To paraphrase Vane Jones, "Knowledge is of little value until shared with others."

Friday, July 4, 2014

Model Power Trucks Part 3B - Making Your Power Truck

These are the parts of a power truck with which we need to concern ourselves.

The Motor
The open frame motor used in the article regarding the building a power truck is no longer available. After searching the internet, it looks like the open frame motor, as we know it, is no longer manufactured.

There are a wide variety of can motors available from various vendors. If I were to build my own power truck, the ability to obtain the exact same can motor in the future is important. The reason being, if the power truck I built now needs a new motor or a new power truck was to be built in the future, the exact same motor may be required.

Trying to pick out a small electric motor today is difficult and confusing. The vendors who supply them have a wide variety in size and specifications. Reading and understanding the information supplied on a manufacturer's web site is hard. The parameters a hobbyist is looking for may not be the same in which an electrical engineer is interested.  For these reasons obtaining a can motor from an established hobby oriented vendor is best.

A number of hobby suppliers have can motors for HO applications. This type of motor is best for an O scale traction power truck. As you will see in the next part regarding the gear box, items for HO applications work well for O scale traction trucks.

No specific can motor is recommended in this blog, any 12-18 v can motor of a size which will fit into the confines of the power truck will do. You can pick out your own motor.

While no specific can motor is recommended, I picked up a can motor from NWSL SKU 18337-9. This motor is slightly larger than I wanted. A power truck made with this motor may provide a power truck where the motor will be sticking up too far.  The installation may require part of the underbody and floor to be cut away.

This can motor has the armature on both ends of the motor. One of the armatures will have to be cut off.

Regarding the size of the motor, just as a reminder, keep in mind NWSL sells more items to HO railroader modelers than our group, the O scale traction modelers. NWSL stocks many products which are better suited to HO modelers.

The motor in an HO trolley model is usually located in the body of the model. The O scale trolley modelers have grown accustom to having the motor mounted in an under the floor power truck.

Gear Box (worm, gear, and casing)
The gear box with the 1:37 worm and gear as mentioned in the article are not available. from PSC. It was the 1:37 gearing which made for a slow power truck which caused me to not use the power truck in any model.

PSC does catalog a modified gear box (brass 48204 or plastic 48204-1) which looks almost like the gear box in the article. The axel is larger in diameter. I have no idea as to which worm and gear would work with this gear box.

NWSL does have a number of worm, gear, and gear box set-ups available. After going over what is available, I was very confused until I settled on the idea of locating a gear box where the diameter of the axle and the wheel sizes used for O scale trolleys would be satisfied.

The usual size of an O scale axle is 0.125". The prototype wheel size of trolleys and interurbans in which I'm interested are 30" to 36" with 36" being the most common. This information brought me to NWSL stock numbers:
212-6, 14:1  Ratio 0.4 mod Gearbox kit fits 1/8" axle;
8066-6, Geared 36" Traction Wheelset (1 wheelset with gear) fits Gearbox #212-6; and
8186-4, 36" Traction Wheelsets (3 wheelsets) 0.135" tread.

One of my concerns is the tread size. I prefer a 0.145" tread over the 0.135" tread. Streetcars with 0.135" tread look great operating on street trackage. The 0.135" tread does not always work well on non-street track where the clearances in switch frogs may be too wide. Many O scale layouts, both trolley and steam/diesel, are still set up for the old 0.172" tread wheels.

A different way of thinking about the wheel thread width and tying it to prototype operation is most trolley museums in the US will change the wheels of streetcars (wheels with a narrower wheel thread and a smaller flange) to standard railroad wheels. Museums prefer the wider thread and larger flanges because these wheels track better (stay on the rails). 

In scale the 0.135" wheel is the streetcar wheel, while the 0.145" wheel is the standard railroad wheel.

The other concern is the gear ratio of 14:1 which seems like a fast speed. Only the installation and operation of the 14:1 gear box in a power truck ratio will tell.

Wheel Sets
Much of what can be included in this part of the building and/or repair of a traction power truck has been stated above. Today the main provider of wheel sets is NWSL.

Many O scale modelers have used NWSL wheel sets in their freight cars. I prefer steel wheels on steel (metal) rail. All of my freight cars with plastic wheels have had their wheels sets exchanged.

Wheelsets are available with either pointed, shouldered, flush, or blunt axles. For most traction models the pointed or shouldered axles are the most common. When building a new power truck the shouldered axle is preferred.

NWSL provides both insulated for 2-rail or non-insulated wheelsets. If your model is to operated only from the trolley wire then non-insulated wheelsets are applicable. However, if there is any chance the model may be operated on a 2-rail layout then insulated wheelsets are warranted.

If you are not too sure of your models future use 2-rail insulated wheelsets. To make a non-insulated truck using insulated wheelsets, insert one wheelset with the insulation on one side into the sideframes while the other wheelset is inserted into the sideframes with the insulation on the opposite side. In the future, one of the wheelsets can be reversed to give an insulated truck.

Always consult the Northwest Short Line catalogue  before ordering an item mentioned in this blog.

More in the next Post regarding the making of your own power truck with today's available parts.


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