In 2019 Domino Sugar donated a 1950 built Plymouth 25 ton critter to the B&O Museum in Baltimore. The critter had been working at the Baltimore Domino plant since 1992. In 2016, it had been rebuilt, repainted and the subject of a naming contest that garnered several thousands of entries, with Sweet Toot being the winner.
Last December, while setting up the Bantrak N-trak layout in the North Car Shop at the museum, my son noticed the locomotive. He tends to like very large and very small things. Inspired by Randgust’s construction of a 25 ton GE critter, we set out to see if we could build Sweet Toot.
Like Randy, we started off with Damin Keenan’s Shapeways 25 ton GE shell. We also followed Randy’s lead in using a Tsugawa Yokou Chassis. I decided to use the stock motor as a starter. Since the goal is to run this on FreemoN, where switch frogs are powered and the short wheel base is less of a problem, I figured it would be a good excuse to experiment with a Doehler & Haass PD10MU decoder from DM-Toys. At 8.5x11.7x1.8mm, it looked like it would fit in the cab. This decoder is described as having “Two small capacitors'' on the decoder for “driving without data loss.” Would this decoder run the stock motor on the TU-7T chassis at slow speeds? The stock chassis on DC tends to have two speeds. Stopped and warp. This decoder is also interesting since it is low cost.
http://www.randgust.com/Finished.htmhttps://www.dm-toys.de/en/product-details/DH_PD10MU-3.html
The shell is a GE. Sweet Toot is a Plymouth. Modifications included;
- Removing the truck sides;
- Extending the hood front and making a new front radiator;
- Cutting out windows and filling a couple in to look more like the proto;
- Cutting off the rear coupler support and pushing it back to support a back deck;
- Build out the air tank for the back deck;
- Install Gold Metal stirrups;
- Install some handrails;
- Add the box on the front left hood;
- Exhaust stack, bell, orange safety lights, front and rear lights, and horn;
Whenever possible, I used lead or another metal to make the parts, including lead strips along the hood that make the yellow strip. The front of the hood was cut off and extended to the square shape of a Plymouth with Styrene. The radiator was made from lead sheet, scribed with an X-acto knife with vertical lines for the radiator.
The bell and horn were found in a parts bin and not exact to prototype. Railings are Atlas railings off a junk box RS3 assembly. I cast a pewter weight to fill the hood. While the weight would help with pulling power (did we really expect to pull more than 1-2 cars?), it would also help with electrical contact.
In the end, it weighs in at 17.92 grams. For comparison, weight by axle:
Sweet Toot: 8.96g
Bachmann F-7: 21.04g
Kato SD-80Mac: 22g
Kato ES4400: 19.2g
Bachmann 44 ton: 8.83g
The chassis has a vertical motor. I’ve had REALLY good results with the Toma Motor Works chassis for single truck trolleys, but Kenji’s chassis all have horizontal motors that did not fit in the shell of the critter. The decoder is alongside the motor inside the cab. Lead was used to fill as much of the rest of the cab as possible. I also used folded lead sheeting to fill the space between the ends of the chassis and the bumper ends of the shell.
The air tank is brass tubing filled with pieces of lead and Tamya white putty to make the ends. The tank straps and supports are lead. The headlights are bits of styrene. I have not tried to light the headlights. The exhaust stack are bits of K&S brass tubing. The windows are filled with painted styrene. The couplers are MT 2004’s carefully painted like the prototype.
For the lettering, not having easy access to a decal machine, with a nice side photo of the locomotive, I clipped the artwork off the side of the cab and used GIMP to clean it up a bit, adjust color and size. I then printed onto glossy photo paper. Next I used a razor to split the paper back off the plastic film, and sanded the back of the film to make it thinner and smoother. This was then glued on to the body.
Out of the box performance with the D&H decoder was ok. This was my first attempt at really digging into motor tuning parameters. Unlike most decoders where a basic speed curve is defined by CV’s 2,5 and 6, D&H combines these into a single CV, CV48, which they call speed step. It allows you to select from 8 predefined characteristics or curves. At first, I thought this would be constraining, but it made the tuning process easier, since I first tested 7 (bad performance) to 0 and settled on using the 2nd CV-48=1) as providing the best performance.
I also tuned the motor frequency, impulse width and shunting speed CV’s, partly based on tuning tips for coreless motors listed on a FAQ on the D&H website. In the end performance is better, but not amazing. It will creep at a slow speed, but not anything close to something like on track tie per minute. It has a tendency to stall after stopping. It has an outrageously high top speed.
And what about those “Two small capacitors” that are supposed to provide some level of keep alive? The wheelbase of the TU-7T is 9mm. The plastic frog of a Peco switch is about 18mm. At a scale speed of about 30mph, the locomotive will successfully pass over the frog the majority of the time.
The TU-7T has low profile wheels, so we look forward to running Sweet Toot on Freemo-N with juiced frogs.
Cheers,
Bob
