What is the difference, if any, between a “Can Motor” and a “Coreless Motor”? Thanks.
A can motor is pretty much the standard used by most manufacturers. They have a segmented iron core mounted on the shaft, and insulated copper windings are wrapped around the segments. The core is surrounded by magnets, and the motor is usually fully enclosed. Because of the heavy iron core, the can motors have pretty good heat dissipation under load. The motor’s shape can be a full cylinder or have flat sides.
A coreless motor has no iron core. The copper windings are carefully wound into more of a cup shape, and are held together by epoxy or some form of plastic. The cup of windings surrounds a large cylinder shaped magnet with a hole in the middle for the shaft. Coreless motors are usually stronger than can motors and can accelerate much quicker, but the lack of an iron core doesn’t allow good heat dissipation. They are always fully enclosed, and are always shaped like a cylinder.
I like using coreless motors for my projects. The low speed control, current draw, and noise levels are almost always better than iron core motors, and even small ones can have very high torque. The lack of heat dissipation isn’t a problem as long as everything can move freely.
I’ll add one other advantage of coreless motors:
You may notice that when there is no power or very low power that iron core motors sort of thunk as the poles pass the magnets; this doesn’t happen with coreless motors. Because there is no iron core, the magnets allow the armature to spin freely. This gives them better capability for low speed operation and it acts much like a built-in flywheel.
I’ve heard comments about heat dissipation, but it’s never been a problem for me. I’m sold on coreless motors (although, I really have no complaints about good skew-wound iron core motors).
A “Can Motor” has two ceramic magnets inside a steel can shaped case. Compared to the traditional open frame Pittman style motor, a can motor has a stronger permanent magnet field due to the greater magnetic strength of ceramic magnets vs Alnico magnets, and a shorter magnetic path. For model railroad work, can motors have greater low speed torque and lesser current draw than traditional open field motors. I replaced a traditional motor with a can motor in a Mantua Pacific. The can motor reduced current draw from 1 amp to 0.1 amps, and reduced the slowest speed from 5 scale miles/hour to 0.05 scale miles/hour.
A coreless motor has no iron core in the armature, just copper or aluminum wire. They are also can motors with ceramic magnets and a steel can case. The much lighter armature allows the motor to accelerate or change direction more rapidly. Coreless motors are prized for electronic servo mechanisms, such as the servo used to position the heads in disc drives. The lighter armature raises the frequency response of the motor/arm/head assembly. Coreless motors don’t offer much in model railroading applications. They are used because they are available and nicely made, but a nicely made iron armature (core) can motor will have more torque than a coreless motor, all things being equal.
Actually, coreless motors typically use metal magnets, like Alnico, Samarium Cobalt, and Neodymium. The coreless motors with Alnico magnets are usually weaker than similar sized can motors, but the ones with “rare earth” magnets are some of the strongest available. As an example, I repowered the Bowser 2-8-2 in my signature with a small coreless motor. The motor I used is about 39% the size of the original Bowser motor, but has about 53% as much torque (based on values found around other websites). The engine is very heavy, but that little motor can still slip the drive wheels without too much trouble, and only draws about 1/5th as much current as the Bowser motor! Some coreless motors even have double ended shafts, so I think there’s plenty of use for them in model railroading.[:D]
And as another example before I go, I repowered an old Tenshodo GP20 with a coreless motor similar in size to the old Pittman style motor. It’s about twice as powerful as the old open-frame motor, draws much less current, runs quieter, and has a better speed range.[:D] I can keep the thing running at less than 1V at only a couple scale MPH.[:D]
The regular can motor can dissipate heat faster than a coreless motor and it can run hot for a much longer period of time. A coreless motor on the other hand can’t handle a lot of heat and can be easily damaged. If the intended application is going to put a heavy load on the motor at a low you’ll be better off with a motor that has an iron core as it can survive more heat. This article explains the pros and cons of the different types. The bottom part of ‘motor types’ is especially enlightening.
For me the “benchmark” has always been the Sagami 20X32 motor, I can’t say that I’ve ever used a “coreless” motor unless I have one in an engine that I bought 2nd hand somewhere. For my money that Sagami is the best, unfortunately the old version of the 20X32 was replaced sometime ago and it’s not as good as the original was therefore I went looking for a substitute that had a “similar” power and torque rating. Much to my surprise I discovered that the Kato motor not only comes the closet but is also in the same price range. Since then I have purchased a couple dozen of them and can report that they will power most anything you want to try with them. They are double shaft so if you are putting them in a steam engine all you do is chop one side off, they also work beautifully in brass diesels or as replacement motors for Athearns.
They basically make 2 versions, one for the switcher, a smaller but also powerful motor, great for Shays and such, and the “standard” size from their SD40’s and Dash 2 line as well as all of the newer versions.
They have 3 key features, they’re roughly the same price as the old Sagami 20X32 motors, they have roughly the same power and torque ratings, and most importantly…they’re readily available!!!
After almost 40 years the factory motor in my old Tenshodo Big Boy was getting “weak”, I replaced it with one of the Kato’s and it runs better than the day it was made.
Mark
Other posters have covered most of the differences between coreless and can motors. The one difference not covered so far is the size vs torque issue. When you step down into HO 19th Century steam and HOn3 and smaller N steam, space for a conventional can motor becomes an issue. Getting a can motor smaller than 10mm diameter to have sufficient torque is not a simple feat.
The older coreless motors also suffered from too little torque - which meant overheating when the locomotive was pulling a load. But today’s coreless motors with rare earth magnets are a joy, provided temperature is kept under control. A 6mm rare earth magnet coreless motor will have the torque to pull all the cars a small HOn3 loco can pull without slipping drive wheels.
Given the high RPMs of a coreless motor, the ideal coreless motor for small locomotives seems to be the 24 volt models run at 12 volts. This is especially true if a gear head is used - the lower RPM keeps the gear head noise down.
If you are going the DCC route with a coreless motor, you will want to set the PWM pulse frequency fairly high (use Silent Drive decoders). Which means a high gear ratio to gain back the very slow speed running that low frequency PWM delivers. High gear ratios are a better solution for our models as long as gear noise can be kept reasonable. The gear ratio multiplies torque, and limits top speed to a realistic level for our shortened layouts.
If using DC control, throttles with softened pulses are a lot safer with coreless motors. Examples of such throttles are the MRC line, the Cooler Crawler, and throttles that suppress the pulse after a certain voltage is reached or have a DC component on which the pulse rides.
A good small steamer, geared for a maximum speed of 40 scale MPH at 12 volts, is a joy to operate on
To all who responded to my question, many thanks. You all provided great information and I appreciate you taking the time and effort to do so.
Glenn M