5-pole, skew wound motor

[brothaslide]

I remember learning about electric motors in college, but that was a long time ago. On most every add I see for a loco, I see that a 5-pole, skew wound motor is used. Personally, I don't care what type of motor an engine has as long as it runs smoothly and has great slow speed characteristics.

Is there some sort of advantage to a 5-pole, skew wound motor or is this just a marketing thing? Is ther such a thing as a 6-pole or 4-pole, skew wound motor?

[jeffrey-wimberly]

QUOTE: Is there some sort of advantage to a 5-pole, skew wound motor or is this just a marketing thing? Is ther such a thing as a 6-pole or 4-pole, skew wound motor?

Yes, there are. Pretty much, it's a marketing tactic. I have locos with 5 pole motors and 7 pole motors, one of which I rewound myself (that'll never happen again!). They all run pretty much the same. I've seen locos, cheap and expensive, with 5 pole motors. The expensive ones perform a lot better. This has more to do with the quality and workmanship than what kind of motor is in it

[Anonymous]

Not a gimmick. It provides a much smoother turning motor at low speeds.
The armature is skewed, at angle with the shaft and eliminates most of the notchy attributes of an armature that is square with the shaft.

I doubt there are even number of pole motors.
So this time is is not just marketing mumble jumble... what a surprise.

[jeffrey-wimberly]

I stand corrected. You learn something new every day. That's the great thing about this forum.

[Anonymous]

The primary reason for not having an even number of poles is it would be possible for the motor to not start turning if it had stopped between poles and it requires momentum to keep turning during these dead spots.

[jeffrey-wimberly]

These are things I really never thought about. All the years that I've worked in electronics, I've mainly worked with computers and circuit boards. I never gave motors more than a passing thought. All the motors I needed were already built into the hardware.

[jrbernier]

With a perm magnet motor, you need an odd number of poles - You will lock-up when you stop and not be able to get it started again. The greater number of poles, the less 'cogging' or stutter you gets when you apply juice. The skewed armature helps this even more. If you have a chance to run some of the old 3 pole AHM engines, you will see the difference! Since the advent of enclosed 'can' motors, I have never bothered to 'look' inside - most just run......

Jim

[Anonymous]

QUOTE: Originally posted by jeffrey-wimberly

These are things I really never thought about. All the years that I've worked in electronics, I've mainly worked with computers and circuit boards. I never gave motors more than a passing thought. All the motors I needed were already built into the hardware.

The motors you speak of in computers such as cooling fans, floppy, CD, DVD and hard drives are brush-less. These are even a different type all together. The one's in the DVD, hard-drive, floppy but not the cooling fan use additional electronic switchers to make them run.

I just retired two years ago after 42 years in the computer industry. Both hardware and software. I really enjoyed it but enjoy retirement even more!

[jeffrey-wimberly]

I know what you mean about enjoying retirement. I'm only 45, due to be 46 next month. I had to stop working for medical reasons, plus most places won't employ me because I'm too big of an insurance risk. So I have a lot of free time on my hands.

[Darth Santa Fe]

5-pole skewed motors are the most commonly used in high quality engines right now, because they have good slow speed, are fairly powerful, don't run at super-high speeds, and run smoothly. A well designed 3-pole skewed motor, like the Mabuchis used in IHC engines, will run as well as a high quality 5-pole motor. 7-pole skewed motors would probably have the best slow speed, because there are so many poles. An example of a 7-pole skewed motor is the old Lindsay enclosed motors, which were some of the best running motors of the 50s and 60s.

A 6 or 4-pole motor would get stuck every time you tried to start it.

[jeffrey-wimberly]

I know what you mean. The smoothest running motor I hame is a 7 pole type. It's in an Athearn SD40-2 as a replacement for the original motor. I rewound this motor years ago after it burned up on me. I can assure you, I will never attempt to rewind one again. That's way too much work.

[tsgtbob]

Another bit of history here. American Flyer Alco PAs used a pair of skew wound 5 pole motors since they were introduced in 1950.
For our purposes, the longer the motor, the higher torque it will produce. Larger diameter, but shorter motors produce more speed.
This is one advantage of being in O scale. I can put one BIG honking motor in an F unit, and still have room for a DCC decoder!

[fwright]

The skewing of the armature shafts is the most recent development in the effort to get reasonably priced, physically very small motors to run smoothly at very slow scale speeds. As others have said, the skewing reduces the cogging effect, but also reduces torque. Insufficient torque results in the motor stalling under load (and often over-heating). Insufficient torque is seldom a problem in the smaller scales because we run out of traction long before we run out of torque. In larger scales, the situation is different. But then 2 scale MPH is nearly twice as fast physically in O scale as in HO, and 3.5 times as fast as in N, so motor cogging is not nearly as much of an issue.

Number of poles, strength and concentration (shape) of magnetic field, length of motor, and skewing of armature all affect cogging to some extent. You can feel what cogging is by turning the armature by hand of an open field motor. Cogging is the greatest impediment within the motor itself to sustained slow speed running.

Other methods to reduce the cogging effect are the use of flywheels, high gear ratios, pulsed DC, and coreless motors. Keep in mind, there are very few motors specifically designed for model railroading. If we had specifically designed motors, they would tend to be (for Z through HO) small diameter, low RPM, longish, 7 or even 9 pole, skewed armature motors using shaped rare earth magnets. Coupled with flywheels and extreme precision, quiet gear trains with adequate reduction for full scale speed at 12 volts, these locomotives would perform visibly better across the board. They would also cost at least $50-$80 additional.

my thoughts, your choices
Fred W

[brothaslide]

QUOTE: Originally posted by caellis

QUOTE: Originally posted by jeffrey-wimberly

These are things I really never thought about. All the years that I've worked in electronics, I've mainly worked with computers and circuit boards. I never gave motors more than a passing thought. All the motors I needed were already built into the hardware.

The motors you speak of in computers such as cooling fans, floppy, CD, DVD and hard drives are brush-less. These are even a different type all together. The one's in the DVD, hard-drive, floppy but not the cooling fan use additional electronic switchers to make them run.

Would there be any advantage to running a brush-less motor in a loco?

[gmcrail]

QUOTE: Would there be any advantage to running a brush-less motor in a loco?

Yes, they are a much smoother-running motor, but you must avoid mounting a worm gear (or any other gear) directly to the shaft of a brushless motor. They are not designed to withstand the fore-and-aft stresses our models exert. Use a universal joint/shaft mount to connect the motor to the mechanism.

[Anonymous]

Brushless motor are generally too large for HO loco's. Plus you would have to find mounting space for the controller.
Maybe some day a brushless motor suitable for HO will become available. They are also several times the price of our current 'can' motors.

Do not confuse brushless motors with coreless. Not the same. A coreless motor is about the same size as the brushless.

An earlier post commented on skewed motors not having as much torque as a non skewed motor and therefore not suitable for larger scale.
However larger scale locos have room for much larger diameter motors. And the larger diameter does have a positive affect on torque.