Response to Austrains' announcement of a C30 tank and C30T
An Announcement from Austrains - SDS acquisition
Connecting loco and tender - Hornby Top Tips
Trainorama 830 class 847 review
Under the Portuguese Sun - Tree planting
Bachmann new GWR Earl Class review
Reconnecting with a childhood hobby
James May urges nation to 'save Hornby' as shares plunge 62%
Hornby boss quits after third profit warning in five months
Statement from Ixion Model Railways Ltd
Prototype diesel-electric locomotives use a diesel engine driving an electric generator to power DC (or more recently AC) motors wrapped around a single axle of a wheelset.
The equivalent is not usually found in HO scale… until now. There is a story behind this, with a path leading in unanticipated directions.
A “working” HO single axle traction motor can be built.
This bit of experimental modeling starts here, but this is likely not the end of the story. These motors are so small that two can be mounted in a Bettendorf freight truck and they can hide behind the side of an HO 33” scale wheel.
Dual HO Traction Motors
The inspiration for this project came from a friend and fellow modeler, Jon Harrison, who models the Cajon pass and its rail movements, topographically and prototypically accurately. It is impressive. On the prototype, during the 1940’s one to three steam helpers would be assisting Eastbound freights. As was customary on the Sante Fe, the helpers would be cut in, in front of the caboose on the rear. When the train reached Summit, the rear helpers would cut off and back the caboose into a graded siding, where the brakes would be set on the caboose. The helpers would move out and position themselves for their return. With the siding switch thrown, the caboose brake would be released and the caboose would coast down the grade and couple onto the back of the train with no further train movements (most of the time). If the caboose didn’t make it all the way, the helper could complete the shove onto the rear of the train. Jon had tried many variations, but could not get his caboose to consistently connect to the end of his train. It needed a little extra boost to assure coupling. We discussed using a band drive around one of the axles (much like the old Athearn HiFi drive) powering the caboose simulating coasting, but the drag, when not energized, would likely be a problem. One would also need to find precisely the right strength band to enable movement but limit the drag.
DC Motors and Athearn Truck
After thinking about this for some months, I thought a free-wheeling, un-geared traction motor (a small DC motor) might do the job. The motor shaft would support the two wheels, and turn freely when not powered. But it would have to be a dual shaft motor and very small. I actually started looking for two coreless vibrator motors that I could mount back to back. There are 4 by 6 mm motors, but when placed back to back, they require longer clearances for electrical lead attachments, and motors of that size have very little torque. I finally found a dual shaft N10 DC motor on Ebay: https://www.ebay.com/itm/262973201686
That was just about the right size. It also had a normal, wound armature. The shaft was 1.0mm metal. It had to be insulated from the wheel rims, which I also wanted to be metal, not plastic.
The initial design would use Kadee wheelsets, which have metal wheels and plastic axles. The axle was cut close to the back of the wheels as possible, and then sanded down using a Dremel disk sanding tool.
Sanded Wheel insides
I started to lay out the axle centers for hand drilling when I realized that the 1mm holes needed for the motor shafts had to be as centered and as perpendicular as possible to eliminate wheel wobble. So I mounted each wheel in a three piece self-centering lathe chuck and drilled the 1mm holes in the plastic axle centers. I made a small depth gauge for each axle hole, so that it was about 0.5mm deeper than the motor shaft. This was so I could add a tiny amount of glue to hold the axle in place and have a bit of room to accommodate the excess glue. I used Loctite 620 shaft cement to do the job.
Before attaching the wheels, I attached the smallest ultraflexible wire I had on-hand. This was about 34 gauge stranded wire with a rubber not plastic insulation. Look for ultra-flexible “tone-arm” wire used in record players. I have had some good luck with the individual wire used in some computer mouse cables too. Miniatronics also offers some Ultra Flexible 30 Gauge Wire. Before soldering each wire to the motors, I looped the wire through the tiny eyelets, and bent over the eyelet towards the outside of the motor case. This gives the flattest attachment with maximum wheel clearance. Next I drilled two 1/16th inch holes on opposite sides of the truck bolster to accommodate the wires entering the car floor. The motors with their glued wheels were then inserted into the truck. Two 1/8 inch pieces of .005 phosphor bronze metal were cut and AC glued to the motor housing top and bottom to stop the motor housings from spinning. After routing the wires through the car floor, the trucks were attached with 2-56 screws. I used Athearn plastic Bettendorf truck frames.
The other truck was prepped with Intermountain wheels, whose wheels were polished clean with a brass wire brush. Doubled 0.008 phosphor bronze wire was soldered to a small brass pad, drilled for to clear a 0-80 self
tapping screw. Two such assemblies were screwed to the top of the plastic truck frame and bent to wipe each side of each wheelset, enabling four wheel pickup. Small wires soldered to the wiper assemblies were inserted in 1/16th holes through the car floor to provide track pickup for the traction motors.
Driving for Traction
First I want to emphasize that the original intent was to give the Cajon caboose a kick as it was coasting downhill. That is a far cry from driving a 2-10-2 with a 50 car train up a grade. Nonetheless, I thought that the controlled Pulse Width Modulation (PWM) drive from a DCC decoder might be able to be “tuned” to control the motor pair in a single truck. The motors are rated 3-6 Volts and I figured that the BEMF control feature might come in handy. Putting the 2 motors in series should add the generated BEMF, even though it may be somewhat noisy or even erratic when the decoder reads it. I was concerned whether these tiny motors would have enough torque to move the caboose at all. I was also concerned whether these were strong enough to overcome the starting friction on a flat track. Slow speed control was a vague hope too. I really didn’t know how this would perform.
I used a Digitax DZ123 decoder, with torque and BEMF turned on. After a little fiddling around, I settled on these CV settings (using JMRI decoder terms):
Kick Start 3
Acceleration Rate 0
Deacceleration Rate 0
Motor Drive Frequency 230
Static compensation for speed stabilization 128
Dynamic compensation for speed stabilization 80
Solo operation droop compensation for speed stabilization 6
Use Vstart, Vmid, Vhigh
Satrt Volts 1
Mid Volts 49
Max Volts 123
This article first appeared on model-railroad-hobbyist.com
About this website
Railpage version 3.10.0.0037
All logos and trademarks in this site are property of their respective owner. The comments are property of their posters, all the rest is © 2003-2020 Interactive Omnimedia Pty Ltd.
You can syndicate our news using one of the RSS feeds.