Bachmann Can versus Precision Motors

[jackstrat]

What is the difference between "can" and "precision" motors?

How can I determine which motor (can, precision, 3-pole, 5-pole) a Bachmann locomotive incorporates?

Thanks
jack l

[richg]

Do some Google searches for the different types of motors. You will get many hits. Call it a learning experience.

Rich

[Jim Banner]

"Can" motors are enclosed in and held together by a cylindrical shell, much like a deep drawn tin.  The open end is often closed with a plastic moulding which also serves to hold one of the bushing and both of the brushes.  The original "open frame" motors had large spacings between the armature and the pole pieces to allow large variations in manufacturing.  The can motors are made to much closer tolerances so the armature to pole piece gap can be greatly reduced.  The smaller the gap, the more efficient the motor and the less current it draws for a particular power output.  Unfortunately, the smaller the gap, the more "cogging" that occurs.  Cogging can be felt as a lack of smoothness when you turn the motor shaft by hand - it is harder to turn when an iron part of the armature is in front of a pole piece and easier to turn between the iron parts.  The two commonest solutions are to increase the number of the sections the armature is divided into.  These are properly called "teeth" but often referred to as "poles."  The other solution is to cut the slots between teeth in a spiral fashion so that the amount of metal presented to the pole pieces of the permanent field magnets is always the same.  Motors with spiraling slots are referred to as "skew wound."  For many years, the five pole, skew wound can motor was the holy grail of model railroaders.

But it turns out that using both a greater number of poles AND skew winding is not always the very best solution.  Skew winding tends to reduce torque, which partially offsets the reason for skew winding, namely enhanced low speed performance.  One solution lately has been the three pole skew wound motor.

There is another solution to cogging and that is to remove all of the iron from the motors armature, except maybe its shaft.  They are usually referred to as "coreless" motors.  These motors can be made with very small spacing between the armature and the field magnets (they are sometimes said to "tightly coupled") which makes them very efficient.  Unfortunately, the lack of an iron core reduces the cooling available to the armature, rendering them unsuitable for most forms of power used with model railroading.

"Precision" motors exist but in model railroading, they are largely a figment of the PR Department's collective mind.  True precision can motors are usually built inside a machined cylindrical shell with machined metal end pieces.  One or both ends are typically press fit, then electron beam welded in place.  Shaft bearings are often ball races or even roller bearings instead of simple bushings, and end play is often carefully controlled.  They could be skew wound but precision motors of the size used in H0 model railroading often reduce cogging by using 12 or more poles.  Needless to say, these precision motors are not cheap, often costing as much as a brass locomotive.  More affordable "precision motors" as the term in used in model railroading often include only one or a few of features associated with their truly precision cousins.

Now that you know a bit more about motors, I should mention that they are only one of the components that determine how well a model locomotive runs.  Obviously a bad motor will keep a locomotive from ever running really well, but even the best of the best motors will not guarantee great running.  To me, the bottom line is to see how well the overall package, which includes all the mechanical parts and some of the electrical parts, perform together.

Jim

[pipefitter]

Thanks Jim, for your informative reply. It is very helpful to me too!

Robert

[jonathan]

Perhaps I'm becoming a model train geek, but I found the information riveting as well. 

I only ever worried about weather a loco had an open frame or "can" motor.

I hope that Jim keeps sharing his knowledge for many years to come. 

Thanks, Jim.

Regards,

Jonathan

[mabloodhound]

Thanks Jim for the explanation.   I'm glad you're here to help us old timers out.   Guess some don't have the time so they just send us off to Google.

[Jim Banner]

Dave, Jonathan and Robert, I consider myself lucky to be retired and have the time to talk and help others with their model railroads.  For me, it is an important part of the hobby even if it sometimes take time away from working on my own layouts.  But as a wise teacher once said when, on her retirement, she was asked if she wished she had done more with her life than "just teach."  she replied that she felt every success her pupils had in their life contained a tiny part of her, and when she added up all the tiny parts, they gave her a success much greater than she could ever have achieved on her own.  I sort of feel the same way, that if I have a tiny contribution in a whole lot of layouts and if I added all together, the total would be much more than I could ever hope to build myself.

I have taken off my philosopher's hat and hung it back on its peg.  Now, everybody, Back to Work!

Jim