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SHM 26

Drive

The Tenshodo SPUD drive that was supplied with the kit has, as a fellow modeller put it, basically two speeds: stopped or sonic boom. There are several ways to improve this.

Mashima motor

One way to improve the SPUD is to put another motor in it. Its should fit in size, it should have two motor axles and it should have good slow running capabilities. Mashima provides models that fit that bill.

Another drive

Discarding the SPUD altogether is another option. An good alternative could be the Black Beetle. It is a far more expensive solution but it comes with the Mashima motor and it also offers the option of a 1:30 gearing, improving the slow riding capabilities even further

I will see if a Black Beetle may fit in the limited space I have.

Building a new drive

This wil me a lot more work but it guarantees be that the drive will fit, I can have the motor and gearing of my choice and can give it springed suspension on one axle, improving its road behaviour and current collecting capabilities. By doing this I would also collect valuable experience as this would my first scratch built drive mechanism.

I am going to look into any of these three options

(date written: Jan 3, 2014)

Decoder

Installing a decoder is a fourth option that can be combined with any of the three mentioned before. Another friend offered to help me installing the decoder and he advised me the Kuehn N45.

This decoder measures 8.9 x 11.7 x 2.3 mm only. I want to conceal it in the coal buker so I made a mock up to see if it would in. To make sure that it would this mock was made slightly oversize: 10.4 x 13.4 x 3.2 mm. It turned that I could fit it in four ways

 

Sawing out the hole for the decoder is not overly difficult. Drill fouir holes in a rectangle. No reason to be overly precise but the X-Y-crosstable will help you to setup a nice square.

With a jeweler's saw take the main part out.
And file until square and a tad larger than the decoder. This hole is 12.2 x 10.2 mm, the decoder is 8.9 x 11.7 so I should be able to get it through.

Construction of the chassis

After having done all the work on the locomotive's body I turned my attention to the drive. For now I have decided to use the original drive supplied with the kit. I just want to finish the loco. It will sit in a display most of its life anyway
Brake shoe
Cut and filed

Drilling.

For this purpose the four brake shoes were glued to strip of wood (a coffee stirring stick)

Rodding in place
Brake shoe soldered
Done. Drive unit holder ready
   

One problem I have been dreading is the cumbersome way Philotrain designed the connection of the crank pins with the spoke wheels of the Tenshodo SPUD that is supplied with the kit. Four little 8-shaped brass etching are supposed to create a distance between the axle and the crank bolt. There is no way I could imagine this would work out a reliable join.

 

So I took a dive in my spares and supplies box. I found nuts that fit the cranks bolts (M1.4). After a lot of measuring I found I could turn them down to a size where they would fit between the spokes of the SPUD's wheels. I added a ring for two reasons. It would create the necessary clearance between the connecting rod and the wheel surface. It would also prevent the expoxy glue to flow onto the crank bolt and inadvertedly attach that bolt as well.

The crank pin in place. The nuts were turned to a very tight fit and a tiny bit of epoxy filled the gap between the spokes. After curing I could unscrew all four crank pins without trouble. Another difficult job done.
Coupling rods deburred and sanded smooth
Chemically blackened. The colour difference does not convince on the photo but it is clearly visible in reality.
To demonstrate the blackening effect I blackened a scrap skirt and then scrubbed half of it back to brass
Adding the counter weight was not trivial for the driven (rear) axle, at the left of this photo. The inner motion has to be counterbalanced and this results in an odd shift of the counter weight. Again I was happy to have so many detail photos of the prototype. Note that I have blackened the wheels.
The SPUD's casing had a little play in the confines of the brass holder. I found this when I saw the locomotive list once I had put it on its power unit. I added two strips of styrene to eliminate this

I tried to fit a decoder to make it run smoother and more controllable but the bad electrical pickup played havock with the performance of the drive unit. So I removed the decoder.

After quartering it ran but not overly convincing. I decided to waste no time on this drive anymore. I have decided to finish this loco and put it on display. If I have the courage I'll build a whole new drive for it.

The final drive unit. The original SPUD has no wires but I cut the SPUD's internal conductors to fit the decoder. So after removal of the decoder I had to rewire it.