

So I pulled them off the track and both were warm. I took the shell off the slowest one, used my tricky "Shave the Tanks Buckle Nub" with a new #11 blade, then took the tank off, and disassembled.

What I seen this time was the black plastic shaft bearing blocks were wedged crooked, and the worm shaft was not in line with the motor shaft.

I whipped out my Nair Drill ( a fingernail rotary tool that looks like a mini dremel ) with 220 sanding disc, and sanded all 4 sides of the plastic bearing blocks, and aligned all the shafts up straight, then put it all back together.

Don't get me wrong, this took a bit of careful work to do, but when I had it all back together, I popped the shell back on and put it on my test oval, and now I get 60ma at 8 volts with the shell on! Now the loco makes noise too, but that is because the bearing blocks are moving around. This is by far the best I have achieved for reducing friction in one of these locos. Happy Happy, Joy Joy!

Now I am committed towards tearing the other apart and reducing friction in it, so I can MU them. I need to get decoders in them too.

 

Here are a few more observations:

The motor by itself draws 20 milliamps at 8 volts.

The locomotive stalls at 100 milliamps, meaning the motor has power but is not turning.

When you get total current draw to less than 70 milliamps, the motor does not get hot.

At 80 milliamps and above, the motor gets too hot, and the locomotive runs too slow.

The bottom line is you have to get the current draw to less than 70 milliamps if you want a locomotive that will run well. To do this, you have to free up any friction inside that you can.

That includes free spinning truck gears, motor shaft and worm shafts must be inline so the rubber tube that connects the shafts to the motor is not kinked.

The rubber tube being kinked it the major cause of friction based off all 5 of my locos, with the exception that I had plastic scrap flash in the gears of one of the trucks too.

It takes a bit of extremely careful work to tune up one of these locomotives, and doing so is very risky work, but when it is tuned up just right, these locos pull like mules, and I cannot say anything negative about how they look. They are simply stunning! Now that I have a handle on tweeking them, I am very happy!

-Robert

 

Stall current is 100 milliamps. Each engine as delivered drew about 90ma and ran too slow. After sanding down the plastic bearing blocks, and adjusting the coupling tubing, current for both locos together was reduced from 180 milliamps to 65ma, and they now run very fast!

This is 2 locos running at 8 volts drawing 65ma for the pair:





Pleasing! Very pleasing! Now I can DCC them.

 

Yes, I noticed the headlights are nose lights on the SD75. I am in the process of DCC and ditchlighting one right now. The smallest decoder that has functions supporting Ditch Lights is the NCE Z14SR.

I fit the NCE decoder by turning it diagonal and milling away half the thickness of the shell inside where the components on the PCB stick out, which leaves enough room to do the wiring:


The Ditch Lights are 0603 white SMT LED's, and are going to be wired to the front of the decoder:

 

There is no such thing in Z scale. That is what I am waiting for before I go DCC. A drop in decoder. Not everyone has Robert skills.

 

Well, I finished one loco today. I started at 7:00am and finished at 4:30pm. That was a job, but I think it was worth it. It runs great, but has a small amount of mechanism noise due to sanding down the bearing blocks.

I painted the LED's Floquil Engine Black, then Tamiya X-26 Clear Orange to kill the blue, and this is what light shined through:


I still need to paint the LED inside the nose to kill off some of the "Rudolf" effect.

 

Nice Project Torsja! I did not know you were doing DCC too! That's great!

The NCE decoder is 14.5mm x 8.6mm x 3.2mm, and I sanded it down as small as I could. I also sanded down the corners off the components to bring the size down of the decoder. It has 4 functions and effects, like ditch light, that I needed.

The Lenz Gold Mini that I put into the first SD70 I modified, is 11mm x 8.9mm x 2.8mm, but it only has 2 functions, and no effects.

The Uhlenbrock looks like a good choice for steamers, as you only need the reverse light and firebox flicker, and you can wire the headlight to always be on as a DCC power indicator. At least that's what I do.

Wire the headlight as a DCC track power indicator, use the yellow wire for tender backup light, and use the white wire hooked up to an orange LED, then use mars light, gyralight, or rotary beacon effect to simulate firebox flicker.

 

It would be nice if the drop in decoder has 4 functions, so the modeler can do ditch lights, or a beacon or whatever else he wants besides just directional lighting.